Implementation of AAS methods for the quantification of Hg and hexavalent Cr in recycled paper used for food packaging

Total mercury and hexavalent chromium were determined in recycled paper samples and cardboard packages intended to come in contact with food using atomic absorption spectrometry (AAS). For the detrmination of mercury, the samples were digested with a mixture of concentrated HNO 3 and H 2 O 2 and determined by cold vapor generation. Hexavalent chromium was extracted directly from the paper and cardboard with a solution of NaOH and determined by electrothermal atomization AAS. The detection limits were 0.38 and 0.50 μg/L for mercury and hexavalent chromium, respectively. The determinations were performed in the linear range of 0.38-10.0 and 0.50-50.0 μg/L. For mercury, the precision was 5.1% and 6.0% for the analytical and overall procedure, respectively. For hexavalent chromium, it was 6.3% for both situations. For the recovery studies, several determinations for each metal were conducted in different aliquots of the same sample, using the standard additions method for several different concentrations, resulting in recoveries better than 91%. The stability of hexavalent chromium in these matrices was evaluated by adding different concentrations of standard hexavalent chromium solutions to several portions of recycled paper which were left standing for different times of contact. Subsequently, specific alkaline extraction of the species was carried out and the respective concentrations determined. For the quantification of mercury and hexavalent chromium, the methods were applied to 19 recycled paper samples of several grammages obtained from industry and to 43 cardboard packages obtained in local markets. For recycled paper, the mean levels were found to be 0.199 μg/g (0.038-2.20 μg/g) for mercury and 0.464 μg/g (0.093-1.22 μg/g ) for hexavalent chromium. For cardboard packages, the mean levels were 0.072 μg/g (0.038-0.660 μg/g) and 0.228 μg/g (0.069-0.359 μg/g) for mercury and hexavalent chromium, respectively.