Indirect UV detection in HPLC determination of UV-transparent non-electrolytes in pharmaceutical dosage forms

After briefly reporting the basic concepts of indirect UV detection in HPLC, methods for the quantitative determination of ethanol, glycerol and isopropanol in pharmaceutical forms for human use, and propylene glycol and N,N-dimethylacetamide in pharmaceutical form for veterinary use are proposed. Nicotinamide, sulfanilamide and isoniazid are used as UV-absorbing components (probes) of mobile phase. The last two are new probes suitably selected and proposed to optimize the determination. Also, the dependence of method sensitivity from the probe concentration is shown. Good accuracies and precisions are obtained. The methods are simple and quick and the assays of the analytes do not go through interferences from the other substances present in the pharmaceutical forms.