A chemometric investigation of the selectivity of multisolvent mobile phase systems in RP-HPLC

The selectivity of multisolvent mobile phase systems consisting of water, methanol, acetonitrile and tetrahydrofuran was studied when the solvent strength decreases at a constant ratio of the modifiers. From the retention measurements of six benzene derivatives on an octylsilica column at eleven different mobile phase compositions the relation between the logarithm of the capacity factor of each solute and the mobile phase composition was modeled by a quadratic equation. From the models the capacity factors of the solutes were predicted for 3 binary, 3 ternary and 7 quaternary mobile phase systems when the fraction of water decreases and the ratio of the organic modifiers is kept constant for the tenary and quaternary solvent systems. The selectivity factors, alpha, of five pairs of solutes were calculated from the capacity factors and plotted against the solvent strength of the mobile phase systems. The selectivity remained not constant, but varied with the solvent strength: if the water fraction of a multi-solvent system is changed at a constant ratio of the modifiers, not only the solvent strength, but also the selectivity changes. The consequence of this result for optimization strategies is discussed

Multicriteria steepest ascent in a design space consisting of both mixture and process variables

Steepest ascent is shown to be a feasible method for problems where two or more responses are to be optimized. With the aid of Pareto optimality the (one response) standard method is adapted for the use of more responses. A special kind of steepest ascent problem involves the presence of both mixture and process variables. This problem is solved by the use of projection designs. The combined method is demonstrated with a simulated problem

The Simultaneous Spectrophotometric Assay of the Active Constituents of Multicomponent Analgesics Using Kalmanfiltering

UV-spectrophotometry in combination with Kalmanfiltering is used for the assay of analgesics in tablets. Commercial products containing various combinations of acetylsalicylic acid, salicylic acid, caffeine, phenacetine and acetaminophen are analyzed. For comparison, these tablets were also analyzed by HPLC. The accuracy and precision of both methods are comparable. The described spectrophotometric assay with the aid of Kalmanfiltering represents a new, rapid and low-cost alternative to existing analytical procedures for analgesics

Estimation of individual ultraviolet spectra in incomplete two-component separations by high-performance liquid chromatography

A method is described for the estimation of spectral features in a two-component chromatographic peak by means of a u.v. diode-array detector. The calculation relies on the assumption that the front of a fused chromatographic peak contains a single pure component. The spectrum of this component is used in calculating the concentration profile of the other component, thus allowing the determination of a solution band for the spectrum of the second component. The boundaries of the solution band are based on non-negativity restrictions of chromatographic and spectral features. The method does not require the use of principal components analysis