Chromatography Forum

Hi everyone I would be grateful if you could clarify something for me. We run synthetic urine samples spiked with codeine. In these we get nice peaks. In unknown samples from people on drug treatment programmes that we know have codeine present in them as a result of running the on the GC-MS firstly we get no peaks. Is it possible that ion suppression is the problem or what other issues might there be. It appears that the synthetic urine samples analysed by either GC-MS or LC-MS you can find codeine so the problem seems to be with the unknown samples.

To clarify we run the unknown samples using LC-MS/MS using Agilent LC and a 3200 QTRAP. The sample matrix is urine and the LC column and conditions are -mobile phase is A: 4mM Ammonium Acetate + 0.1% Formic Acid B: 0.05% Formic acid in MeOH + 2% IPA and the column is a Thermo Hypurity C8 50x3mm 5µm Column.
Many thanks in advance...

What is your sample prep for the urine samples? That would
be the first place I'd look.

Thanks for your reply. The sample prep is dilute and shoot (urine diluted 1/10) using water/methanol.

You might need to adjust your gradient - i.e. have an
isocratic hold at the beginning of your run so that
codeine does not elute in the "suppression region"

You may also need to evaluate sample cleanup prior to injection.

For your information - below is LC-MS/MS of codeine in whole blood on
Unison US-C18 (5um).

http://www.silvertonesciences.com/files/TI365E.pdf

I would think that the problem might be the dilution with methanol. Codeine will elute rather early, and with methanol in your sample matrix (how much?) it may not be retained at all any more.

My suggestion: dilute the sample with water, or do not dilute at all.