2009

Rapid high performance liquid chromatography method development with high prediction accuracy, using 5 cm long narrow bore columns packed with sub-2µm particles and Design Space computer modeling, Sz. Fekete, J. Fekete, I.Molnár, K.Ganzler, J. Chromatogr. A, 1216 (2009) 7816–7823 (pdf) 
The paper describes a strategy for the systematic development of ultra high pressure liquid chromatographic (UHPLC or UPLC) methods using 5 cm×2.1mm columns packed with sub-2µmparticles and computer simulation with the DryLab^® package. Data for the accuracy of computer modeling in the Design Space under UPLC conditions are reported. An acceptable accuracy for these predictions of the computer models is presented. The work illustrates a method development strategy, focusing on time reduction up to a factor 3–5, compared to the conventional HPLC method development and exhibits parts of the Design Space elaboration as requested by the FDA and ICH Q8R1. Furthermore this paper demonstrates the accuracy of retention time prediction at elevated pressure (enhanced flow-rate) and shows that the computer-assisted simulation can be applied with sufficient precision for UHPLC applications (p > 400 bar). Examples of fast and effective method development in pharmaceutical analysis, both for gradient and isocratic separations are presented.

Aspects of the “Design Space” in High Pressure Liquid Chromatography Method Development, I. Molnár, H.-J. Rieger, K.E. Monks, J.Chromatogr., in print

The paper describes a multifactorial optimization of 4 critical HPLC method parameters, i.e. gradient time (t_G), temperature (T), pH and ternary composition (B₁:B₂) based on 36 experiments. The effect of these experimental variables on critical resolution and selectivity was carried out in such a way as to systematically vary all four factors simultaneously.The basic element is a gradient-time temperature (t_G-T) plane, which is repeated at three different pH’s of the eluent A and at three different ternary compositions of eluent B between methanol and acetonitrile.The so-defined volume enables the investigation of the critical resolution for a part of the Design Space of a given sample.Further improvement of the analysis time, with conservation of the previously optimized selectivity, was possible by reducing the gradient time and increasing the flow rate.Multidimensional robust regions were successfully defined and graphically depicted.

2008

"LC Determination of Lercanidipine and Its Impurities Using DryLab Software and Experimental Design Procedures" I.Popovic, D.Ivanovic, M.Medenica, A.Malenovic and B.Jancic-Stojanovic, Chromatographia 67, (2008) 449-454 (pdf) 
The main objective in all optimization procedures is to define the most appropriate conditions for rapid, sensitive, precise, and reproducible analysis, as economically as possible. Experimental design and DryLab optimization software have been used to optimize a liquid chromatographic method for separation of lercanidipine and its three impurities. In both methods of optimization the acetonitrile content and pH of the mobile phase were factors extracted for analysis; resolution of a critical pair was output in both cases. Data obtained from both optimization methods were compared and appropriate conclusions were extracted with the objective of gaining a complete view of chromatographic behavior. Detailed description was obtained by use of a three-dimensional graph and DryLab maps.

"A Stepwise Strategy for Developing a Robust HPLC Separation for a Novel Diabetes Compound"
Karthik Jayaraman, Frank Hu, Frank Tomasella and Merill Davies, American Chemical Society, Middle Atlantic Regional Meeting, Proceedings (2008) 191.
A stepwise method development strategy was employed in developing a robust HPLC method to resolve several closely eluting process impurities associated with a novel diabetes compound. The strategy consisted of rapid column screening, optimization of mobile phase compositions and separation temperature, DryLab modelling, and experimental verification of optimized separation conditions.

The column evaluation process involved screening of a series of 20 columns varying in bonding chemistry using four sets of mobile phases composed of water, acetonitrile and/or methanol at three different pHs. The screening process resulted in identifying two promising columns: XBridge Shield RP18 and SunFire C18. The effects of organic modifiers and separation temperatures were then evaluated to narrow down the chromatographic separation parameters. DryLab® was used to predict optimized gradient profile and separation temperature. Finally, the DryLab® predictions were verified experimentally.

The study demonstrates that factors such as stationary phase composition, organic modifiers, pH and separation temperature have profound and oftentimes complex effects on chromatographic conditions. Therefore, it is critical to adopt a rational strategy as demonstrated here to evaluate the interplay of these factors, there by greatly enhancing method development efficiency

"Computerized Design of Robust Gradient HPLC Methods"
Imre Molnar and Hans-Jürgen Rieger, American Chemical Society, Middle Atlantic Regional Meeting, Proceedings (2008) 261.
The development of gradient methods in HPLC is a difficult task. The transfer of the methods requires deep understanding the process in the column and the factors, which are required for a safe operation in the routine lab. The talk will discuss the aspects, how to make reliable methods using computerized design in the development.

2006

"Application of a column selection system and DryLab software for high-performance liquid chromatography method development"
Ryan M. Krisko, Kieran McLaughlin, Michael J. Koenigbauer, Craig E.Lunte, J.Chromatogr. A, 1122 (2006) 186–193. (pdf)
This paper describes a strategy for the development of chromatographic methods for drug candidates based upon the use of simple MS-compatible mobile phases and optimization of the chromatographic selectivity through variations of the stationary phase and mobile phase pH. The strategy employs an automated column selection system and a series of HPLC columns, varying in hydrophobicity and silanol activity, in combination with DryLab software to develop chromatographic methods for the separation of mixtures of bupivacaine and its metabolites; acidic, basic, and neutral compounds; and atenolol, nitrendipine, and their degradation products.

"Retention modeling in ternary solvent gradient elution reversed phase chromatography using 30 mm columns"
Melvin R. Euerby, Federico Scannapieco, H.J.Rieger, I.Molnar, J.Chromatogr. A 2006, 1121 219-227. (pdf)
An optimization strategy for ternary solvent-strength gradient elution RP chromatography is described in which a 2-dimensional model of gradient time (2 levels) against ternary proportions of organic modifiers (4 levels) was constructed. From the resolution surface the optimum ratio of organic modifiers could be selected. Excellent retention time and acceptable peak width and resolution simulations were obtained. The separation could be further optimized from the same input data by using a standard one-dimensional model in order to optimize for gradient slope, duration and shape. Excellent retention time and acceptable peak width and resolution simulations were obtained (< 1, 2 and 6% error respectively).

Comparison of retention models for polymers   1. Poly(ethylene glycol)s ; Mubasher A. Bashir, Wolfgang Radke * ; Journal of Chromatography A, 1131 (2006) 130–141.

2005

"Searching for Robust HPLC Methods: Csaba Horváth and the Solvophobic Theory"
I.Molnar, Chromatographia, Supplement Vol. 62, 2005, p.7. (pdf)
This paper is written to honor Csaba Horváth and to remember his work on Reversed Phase Chromatography, (RPC) a theoretical fundament of the mechanism of retention on nonpolar stationary phases, called the "Solvophobic Theory" from the subjective point of view of the author. The paper is trying to compile a few stations in the development of this important theory, which is valid more than ever and look out for its consequences in developing robust methods for routine work, especially in the daily applications of RPC in industrial settings worldwide. Reliable product quality requires the understanding of selectivity changes, which in RPC govern the development of robust and reliable methods, applying continuous changes of liquid chromatographic parameters in aqueous eluents. It was Horváth, who laid the fundaments of this valuable technique, which makes the application of RPC to a still growing use in scientific research and in pharmaceutical and chemical production. Although the Solvophobic Theory of RPC was reflecting only a part of Horváths scientific work, the impact of RPC in life science is tremendeous and the technique RPC is today one of the most popular, most widely used tools in analytical chemistry and will remain for long time in use due to its stability and to its robustness.

