Determination of lorazepam by fluorimetric and photochemical-fluorimetric methods

Abstract

The photoisomerisation of lorazepam was studied by spectrofluorimetry and ultraviolet spectrophotometry. It was found that lorazepam leads to a strongly fluorescent photoproduct on irradiation in 0.2 M NaOH solution. The effect of pH on the fluorescence intensity of lorazepam and its photoproduct was investigated and their pK_a values were calculated. A fluorimetric method with a detection limit of 16 ng ml^–1 and a photochemical-fluorimetric method with a detection limit of 0.3 ng ml^–1 were developed for the determination of lorazepam. The former method was applied to the determination of the drug in tablets; the latter, which is more sensitive, was used for the determination of lorazepam in serum.