“PRISMA” Model for Computer-Aided HPLC Mobile Phase Optimization Based on an Automatic Peak Identification Approach

Abstract

The tripartite “PRISMA” optimization model, as part of the “PRISMA” system, includes all possible solvent combinations between 1–4 solvents, with a possible fifth one as modifier. The solvent composition is characterized by the solvent strength (S_T) and the selectivity points (P_S).

At a constant S_T the correlation between the P_S and the retention data (horizontal function) can be described by a quadratic function. For constant P_S the solvent strengths and retention data correlate (vertical function) with a logarithmic function. These correlations are used to formulate a mathematical model for the dependence of retention times (capacity factor) on the mobile phase composition. Unknown compounds are estimated in the mathematical model from a sequence of standard chromatograms after having identified individual peaks by an automatic procedure. Only retention times, relative peak areas, and information about the mobile phase compositions are required as input for the identification approach. The approach involves a combination of statistical methods which exploit both the basic properties of retention data and the mathematical relation between retention data, selectivity points, and solvent strength as derived from the “PRISMA” model. Diagnostic information for checking the identification is generated as a by-product. The mathematical model completed by the estimated constants predicts the expected retention times for each possible mobile phase combination. Peak start and peak end times are predicted in a way similar to the retention times, once the identification has been performed. The most important aspects of a chromatogram can thus be predicted for arbitrary mobile phases.

The separation quality of predicted chromatograms is assessed by the chromatographic response function (CRF). The optimal mobile phase combination is that which theoretically generates the chromatogram with the maximal CRF value. This optimal composition is found by a simple mathematical procedure, which maximises the CRF in dependence upon the mobile phase combination. The optimum found is a local one if the starting set of chromatograms contains no variation of the solvent strength, and a global one if, in the set of starting chromatograms, the solvent strength is varied in a suitable way. Recommendations for the starting position are given.

Twelve measurements are necessary for a local optimum, and 15 for the global one. To increase the accuracy, six measurements at three different solvent strength levels are proposed. Generally the highest and the lowest solvent strength level differ by ±(5)% from the middle level.

This strategy is also relevant when modifiers are used in constant amounts. The chromatographic behavior of substances to be separated can be predicted with 1% accuracy from correlations of k' values and selectivity points. Based on these relationships, an automatical mobile phase optimization strategy for isocratic separations is suggested with the “PRISMA” model.     

Practitioner's guide to method development in thin-layer chromatography

The authors provide a personal perspective of method development in thin-layer chromatography for the novice and more experienced chromatographer alike. No attempt has been made at a comprehensive survey of the literature. Instead we provide an overview with insights into a smaller number of approaches that the authors have found useful in their own work and indicate the factors responsible for the variation in retention and their control. The main topics covered are the relationship between sorbent chemistry and retention, the selection of primary solvents for mobile phase optimization and mobile phase optimization using the PRISMA and solvation parameter models.     

Green analytical chemistry-driven response surface modeling to stability-indicating chromatographic method for estimation of cilnidipine and application of high-performance thin-layer chromatography–mass spectrometry for characterization of degradation products

Cilnidipine is a calcium channel blocker that is used to treat cardiac diseases such as angina and high blood pressure. Several column and planar chromatographic methods for estimating cilnidipine in pharmaceutical dosage forms have been documented. However, these method developments have been carried out employing organic solvents such as acetonitrile, methanol, toluene, chloroform, and others as mobile phase components or as sample pretreatment diluents. These organic solvents are neurotoxic and teratogenic to humans and aquatic animals, according to International Council for Harmonization Q3C (R8) recommendations. According to the green analytical chemistry approach, such organic solvents should be reduced or removed during the development of chromatographic methods for environmental protection and the safety of human and aquatic animal life. As a result, the stability-indicating chromatographic estimation of cilnidipine was performed utilizing less toxic organic solvents. To prevent organic solvent waste during method development, mobile-phase optimization was performed using the design of experiment-based response surface modeling. Cilnidipine has been subjected to hydrolysis, oxidation, photolysis, and dry-heat decomposition to determine its stability. The greenness profiles of the suggested and published chromatographic methods were examined using the national environment method index, analytical greenness calculator, green analytical procedure index software, and eco-scale assessment tool.     