"Examples of Computer-assisted Robustness Studies",
G.Kleinschmidt, R.Hohl in Method Validation in Pharmaceutical Analysis, J.Ermer,J.H.Miller, 126-141 (2005), VILEY-VCH, Weinheim
The article describe the use of DryLab in robustness testing of HPLC methods

2004

"Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity Part II: Strategies for optimization of separation,"
Valérie Harang, Sven P. Jacobsson and Douglas Westerlund, Electrophoresis A. 25, 1792–1809 (2004). (pdf)
The separation of anionic, cationic, and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied. The concentration of sodium dodecyl sulfate (SDS; surfactant) and 2-propanol (organic solvent) was varied in a three-level full factorial design. 29 different model substances were chosen with different hydrophobicities and charges (neutral, positive, and negative).

2003

"Computer-Assisted Method Development and Optimizationin High-Performance Liquid Chromatography,"
T.H. Hoang, D. Cuerrier, S. McClintock, and M. Di Maso,J. Chromatogr. A., 991, 281 (2003).
DryLab is used for the optimization of a model drug candidate and its degradation products. Accuracy of DryLab predicted retention times and resolution is compared with experimental values.

2002

"Optimizing Multilinear Gradients in HPLC "
T.Jupille, L.Snyder, I.Molnar, LC GC Europe, 2002, 2-6.
Multi-linear gradients have not been widely used in general-purpose HPLC in part because of experimental inconvenience in method development. Even with the use of computer modeling, identifying an optimum set of breakpoints has been done primarily by trial and error. Combining a spreadsheet with controllable chromatography modeling software has allowed to implement a systematic approach to bi- and tri-linear gradient optimization.

"Advanced high performance liquid chromatography method development: Discovering unexpected choices in chromatography", H.J.Rieger, I.Molnar, J.Chromatogr., 2002, 948, 43. (2002)
The influence of some important experimental parameters on resolution of chromatograms as well as the validity of widely used rules of thumb and of common expectations about how to improve resolution is discussed. It will be shown on selected examples, that the general expectations about how the experimental parameters have to be adjusted for better resolution does not cover all chances for resolution improvement. The tool for understanding the method and to discover all chances for increasing selectivity is the resolution map of a method.

"Computerized design of separation strategies in reversed-phase liquid chromatography: Development of DryLab software", I.Molnar, J.Chromatogr. A, 956 (2002).(pdf)
The development of the DryLab Software is a special achievement in analytical HPLC, which took place in the last 16 years. This paper tries to collect historical building stones and fundaments, which were laid down by the eminent work of Lloyd Snyder, John Dolan, Tom Jupille and many other enthusiastic scientist, from which DryLab has been put together to its state, where it is today. DryLab, being always a subject to changes, according to the needs of the user, never stopped to go on. Under the force of an ever changing science market, the development team of DryLab had to consider not just scientific improvements, but also new technological achievements, such as the introduction of Windows 1.0 and 3.1, later Windows NT and Windows 2000. The recent availability of new 32 bit program-ming tools allowed to carry out calculations of chromatograms much faster, to be able to show peak movements, which result of slight changes - for example - in eluent pH. DryLab is a great success of an interdisciplinary and intercontinental cooperation of many scientists.

"Temperature Selectivity in Reversed-Phase High Performance Liquid Chromatography," John W. Dolan,
J. Chromatogr. A., 965, 195 (2002)..
Reviews the influence of temperature on chromatographic selectivity in reversed-phase HPLC.

"Two-dimensional optimization using different pairs of variables for the reversed-phase high-performance liquid chromato-graphic separation of a mixture of acidic compounds." T.H.Jupille, J.W.Dolan, L.R.Snyder, I.Molnar, J.Chromatogr., 948 (2002) 35.
For ionizable compounds such as organic acids, best results were obtained recently with simultaneous optimization of %B and pH, regardless of ionic strength or temperature. Changes in the pH of eluent A, adjusted to bracket the pK-values of acids (works also for bases and zwitterions), help to understand changes in critical resolution values due to shifts in peak positions.

"Computer-assisted optimization in the development of a high performance liquid chromatographic method for the analysis of kava pyrones in Piper methysticum preparations.", A.H.Schmidt, I.Molnar, J.Chromatogr., 948 (2002) 51.(pdf)
A new strategy for neutral compounds, contained in many phytopharmaceuticals, was presented at HPLC 2001 in Maastricht by Molnar and Schmidt. The systematic work with kava pyrones and three different organic modifiers, methanol, acetonitrile and 2-propanol, by simultanously changing gradient slope versus temperature or gradient slope versus pH reveals the true composition of such mixtures.

"Advanced high performance liquid chromatography method development: Discovering unexpected choices in chromatography", H.J.Rieger, I.Molnar, J.Chromatogr., 948 (2002) 43.
The analytical chemist is interested to learn more about the influence of the experimental parameters on the resolution, but can often only rely on experiments, he was able to carry out in a given time in a project. There are however often as many chances to improve resolution in the "unexpected" direction as by varying them in the "expected" way. The tools for understanding the method and discover all chances for improved selectivity are the different resolution maps.

"Lipophilicity and pKa Estimates from Gradient HighPerformance Liquid Chromatography", Roman Kaliszan, Piotr Haber, Tomasz Baczek, Danuta Siluk, and Klara Valko, J. Chromatogr. A., 965, 117 (2002).
DryLab is used in a study in which the linear solvent strength model of gradient elution is applied to estimate parameters of lipophilicity and acidity of a series of drugs and model chemicals.

"Computer Optimization of the RP-HPLC Separation of Some Taxoids from Yew Extracts,", M.L. Hajnos, M. Waksmundzka-Hajnos, K. Glowniak, Acta Chromatographica, 12, 211 (2002).
DryLab G is used to optimize the reversed-phase HPLC separation of taxoids from yew.

"Variability of Column Selectivity for Reversed-Phase High-Performance Liquid Chromatography. Compensation by Adjustment of Separation Conditions", J.W. Dolan, L.R. Snyder, T.H. Jupille, and N.S. Wilson, J Chromatogr. A., 960 (2002) 51-67.

"Use of DRYLAB to compare octadecylsilane and carbon supports for reversed-phase chromatography of triazine herbicide test solutes"
Adam P.Schellinger, Yun Mao, Peter W.Carr,
Anal.Bioanal.Chem. 373 (2002) 587-594.

Two different stationary phases, carbon coated ZrO2 and C18 modified silica were compared. They show very different selectivity. The DryLab software was used to evaluate the different selectivities using a sample of triazine herbicides.

2001

"Isocratic Liquid Chromatographic Method for the Analysis of Roxithromycin and Structurally Related Substances in Bulk Samples"
H.K.Chepkwony, F.N.Kamau, E.Rodriguez, E.Roets, J.Hoogmartens,
Chromatographia, 54 (2001) 725-729
DryLab-Software was used to determine the optimum column temperature and mobile phase pH for the separationof mixtures of roxithromicin and related compounds

" Unexpected Results in Chromatography", I.Molnar, LC-GC-International, 14,4 (2001) 231.
Unusual experiments can provide surprisingly good analytical solutions. When developing chromatographic methods, analysts use in most cases a combination of experience and instinct to choose initial starting conditions. This is often followed by a period of trial-and-error optimization, until the desired method is achieved. The article illustrates, how the process of chromatographic method
development can be improved using computer modelling and simulation.

" Computer-Assisted Scale-Up from Analytical HPLC to Preparative MPLC for the Separation of Phenolic Compounds ",
T. Wennberg, J.P. Rauha, and H. Vuorela, Chromatographia, 53 (Suppl.), S240-S245 (2001).
Two gradient runs were used to initiate DryLab simulation. When optimized gradient conditions were determined, DryLab was used to predict separation for a larger column.

" Automatization for Development of HPLC Methods ",
M. Pfeffer and H. Windt, Fresenius J. Anal. Chem., 369(1), 36 (2001).
DryLab is used to optimize mobile phase and temperature after evaluating chromatograms of gradient elution separations performed automatically by column switching. The automated procedure was applied to more than three dozen substances (steroidal intermediates) with a time savings of more than a third.

