ABSTRACT:During the past few years, there has been an increasing interest in rapid visual tests that could be performed outside the laboratory, for example on farms, in store houses or in food production plants. Hence, cost effective and simple screening methods are required for residual analysis of environmental and food samples onsite. Here, a simple and instrumental independent dipstick immunoassay for sulfamethazine detection is described. The polyclonal antibody was optimised in terms of coating dilution on a nitrocellulose membrane, dilution of peroxidase tracer conjugate, blocking agents and incubation times. Test results assessed by visual measurement can be available within 20 minutes. In buffer, water, skimmed milk and pig manure extract, sulfamethazine fortified at 50 and 100 µg/l has exhibited clear visual differentiation in colour development (lower intensity) in comparison to the control spot intensity (high intensity) of the dipstick.

A simple, precise, accurate stability-indicating gradient reversed-phase high-performance liquid chromatographic (RP–HPLC) method was developed for the quantitative determination of zotepine (ZTP) in bulk and pharmaceutical dosage forms in the presence of its degradation products (DPs). The method was developed using Phenomenex C18 column (250 mm×4.6 mm i.d., 5 µm) with a mobile phase containing a gradient mixture of solvents, A (0.05% trifluoroacetic acid (TFA), pH=3.0) and B (acetonitrile). The eluted compounds were monitored at 254 nm; the run time was within 20.0 min, in which ZTP and its DPs were well separated, with a resolution of >1.5. The stress testing of ZTP was carried out under acidic, alkaline, neutral hydrolysis, oxidative, photolytic and thermal stress conditions. ZTP was found to degrade significantly in acidic, photolytic, thermal and oxidative stress conditions and remain stable in basic and neutral conditions. The developed method was validated with respect to specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness as per ICH guidelines. This method was also suitable for the assay determination of ZTP in pharmaceutical dosage forms. The DPs were characterized by LC–MS/MS and their fragmentation pathways were proposed.