在常规的硫氰酸盐光度法测定钼的硫酸介质中,加入80 g·L-1乙二胺四乙酸二钠盐(EDTA-2Na)溶液7 mL,使48 mg·L-1以下共存的铅(Ⅱ)无法生成硫酸铅,不干扰钼的测定,应用此条件测定了含铅量较高的矿石中钼的含量。样品(0.100 0~0.500 0 g)于高铝坩埚中,用过氧化钠3 g融熔,熔块用水浸出,定容至100 mL,分取部分试液,加入EDTA-2Na溶液7 mL后按常规条件显色,用双波长方法以460 nm(λ1)为测定波长,650 nm(λ2)为参比波长测量吸光度(A),计算ΔA(Aλ1-Aλ2)。钼的质量浓度在6.0 mg·L-1以内与相应的ΔA之间呈线性关系,方法的检出限(3s/k)为8.1×10-3mg·L-1。应用此方法测定了2个CRM(GBW 07238,GBW 07285)中的钼量,测定值与认定值相符,测定值的相对标准偏差(n=9)依次为2.8%,1.2%。

In the H2SO4 medium of the conventional method of thiocyanate photometric determination of molybdenum, by addition of 7 mL of 80 g·L-1 EDTA-2Na solution, the interference of co-existing Pb2+ up to 48 mg·L-1 due to formation of PbSO4 was eliminated. This procedure was applied to SCN--photometric determination of molybdenum in ore samples with high lead contents. The ore sample (0.100 0-0.500 0 g) was fused with 3 g of Na2O2 in a high-aluminum crucible, the melt was taken up with water, and made up its volume to 100 mL. An aliquot of the sample solution was taken, and its molybdenum content was determined by the conventional SCN--photometric procedure after addition of 7 mL of the EDTA-2Na solution. Value of absorbance difference (ΔA=Aλ1-Aλ2) of colored solution was measured by dual-wavelength-spectrophotometry, using 460 nm (λ1) as the measuring wavelength and 650 nm (λ2) as the reference wavelength. Linear relationship between values of ΔA and respective mass concentrations of molybdenum was kept within 6.0 mg·L-1, with value of detection limit (3s/k) of 8.1×10-3mg·L-1. The proposed method was used to determine molybdenum in 2 ore CRMs (GBW 07238, GBW 07285), giving results in consistency with the certified values, and RSD′s (n=9) of the 2 CRMs found were 2.8%, 1.2% respectively.