" Computer-Assisted High-Performance Liquid Chromatography Method Development with Applications to the Isolation and Analysis of Phytoplankton Pigments ", Laurie Van Heukelem and Crystal S. Thomas, J. Chromatogr. A., 910, 31 (2001).
DryLab is used in method development with the goal of enhancing separations through the exclusive use of gradient time and column temperature. The resulting method is simple, fast, demonstrates excellent transferability and is ideal for the quantitative analysis of pigments in dilute natural water samples.

"Computer-Assisted Optimization of Reversed-Phase HPLC Isocratic Separations of Neutral Compounds", T.Baczek, R.Kaliszan, H.A.Claessens, M.A.van Straten, LC-GC-Europe, 14,6, (2001) 304.
Rational selection of optimized experimental conditions for chromatographic separation of analytes is realized nowadays by means of specialized method development software. Two such programs, DryLab (LC Resources, USA, in Europe: Molnar-Institut, Berlin) and ChromSword (Merck, Darmstadt), were compared in a few aspects in this paper. The aim was to make a comparison of the quality of the software packages in the separation of neutral compounds, performed isocratically in RP-HPLC systems. A discussion of the differences in predicted and experimental chromatographic retention parameters is reported. The conclusion reached is, that the two programs provide good predictions of retention data, when predictions are based on %B changes using two initial experimental runs. An additional option of ChromSword, employing the quantitative structure-retention relationship (QSRR), did not to provide precise predictions of the separation, because molecular structural data were used as inputs. Predictions based on molecular structure were unaccurate. The comparison of the performance was only done with ca. 5% of the funtional capabilities, which DryLab was offering. Gradient data were not compared at all.

2000

"Computer Simulation for the Convenient Optimization of Isocratic Reversed-Phase Liquid Chromatography Separations by Varying Temperature and Mobile Phase Strength (%B)", R.G.Wolcott, J.W. Dolan, and L.R. Snyder, J. Chromatogr. A. 869, (2000) 3.
Software is described that allows the rapid development of separations by means of isocratic reversed-phase liquid chromatography (RP-LC) based on the optimization of column temperature (T) and mobile phase strength (%B). For a given sample, four initial experiments are carried out at two different temperatures, using either isocratic or (better) gradient elution. If isocratic experiments are chosen for computer simulation, it is necessary to select appropriate values of %B for these initial runs. Literature data for solute retention as a function of T are reviewed as a basis for estimating values of %B at the two values of T selected. The paper describes use of a newly introduced version of DryLab to optimize reversed-phase isocratic separations by varying temperature and %B.

" Selectivity Differences for C18 Reversed-Phase Columns as a Function of Temperature and Gradient Steepness. I. Optimizing Selectivity and Resolution" ,
J.W. Dolan, L.R. Snyder, T. Blanc and L. Van Heukelem, J. Chromatogr. A., 897, 37 (2000).
Different C18 columns were used with DryLab for the optimization of temperature and gradient steepness for the separation of impurities from a pharmaceutical product. For this application, each of nine different columns gave similar results (a resolution Rs equal to 2.1-2.7), while a column with an embedded polar group gave somewhat better separation (Rs = 3.2).

" Selectivity Differences for C18 Reversed-Phase Columns as a Function of Temperature and Gradient Steepness. II. Minimizing Column Reproducibility Problems ", , J.W. Dolan, L.R. Snyder and T. Blanc, J. Chromatogr. A., 897, 51 (2000).
The replacement of a column in a routine HPLC procedure sometimes leads to an inferior separation because of batch-to-batch changes in selectivity. Two procedures, both based on DryLab, are described to either anticipate or solve this problem.

" Reversed-Phase Separation of Isomers by Varying Temperature and Gradient Time ", , L.R. Snyder and J.W. Dolan, J. Chromatogr. A, 892, 107 (2000).
The difficulty in separating two compounds generally increases as the molecular structures of the two compounds become more similar. Isomers represent a "worst case" scenario, which can serve as a test of the efficacy of a given method development approach. We have advocated the use of DryLab for method development, with particular stress on simultaneous changes in temperature T and either isocratic %B or gradient time tG for the purpose of optimizing selectivity and band spacing. The application of the latter procedure to 137 different isomer pairs resulted in the separation of 90% of these pairs with a resolution of at least Rs = 1.0. It is concluded that optimizing temperature and gradient time is a good first step in method development.

" Gradient Elution Chromatography ", J.W. Dolan and L.R. Snyder, in Encyclopedia of Analytical Chemistry: Instrumentation and Applications, R.A. Meyers, (Ed.), John Wiley & Sons, Ltd., Chichester, Vol. 13, pp. 11342-11360 (2000).
Excellent description of the mathematical background and practical aspects of HPLC gradient elutiontechnique.

"Transferability of Liquid Chromatography Methods Carried Out at Temperatures Other than Ambient ," R. G. Wolcott, J.W. Dolan, L.R. Snyder, S.R. Bakalyar, M.A. Arnold, and J.A. Nichols, J. Chromatogr. A. 869, (2000) 211.
When separations by reversed-phase liquid chromatography (RP-LC) are carried out at temperatures other than ambient, resulting retention times and bandwidths can depend on the equipment used. As a result, an RP-LC separation that is adequate when carried out on one LC system may prove inadequate when the separation is repeated on a second system. In the present study, various temperature-related problems that can result in a failure of method transfer for non-ambient RP-LC methods were examined. Means for correcting for such effects, and thereby ensuring method transferability, are described. Using temperature to optimize HPLC separation, care must be taken to ensure that the column is at the correct temperature. An experimental study is described that leads to simple rules for ensuring good method transfer for methods run at temperatures > ambient.

"Determination of albendazole and its main metabolites in ovine plasma by liquid chromatography with dialysis as an integrated sample preparation technique", P.Chiap, B.Evrard, M.A.Bimazubute, P.de Tullio, Ph.Hubert, L.Delattre, J.Crommen, J.Chromatogr.A., 870. (2000) 121.

Optimization of the HPLC separation conditions for the determination of albendazol and its main metabolites by gradient elution using a 2-dimensional tG-T-DryLab-model is demonstrated. The optimal separation of the compounds of interest from endogenous plasma constituens was obtained by simultaneously optimizing gradient range, temperature and gradient time. DryLab sufficiently resolved the peaks of interest from the endogenous plasma components. The results show excellent comparisons of the DryLab models with the real experiments. .

1999

"Computer Simulation for the Convenient Optimization of Isocratic Reversed-Phase Liquid Chromatography Separations by Varying Temperature and Mobile Phase Strength (%B)," R.G. Wolcott, J.W. Dolan, and L.R. Snyder, J. Chromatogr. A. Chromatogr. A. 869, 3 (1999).
Software is described that allows the rapid development of separations by means of isocratic reversed-phase liquid chromatography (RP-LC) based on the optimization of column temperature (T) and mobile phase strength (%B). For a given sample, four initial experiments are carried out at two different temperatures, using either isocratic or (better) gradient elution. If isocratic experiments are chosen for computer simulation, it is necessary to select appropriate values of %B for these initial runs. Literature data for solute retention as a function of T are reviewed as a basis for estimating values of %B at the two values of T selected.
Describes use of a newly introduced version of DryLab to optimize reversed-phase isocratic separations by varying temperature and %B.

