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Application of sunscreen is one of many ways to protect skin from the harmful effects of UV radiation. Sunscreen products are widely used and regulated as over-the-counter drug products in the United States. The U.S. Food and Drug Administration recommends an assessment of human systemic absorption of sunscreen active ingredients with a Maximal Usage Trial. The FDA conducted a clinical study to determine the systemic exposure of sunscreen active ingredients present in 4 commercially available sunscreen products of different formulation types under maximal usage conditions. To support this clinical study, a sensitive and specific LC-MS/MS method for the simultaneous determination of the two sunscreens avobenzone and oxybenzone in human plasma was developed. Phospholipid removal 96-well protein precipitation plates were used for sample clean-up and the extracted samples were chromatographed on an Ethylene-Bridged Hybrid (BEH) C 18 column in isocratic flow using 10 mM ammonium formate in 0.1% formic acid and methanol (24:76, v/v) as a mobile phase. A triple quadrupole mass spectrometer in multiple reaction monitoring (MRM) mode was used to acquire data. The method was validated as per current FDA bioanalytical method validation guidance, in the ranges 0.20-12.00 ng/mL for avobenzone and 0.40-300.00 ng/mL for oxybenzone. The validated method was used toanalyzethese active ingredients in human clinical study samples., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In mass spectrometry, compounds that have different ionization properties experience challenges in simultaneous analysis. In the present paper, the authors proposed a polarity switching (+ve and -ve) LC-MS/MS method to analyze oxycodone and topiramate in a single run. The developed method was validated in the range of 5-1000 ng/mL for oxycodone and 20-5000 ng/mL for topiramate as per the US FDA guidelines. The mass spectrometer was operated in multiple reaction monitoring (MRM) mode to analyze oxycodone and topiramate simultaneously using oxycodone-d 6 and topiramate-d 12 as internal standards, respectively. Sample preparation was performed in 96-well protein precipitation plates using acetonitrile. Processed samples were analyzed using a C 18 column with a gradient mobile phase composed of 10 mm ammonium formate with 0.1% formic acid and acetonitrile. The method was validated for selectivity, specificity, linearity, precision and accuracy, dilution integrity and stability. After validation, this method was successfully applied to quantify oxycodone and topiramate in plasma of concomitantly treated Sprague Dawley (SD) rats., (Published by Elsevier B.V.)