HPLC analysis of noradrenaline in microdialysis samples

[ag_stealth]

Hi all,

The problem I am having is that I cannot detect noradrenaline (NA) in brain microdialysis samples using an Antec Decade II electrochemical detection system. In fact even if I inject a standard solution of NA in artificial cerebrospinal fluid (aCSF) into the system, the detector just goes off scale. However I can achieve resonable detection limits when I inject NA standards in mobile phase (MP).

I am using fairly standard conditions for NA detection according to the literature but I obviously must be doing something wrong.

MP composition: 154mM NaCl; 4mM KCl; 2.2mM CaCl2; pH 6.2
Flow rate is: 0.65 ml/min
CSF composition: 10.4mM Citric Acid; 61mM Sodium Acetate;
Methanol 7%; pH 5.1

Please share your experience if you have've encountered a similar problem before.

Any help or advice would be much appreciated.

Thanks very much.

Alex.

[HW Mueller]

For what do you have CaCl2 in there?

[ag_stealth]

For what do you have CaCl2 in there?

I was trying to replicate the method other people used to detect NA in microdialysates.

Do you think calcium chloride might be causing this problem? The problem occurs when CSF is injected, when I inject my standards in MP its all good, but obviously microdialysis samples have to be in CSF.

Thanks.

[HW Mueller]

I am not sure, you would have to look at Ca++ interaction with citrate and carboxylate. Actually, if there was an interaction I would expect the possibility of precipitation, not an increase in detector response. What would happen if you had precipitation on the detector electrodes?
Actually If I would have to do this I would see to it that the Ca++ and the CSF (at least most of the matrix) would be taken out of the chromatography.