Signal to Noise

[konkous]

Hello,

I'm currently running a on-line SPE method for the quantitative determination of a pharmaceutical substance. Despite the fact that my signal to noise ratio is about 16 for my first standard it seems that it is much lower (about 5 or 6) for the quality control samples which have the same concentration as my first calibrator. Is there a way i can justify this because there is absolutely no problem regarding the quantitation of the specific samples (both their accuracy and repeatability).

[tom jupille]

What got worse, the signal or the noise?

[konkous]

What got worse, the signal or the noise?

Thank you for the immediate response. It seems that as more samples are injected the noise gets more intense. The signal of my analytes is stable.

[MG]

If your samples are plasma, then nonpolar compounds such as lipids can build up on your column over time. This can contribute to background noise or even suppress signal and cause your QC's to fail. Washing your SPE and/or analytical column with a stronger solvent at the end of each run, or extending your existing wash time, might be worth trying.

[tom jupille]

The other thing you might take a look at is optimizing the m/z scan range on the MS.