"Reversed-Phase Separation of Complex Samples by Optimizing Temperature and Gradient Time. I. Peak Capacity Considerations," J.W. Dolan, L.R. Snyder, N.M. Djordjevic, D.W. Hill, L. Van Heukelem, and T.J. Waeghe,
J. Chromatogr. A., 857, 1 (1999).
The separation of samples that contain more than 15–20 analytes (n > 15–20) is typically difficult and usually requires gradient elution. We have examined the reversed-phase separation of 24 samples with 8#n#48 as a function of temperature T and gradient time tG. The required peak capacity was determined for each sample after selecting T and tG for optimum selectivity and maximum sample resolution. Comparison of these results with estimates of the maximum possible peak capacity in reversed-phase gradient elution was used to quantify the maximum value of n for some required sample resolution (when T and tG have been optimized). These results were also compared with literature studies of similar isocratic separations as a function of ternary-solvent mobile phase composition, where the proportions of methanol (MeOH), tetrahydrofuran (THF) and water were varied simultaneously. This, in turn, provides information on the relative effectiveness of these two different method development procedures (optimization of T and tG vs % MeOH and %-THF) for changing selectivity and achieving maximum resolution.

(summary) The ability of gradient elution to separate complex samples containing 9–48 components was studied using changes in temperature and gradient time to control selectivity and maximize resolution. It is concluded that samples with >15–20 components will be difficult to separate with Rs > 1. Other means of optimizing resolution (mixed organic solvents) appear no better in this respect.

"Reversed-Phase Separation of Complex Samples by Optimizing Temperature and Gradient Time. II. The Use of 2-Run Assay Procedures," J.W. Dolan, L.R. Snyder, N.M. Djordjevic, D.W. Hill, L. Van Heukelem, and T.J. Waeghe,
J. Chromatogr. 857, 21 (1999).
(abstract) By optimizing column temperature T and gradient time tG, complex samples can often be separated by means of reversed-phase high-performance liquid chromatography (RP-LC). Conclusions reached in Part I suggest that the complete separation of such samples will be difficult, however, when more than 15–20 components are present in the sample. An alternative approach is to carry out two separations with different conditions (T, tG) in each run. The combination of results from these two runs then allows the total analysis of the sample, providing that every sample component is adequately resolved in one run or the other. Examples of this approach, carried out by means of computer simulation, are shown here for several samples of varying complexity. Also considered is the ability of a single separation where T and tG are optimized to enable the separation and analysis of one or more individual sample components from complex mixtures (e.g., drugs in animal plasma), including the resolution of isomeric compounds from each other.

(summary) Samples containing more than 15–20 components are difficult to separate in a single HPLC run. However, if two runs are carried out with different conditions, it is possible to separate some compounds in one run and other compounds in the second run. Together, this may result in separation of every component in one run or the other.

"Reversed-Phase Separation of Complex Samples by Optimizing Temperature and Gradient Time. III. Improving the Accuracy of Computer Simulation," J.W. Dolan, L.R. Snyder, L.C. Sander, P. Habner, T. Baczek, and R. Kaliszan,
J. Chromatogr. 857, 41 (1999).
(abstract) Previous studies have shown that four experimental runs, where both temperature T and gradient time tG are varied, can be used for the reliable prediction of separation as a function of these two variables (2-D optimization). Computer simulation (e.g., DryLab®) can then be used to predict "optimized" conditions for maximum sample resolution using either isocratic or gradient elution. Samples that contain a large number of components (e.g., n > 15–20) present a greater challenge. Resolution for these more complex samples is often quite sensitive to small changes in T or tG, in turn requiring greater accuracy in predictions that result from computer simulation. In the present study of several samples, we have examined computer simulation errors that can arise from inexact expressions for retention time as a function of T, tG, or isocratic %B. Resulting conclusions are applicable to both complex and simpler samples, in either 1-D or 2-D optimization. Means to anticipate and minimize the impact of these predictive errors are examined.

(summary) A detailed examination is made of the accuracy of DryLab predictions when either gradient time, %B or temperature is varied. It is concluded that these predictions should be generally adequate, except in the case of using gradient data for isocratic predictions. The latter are less reliable, with an average error equivalent to 0.5–1.0 Rs units.

"Gradient Elution Chromatography," in Encyclopedia of Analytical Chemistry: Instrumentation and Applications, J.W. Dolan and L.R. Snyder (John Wiley & Sons, New York).

"Essential Guides to Method Development in HPLC," in Encyclopedia of Separation Science, J.W. Dolan and L.R. Snyder (Academic Press, London).

"A New Approach for the Reversed-Phase Separation of Peptide and Protein Mixtures," J.W. Dolan and L.R. Snyder,
LC•GC, 17(4S), S17–S24 (1999).
Illustration of the use of DryLab to optimize reversed-phase peptide and protein separations for both assay and purification goals.

"Critical comparison of retention models for optimization of the separation of anions in ion chromatography
III. Anion chromatography using hydroxide eluents on a Dionex AS11 stationary phase"
John E.Madden, Nebojsa Avdalovic, Peter E.Jackson, Paul R.Haddad
J.Chromatogr.A, 837 (1999) 65-74
Extensive experimental retention data were gathered for 21 anions (fluoride, acetate, formate, bromate, chloride, nitrite, methanesulfonate, bromide, chlorate, nitrate, jodide, thiocyanate, succinate, sulfate, tartrate, oxalate, tungstate, phthalate, chromate, thiosulfate and phosphate) using hydroxide eluents of varying concentration. Although the purely theoretical LSSM was found to give adequate performance, the EEPM (in which a linear relationship is assumed between the logarithm of the retention factor and the logarithm of eluent strength, but the slope is determined empirically) and DryLab performed better, with DryLab giving the best accuracy and precision of the 3 models.

1998

"Reversed-Phase Gradient Elution: How to Get Better Results with Less Work," I. Molnar, L.R. Snyder, and J.W. Dolan, LC•GC Intern., 11, 374 (1998).
Examples of HPLC method development where different variables are optimized by means of DryLab: gradient time and temperature or gradient time and pH. Problems with complex samples and method transfer can be solved by means of computer simulation.

"Systematic Approaches to HPLC Method Development for Reversed-Phase Separation," L.R. Snyder and J.W. Dolan, Chem. Anal.(Warsaw), 43, 495 (1998).
A summary of the present status of computer-assisted reversed-phase HPLC method development, with emphasis on two different approaches for optimizing selectivity and resolution: optimizing a) the %-acetonitrile and %-methanol in the mobile phase, or b) temperature and either gradient time or isocratic %B.

"Simultaneous Variation of Temperature and Gradient Steepness for Reversed-Phase HPLC Method Development. I. Application to 14 Different Samples Using Computer Simulation," J.W. Dolan, L.R. Snyder, N,M. Djordjevic, D.W. Hill, D.L. Saunders, L. Van Heukelem and T.J. Waeghe, J. Chromatogr. A, 803, 1 (1998).
DryLab was used to optimize the separation of 14 "difficult" samples (having 9–40 components) by means of changes in temperature and gradient time. Nine of these samples could be separated with Rs > 1. Predicted separations agreed closely with experimental results.

"Simultaneous Variation of Temperature and Gradient Steepness for Reversed-Phase HPLC Method Development. II. The Use of Further Changes in Conditions," J.W. Dolan, L.R. Snyder, D.L. Saunders and L. Van Heukelem, J. Chromatogr. A, 80 , 33 (1998).
Various means were explored in order to further improve separation after optimizing temperature T and gradient time tG: (a) optimizing the initial %B in the gradient, (b) using segmented gradients, (c) changing some other variable (pH, solvent, column), followed by reoptimizing T and tG. Option (a) resulted in a 0–20% further increase in Rs; option (b) resulted in <10% increase in Rs; option (c) resulted in an 0.1–3-fold increase in Rs. However, option (c) requires further experiments, whereas options (a) and (b) do not.

"The Linear-Solvent-Strength Model of Gradient Elution," L.R. Snyder and J.W. Dolan, Adv. Chromatogr., 38, 157–160 (1998).
A review of the best current model for reversed-phase gradient elution showing how it can be used to predict separation as a function of gradient conditions.

" A Computer-Assisted Strategy for HPLC Method Development. II. Simultaneous Changes in Temperature and Gradient Steepness Combined with Change in One or More Other Variables ", J.W. Dolan, L.R. Snyder, D.L. Saunders, and L. Van Heukelem, J. Chromatogr. A, 803 (1998).

