Simultaneous ultrasound-assisted emulsification-derivatization as a simple and miniaturized sample preparation method for determination of nitrite in cosmetic samples by microvolume UV-vis spectrophotomety

A simple and miniaturized approach based on ultrasound-assisted emulsification-derivatization is proposed for the determination of nitrite in cosmetic samples by UV-vis micro-spectrophotometry. Oil/water emulsions were formed using 15 mg of cosmetic sample and 1 mL of an aqueous medium containing 0.5% w/v SDS and 1% v/v acetic acid. When powerful sonication systems were used to make emulsions, i.e. probe or cup-horn sonoreactor, stable and transparent emulsions were obtained in one or half minute per sample, respectively. The Griess reaction in these special conditions (i.e. sonication and the presence of an organized medium) was investigated. The absence of matrix effects allows external calibration with aqueous standards for nitrite quantification. Analytical features were compared to those of the European official method 82/434/EEC. Detection limit, sample throughput and reagent consumption were significantly improved.