Peak area loss

[Propanal]

Hallo,

I have a question regarding loss in peak area of our analyte (propanal).
We use an Agilent Headspace Sampler G1888 together with GCMS. We run a propanal standard each week and normalize the peak area to a definite concentration. what we see is, that the peak area falls down linearly. compared to july, the peak area is now 3 times less.
We run this standard in water. the vial cups are tight. MS tune reports are fine, no air leaks, ion source is clean.
real samples and standard peak areas have a very low standard deviation between two measurements. calibration of propanal gives a correlation coefficient of 0,99.
if there was a leak, the areas of samples with a same concentration should be different, shouldn´t they?
could the headspace needle be the problem?

thank you for your assistance,
propanal

[chromatographer1]

Do you make up your own standards?

best wishes,

Rod

[Peter Apps]

Do you run any other samples on the same MS ?, if you do, what has happened to their peak areas ?.

Peter

[Propanal]

Hallo,

we run samples (powders dissolved in water -->emulsions), that contain oil and oils as such. we store the samples with regard to lipid oxidation. propanal develops during storage. normally, propanal should increase during storage up to a certain time, but at the moment we only detect traces of propanal in the real samples. for calibration, we add propanal to the different matrices (emulsion, oil,..), but as already written, in comparison to older calibration times, the peak areas ar decreased.

Propanal

[Propanal]

Hello Rod,

yes, we make our own standards. in water, oil, emulsions, dissolved powders to account for any matrix effects.

Propanal

[Peter Apps]

What I meant was, do you run any samples besides the headspace that contains propanal ?. If you are doing liquid injections for instance and the peaks are also getting smaller the headspacer is eliminated as a cause of the problem. I presume that you have a 6890-5973 GC-MS ? What tune programme are you using ?

Peter

[chromatographer1]

Propanal is quite reactive and your spiking reagent may be going back or there may be differences in the matrix which cause the analyte to react and decrease in size.

I think you are looking for consistency where there may not be any.

Consistently spike on a weight basis and calibrate as needed.

Also check your reagent quality after opening and storage against a reliable standard or reference material which does not degrade with time and exposure to air.

best wishes,

Rod

[Propanal]

Thank you both for your comments!

We only run headspace samples.

@ chromatographer:
I do not really understand
"Consistently spike on a weight basis and calibrate as needed".

In the meantime, I cleaned the headspace sample probe and did the steam cleaning procedure (at least I tried..).

we should order new propanal, you are right. but the peak area loss is evident even if we use new standard (as was last year)..

regards, propanal