"Maintaining Fixed Band Spacing when Changing Column Dimensions in Gradient Elution," J.W. Dolan and L.R. Snyder, J. Chromatogr., 799, 21 (1998).
The usual rule for maintaining the same gradient separation when changing column dimensions is to keep (gradient time) x (flow rate)/(column volume) constant. However, this also requires maintaining the equipment dwell volume constant as well. Examples are shown of large changes in separation when the dwell volume is ignored

"Robuste HPLC-Methoden", I. Molnar, LaborPraxis, Juli-September 1998
Teil 1: Der Validierungsprozess bei HPLC-Analysen und die rasche Beurteilung von Schwachstellen in der Chromatographie
Teil 2: Definition und Überprüfung der Robustheit
Teil 3: Robuste isokratische und robuste Gradientenmethoden
Teil 4: Zulässige Toleranzen der eingestellten Atrbeitsparameter

1997

"Validation of Robust Chromatography Methods Using Computer-Assisted Method Development for Quality Control. II," Imre Molnar, LC•GC Internat., 10(1), 32 (1997).
Illustration of the use of robust resolution maps as provided by DryLab to improve method robustness and transfer.

"Computer-Assisted Separation by HPLC with Diode Array Detection and Quantitative Determination of Furanocoumarins from Archangelica Officinalis," W. Markowski and K.L. Czapinska, Chem. Anal. (Warsaw) 42, 353 (1997).
Use of DryLab to optimize a gradient elution separation. Predicted and experimental retention times were in good agreement.

"Determination of 1,8-Dihydroxyanthranoids in Senna " Wolfgang Metzger and Klaus Reif, J. Chromatogr., A., 740, 133 (1996).
A new method for the determination of 1,8-hydroxyanthranoids in senna was developed with the use of DryLab.

"Computer Optimization of the High-Performance Liquid Chromatographic Enantioseparation of a Mixture of 4-dinitrophenyl Amino Acids on a Quinine Carbamate-Type Chiral Stationary Phase Using DryLab," M. Lammerhofer, P. Di Eugenio, I. Molnar, and W. Lindner, J. Chromatog. B, 689, 123 (1997).
First application of DryLab to the separation of chiral isomers.

"Changing Reversed-Phase High Performance Liquid Chromatography Selectivity. Which Variables Should be Tried First?" L.R. Snyder, J. Chromatog. B, 689, 105 (1997).
The relative effectiveness of different ways to change selectivity is compared. Mixing two organic solvents such as methanol and tetrahydrofuran is best, changing solvent strength (%B) or column type is next, and temperature provides the smallest change in values of a. However, all of these changes in conditions can be effective for a given sample.

"Selectivity Control in HPLC Method Development," L.R. Snyder, J.W. Dolan, I. Molnar, and N. M. Djordjevic, LC•GC, 15(2), 136 (1997).
First demonstration that the simultaneous optimization of temperature and gradient time can be an effective method development approach for reversed-phase HPLC. Precursor to the later use of DryLab for such predictions.

1996

Determination of 1,8-dihydroxyanthranoids in senna.
W.Metzger, K.Reif
J.Chromatogr.A, 740 (1966) 133-138
The HPLC method development was supported by the DryLab software,
in the simultaneous separation and determination of 17 bianthranyls and anthraquinones in senna drugs. The analytical procedure offers a lot of advantages compared with other published methods.

"Combined Use of Temperature and Solvent Strength in Reversed-Phase Gradient Elution. I. Predicting Separation as a Function of Temperature and Gradient Conditions," P.L. Zhu, L.R. Snyder, J.W. Dolan, N.M. Djordjevic, D.W. Hill, L.C. Sander and T.J. Waeghe, J. Chromatogr. A, 756, 21(1996).
An experimental demonstration that four experimental runs with temperature and gradient steepness varying can be used to accurately predict separation as a function of these two variables.

"Combined Use of Temperature and Solvent Strength in Reversed-Phase Gradient Elution. II. Comparing Selectivity for Different Samples and Systems," P.L. Zhu, J.W. Dolan, and L.R. Snyder, J. Chromatog. A, 756, 41 (1996).
A theoretical procedure for determining the relative ability of temperature or gradient time to change selectivity (values of a).

"Combined Use of Temperature and Solvent Strength in Reversed-Phase Gradient Elution. III. Selectivity for Ionizable Samples as a Function of Sample Type and pH," P.L. Zhu, J.W. Dolan, L.R. Snyder, D.W. HIll, L. Van Heukelem, and T.J. Waeghe," J. Chromatog. A, 756, 51 (1996).
An experimental demonstration of the relative effectiveness of temperature or gradient time to change selectivity for 8 different ionizable samples (mixtures of acids and/or bases). Average change in a was 51% for temperature variation and 74% for change in gradient steepness.

"Combined Use of Temperature and Solvent Strength in Reversed-Phase Gradient Elution. IV. Selectivity for Neutral (non-ionized) Samples as a Function of Sample Type and Other Separation Conditions," P.L. Zhu, J.W. Dolan, L.R. Snyder, N.M. Djordjevic, D.W. HIll, J.-T. Lin, L.C. Sander, and L. Van Heukelem, J. Chromatog. A, 756, 63 (1996).
An experimental demonstration of the relative effectiveness of temperature or gradient time to change selectivity for 9 different neutral samples. Average change in a was 23% for temperature variation and 23% for change in gradient steepness.

"Computer Optimization for RP-HPLC Separation of Some Nucleosides," T.H. Dzido and A. Sory, Chem. Anal. (Warsaw), 41, 113 (1996).
Demonstration of the accuracy of DryLab predictions for these separations.

"Validation of Robust Chromatography Methods Using Computer-Assisted Method Development for Quality Control. I." Imre Molnar, LC•GC Internat., 9(12), 800 (1996).
Describes problems in method robustness and the use of computer simulation to recognize and to solve these problems.

"High-Performance Liquid Chromatographic Separation of the Impurities in a Pharmaceutical Raw Material with the Aid of Computer Simulation," H.W. Bilke, I. Molnar, and Ch. Gernet, J. Chromatog. A, 729, 189 (1996).
Varying gradient time and pH resulted in the adequate separation of this 15-component sample, but the method is very sensitive to changes in pH. Experimental results are in good agreement with DryLab
predictions.

"The Optimization of Peptide Mapping via Computer Simulation," L.R. Snyder in New Methods in Peptide Mapping for the Characterization of Proteins, W. Hancock, ed., CRC Press (Boca Raton, Florida, 1996), p. 31.
Examples of the separation of various peptide samples by means of gradient optimization using DryLab. Comparisons of predictions vs experiment showed good agreement.

"Initial Experiments in HPLC Method Development. I. Use of a Starting Gradient Run," L.R. Snyder and J.W. Dolan, J. Chromatog. A., 721, 1 (1996).
A single reversed-phase gradient run can be used to accurately predict the best %B value for a corresponding isocratic separation with an accuracy of about 1%.

"Initial Experiments in HPLC Method Development. II. Recommended Approach and Conditions for Isocratic Separation," J.L. Lewis, L.R. Snyder, and J.W. Dolan, J. Chromatog. A., 721, 15 (1996).
A synthetic mixture of 11 substituted benzenes is used to evaluate a new approach to method development. A single gradient run is carried out initially and used to select conditions for separation as a function of various ternary solvent mixtures in isocratic reversed-phase HPLC.

"New Approaches to HPLC Method Development," L.R. Snyder, Today's Chemist at Work, 5(1) 29 (1996).
The relative advantage of using different variables to optimize selectivity and resolution are compared. Since most samples can be separated using any variable(s) for this purpose, it is important to consider other consequences of this choice: convenience, cost, method robustness, etc. It is concluded that the use of either temperature and either gradient time or isocratic %B, or changes in % acetonitrile and % methanol are generally superior in this respect.

