氢氧化锰共沉淀分离-催化极谱法测定土壤中有效钼

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0.8～20μg.L-1范围内呈线性关系。此方法的检出限(3s/k)为0.002 6μg.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。

Catalytic Polarographic Determination of Available Molybdenum in Soil after Separation by Co-precipitation with Manganese Hydroxide

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.