Sequential voltammetric determination of trace metals in meals

An analytical procedure for the sequential determination of Zn(II), Cr(VI), Cu(II), Sb(III), Sn(II), Pb(II) by square wave anodic stripping voltammetry (SWASV) and Fe(III), Mn(II), Mo(VI) by square wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is described. The digestion of each matrix was carried out using a concentrated HCl–HNO3–H2SO4 attack mixture, employing dibasic ammonium citrate buffer solution (pH 6.9 and 8.7) as supporting electrolytes. The analytical procedure was verified by the analysis of the standard reference materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (sr) was of the order of 3–5%; the accuracy, expressed as relative error (e) was generally of the order of 3–6%. In presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Finally, the analytical procedure was transferred and applied to commercial meals sampled on market. A critical comparison with atomic absorption spectroscopic measurements is also discussed.