Abstract
The efficiency of spectral suppression, absorbance ratio and spectral overlay for peak purity testing using a diode array detector has been compared on a strongly overlapping model systea (cefotaxime and theophylline). Spectral overlay and spectral suppression have a comparable sensitivity (0.3 % of impurity can be detected) spectral suppression allows an accurate determination of impurity at 1% level; absorbance ratio is the less powerful technique.