Abstract

Background: Dietary supplements are products that aim to complement the diet of healthy individuals, and may show nutritional, metabolic and physiological effects. The consumption of dietary supplements is increasing every year all over the world and has been accompanied by an increased frequency of adulteration of these products with synthetic pharmaceuticals. Analytical methods that allow testing for the presence of synthetic drugs in dietary supplements are needed to detect such fraudulent practices.

Methods: A method was developed for the rapid identification and quantification of diuretics (hydrochlorothiazide, chlorthalidone and furosemide) and stimulants (caffeine and synephrine) by ion-pair chromatography with pulsed amperometric detection in dietary supplements. Dietary supplements were purchased online from randomly chosen websites and from physical stores. The search was restricted to products that advertise and market food supplements with claims of weight loss, fat burning, appetite reduction or metabolism acceleration (thermogenics).

Results: A mobile phase composed of 5 mmol L-1 sodium phosphate using 0.3 mmol L-1 sodium dodecyl sulfate as ion-paring reagent and 50% (v/v) methanol as organic additive leads to the efficient separation of hydrochlorothiazide, chlorthalidone, furosemide and amiloride. PAD cycle of the studied drugs involved an oxidation (+1.0 V for 0.4 s) and a reducing potential (-0.2 V for 1.2 s) on the gold electrode surface as a cleaning step. In addition, the drugs were detected by applying an optimized pulse of +0.8 V for 0.4 s, completing the 2 s detection cycle applied to the gold electrode. Caffeine was found to be present in 50% of the studied samples and about 20% of them presented caffeine levels above the quantity considered safe for daily intake. In addition, hydrochlorothiazide and furosemide were found as diuretics in the formulations. Hydrochlorothiazide was found as diuretic in amounts higher than the therapeutic dose in circa 5% of the samples, being that the same incidence found for the stimulant synephrine in the analyzed samples.

Conclusion: A new IPC-PAD method using an amperometric cell with a gold disc electrode enabled the simultaneous separation and sensitive detection of the diuretics hydrochlorothiazide, chlorthalidone and furosemide in the presence of the stimulants caffeine and synephrine. Caffeine was found to be present as a stimulant in 50% of the studied samples available as encapsulated or bulk forms from different websites and physical stores. Furthermore, about 20% of the samples presented caffeine levels above the quantity considered safe for daily intake. Beyond caffeine, synephrine was found as stimulant in circa 5% of the studied samples. Lastly, hydrochlorothiazide was found in amounts above the therapeutic dose in 5% of the samples.

Keywords: Amperometric detection, ion-pair chromatography, dietary supplements, diuretics, stimulants, pulsed amperometric detection (PAD).

Graphical Abstract