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topic 4622

Boric acid determination, autotitration


Currently I have some problems with autotitration of boric acid in nickel plating bath, autotitrator is MT 70ES. I add mannitol into sample and use NaOH as titrant, with pH electrode to measure endpoint. In last three months, I found signal at endpoint became lower and lower, dropped from about 2000 mv/ml to 100 mv/ml, meanwhile endpoint became noise and results were not so repeatable. After evaluation, I did not find any problem with autotitrator and chemicals, for new prepared nickel bath, signal at endpoint is still about 2000 mv/ml.

Q1: why does signal drop so much with extension of nickel bath life?

Q2: Is there any way to recover endpoint signal to high level, eg. 1000 mv/ml?

Wang Li Ping
- Singapore


My guess is that you have drag in and or breakdown products that are forming a buffer that interferes with your titration.

I used color indicators, but the result is pH sensitive so are somewhat equal. I never saw the phenomenon you speak of.

James Watts
- Navarre, Florida

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