作为铂样品国际实验室间比对分析的参加单位,实验室接受了一种铂-钌合金试样并要求按指定的方法进行分析,选择了重量法测定其中铂含量(ISO 11210-1995).已知该试样中钌的含量在5%(质量分数)左右.为消除钌对铂测定的干扰,对原方法作了以下改进:① 将在950 ℃灼烧(NH4)2PtCl6沉淀所得的海绵状铂称重后重新用王水溶解.溶液有黑色不溶物,经证明为钌,将溶液用紧质滤纸过滤,滤纸及不溶物经950 ℃灼烧并称重,记其量为钌.② 在滤液中按第一次沉淀相同的方法将铂以氯铂酸铵形式沉淀,过滤并在950 ℃灼烧后称得其重量.按文中给出的公式计算铂含量,此计算公式中包括扣除钌含量的计算项.按此改进的方法测得合金中铂的含量与实验室用其他方法所测得的结果一致.

As a participator of the international interlaboratory testing of a jewellery sample,a platinum-ruthenium alloy was received and required to analyze according to the assigned methods. Gravimetric method (ISO 11210-1995) was used by this laboratory for the determination of platinum. It was known that the content of ruthenium in the alloy is around 5%. To eliminate the interference of ruthenium,modification of the conventional gravimetric method was performed in the following way: ① the sponge platinum obtained through the combustion (at 950 ℃) of the precipitate (NH4)2PtCl6 was dissolved again with aqua regia and the black insoluble substance,which was proved to be ruthenium,was filtered onto a close-texture fillter paper,transferred to a tarred crucible,combusted at 950 ℃ for 1.5 h and weighed to constant weight. ② platinum in the filtrate was re-precipitated as (NH4)2PtCl6 and treated in the same way as in the first precipitation. Content of platinum was obtained by calculation according to the formula given in the paper,in which a substraction of the ruthenium content was included. The results obtained by this modified gravimetric method were in consistency with the results obtained by other methods.