Post-Addition of Sulfuric Acid to Wet Digested Biological and Environmental Materials for Mercury Determination by Cold Vapor Atomic Absorption Spectrometry (original) (raw)

1997, Analytical Sciences

The charring of samples and loss of mercury by a nitric-sulfuric acid mixture has been overcome by prior digestion with nitric acid, followed by the addition of sulfuric acid into the final solution. This approach provides optimum decomposition and analytical conditions for a reliable cold vapor atomic absorption spectrometric determination of mercury in biological and environmental materials. In all cases, the presence of sulfuric acid improved the sensitivity of the mercury response significantly. Furthermore, the prior-and post-addition of sulfuric acid gave similar sensitivity and mercury concentrations for all samples. The adequacy of the prior digestion with nitric acid and post-addition sulfuric acid for reliable mercury determination was successfully demonstrated for blood, bone, bovine liver, mushroom, lake sediment, peat and prawn samples. Keywords Cold vapor atomic absorption spectrometry, mercury, wet digestion, biological and environmental materials Cold vapor atomic absorption spectrometry (CV-AAS) is the preferred technique for the determination of trace/ultra-trace concentrations of mercury in various samples because of its ease of operation and attainment of a much lower detection limit. l'2 However, like other techniques, the decomposition of the solid samples and, when necessary, the conversion of mercury to the divalent form, are required for an accurate determination by CV-AAS. Some of the approaches that have been employed for this purpose include the use of nitric acid3-5 and its mixture with sulfuric acid"6'7, hydrochloric acid8 and perchloric acid.6,9,1o The oxidizing power of the digestion acid or mixtures is often supplemented with the addition of either H2O2, KMn04, V205, K2Cr207 or K2S204,5,11-14 A recent evaluation of some of these digestion methods in our laboratories revealed that the nitric-sulfuric acid mixtures was most effective for the CV-AAS determination of mercury in biological and environmental materials.15 However, it was noted that complete recovery of organomercury was not accomplished in some cases. Nevertheless, the recovery of organomercury obtained with the use of nitric-sulfuric acid mixture t To whom correspondence should be addressed.