土壤样品中有效钼用草酸铵-草酸混合溶液(pH 3.3)振摇提取,所得悬浮液用干滤纸过滤,分取部分滤液蒸缩体积后加入10 g·L-1酸性高锰酸钾溶液并蒸发至近干,趁热加0.25 mol·L-1氢氧化钠溶液进行共沉淀分离。分取部分上清液,用硫酸(1+1)溶液酸化后加入混合底液(其中含有二苯基乙醇酸、二苯胍及氯酸钠)及少许钛铁试剂溶液作为与钼(Ⅵ)进行催化反应的试剂体系。用JP-303极谱仪进行测定。在-220 mV峰电位处测得的峰电流值与其相应的钼(Ⅵ)的质量浓度在0.8~20 μg·L-1范围内呈线性关系。此方法的检出限(3s/k)为0.002 6 μg·g-1。用此方法分析了5个土壤标准物质,所测得有效钼的含量与其认定值相符。

Available molybdenum(Ⅵ) in soil sample was extracted by shaking with a mixed solution of (NH4)2C2O4 and H2C2O4 (pH 3.3). The suspended solution was filtered on a dry filter paper and an aliquot of the filtrate was evaporated to near dryness after addition of 10 g·L-1 KMnO4 acidic solution. 0.25 mol·L-1 NaOH solution was added for co-precipitation and an aliquot of the supernatant was taken and acidified with H2SO4(1+1). A mixed base solution (containing diphenyl-glycollic acid, diphenylguanidine and sodium chlorate) together with tiron solution, acting as reagents for the catalytic reaction with Mo(Ⅵ), was added, and the polarographic determination of Mo(Ⅵ) was made with the JP-303 polarograph. Values of peak current at the peak potential of -220 mV were found to keep linear relationship with mass concentration of Mo(Ⅵ) in the range of 0.8-20 μg·L-1. Detection limit (3s/k) of the method found was 0.002 6 μg·g-1. The proposed method was used in the determination of molybdenum in 5 CRM′s of soil, giving results in consistency with the certified values.