Objective To establish a method for determination of lead concentration in soil using automatic digestion by graphite furnace atomic absorption spectrometry (AAS) after optimizing experimental conditions.
Methods The digestion effects on soil standard substance were compared among three kinds of digestive systems in cluding aqua regia (hydrochloric acid:nitric acid=3:1), aqua regia+hydrofluoric acid, and mixed acid (nitric acid+hydrochloric acid+hydrofluoric acid+perchloric acid). The influences of different graphite furnace matrix modifiers, ashing temperature, and in tegral rules on the determination of lead were investigated, and the optimal test conditions were selected. The limit of detection of automatic digestion-graphite furnace atomic absorption spectrometry was measured, and the applicability of the method was evaluated through determining four kinds of soil standard substances.
Results The assay proved to be time-saving and stable using aqua regia+hydrofluoric acid as digestive system. Ammonium dihydrogen phosphate (20 g/L) was an effective matrix modifier to reduce matrix interference and improve peak shape. The background interference was decreased and atomic absorption was enhanced obviously when ashing temperature was 800℃. The le ad content obtained by peak height integral was more stable and accurate than that by peak area integral. Under the optimized conditions, the linear range was 5.0-50.0μg/L, and the limit of detection was 0.080mg/kg. By applying the method, the determination results of four different soil standard materials were all within standard uncertainty range.
Conclusion Automatic digestion-graphite furnace atomic absorption spectrometry is developed for the determination of lead in soil, in which aqua regia+hydrofluoric acid is used as digestive system, ammonium dihydrogen phosphate is chosen as matrix modifier, ashing temperature is set at 800℃, and peak height integral is selected as calculation rule. The method is proved to be time saving, reproducible, and suitable for lead detection in massive soil samples.
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