Multitechnique determination of metals and non-metals in sports supplements after microwave-assisted digestion using diluted acid

Microwave-assisted digestion using diluted acid under oxygen pressure is proposed for sample preparation of sports supplements and subsequent determination of Ca, Cu, Fe, K, Mg, Mn, Na, Zn, P and S by inductively coupled plasma-optical emission spectrometry (ICP-OES). In this sense, 1350 mg of sport supplement were digested in a microwave oven using only 6 mL of 5 mol L-1 HNO3 under 5 bar of oxygen pressure during 15 min. Accuracy of proposed method was evaluated by recovery tests using a standard solution and using a certified reference material. Suitable recoveries (ranging from 86% to 108%) were obtained in both evaluations for all analytes. Results were compared with those obtained by conventional microwave-assisted digestion (without oxygen pressure) for further analytes determination by ICP-OES, and no statistical differences were observed (Student's t-test, confidence level of 95%, p > 0.05). The precision of proposed method was evaluated in terms of repeatability (RSDs <= 3%) and intermediate precision (RSDs 5 <= 7%), and suitable results were obtained for all analytes. In addition, the limits of detection for all analytes using proposed method were lower than those obtained using conventional digestion in view of use a high sample mass and a diluted acid solution for sample digestion. The use of diluted acid reduces risks to analyst - since it eliminates the concentrated acid handling; reduces the consumption of reagents and, consequently, the waste generation, in accordance with the principles of green chemistry. Using the proposed method was possible to perform the determination of ten elements in a single analysis with suitable precision and accuracy. Six sport supplements were analyzed and the results are alarming because in most cases they were in disagreement with those informed on the label. Thus, a suitable quality control of sports supplements should be performed and the proposed method is a green, safe, accurate, precise and sensitive alternative for this purpose.