Direct determination of paracetamol in powdered pharmaceutical samples by fluorescence spectroscopy

The native fluorescence of paracetamol (PA) in the solid state is demonstrated, allowing the development of a rapid, simple and rugged method for direct analysis of pharmaceutical formulations. It is easily adaptable to any spectrofluorimeter, and no chemical treatment of the sample is needed. The fluorescence measurements (λex = 333 nm; λem = 382 nm) are performed directly on the powdered sample, the active substance being diluted in lactose, maize starch, poly(vinylpyrrolidone), talc and stearic acid. The influence of the ingredients of PA formulations is discussed. Fluorescence intensity is linearly dependent on PA concentration within the 100-400 mg g−1 range. The analytical frequency is 200 h−1. Detection and quantification limits were estimated within the 13.0-16.7 and 43.1-55.7 mg g−1 ranges for samples with different ingredient proportions. The method was applied to pharmaceutical formulations and the relative standard deviation of results was <2.7% (n = 20) for all tested ingredient proportions. Results were compared with those obtained by a method recommended by the British Pharmacopoeia and no statistical difference between methods was found at the 95% confidence level.