552.3 IS recovery

[ABricker]

I run HAA5 method 552.3 on a Bruker 450 GC-ECD. I inject only 0.5uL of sample because of the direct oncolumn injection. Does anyone have a the problem of the IS areas increasing with time? I did a new curve Nov 11. Ran 3 more sets of samples in the month of November, and now the first set in December, the IS areas of them all are greater then my 150% window. I make new IS solution with each extracted batch of samples. Each batch of samples the area slowly creeped up. Anyone experiencing the same thing or have fixed this problem in the past?

[Steve Reimer]

Is the response of the tcp the only one increasing? How is the surrogate area behaving? When you say you are making a new IS solution is it from a fresh ampule or is it from an opened stock?

When I ran that method I didn't have problems with the IS solution but the derivatization was often variable. TAME was better than MTBE but not doing the method was even better.

[ABricker]

When I look back at a std from the curve and the same amt standard I ran Friday, all the area responses are increasing. How is my detector getting more and more sensitive?
The new IS solution is from an open stock ampule that isn't expired. Would a fresh ampule every time really make a difference?

[Jesse Robinson]

How long is the GC run? Also, what type of liner are you using? For HAA's, I have found that double tapered inlet liners work best, specifically the cyclo liners that Restek offers. You could also try cleaning the inlet with solvent as well as the split vent. It's possible your split vent line is contaminated which is causing the increase in response. Also, changing the inlet seal could help the issue as well. Something else that might help, before analyzing standards or samples, analyze a high level standard. This helps fill any active sites in the system and might help equilibrate the instrument a little faster.

[Steve Reimer]

Increasing response across all compounds, along with reduced linear range, is a sign of a dirty detector. I have no experience with Bruker ECDs but for my Agilent/HPs I would test by increasing the make up gas flow. It will lessen the response creep but also decrease your overall signal. If the idle signal was high and the sensitivity increased as you described it it was time to send the detector back for refurbishing.

A quick check would be to analyze something with no prep or derivatization. A standard of chlorinated pesticides for example and then run a sequence of HAAs followed by a reinjection of the same standard. Compare the peak areas. You can also change your injector liner type, volume injected etc. to see if it is an injector or detector problem.

[ABricker]

The run is 22 minutes.
I don't have a liner to change because I direct inject 0.5uL of the sample into the column.
The detector was brand new in April.
I am running pests right now, I'll run a high HAA5 standard when I'm done to see if the areas changed yet again.
Thanks for the ideas.