Optimisation and validation of a GC-MS method for screening for diuretics in adulterated weight loss dietary supplements.

The increasing consumption of dietary supplements for weight management raises concerns about the presence of undeclared pharmaceutical substances, particularly diuretics. These compounds are sometimes added illegally to accelerate water loss and provide misleading weight-loss effects, but their uncontrolled use may lead to dehydration, electrolyte imbalance, kidney impairment, and potential doping violations. In this work, we developed and validated a simple and sensitive gas chromatography-mass spectrometry method for the simultaneous determination in dietary supplements of 14 diuretics of which 10 are sulphonamides. The method was optimised using selected ion monitoring for screening and SCAN mode for confirmation. The method was validated based on the guidelines of the International Conference on Harmonisation (ICH). Detection limits ranged from 15.68 to 160.83 ng/g in solid matrices and from 3.31 to 21.69 ng/mL in liquid matrices. Average extraction efficiency rates were between 65% and 95%. Intra-day and inter-day RSDs precision were below 8%. Furthermore, intra-day and inter-day accuracy ranged from 79% to 110% and from 81% to 112%, respectively, for the solid matrix, whereas for the liquid matrix, it ranged from 83% to 112% and from 82% to 114%, respectively. The validated method was applied to ten dietary supplement samples (capsules, tablets, powders, and liquids) collected from the Tunisian market. None of the tested products contained the investigated diuretics. This method is reliable for routine screening of adulterated supplements, contributing to consumer safety and public health monitoring.