为测定钛合金化铣液和酸洗液中氟的含量,将待测液酸度调节至pH 2.0,加入过量镧(Ⅲ)标准溶液并煮沸2 min,使溶液中F-与La3+生成难溶的LaF3沉淀,加入乙酸-乙酸钠缓冲溶液10 mL。用EDTA标准溶液滴定溶液中过量的镧(Ⅲ),从而间接算出待测液中氟离子的含量。对已知含F-的质量浓度为45.00 g·L-1的氢氟酸溶液连续按所提出的方法测定10次,测得回收率几近100%,测定值的相对标准偏差为0.080%。对化铣液和酸洗液实样分别按本法及硝酸钍滴定法进行测定,所得氟离子的测定值相符。

For the determination of content of F- in samples of chemical milling and acid pickling solution used for titanium alloys, an aliquot of the sample solution was adjusted to pH 2.0 and buffered with 10 mL of HOAc-NaOAc buffer solution; an excess of standard La3+ solution was added to the sample solution and the mixture was heated to boiling for 2 min to precipitate completely the F- as LaF3. Excess of La3+ in the solution was then titrated with standard EDTA solution, and the content of F- was determined indirectly by calculation on the base of the amount of titrant consumed. To test for the accuracy and precision of the proposed method, 10 successive determinations were made with a known HF solution of 45.00 g·L-1 F- by the proposed method, giving values of recovery very close to 100% and of RSD′s of 0.080%. Substantial samples of chemical milling solution and acid pickling solution were analyzed by the present method and checked by the Th(NO3)4 titrimetric method, consistent results were obtained.