1994

"Computer-Assisted Rapid Development of Gradient High-Performance Liquid Chromatographic Methods for the Analysis of Antibiotics," R. Bonfichi, J. Chromatog. A, 678, 213 (1994).
Analysis of a glycopeptide antibiotic. Development of a multisegment gradient.

"Separation of Arachidonic Acid Metabolites by On-Line Extraction and Reversed-Phase High-Performance Liquid Chromatography Optimized by Computer Simulation," H. Fritsch, I. Molnar, and M. Wurl, J. Chromatog. A, 684, 65 (1994).
Development and use of a multistep gradient.

"Temperature as a Variable in Reversed-Phase HPLC Separation of Peptide and Protein Samples. I. Optimizing the Separation of a Growth Hormone Tryptic Digest," W. Hancock, R.C. Chloupek, J.J. Kirkland, and L.R. Snyder, J. Chromatogr. A, 686, 31 (1994).
Groundwork for exploring temperature effects in gradient separations.

"Temperature as a Variable in Reversed-Phase HPLC Separation of Peptide and Protein Samples. II. Selectivity Effects Observed in the Separation of Several Peptide and Protein Mixtures," R.C. Chloupek, W. Hancock, B.A. Marchylo, J.J. Kirkland, B. Boyes, and L.R. Snyder, J. Chromatogr. A, 686, 45 (1994).
Groundwork for exploring temperature effects in gradient separations.

1993

"Computergestutzte Optimierung in der Chromatographie," I. Molnar, LaborPraxis, X(12), 40 (1993).
(Paper in German.)

"Use of Computer Simulations in the Development of Gradient and Isocratic High-Performance Liquid Chromatography Methods for Analysis of Drug Compounds and Pharmaceutical Intermediates," L. Wrisely, J. Chromatogr., 628, 191 (1993).

"Computer-assisted Optimization of the Gas Chromatographic Separation of Equine Estrogens," Arya Jayatilaka and Colin F. Poole, J. Chromatogr., 617, 19 (1993).
Separation of estrogens after acid hydrolysis and conversion to t-butyl-TMS derivatives. Separation on SE-30 capillary. Agreement between predicted and actual retention for a two-segment program averaged better than 1%.

1992

"Optimization of the Separation of the Rp and Sp Diastereomers of Phosphate-methylated DNA and RNA Dinucleotides," A.J.J.M. Coenen, L.H.G. Henckens, Y Mengerink, Sj van der Wal, P.J.L.M. Quaedifleig, L.H. Koole, and E.M. Meijer, J. Chromatogr., 596, 59 (1992).
Reversed-phase separation was studied with respect to pH, organic modifier type and concentration, and reversed-phase packing material. DryLab G was used to deduce the optimum conditions.

"Multiparameter Computer Simulation for HPLC Method Development," J.W. Dolan, J.A. Lewis, W.D. Raddatz, and L.R. Snyder, Am. Lab., 24(3), 40D (1992).
Description of the general principles underlying DryLab I/mp.

"Computer Simulation as a Tool for the Rapid Optimization of the High-Performance Liquid Chromatographic Separation of a Tryptic Digest of Human Growth Hormone," R.C. Chloupek, W.S. Hancock, and L.R. Snyder, J. Chromatogr., 594, 65 (1992).
Discusses importance of peak matching. Agreement between predicted and actual retention was 0.3%.

"Computer-Assisted Enhancement of Gas Chromatographic Principles for the Teaching Laboratory. Prediction of Retention Data and Chromatographic Separation," R.L. Grob, E.F. Barry, S. Leepipatpiboon, J.M. Ombaba, and L.A. Colon, J. Chromatog. Sci., 30, 177 (1992).
Application of DryLab GC to chromatography instruction and teaching.

"Application of the Gradient Elution Technique. Demonstration with a Special Test Mixture and the DryLab G/plus Method Development Software," R. Dappen and I. Molnar, J. Chromatog., 592, 133 (1992).
A 10-component separation was developed using DryLab. Retention predictions were accurate within 0.3 min.

"Determination of By-Products in Atenolol," H. Hoffmann and I. Molnar, Pharm. Ztg. Wiss., 1(5), 137 (1992).
Development of a gradient method for the analysis of five by-products of atenolol. Complete method development took only three days (paper in German).

1991

"Software for Chromatographic Method Development," A. Drouen, J. W. Dolan, L.R. Snyder, A. Poile, and P. Schoenmakers, LC•GC, 9, 714 (1991).
Summary of symposium on computer-assisted method development from the 1991 Pittsburgh Conference.

"Practical Applications of Computer Simulation for Gas Chromatography Method Development," G.N. Abbay, E.F. Barry, S. Leepipatpiboon, T. Ramstad, M.C. Roman, R.W. Siergiej, L.R. Snyder, and W.L. Winniford, LC•GC, 9(2), 1001 (1991).
Application of DryLab GC to wide range of environmental, pharmaceutical, and process samples.

"Computer Simulation of Gradient Elution Separation. Accuracy of Predictions for Nonlinear Gradients," J.D. Stuart, D.D. Lisi, and L.R. Snyder, J. Chromatogr., 555, 1 (1991).
Predictive accuracy is similar in both linear and nonlinear gradients except for slightly larger errors immediately after a change in gradient slope. This is the result of errors in the gradient profile introduced by the mixing volume of the system.

"Separation and Detection of Oxidation Products in Neurolite Raw Material," P.A. Ryan, B.A. Ewels, and J.L. Glajch, J. Chromatogr., 550, 549 (1991).
DryLab G/plus was used to determine the optimum gradient separation conditions.

"Computer Simulation of Isocratic Retentions of Alkylketones Using Gradient Data," J.D. Stuart and D.D. Lisi, J. Chromatogr., 550, 77 (1991).
"Tricking" DryLab G/plus into predicting isocratic retention works. Average error is in the 3–5% range.

"Computer-Aided Optimization of High-Performance Liquid Chromatographic Analysis of Flavonoids from Some Species of the Genus Althaea," T.H. Dzido, E. Soczewinski, and J. Gudej, J. Chromatogr., 550, 71 (1991).
Methods were developed for both acetonitrile-water and methanol–water systems.

"Fast Development of a Robust High-Performance Liquid Chromatographic Method for Ginkgo biloba Based on Computer Simulation," I. Molnar, K.H. Gober, and B. Christ, J. Chromatogr., 550, 39 (1991).
The entire method was developed in less than 8 hours; the equivalent to 50 chromatographic runs were simulated.

"Computer Simulation as an Aid in Method Development for Gas Chromatography. III. Examples of Its Application," L.R. Snyder, D.E. Bautz, and J.W. Dolan, J. Chromatogr., 541, 34 (1991).
Extension of DryLab GC to complex samples.

"Computer Simulation as an Aid in Method Development for Gas Chromatography. II. Changes in Band Spacing as a Function of Temperature," J.W. Dolan, L.R. Snyder, and D.E. Bautz, J. Chromatogr., 541, 21 (1991).
Confirmation of selectivity changes with temperature.

"Computer Simulation as an Aid in Method Development for Gas Chromatography. I. The Accurate Prediction of Separation as a Function of Experimental Conditions," D.E. Bautz, J.W. Dolan, and L.R. Snyder, J. Chromatogr., 541, 1 (1991).
Further validation of DryLab GC approach.

"High-Performance Liquid Chromatography Retention Index and Detection of Nitrated Polycyclic Aromatic Hydrocarbons," T-Y. Liu and A Robbat, Jr., J. Chromatogr., 539, 1 (1991).
DryLab G/plus was used to determine the optimum gradient separation conditions in both acetonitrile–water and methanol–water systems. Predicted and actual retentions typically differed by only 1%.

"Computer-Assisted HPLC Method Development in a Pharmaceutical Laboratory," N.G. Mellish, LC•GC, 9, 845 (1991).
Examples of DryLab use in pharmaceutical method development.

