Determination of Stimulants and Diuretics in Dietary Supplements for Weight Loss and Physical Fitness by Ion-pair Chromatography and Pulsed Amperometric Detection (PAD)

摘要

Background: Dietary supplements are products that aim to complement the diet of healthyindividuals, and may show nutritional, metabolic and physiological effects. The consumption of dietarysupplements is increasing every year all over the world and has been accompanied by an increased frequencyof adulteration of these products with synthetic pharmaceuticals. Analytical methods that allowtesting for the presence of synthetic drugs in dietary supplements are needed to detect such fraudulentpractices.Methods: A method was developed for the rapid identification and quantification of diuretics (hydrochlorothiazide,chlorthalidone and furosemide) and stimulants (caffeine and synephrine) by ion-pairchromatography with pulsed amperometric detection in dietary supplements. Dietary supplements werepurchased online from randomly chosen websites and from physical stores. The search was restricted toproducts that advertise and market food supplements with claims of weight loss, fat burning, appetitereduction or metabolism acceleration (thermogenics).Results: A mobile phase composed of 5 mmol L-1 sodium phosphate using 0.3 mmol L-1 sodium dodecylsulfate as ion-paring reagent and 50% (v/v) methanol as organic additive leads to the efficient separationof hydrochlorothiazide, chlorthalidone, furosemide and amiloride. PAD cycle of the studied drugsinvolved an oxidation (+1.0 V for 0.4 s) and a reducing potential (-0.2 V for 1.2 s) on the gold electrodesurface as a cleaning step. In addition, the drugs were detected by applying an optimized pulse of +0.8V for 0.4 s, completing the 2 s detection cycle applied to the gold electrode. Caffeine was found to bepresent in 50% of the studied samples and about 20% of them presented caffeine levels above the quantityconsidered safe for daily intake. In addition, hydrochlorothiazide and furosemide were found asdiuretics in the formulations. Hydrochlorothiazide was found as diuretic in amounts higher than thetherapeutic dose in circa 5% of the samples, being that the same incidence found for the stimulantsynephrine in the analyzed samples.Conclusion: A new IPC-PAD method using an amperometric cell with a gold disc electrode enabled thesimultaneous separation and sensitive detection of the diuretics hydrochlorothiazide, chlorthalidone andfurosemide in the presence of the stimulants caffeine and synephrine. Caffeine was found to be presentas a stimulant in 50% of the studied samples available as encapsulated or bulk forms from differentwebsites and physical stores. Furthermore, about 20% of the samples presented caffeine levels abovethe quantity considered safe for daily intake. Beyond caffeine, synephrine was found as stimulant incirca 5% of the studied samples. Lastly, hydrochlorothiazide was found in amounts above the therapeuticdose in 5% of the samples.