Hello Scientists,
sometimes I have low repeatibility in HS-GCMS analysis of VOC dissolved in water by methanol solutions spikes. The method generally works well, beacuse months ago I performed also a PT scheme and it was successfully.

The trouble is that sometimes I have low repeatibility, with RSD% on peak Area of about 20-30% for internal standard ChlorobenzeneD5 and it is an hassle because I have to find the cause and solve it.
Acceptable RSD% on peak Area for this analysis should be (on my experience) between 5 and 10% for 8-10 replicates.

Based on your experience, which are the most probable cause of the loss of repeatibility??
- column ruins
- liner dirty
- ion source is dirty
- mass lenses dirty
- anything else??

Thank you very much!

Column: Rxi-624 sil MS 30m 1.4um 0.25mm ID, AOC6000 PAL autosampler, inj volume 300uL, liner volume 800uL, method conditions (normal, they are ok), flow 1.2ml/min.