By Elena on Monday, February 9, 2004 - 02:21 am:
We tried to perform Ph Eur method for assay on Electrochemical detector. The first area of any sample is bigger than the others. So the results vary in a quite large range. I'll be greatful for any advice.
Elena
By Chris Pohl on Monday, February 9, 2004 - 04:22 pm:
Could you please supply a bit more information? I.e.:
Detector operating mode
Chromatographic conditions
Analytes
This might make diagnosis of bit easier.
By Elena on Thursday, February 12, 2004 - 02:29 am:
It is HP 1049 A programmable ecd, pulse mode, the potentials are 0.05 V detection, +0.75V oxidation, and - 0.15 reduction.
Post column reaction with 20mg/ml NaOH, temperature of the column is 55C, temperature of the detector - 35C
The analyte is Tobramycin.
By Chris Pohl on Thursday, February 12, 2004 - 04:15 pm:
One possible explanation could be related to your shutdown and storage methods. Are you stopping the waveform when you turn your instrument off? If not, you should be. If there is no clear way to do this on your detector (I'm not familiar enough with this detector to know one way or the other), you might consider disconnecting the cell from the detector after you finish using it.
The other possibility is that it's a thermal equilibration problem. Generally, it's better to have the detector temperature set higher than the column temperature. Perhaps in your case you can't do this because you observe excessive noise at elevated temperature but that might explain the discrepancy of your first datapoint. In this case, there's probably not much you can do about it.