Systematic optimization of micellar electrokinetic chromatographic separation of flavonoids

Summary A simple and rapid systematic optimization scheme was described for the micellar electrokinetic chromatographic separation of a group of flavonoids. The scheme employed an interpretative optimization approach to predict the optimum conditions for the separation of a group of flavonoids by micellar electrokinetic chromatography. By performing a set of nine pre-planned experiments conducted over the maximum working range for the system, global optimum separation conditions could be determined. To validate the optimization procedure, additional experiments were performed using the optimum experimental conditions derived from the optimization scheme. The results showed that satisfactory separation of all the peaks could be obtained. In addition, the application of the method in micropreparative micellar electrokinetic chromatography of the flavonoids was demonstrated.     

Gas chromatography–mass spectroscopy optimization by computer simulation,application to the analysis of 93 volatile organic compounds in workplace ambient air

GC–MS optimization method including both advantages from chromatographic separation and mass spectrometric detection was designed for a set of 93 volatile organic compounds. Only a few experiments were necessary to determine the thermodynamic retention parameters for all compounds on a RTX-VMS column. From these data, computer simulation was used in order to predict the retention times of the compounds in temperature programmed gas chromatography. Then, an automatic selection of ions from the NIST database was performed and compared to the optimum conditions (full separation of VOC). This simulation-selection procedure was used to screen a numerous set of GC and MS conditions in order to quickly design a GC–MS method whatever the set of compounds considered.     

Macroporous thin films for planar chromatography

A procedure for the preparation of macroporous silica films suitable for planar chromatography is described. The films are produced by a low pH catalyses of alkyltrialkoxysilanes in oversaturated solution of pore forming organic compounds. A segregated three phase system yields thick films (10–60 µm) that have good adhesion to silica glass supports, uniform, mirror like surface and intercalated micron-dimension pores that permit capillarity driven elution of solvents through the film. A phase diagram demonstrating optimal operating conditions for macroporous and microporous film formation is introduced and analyzed.     

Solvent exchange using hollow fiber prior to separation and determination of some antioxidants by high performance liquid chromatography

This study presents a simple and rapid solvent exchange procedure using a hollow fiber. Antioxidants (Irganox 1010, Irganox 1076 and Irgafos 168) and solvents such as tetrahydrofuran (THF), carbon tetrachloride and toluene were selected as model compounds and sample solvents, respectively. After injection of the sample solution into the hollow fiber and solvent evaporation, the precipitated analytes in lumen and pores of the fiber were washed with methanol (the mobile phase for separation and determination by HPLC-diode array detection) and good chromatographic peaks were obtained. The effect of different parameters such as fiber length, volumes of sample and washing solvents were investigated and the optimum conditions were selected. The repeatability of the method was tested and it was found that the relative standard deviation (R.S.D.) was less than 10% for all analytes. Also enrichment factors of 3.03, 2.21 and 1.19 times were obtained for Irganox 1010, Irganox 1076 and Irgafos 168, respectively, when 200 μL sample and 50 μL methanol (washing solvent) were used.     

A new method of thin-layer chromatography with controlled vapor phase

A new version of thin-layer chromatography with controlled vapor phase is described. It has no analogues in planar and liquid chromatography. The method is based on a dynamic change in the physicochemical properties of a chromatographic system as a result of the contact of the plate bearing analytes with a vapor phase of certain composition created in the chromatographic chamber. The active vapor phase is created either by pumping a gas through the chromatographic chamber or by introducing a solvent vapor from another part of the chamber. The composition and properties of the mobile phase are controlled immediately in the course of separation by means of absorption or adsorption of one or another gas with the mobile or stationary phase. By the examples of benzoic acids and nitroaniline isomers in the presence of carbon oxide and vapors of acetic acid, ammonia, and ethanol, it was shown that this procedure utilizes the difference in the protolytic and solvation properties of adsorbates for changing the adsorption equilibrium and the selectivity and efficiency of separation.     

Stationary phase optimized selectivity liquid chromatography: Basic possibilities of serially connected columns using the "PRISMA" principle

A new procedure (stationary phase optimized selectivity liquid chromatography: SOS-LC) is described for the optimization of the HPLC stationary phase, using serially connected columns and the principle of the "PRISMA" model. The retention factors (k) of the analytes were determined on three different stationary phases. By use of these data the k values were predicted applying theoretically combined stationary phases. These predictions resulted in numerous intermediate theoretical separations from among which only the optimal one was assembled and tested. The overall selectivity of this separation was better than that of any individual base stationary phase. SOS-LC is independent of the mechanism and the scale of separation.     