1990

"Computer-Assisted Optimization of Temperature-Programmed Gas Chromatographic Separations," D.E. Bautz and J.W. Dolan, Am. Lab., 22(17), 40T (1990).
Description of commercial program and application to a complex sample (spearmint oil).

"Separation of Large Biomolecules by Gradient Elution," L.R. Snyder in HPLC of Biological Macromolecules, F.E. Regnier and K.M. Gooding, eds., Marcel Dekker (New York, 1990), p. 231.
A review of the use of gradient elution and computer simulation (DryLab G/plus) for the separation of large biomolecules.

"The 30S Ribosomal Proteins as a Model for the Optimized Separation of Large Biomolecules by Reversed-Phase HPLC," B.F.D. Ghrist, B.S. Cooperman, and L.R. Snyder in HPLC of Biological Macromolecules, F.E. Regnier and K.M. Gooding, eds., Marcel Dekker (New York, 1990), p. 403.
Application of DryLab G/plus to the separation of the 30S ribosomal proteins.

"Computer Simulation (Based on a Linear-Elution-Strength Approximation) as an Aid for Optimizing Separations by Programmed-Temperature GC," D.E. Bautz, J.W. Dolan, W.D. Raddatz, and L.R. Snyder, Anal. Chem., 62, 1560 (1990).
Development of the basic theory and assumptions underlying DryLab GC. Preliminary experimental validation of the model.

"High-Performance Liquid Chromatographic Computer Simulation Based on a Restricted Multiparameter Approach. II. Applications," L.R. Snyder, J. W. Dolan, and D.C. Lommen, J. Chromatogr., 535, 75 (1990).
Examples of the independent multiparameter approach described above in J. Chromatogr., 535, 55 (1990).

"High-Performance Liquid Chromatographic Computer Simulation Based on a Restricted Multiparameter Approach. I. Theory and Verification," J. W. Dolan, D.C. Lommen, and L.R. Snyder, J. Chromatogr., 535, 55 (1990).
Basic groundwork for the development of DryLab I/mp. Confirms that multiple variables may be treated independently if the range of variation is kept sufficiently narrow.

"Computer Simulation for Optimization of HPLC of Some Phenolic Pollutants," W. Markowski, T.H. Dzido, and E. Soczewinski, J. Chromatogr., 523, 81 (1990).
Use of DryLab G/plus to develop a multisegment gradient separation.

"Liquid Chromatography Expert Systems: A Modular Approach," J.W. Dolan and L.R. Snyder, Am. Lab., 22(8), 50 (1990).
Brief review of currently available expert system and simulation software approaches.

"A Method Development System for Liquid Chromatography," J.R. Gant, F.L. Vandemark, and A.F. Poile, Am. Lab., 22 (8), 15 (1990).
Use of DryLab programs as the core of a systematic method development strategy.

"Reproducibility Problems in Gradient Elution Caused by Differing Equipment," L.R. Snyder and J.W. Dolan, LC•GC, 8, 524 (1990).
Why gradient separations do not reproduce well on different HPLC systems, and how DryLab can help solve these problems.

"Use of High-Performance Liquid Chromatography in the Pharmaceutical Industry," F. Erni, J. Chromatogr., 509, 141 (1990).
Briefly describes use of DryLab programs for pharmaceutical method development.

"Integration of Computer-Aided Method Development Techniques in LC," J.W. Dolan and L.R. Snyder. J. Chromatog. Sci., 28, 379 (1990).
Comparison of currently available simulation software approaches to LC optimization.

1989

"High-Performance Liquid Chromatography of Thermus Aquaticus 50S and 30S Ribosomal Proteins," I. Molnar, R.I. Boysen, and V.A. Erdmann, Chromatographia, 28(1/2), 39 (1989).
Application of DryLab G to complex protein samples; agreement between predictions and observed retention times better than 0.7%.

"Predicting Reversed-Phase Gradient Elution Separations by Computer Simulation: A Comparison of Two Programs," J. Schmidt, J. Chromatogr., 485, 421 (1989).
Compares DryLab G and LCSIM predictive accuracy in relationship to measured dwell volume.

"Separation of Mixtures of OPA-Derivatized Amino Acids by Reversed-Phase Gradient Elution, The Accuracy of Computer Simulation for Predicting Retention and Bandwidth," J.D. Stuart, D.D Lisi, and L.R. Snyder, J. Chromatogr., 485, 657 (1989).
A further test of the accuracy of bandwidth predictions by DryLab G/plus.

"Computer-Assisted Development of a High-Performance Chromatographic Method for Fractionating Selected Nitro Derivatives of Polyaromatic Hydrocarbons," D.J. Thompson and W.D. Ellenson, J. Chromatogr., 485, 607 (1989).
Using DryLab G to develop a segmented gradient.

"Development of a High-Performance Liquid Chromatographic Method for Fluoroxypyr Herbicide and Metabolites Using Computer Simulation with DryLab G Software," R.G. Lehman and J.R. Miller, J. Chromatogr., 485, 581 (1989).

"Practical Approach for High-Performance Liquid Chromatographic Method Development: Assaying Synthetic Intermediates of a Leukotriene Inhibitor," J. Fulper, J. Chromatogr., 485, 579 (1989).
Application of DryLab I.

"Peak Tracking in High-Performance Liquid Chromatography Based on Normalized Areas. A Ribosomal Protein Sample as an Example," I. Molnar, R. Boysen, and P. Jekow, J. Chromatogr., 485, 569 (1989).
Using DryLab G to identify a "hidden" band in a protein separation.

"Prediction of Retention Times in Ion-Exchange Chromatography," T. Sasegawa, Y. Sakamoto, T. Hirose, T. Yoshida, Y. Kobayashi, and Y. Sato, J. Chromatogr., 485, 533 (1989).
Application of DryLab G to ion-exchange separations of biomacromolecules.

"Computer-Aided Optimization of High-Performance Liquid Chromatography in the Pharmaceutical Industry," E.P. Lankmayr, W. Wegscheider, J.C. Gfeller, N.M. Djordjevic, and B. Schreiber, J. Chromatogr., 485, 183 (1989).
Integration of DryLab programs into an overall scheme for efficient method development.

"DryLab Computer Simulation for HPLC Method Development. II. Gradient Elution," J.W. Dolan, D.C. Lommen, and L.R. Snyder, J. Chromatogr., 485, 91 (1989).
Review of the application of DryLab G/plus to various samples.

"DryLab Computer Simulation for HPLC Method Development. I. Isocratic Elution," L.R. Snyder. J.W. Dolan, and D.C. Lommen, J. Chromatogr., 485, 63 (1989).
Review of the application of DryLab I/plus to various samples.

1988

"Design of Optimized High-Performance Liquid Chromatographic Gradients for the Separation of Either Small or Large Molecules. II. Background and Theory," B.F.D. Ghrist and L.R. Snyder, J. Chromatogr., 459, 25 (1988).
Analysis of differences in sample response to changes in gradient conditions.

"Design of Optimized High-Performance Liquid Chromatographic Gradients for the Separation of Either Small or Large Molecules. I. Minimizing Errors in Computer Simulations," B.F.D. Ghrist, B.S. Cooperman, and L.R. Snyder, J. Chromatogr., 459, 1 (1988).
Discussion of errors that can affect predictive accuracy of DryLab and recommendations for correcting such errors.

"Computer Simulation in HPLC: Making Multistep Gradients Practical," T.H. Jupille, J.W. Dolan, and L.R. Snyder, Am. Lab., 20(12), 20 (1988).
Application of principles of DryLab G.

"Quantitative Determination of Limonin in Citrus Juices by HPLC Using Computerized Solvent Optimization," P.E. Shaw and C.W. Wilson, J. Chromatog. Sci., 26, 478 (1988).
Use of DryLab I for solvent optimization.

