Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification of pseudoephedrine enantiomers

Non-parametric linear regression of discrete Fourier transform convoluted densitometric peak responses

The manuscript discusses the application of chemometrics to the handling of TLC response time data. Derivative treatment of chromatographic response data followed by convolution of the resulting derivative curves using 8-points sinx(i) polynomials (discrete Fourier functions) was found to be beneficial in eliminating the interference due to background noise in TLC-densitometric measurements. It also compares the application of Theil's method, a non-parametric regression method, in handling the response data, with the least squares parametric regression method, which is considered the de facto standard method used for regression. Theil's method was found to be superior to the method of least squares as it assumes that errors could occur in both x- and y-directions and they might not be normally distributed. In addition, it could effectively circumvent any outlier data points.

Chromatographic multivariate quality control of pharmaceuticals giving strongly overlapped peaks based on the chromatogram profile

In the present paper, the simultaneous quantification of two analytes showing strongly overlapped chromatographic peaks (alpha = 1.02), under the assumption that both available equipment and training of the laboratory staff are basic, is studied. A pharmaceutical preparation (Mutabase) containing two drugs of similar physicochemical properties (amitriptyline and perphenazine) is selected as case of study. The assays are carried out under realistic working conditions (i.e. routine testing laboratories). Uncertainty considerations are introduced in the study. A partial least squares model is directly applied to the chromatographic data (with no previous signal transformation) to perform quality control of the pharmaceutical formulation. Under the adequate protocol, the relative error in prediction of analytes is within the tolerances found in the pharmacopeia (10%). For spiked samples simulating formulation mistakes, the errors found have the same magnitude and sign to those provoked.

Strategies for the enantiomeric determination of amphetamine and related compounds by liquid chromatography

This paper summarizes recent research on the stereospecific analysis of amphetamine, its analogs and metabolites, by liquid chromatography. The different methods proposed have been evaluated and compared in terms of resolution power, time of analysis, sensitivity, or potential for automation. Chiral derivatization, followed by separation of the diastereomers formed in achiral chromatographic systems, is still the method preferred for the analysis of amphetamines at trace levels, as derivatization also improves analyte detectability. This is the method of choice for the enantiomeric analysis of amphetamines at the low concentrations typically encountered in biological samples. In recent years, special attention has been devoted to the development of alternatives for the automation of the analytical process by integrating the derivatization step into the chromatographic scheme. A promising alternative is the employment of beta-cyclodextrins as chiral selectors, both immobilized on the stationary phase and added to the mobile phase. However, with a few exceptions, beta-cyclodextrins perform better for non-derivatized amphetamines. Therefore, the utility of these selectors in the analysis of biological samples is limited. The reliability of less-used chiral stationary phases (Pirkle type, cellulose based or protein based), as well as methods based on the mathematical treatment of the chromatographic signal, are also discussed.