This manuscript discusses the application of chemometrics to the handling of capillary electrophoresis (CE) response data using the internal standard method. Derivative treatment (D method) of CE response data was used. Furthermore, convolution of the resulting derivative curves using discrete Fourier functions, the so-called D/FF method, was applied. This approach is extremely beneficial where ideal baseline separation of electrophoretic peaks cannot be achieved, as in the case of drug isomers, structural related impurities or degradation products. The potential of these methods for resolving overlapping peaks was evaluated using the hydrolysis of hydrochlorothiazide (HCT) as an illustrative model. CE analysis was performed using a deactivated fused silica capillary (55 cm effective length and 75 µm i.d.), and background electrolyte solution consisted of phosphate buffer (20 mm, pH 8.0). Both chemometric methods allowed the determination of the intact drug (HCT) and its degraded form with high a degree of accuracy and precision. This was found to be beneficial in studying the degradation kinetics of hydrolysis of HCT at different temperatures. The corresponding pseudo-first order rate constants and half-lives were calculated. Finally, the proposed method made use of diode array detection as a tool for peak identity and purity confirmation. Copyright © 2013 John Wiley & Sons, Ltd.