"Computer Simulation as a Means of Developing an Optimized Reversed-Phase Gradient Separation," J.W. Dolan, L.R. Snyder, and M.A. Quarry, Chromatographia, 24, 261 (1988).
An in-depth discussion and applications of DryLab G.

"Developing a Gradient Elution Method for Reversed-Phase HPLC," J.W. Dolan and L.R. Snyder, LC•GC, 5, 970 (1988).
Application of DryLab G method development strategy to a real sample.

"Design of Optimized High-Performance Liquid Chromatographic Gradients for the Separation of Either Small or Large Molecules. III. An Overall Strategy and its Application to Several Examples," B.F.D. Ghrist and L.R. Snyder, J. Chromatogr., 459, 43 (1988).
An efficient approach to gradient design for complex samples.

"Solvent-Strength Selectivity in Reversed-Phase HPLC," L.R. Snyder, M.A. Quarry, and J.L. Glajch, Chromatographia, 24, 33 (1988).
Extensive data base that shows that the DryLab I approach is generally applicable to most samples; examples of combined solvent-strength and solvent-type optimization for several samples and three different organic solvents.

1987

"Selectivity in Reversed-Phase Gradient Elution as a Function of Gradient Conditions," J.W. Dolan and L.R. Snyder, Chromatography, 2, 49 (1987).
Initial discussion of the application of DryLab G to various samples.

"Predicting Bandwidth in the HPLC Separation of Large Biomolecules. Predicting Bandwidth in the HPLC Separation of Large Biomolecules. A General Model for the Four Common HPLC Methods," M.A. Stadalius, B.F.D. Ghrist, and L.R. Snyder, J. Chromatogr., 387, 21 (1987).
Verification of DryLab G approach to bandwidth calculations. Several hundred examples.

"HPLC Method Development and Column Reproducibility," J.W. Dolan, L.R. Snyder, and M.A. Quarry, Am. Lab., 19(8), 43 (1987).
Application of DryLab 4-5 (the first DryLab program to model retention effects) to the problem of column-to-column reproducibility; adjusting conditions to minimize retention differences.

"Band Spacing in Reversed-Phase HPLC as a Function of Solvent Strength. A Simple and Fast Alternative to Solvent Optimization for Method Development," M.A. Quarry, R.L. Grob., L.R. Snyder, J.W. Dolan, and M. Rigney, J. Chromatogr., 384, 163 (1987).
General discussion of the potential of band-spacing changes via a change in solvent strength. Application of DryLab 4-5 (the ancestor to the binary isocratic reversed phase model in the present DryLab for Windows) to new samples.

"Computer Simulation in HPLC Method Development. Reducing the Error of Predicted Retention Times," L.R. Snyder and M.A. Quarry, J. Liq. Chromatogr., 10, 1789 (1987).
Further work on improving the accuracy of DryLab I and DryLab G predictions; verification of this approach.

"Predicting Bandwidth in the HPLC Separation of Large Biomolecules. Size-Exclusion Studies and the Role of Solute Stokes-Diameter versus Particle Pore-Diameter," B.F.D. Ghrist, M.A. Stadalius, and L.R. Snyder, J. Chromatogr., 387, 1 (1987).
Fundamental data base that finalizes model behind DryLab G predictions for large molecules.

1986

"HPLC Computer Simulation. Optimizing Column Conditions," L.R. Snyder and J.W. Dolan, Am. Lab., 18(8), 37 (1986).
First description of DryLab 1 (the ancestor of the column optimization portion of the present DryLab for Windows) as applied to a steroid sample.

"Fast Method Development for Reversed-Phase HPLC. The Use of Computer Simulations," L.R. Snyder, J.W. Dolan, and M.P. Rigney, LC•GC, 4, 921 (1986).
First description of DryLab 4-5 (the ancestor of the binary isocratic reversed phase module of DryLab for Windows) as applied to a mixture of nitro-aromatic compounds.

"HPLC Separation of Large Molecules. A General Model," L.R. Snyder and M.A. Stadalius in High Performance Liquid Chromatography. Advances and Perspectives, Academic Press (New York, 1986); Vol. 4, p. 195.
Summary of the basic model that underlies DryLab G applied to large molecules.

"Prediction of Precise Isocratic Retention Data from Two or More Gradient Elution Runs. An Analysis of Some Associated Errors," M.A. Quarry, R.L. Grob., and L.R. Snyder, Anal. Chem., 58, 907 (1986).
Development and validation of DryLab I and DryLab G approach for using initial gradient runs to predict either isocratic or gradient separation.

"Separation of Peptide Mixtures by Reversed-Phase Gradient Elution. Use of Flow Rate Changes for Controlling Band Spacing and Improving Resolution," J.L. Glajch, M.A. Quarry, J.F. Vasta, and L.R. Snyder, Anal. Chem., 58, 280 (1986).
First paper to show that a change in solvent strength or equivalent gradient conditions can lead to major changes in band spacing for reversed-phase LC.

1985

"Selecting Column Conditions for Reversed-Phase HPLC Separation. II. Column Configuration and Column Evaluation," L.R. Snyder and P.E. Antle, LC Magazine, 3, 98 (1985).
Simplified summary of the model described in J. Chromatogr., 282, 263 (1983) for DryLab I, with a discussion of its practical implications.

"Optimization Model for the Gradient Elution Separation of Peptide Mixtures by Reversed-Phase HPLC. Application to Method Development and the Choice of Column Configuration," M.A. Stadalius, H.S. Gold, and L.R. Snyder, J. Chromatogr., 327, 93 (1985).
Application of the model described in J. Chromatogr., 327, 27 (1985) to the separation of protein/peptide mixtures by reversed-phase gradient elution.

"Optimization Model for the Gradient Elution Separation of Peptide Mixtures by Reversed-Phase HPLC. Verification of Bandwidth Relationships," M.A. Stadalius, H.S. Gold, and L.R. Snyder, J. Chromatogr., 327, 27 (1985).
Further verification of a preliminary model for predicting the gradient separation of peptides and proteins by reversed-phase gradient elution.

1984

"Optimization Model for the Gradient Elution Separation of Peptide Mixtures by Reversed-Phase HPLC. Verification of Retention Relationships," M.A. Stadalius, H.S. Gold, and L.R. Snyder, J. Chromatogr., 296, 31 (1984).
Development and verification of a model for computer-simulation of reversed-phase gradient elution of peptides and proteins.

"Measurement and Use of Retention Data from High-Performance Gradient Elution. Correction for ‘Nonideal’ Processes Originating Within the Column," M.A. Quarry, R.L. Grob, and L.R. Snyder, J. Chromatogr., 285, 19 (1984).
Analysis of separation phenomena that can limit accuracy of gradient retention data.

"Measurement and Use of Retention Data from High Performance Gradient Elution. Contributions from Nonideal Gradient Equipment," M.A. Quarry, R.L. Grob, and L.R. Snyder, J. Chromatogr., 285, 1 (1984).
An analysis of instrumental factors that can limit the accuracy of gradient retention data.

1983

"High Performance Liquid Chromatographic Column Efficiency as a Function of Particle Composition and Geometry, and Capacity Factor," R.W. Stout, J.J. DeStefano, and L.R. Snyder, J. Chromatog., 282, 263 (1983).
Development of the final model that predicts plate number and bandwidth as a function of conditions for small-molecule samples; used in DryLab I and DryLab G.

"Gradient Elution in Reversed-Phase HPLC Separation of Macromolecules," L.R. Snyder, M.A. Stadalius, and M.A. Quarry, Anal. Chem., 55, 1412A (1983).
Preliminary model for predicting large-molecule separations by gradient elution, particularly for reversed-phase LC.

1982

"Gradient Elution" L.R.Snyder

High Performance Liquid Chromatography. Advances and Perspectives, Cs. Horváth, ed., Academic Press (New York, 1980), Vol. 1, Ch. 4.
Development of the basic theory relating gradient and isocratic separations; essential to later work on DryLab I and DryLab G.