Stanley N. Deming

Retention mechamism for reversed-phase ion-pair liquid chromatography

The retention mechanism of reversed-phase “ion-pair” liquid chromatography was investigated. The study demonstrates that for a methanol—water (35:65), pH 3 mobile phase and a μbondapak C18 stationary phase: sodium pentane-, hexane-, heptane-, and octanesulfonate, and otylamine hydrochloride ion-interaction reagents are retained by the stationary phase; ion-pair formation does not occur in the mobile phase; the capacity factor of solute ions is increased by mobile phases containing ion-interaction reagents of the opposite charge over the range 0 to 20 mM; the retention behavior of neutral molecules is independent of ion-interaction reagent concentration from 0 20 mM; solute ions are rapidly eluted by mobile phases containing ion-interaction reagents of the same charge, and the capacity factor is relatively independent of the ion-interaction reagent concentration from approximately 2 to 20 mM; ion-interaction reagents are locally desorbed from the stationary phase by the injection of solute ions of the same charge; ion-interaction reagents are locally adsorbed by the injection of solute ions of the opposite charge. Because neither the conventional ion-pair formation hypothesis no a simple ion-exchange hypothesis has been entirely satisfactory in interpreting the data, a broader mechanistic model is presented to account for experimental results.

Optimization strategies for the development of gas-liquid chromatographic methods

Abstract The utility of the sequential simplex method in chromatographic methods development is demonstrated by the experimental optimization of separation for several mixtures of isomeric octanes. Column oven temperature and carrier gas flow-rate are varaied simultaneously during the optimization process. Factorial experiments and regression analysis are used to understand the factor effects in the regions of the optima. A chromatographic response function based on the peak separation function of Kaiser is described. Its use as an operational measure of performance in the separation of multicomponent systems is illustrated.

Multifactor optimization of reversed-phase liquid chromatographic separations

Abstract The single-factor “window diagrma” technique of Laub and Purnell is extended to the multifactor case, and is successfully applied to the reversed-phase liquid chromatographic separation of a nine-component mixture.

Combined effects of pH and surface-active-ion concentration in reversed-phase liquid chromatography

Abstract The combined effects of pH (3.6–6.0) and octylamine hydrochloride concenttration (0–5.0 mM) in methanol—water (20:80) eluents were determined for hydrocinnamic, trans-cinnamic, phenylacetic, trans-p-coumaric, trans-ferulic, trans-caffeic and vanillic acids; for phenylethylamine; and for phenylalanine. The effects are described by a simple ion-interaction model that does not require ion-pair formation in either phase and is not based upon classical ion exchange. The simplicity and generality of the mathematical forms of the model make it useful for predicting retention behavior.

Teaching the fundamentals of experimental design

Abstract The success of chemometric techniques that operate on data obtained from experiments is often considerably improved if the data have been acquired by a systematic design. The intimate relationships among good chemometric results and good models, good measurement processes, and good experimental designs are shown. A bibliography of the applications of sequential simplex optimization in chemometrics is presented.

Quantitation of Alkyl Sulfonates Using UV Detector Sensitive “Ion-Pair” Reagents in Reversed-Phase Liquid Chromatography

Abstract Amplification of detector response by means of detector-sensitive ion-pairing reagents demonstrates good sensitivity, linearity, and precision for the quantitation of alkylsulfonate ions by means of ultraviolet absorbance detection at 254 nm.

Optimized reverse-phase high-performance liquid chromatographic separation of cinnamic acids and related compounds

Abstract The effect of mobile-phase pH on reverse-phase high-performance liquid chromatographicseparation is studied for a nine-component sample containing cinnamic, ferulic, hydrocinnamic, p -coumaric, caffeic, phenylacetic, vanillic, and β -phenylpyruvic acids and phenylethylamine. A systematic optimization strategy is utilized: Retention times of each component are measured for mobile phases buffered with citric acid at pHs of 3.0, 4.0, 5.0, and 6.0; a mathematical model is fit to the chromatographic data; the model parameters are used to construct a window diagram which provides an estimate of the mobile-phase pH required for optimum separation.

Computer-assisted optimization in high-performance liquid chromatographic method development

Abstract Computer-assisted optimization in high-performance liquid chromatography has been encouraged by a need to define method development strategies for automated chromatographic instruments. Several algorthms have been developed for the optimization of various aspects of chromatographic performance. Additional experimental designs have been used to understand the influence of factors on the performance of the chromatographic system.

Automated development of analytical chemical methods : The determination of senun calcium by the cresolphthalein complexone method

Abstract The cresolphthalein complexone method for serum calcium determination was investigated by means of a modified Technicon Autoanalyzer II under computer control. Simplex optimization of reagent concentrations, followed by response-surface mapping in the region of the optimum produced a method yielding 8.5% greater calcium sensitivity and 15% lower baseline absorbance than the standard method, with comparable insensitivity to interferences, and only a very slight sacrifice in linearity; a comprehensive operational understanding of the chemical system was also obtained.

Difficulties in the Application of Simplex Optimization to Analytical Chemistry

Abstract The propagation of mistakes and misunderstandings in the application of simplex optimization to analytical chemical problems is delineated. Proper selection of factors and response is discussed.