OPA Derivitised Cysteine - consuming cysteine as S-H?
Posted: Mon Mar 26, 2012 5:25 am
Hey there all.
I work for a contract manufacturing company that mainly makes nutritional supplements / complementary medicines and we make a diverse range of products for numerous customers. Some of the supplements that we make contain numerous amino acids, of which most we can test with some confidence using OPA derivitisation methods running on Agilent 1100's using UV detectors... however...
We constantly have issues with cyteine and cyteine HCl giving lower than expected assay results. When I reviewed the issue, and started to understand the method used and the cysteine itself, I came across something that I found interesting.
The OPA method uses mercaptoethanol during the derivitisation process. I see that cysteine also has a prominent S-H group dangling off the end. I was wondering if the community here agrees that we may be having some of the cysteine reacting as the R-S-H instead of the mercaptoethanol, and hence leading to the lower results we are observing?
Any input or other indications would be greatly appreciated.
Please note that it has been many years since I have been in the lab, so if we could keep it simple, that would be great!
Thanks All - Matt C
I work for a contract manufacturing company that mainly makes nutritional supplements / complementary medicines and we make a diverse range of products for numerous customers. Some of the supplements that we make contain numerous amino acids, of which most we can test with some confidence using OPA derivitisation methods running on Agilent 1100's using UV detectors... however...
We constantly have issues with cyteine and cyteine HCl giving lower than expected assay results. When I reviewed the issue, and started to understand the method used and the cysteine itself, I came across something that I found interesting.
The OPA method uses mercaptoethanol during the derivitisation process. I see that cysteine also has a prominent S-H group dangling off the end. I was wondering if the community here agrees that we may be having some of the cysteine reacting as the R-S-H instead of the mercaptoethanol, and hence leading to the lower results we are observing?
Any input or other indications would be greatly appreciated.
Please note that it has been many years since I have been in the lab, so if we could keep it simple, that would be great!
Thanks All - Matt C
