The quantification of glucosamine in dietary supplements was investigated by using capillary with capacitively coupled contactless conductivity detection (CE-C4D). Optimal conditions included electrophoresis buffer solution 10 mM Tris/Ace; pH = 5,0; sample injection height 25 cm; sample injection time 30 s; separation voltage 20 kV. The limit of detection (LOD) and the limit of quantification (LOQ) of glucosamine were 8.00 ppm and 26.67 ppm, respectively. Calibration curve was constructed over the range from 20 to 1000 ppm giving a good linear correlation coefficient (R2 = 0.9993). The relative standard deviation (RSD) ranged from 1.28% to 2.33% (n = 3) and the recovery efficiency ranged from 95.2 to 102.3% which indicated good precision and trueness of our method. The method was applied to determine glucosamine in 4 dietary supplement samples randomly collected at the local markets. The CE-C4D results were compared with those obtained by reference HPLC-FLD method, showing good agreement between the two methods (relative error < 15%).
Dietary supplements are currently popular because of their natural origin, especially male enhancement products. However, some of these products have been found to contain erectile dysfunction drugs that inhibit the enzyme phosphodiesterase-5 (PDE-5), leading to adverse effects on human health. In this study, capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) was used to determine four PDE-5 inhibitors (including acetyl vardenafil, homosildenafil, hydroxy acetildenafil and mirodenafil) in dietary supplement samples. The optimum analytical conditions included electrolyte solution of 20 mM arginine (Arg)/acetic acid (Ace)/acetonitrile (ACN) 20% pH 6.5, silica capillary 50 μm inner diameter with effective length of 50 cm, separation voltage of 20kV, siphoning hydrodynamic injection at a height of 25 cm for 30 s. At the optimum analytical conditions, the limits of detection of acetyl vardenafil, homosildenafil, hydroxy acetildenafil, and mirodenafil were 2.1, 1.6, 2.3, and 1.3 mg/L, respectively. The analysis of four PDE-5 inhibitors by CE-C4D also showed good repeatability (< 5 %) and recovery (> 97 %). This method was further applied to simultaneously determine the amount of acetyl vardenafil, homosildenafil, hydroxy acetildenafil, and mirodenafil in three functional products. All four PDE-5 inhibitors were not detected in these samples. To demonstrate the utility of this method, the mixture of four PDE-5 inhibitors standard solutions was added to three samples. The recovery was between 98.8 % and 100.6%, illustrating the potential applicability of the method of determining PDE-5 inhibitors in dietary supplement samples.
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