IC and Ion Selective Electrode Question

[ilawrence]

Our lab currently analyzed for NH4+ using an Ion-Selective Electrode. Sample prep. is easy. 5ml of 10N NaOH into 100mls of sample.
Question #1 Why are we using caustic in our sample prep?

We are trying to move this analysis to IC. Using IC would we see NH4+ using this sample sample prep?

Any information would be helpful.

Thanks

[Consumer Products Guy]

My guess is that the ion sensing electrode is sensing ammonia, which you formed from the ammonium when NaOH was added.

I think for IC you'd need to stay acidic, as NH4+.

[Markus Laeubli, Metrohm]

Consumer Products Guy is right. Ammonium selective electrode uses a gas diffusion membrane. Caustic is needed to move ammonia through the membrane into the internal buffer.

Using Ion chromatography for ammonium determination caustic is not required as ammonium cation (NH4+) is quantified. Therefore the pH should be neutral to slightly acidic. Depending on the sample matrix no sample preparation might be necessary.

[Banning]

Our lab currently analyzed for NH4+ using an Ion-Selective Electrode. Sample prep. is easy. 5ml of 10N NaOH into 100mls of sample.
Question #1 Why are we using caustic in our sample prep?

We are trying to move this analysis to IC. Using IC would we see NH4+ using this sample sample prep?

Any information would be helpful.

Thanks

Why are you trying to move to IC?

[ilawrence]

I don't believe the results from the probe. Especially low levels.

[Markus Laeubli, Metrohm]

I don't believe the results from the probe. Especially low levels.

As long as you are preparing the sample according to the requirements of the Ammonium electrode and you are working in the linear calibration range, there should be no problem with the use of ISE. But you are right for low levels (out of the calibration) the results are questionable.