Influence of selected mobile phase properties on the TLC retention behavior of ziprasidone and its impurities

ABSTRACT

Influence of nine different solvents, either alone or in a mixture, on the retention behavior of ziprasidone and its five impurities were examined by normal-phase thin-layer chromatography. Migration distances of the examined compounds obtained under the examined chromatographic conditions were correlated with calculated mobile phase properties, such as Snyder polarity and Hansen solubility. Linear or second-order polynomial relationships with high correlation coefficients were established between investigated variables. The obtained mathematical functions and statistical results indicated that selected mobile phase properties can be used for the prediction of the retention behavior of ziprasidone and its five impurities.     

Critical compilation of solute-micelle binding constants and related parameters from micellar liquid chromatographic measurements

Over 150 solute-micelle association (binding) constants and free solute retention factors are reported for a variety of neutral compounds and PTH-amino acids. The solute-micelle parameters were calculated from critically evaluated micellar liquid chromatographic data. The potential utility of these parameters for the optimization of micellar liquid chromatography and micellar electrokinetic capillary chromatography, including selection of the surfactant and/or stationary phase and the optimization of surfactant concentration, is briefly discussed.     

Optimization and characterization of the chiral separation of citalopram and its demethylated metabolites by response-surface methodology

Summary Response-surface modelling and sequential optimization have been used for optimization and characterization of the separation of the enantiomers of citalopram, desmethylcitalopram, and didesmethylcitalopram on an acetylated β-cyclodextrin column. In the model chosen the separation conditions mobile phase methanol content, buffer concentration, column temperature, and pH were varied to investigate their influence on the chromatography. It was found that what is good for selectivity within an enantiomer pair is bad for selectivity between enantiomer pairs. Because within-pair and between-pair selectivity does not reach its optimum at the same conditions, a middle course approach has to be followed. Use of an experimental design for this investigation enabled understanding of the mechanisms of within- and between-pair separation for citalopram, desmethylcitalopram, and didesmethylcitalopram. Sequential optimization can be a quicker means of optimizing a chromatographic separation; response-surface modelling, in addition to enabling optimization of the chromatographic process, also serves as a tool for leaming more about the separation mechanism.     

Optimization of Mobile Phase Composition in Liquid Chromatography—A Survey of Most Commonly Used Chemometric Procedures

Abstract

Chemometrics offers techniques to reduce the number of experiments necessary for obtaining reliable predictions about the optimum conditions for liquid chromatographic separations. This article describes the different chemometric procedures that are currently used for mobile phase optimization. These procedures can be divided in three stages: the selection of the optimization criteria, the choise of the experimental set-up (design) and the evaluation and interpretation of the results. The optimization criteria usually involve resolution (either expressed as α, Rs or P), often analysis time and sometimes column length. The experimental set-up can be either sequential (e.g. simplex algorithm) or simultaneous (e.g. factorial designs). Data can be evaluated either graphically or by mathematical methods. The applicability of the different methods in general and for specific problems is discussed, using examples from the literature.     

Determination of 1,1-Dimethylhydrazine by Reversed-Phase High-Performance Liquid Chromatography with Spectrophotometric Detection as a Derivative with 4-Nitrobenzaldehyde

A procedure was developed for the determination of 1,1-dimethylhydrazine by reversed-phase high-performance liquid chromatography with spectrophotometric detection and preliminary derivatization by the reaction with 4-nitrobenzaldehyde. Conditions were selected for the chromatographic separation and the detection of the peaks of the reagent and 4-nitrobenzaldehyde dimethylhydrazone. The optimum conditions were found for the derivatization of 1,1-dimethylhydrazine with 4-nitrobenzaldehyde. The determination limit of 1,1-dimethylhydrazine in aqueous solutions was 120 g/L (2 M/L).     

Orthogonal Design-Directed Optimization of an LC Method for Fingerprinting Mai-Luo-Ning Injection, and Validation of the Method

A novel hierarchical chromatographic response function (HCRF)-directed orthogonal design procedure has been used for optimization of an high-performance liquid chromatography method for fingerprinting Mai-Luo-Ning (MLN) injection. The method was then successfully validated. Five major controllable chromatographic conditions at four levels were included in the orthogonal design. A total of 16 chromatographic runs resulted in the optimum chromatographic conditions-a 250 × 4.6 mm i.d., 4-μm particle, C₁₈ column, a mixture of methanol and 0.025% aqueous formic acid in water as mobile phase, flow rate 0.8 mL min^?1, column temperature 35 °C, and detection wavelength 240 nm. The mobile phase gradient was then further optimized step by step by observation of the chromatographic profiles obtained. Fingerprints of MLN injection and its constituent single herb injections were separately acquired by use of the optimized method. Attribution of the 18 largest peaks observed in the MLN fingerprint indicated that Flos Lonicerae was the main ingredient. Validation of the method for precision, repeatability, and stability proved it was highly reproducible. This chromatography fingerprint method could be very useful for quality control of MLN injection. The original HCRF-directed orthogonal design approach proposed should be generally useful for developing chromatographic fingerprinting methods.     

