[krivan]

Hi,

I am an electronic engineer having to test his device with some chemicals and to this I'd like to ask for your help.

I have used commercial pH4/7/10 buffer solutions from Thermo Scientific and as I've changed the buffers on top of my semiconductor device I've seen clear output voltage changes. So far it is OK.
Now I have to do some tests in a way that I mix 1ml of a pH buffer with 100ul of a made-up solution [detailed below] and monitor the response of the device.

I made a solution from 1g of citric acid [was in powder form] and 25ml of DI water. I mixed 100ul of this citric acid solution with 1ml of the pH buffers and at each case [pH 4/7/10 buffer] the output of the electronic circuitry showed a large voltage change, as expected.

***Question 1***: Can somebody please advise how to calculate the concentration of citric acid in the above mentioned made-up solution?

Also, I want to do the same other way round with a made-up alkaline liquid. At the moment I have NaOH ph12 that I diluted down from ph14 by DI water. Using this I could see hardly any change in the output signal.

***Question 2***: Does somebody have an idea how to make up a solution that has strong effect similar to the mentioned citric acid stuff but alkaline?

Thanks,
Krivan

[Borek]

1. Convert mass to moles, divide by volume - that's your molar concentration in the original solution. Multiply the concentration by 100 uL - that's amount you transfer. Divide by 1.1 (1mL + 100 uL - total volume) and you know formal concentration.

2. Have you tried to use pH 14 solution instead of the diluted one?

Note: my guess is you are working on some kind of pH meter or pH electrode. Qualitative tests are OK, but you will need also a quantitative ones - and without knowing how to precisely calculate pH of the solution you will be not able to do any tests. And these calculations can be challenging, especially when dealing with systems you have just described (buffer with added multiprotic weak acid).