Determination of Cadmium in Soil and Sediment by Graphite Furnace Atomic Absorption Spectrometry with Nanopalladium Matrix Modifier

The treated soil or sediment sample (0.2-0.5 g) was taken, digested in 6 mL of nitric acid, 2 mL of hydrochloric acid and 2 mL of hydrofluoric acid under program of temperature elevation of microwave digestion. After cooling to room temperature, 2 mL of nitric acid, 1 mL of hydrofluoric acid and 1 mL of perchloric acid were added and open heating was carried out to drive away acid at 130 ℃. After digestion was completed and yellow smoke disappeared, the solution was continued to heat to nearly dryness. The residue was dissolved in an appropriate amount of 1% (volume fraction) nitric acid solution, and its volume was made up to 50 mL. Cadmium in the above solution was determined by graphite furnace atomic absorption spectrometry (GFAAS), using 5 μL of 0.60 mg·L^-1 nanopalladium solution as matrix modifier at the ashing 2 temperature of 650 ℃ and atomization temperature of 1 500 ℃. As shown by the results, nanopalladium provided a protective atmosphere from the graphite furnace drying stage, and could react with cadmium to form an alloy to prevent the loss of high temperature ashing. Nanopalladium also could remove matrix interference at a higher ashing temperature, and had a coating effect on the graphite tube during the temperature programming process, which could increase the service life of graphite tube by more than 50%. Linear relationship beteewn the mass concentration of cadmiumcan and the corresponding absorbance was found within 2.00 μg·L^-1, and the detection limit (3.143s) was 0.007 8 mg·kg^-1. This method was applied to the determination of national reference materials, and the determined values were within the range of the certified values, with RSDs (n=6) of the determined values in the range of 1.4%-3.7%. This method and inductively coupled plasma mass spectrometry (ICP-MS) reported in the literature were simultaneously used to analyze the actual soil and sediment samples, and the F-test and t-test were used for statistical evaluation. It was shown that there was no significant difference in the determined data and their precision between the two methods.