Analytical determination of ultra low levels of micronutrients in soil solutions is one of the major problems limiting trace element studies in alkaline sodic soils. The low concentrations of trace metals in environmental samples are often measured by the graphite furnace atomic absorption spectrometry (GFAAS) technique. However, considerable difficulty was found with zinc (Zn) determination in alkaline sodic soil solutions. The effects of various chemical modifiers (phosphoric acid, ammonium phosphate, nitric acid, and palladium (Pd)] on GFAAS determination of ultra trace levels of Zn in soil solutions of four alkaline sodic soils were investigated in this study. The concentration of Zn in the soil solution was significantly (P<0.01) higher in the presence of modifiers relative to that determined in the absence of modifiers. In addition, coefficient of variance [(CV) 21.5%] in the absence of chemical modifiers was up to three times higher than those determined with chemical modifiers (7 to 10.2%). Chemical modifiers also decreased the characteristic concentration (increased sensitivity). The decrease ranged from 22.1 to 34.6% for Pd and phosphoric acid, respectively, compared to that in the absence of chemical modifiers. The maximum ashing temperature for standard Zn solution increased from 300°C in the absence of modifiers to 800°C with phosphoric acid and ammonium phosphate, indicating increased stability of Zn at high temperatures. Based on the recovery test data, characteristic concentration, atomization temperature, and the shape of atomic signal peak, analysis of Zn in the presence of phosphoric acid was recommended for soil solution Zn.

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