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- Posts: 22
- Joined: Fri Apr 30, 2021 1:10 pm
- Location: Italy
I have a TD-GCMS and some times, a standard show a great shift in retention time only for the second half of chromatogram. Benzene, Toluene-D8 and Toluene show the same ret.time of previous injection, while ethylbenzene, m,p-xylene and o-xilene shift of about 0.15min. Peak area and peak shape are always good even in the shifted chromatograms.
What I inject is a control standard solution of BTEX in methanol added to a sorbent tube by 1uL with syringe under inert gas flow.. I used this method and this tecqunique since 2016 so the method is good and validated. This thing happens for example just one time in a 5 replicated analysis and then happens againg after few days.
The method of thermal desorber is a primary desorption of 9minute form tube to trap at 45mL/min and then10minutes of trap heat at 280°C at 1mL/min so and the GCMS run starts exatcly when trap heating starts too. My method is in accordance with ISO 16000-6 and ISO 16017-1.
In my opinion the problem is note related to classic troubleshooting like leaks in carrier of bad column installation because the problem is related only to second part of chromatogram (full chromatogram is 30min, the problema start with ethylbenzene at about 14minutes), so do not give me simple and old explanation, but I need some useful tip.
I think that the problem is related to Thermal desorber and not to GCMS, beacuse trap heating stop after 10minutes and in that moment it changes some flows and pressure to go in stand by condition.
I cannot understand what happen. Can you help me? Thank you very much