EVALUATION OF DIFFERENT TECHNIQUES FOR PEAK PURITY ASSESSMENT ON A DIODE-ARRAY DETECTOR IN LIQUID-CHROMATOGRAPHY

The efficiencies of nine different techniques implemented on a diode-array detector in liquid chromatography for peak homogeneity determination were compared at a concentration level of a drug that can be found in biological samples. Solutions of cefotaxime sodium (analyte) spiked with various amounts of a model impurity (theophylline) were injected under chromatographic conditions giving severe overlap of the peaks (R(s)=0.14). Under the conditions used, the most efficient techniques implemented in the instrument were spectral suppression (ca. 0.5%), derivative spectrum (<1%), followed by spectral overlay, absorbance ratio plot (<5%), multiple-wavelength chromatograms overlay and purity parameter (ca. 5%). The numerical value of the absorbance ratio could also be exploited statistically to detect 0.5% of impurity. Theophylline at levels up to 10% could not be detected using three-dimensional plots, contour diagrams and derivative chromatograms.