In this work, liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed and validated for screening and confirmation of 64 illicit compounds in dietary supplements. The target compounds were illegally used pharmaceutical drugs, prohibited compounds, and not authorized ingredients for different therapeutics (sexual enhancement, weight loss, muscular strengthening, and relaxing products). The validation procedure was performed to evaluate selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, and precision according to the Association of Official Analytical Chemists guidelines. The linearity was >0.98 in the range of 0.5–200 µg L−1. The LOQs were in the range 1–10 µg kg−1 for all target compounds. The accuracy (expressed as recovery) was 78.5–114%. The precision (expressed as the relative standard deviation) was below 9.15%. The developed method was applied for the determination of illicit compounds in dietary supplements collected from websites. As a result, the total detection rate was 13.5% (27 samples detected in 200 samples). The concentrations of detected samples ranged from 0.51 to 226 mg g−1. The proposed methodology is suitable for monitoring the adulteration of illicit compounds in dietary supplements.
The Limit of Detection in Generalized Least-Squares Calibrations: An Example Using Alprazolam Liquid Chromatography-Tandem Mass Spectrometry Data