Chromatography Forum

Hello,

I'm currently learning the ins and outs of a 6460. Is it common for the ITSD area to drift by a magnitude of ~2 fold (Example: ITSD area of one sample 40,000 vs ITSD area of another sample 100,000)?

When I back calculate my QC samples to my standard curve, the numbers work and fall within range.

Just seems weird that my ITSD would drift so much unless my pipetting is absolutely terrible.

Sorry for the newbie question.

If you inject the same vial multiple times does the drift still occur?

That will narrow it down to prep technique or instrument problems.

For each sample, I do four injections in a row. The first two I toss and last two I use. I've found that my instrument has trouble transitioning to new samples so I do my experiments in quadruplicates.

The drift occurs from say Sample 1 to Sample 50. Sample 1 will have a high internal standard signal and Sample 50 will be 1/2 or 1/3 of Sample 1.

Thanks for your help by the way.

To answer your question yes there is drift at the beginning injections. So if I run quadruplicates, the first 2 injections will be janky, but the last 2 are consistent.

If sample 1 and sample 50 are the same sample injected twice, and if you see a trend for a consistent decrease of the ISTD signal over the batch, then you probably have a contamination of your MS with too dirty samples (although there might be other causes involved).

If samples 1 and 50 are two different samples, you cannot say much because matrix effects can be variable and explain the difference observed.