磷钼蓝体系薄层树脂相吸光光度法测定痕量钼的研究

THIN-LAYER RESIN-PHASE-PHOTOMETRIC DETERMINATION OF TRACE-AMOUNTS OF MOLYBDENUM WITH PHOSPHO-MOLYBDENUM-BLUE METHOD

提出了在酸性条件下,以磷钼蓝反应为基础的薄层树脂相吸光光度法测定钼。此方法灵敏度较高(ε705=8.1×104L·mol-1·cm-1),比液相光度法提高10倍,精密度理想(钼浓度为20μg/25ml,n=6),RSD为2.8%。应用此法测定天然水中钼,线性范围为0～18μg·ml-1,回收率为97%～102%。

0.5g of phosphate-form anion exchange resin is added to 25ml of test solution containing an appropriate amount of Mo(Ⅵ) and having an acidity of 0.2mol·L^(-1) of HCl, that is 2.5ml of 2mol·L^(-1) HCl in 25ml of solution. After mixing for 20min with a magnetic stirrer, heteropoly acid is formed between Mo(Ⅵ) ion and phosphate ion on the resin, which is further reduced to 'molybdenum blue' with a reducing solution containing ascorbic acid, sodium potassium tartrate and sulfuric acid. The absorbance of the resin adsorbed with the 'molybdenum blue' is then measured at 705nm ( λ _(max) of molybdenum blue) against resin blank prepared in the same way but containing no molybdenum(Ⅵ). The resin-phase photometric method gives a molar absorptivity of ( ε _(705)) 8.1×10~4L·mol^(-1)·cm^(-1), which is about 10 times higher than that in water phase [ ε _(705) (in H_2O solń)=7.8×10~3L·mol^(-1)·cm^(-1)]. RSD ( n =6) tested at the concentration level of 20μg per 25ml achieve to a value of 2.8%. Recoveries obtained are in the range of 97%～102%.