Eutectic Thin-Layer Chromatography as a New Possibility for Quantification of Plant Extracts—A Case Study

Deep eutectic solvents (DES), compared to classic ones, have interesting properties, such as the ability to solubilize compounds differing in polarity or increased dissolution of selected chemical compounds. They also offer specific interactions between the mobile and stationary phases. Those features make them promising solvents in chromatographic techniques, including the use in the separation of complicated samples. The first quantitative analysis with eutectic thin-layer chromatography (TLC) is presented in the paper. As a case study, five alkaloids from Chelidonium maius were selected as target compounds. A wide range of terpene-based DESs was investigated to develop the chromatographic system, both pure and after dilution. Moreover, a novel approach was employed to adjust polarity, involving mixing DESs differing in chromatographic properties. This procedure has proved to be effective. The best results were obtained with a 2:1 (wt/wt) mixture of DESs: camphor + phenol and menthol + limonene, with a 20% addition of methanol. The chromatographic system was validated and checked on the real sample, which made it the first applicable and operational quantitative eutectic TLC system.     

Comparison of the performance of non-ionic and anionic surfactants as mobile phase additives in the RPLC analysis of basic drugs

Surfactants added to the mobile phases in reversed-phase liquid chromatography (RPLC) give rise to a modified stationary phase, due to the adsorption of surfactant monomers. Depending on the surfactant nature (ionic or non-ionic), the coated stationary phase can exhibit a positive net charge, or just change its polarity remaining neutral. Also, micelles in the mobile phase introduce new sites for solute interaction. This affects the chromatographic behavior, especially in the case of basic compounds. Two surfactants of different nature, the non-ionic Brij-35 and the anionic sodium dodecyl sulfate (SDS) added to water or aqueous-organic mixtures, are here compared in the separation of basic compounds (β-blockers and tricyclic antidepressants). The reversible/irreversible adsorption of the monomers of both surfactants on the stationary phase was examined. The changes in the nature of the chromatographic system using different columns and chromatographic conditions were followed based on the changes in retention and peak shape. The study revealed that Brij-35 is suitable for analyzing basic compounds of intermediate polarity, using "green chemistry", since the addition of an organic solvent is not needed and Brij-35 is a biodegradable surfactant. In contrast, RPLC with hydro-organic mixtures or mobile phases containing SDS required high concentrations of organic solvents.     

“改进的棱柱形”优化系统在高效液相色谱中的建立和应用 Ⅰ.“棱柱形”溶剂强度优化系统的改进

本文建立了适于高效液相色谱的“Improved-PRISMA”优化系统,利用全范田二元线性梯度淋洗进行溶剂强度的优化,只需一次实验即可得知所需溶剂的最佳强度,简化了原“PRISMA”系统选择溶剂强度的过程。将此系统用于七个有机磷化合物的分离,得到了满意的结果。     

Some features of thin-layer chromatography in chambers of different types

The following characteristics of planar chromatography in the ascending flow of the mobile phase were compared for the main N, S, and O chambers: the movement of the mobile phase front, the efficiency of the chromatographic process, and the retardation factors. The optimum results were obtained for S and O chambers.     

可调移动重叠分离图法用于高效液相色谱多台阶梯度分离条件优化的研究

计算机辅助高效液相色谱（HPLC）分离条件优化可以低成本、快速地得到优化的分离条,因而已较为广泛地用于复杂样品的分离分析。基于移动重叠分离图方法,又发展了一种新型的多台阶梯度分离条件的优化方法可调移动重叠分离图法。该方法通过预测不同流动相条件下各组分的保留时间、峰宽和分离度,绘制出对于样品中各组分的重叠分离区域图。在对当前台阶流动相组成进行优化的同时,考虑其对后面一到两个台阶上流出组分保留的影响,实时地重新绘制对于后面台阶上流出组分的重叠分离区域图。通过观察当前台阶流动相条件对当前台阶和后面台阶上流出组分分离的影响,综合考虑样品中所有组分的分离情况,找到更接近全局最优的分离条件。通过扫描的方法对优化得到的分离条件进行微调,能够进一步提高分离效果。采用文献数据对可调移动重叠分离图法的应用加以说明,在二元流动相体系下,证明了该方法在HPLC方法建立方面的优越性。