Determination of Toxic Metal Ions in Beverages by Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

  When toxic metal ions are mixed with a beverage in a criminal case, it is required to make accurate identification and determination of these ions. In this study, the application of inductively coupled plasma atomic emission spectrometry (ICP-AES) was investigated to determine the toxic metal ions of Cu, Cd, Tl and Pb in beverages. Samples were prepared by dissolving the salts of these ions in oolong tea, orange juice and canned coffee. Considering the human LDLo, mouse LD₅₀ and guinea pig LDLo, concentration of each ion was adjusted to one tenth of these values corresponding to 229, 492, 40.5 and 5630 μg/ml, respectively. Some of these samples produced the precipitate and the metal ions in the supernatant and the precipitate of oolong tea were determined separately after centrifuging. As the result, 87.2%, 94.5% and 91.1% of Cu, Cd and Pb were found in the supernatant while 12.5%, 2.2% and 8.3% were in the precipitate. Each metal ion in the oolong tea could be recovered quantitatively after the dissolution of the precipitate by the addition of 1 ml of concentrated nitric acid. Sample solutions made of orange juice and canned coffee were centrifuged and then the precipitates were vigorously washed three times with diluted nitric acid (2+98). The supernatants and the eluents of the precipitates with the diluted nitric acid were subjected to ICP-AES. Each metal ion in any of the tested beverages could be determined with a satisfactory recovery rate except for Pb in the canned coffee. The recovery rate in the canned coffee could be improved from 92.4% to 96.0% by adding concentrated nitric acid before centrifugation. It was concluded that the toxic metal ions of Cu, Cd, Tl and Pb in the beverages could be accurately analyzed with ICP-AES by using the appropriate pretreatment.