After the FDA's ban of ephedrine-containing supplements, Citrus aurantium appeared as an alternative to ephedra in herbal weight loss products. Synephrine, the most abundant active component of C. aurantium, exists in three different structural or positional isomeric forms (ortho-o-, meta-m-, and para-p-). Dietary supplements contain m- and p-synephrine, both alpha-adrenergic agonists,while the m-isoform is the most potent at alpha(1)-adrenoreceptors. In spite of the pharmacokinetic and toxicological interest in the study of these compounds, adequate methods for their quantification in biological samples are yet to be developed. Thus, in the present study, a sensitive gas chromatography-ion trap mass spectrometry (GC/IT-MS) method was developed and validated for the simultaneous quantitation of m- and p-synephrine in a cellular matrix after solid phase extraction (SPE). The validation of the method was performed through the evaluation of the following parameters: selectivity, linearity, specificity, precision, accuracy, limit of detection, limit of quantification, and recovery. The method's applicability was studied in two different biological matrices by evaluating p- and m-synephrine uptake in Caco-2 cells and also in freshly isolated cardiomyocytes from adult rat. The developed GC/IT-MS method was shown to be selective, accurate, precise, and valid for simultaneous determination of p- and m-synephrine in biological samples.
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