1959年G·Gopala Rao等提出用硫酸肼作还原剂,将六价钼还原为五价,然后用硫酸铈或钒酸铵滴定.该法具有简便、选择性好等优点,但因微量杂质〔如铜(Ⅱ)离子〕的催化作用而使钼还原不完全,同时因指示剂选得不妥〔过早显色〕又很不稳定.1974年湖南冶金研究所在该法基础上提出以8一羟基喹啉来消除微量铜离子的催化 In 1959 G · Gopala Rao put forward the use of hydrazine sulfate as a reducing agent, hexavalent molybdenum reduced pentavalent, and then titration with cerium sulfate or ammonium vanadate. The method has the advantages of simple, good selectivity, but due to trace impurities [ Such as copper (II) ion catalytic reduction of molybdenum and incomplete, at the same time due to the improper selection of the indicator 〔premature color〕 very unstable .1996 Hunan Institute of Metallurgy on the basis of the law proposed to 8 Hydroxyquinoline to eliminate the trace copper ion catalysis