GC/MS Loss of signal over time

Question

Good morning everyone,

I am measuring some 'dirty' samples (flavour products) over a couple of days to measure impurities.

Every day I am creating a new calibration curve and injecting a couple of samples.

I am noticing that every day the signal of my calibration standard is lower than the day before.

My question is what could be causing this loss of signal, and how can i fix it?

Some information:

7890B GC with a 5977B single quad MSD

Max temperature: 240 (20C below column max)

Result for highest standard, in areas:
Day 1 100.000

Day 2 85.000

Day 3 70.000

Thanks in advance,

Koos

gchaplai · Accepted Answer

1) Have you searched for an air leak through either a sniffer or through an air water check on the MS? If there is a leak somewhere then this would account for your loss of signal. We have experienced this previously with a leak on the inlet column ferrule, septum, and reducing nut. 2) If you system is leak free, it could be your split vent trap filling, hindering pressure control in the inlet. It may need changing. 3) When was your system last tuned? You maybe experience loss of signal becase of loss of detector sensitivity, especially if the areas are low to begin with (<10'000 counts) 4) Failing this, it could be something as simple as you have a small blockage in your syringe I have a list of possible areas it could be: GC Inlet Ferrule Column Transferline ferrule Syringe HED (High Energy Dynode) horn HED (High Energy Dynode) power supply Septum Standards need replacing Source Split Vent Trap EPC Empty wash vials GC Inlet nut Mass Spec chamber dirty Gold Seal Liner Transferline nut Mass Spec O-ring Split Vent Line

GC/MS Loss of signal over time

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