proficiency problems with drinking water volatiles

[chloesabrina]

I am hoping somebody can help me out here. We had a proficiency sample in for drinking water which I failed 50 out of 60 compounds reported (low). I cleaned my source and changed the inlet liner and re-calibrated. I re-prepped the proficiency back up and ran again. Everything looked great except for TCE and PCE - they both still failed on the low side. Is it a trap problem or do you think transfer line? Any suggestions are welcome

[Steve Reimer]

Is this a new analysis for you or is this one failure in a string of successes? Are you running 524.2 or 524.3/524.4? How close is your 2nd source standard to the primary? What equipment are you using? So many questions, so few answers.

[chloesabrina]

This is one failure in a string of successes - I am running a modified 524.2 - but I use SIM and calibrate from 0.05-10ppb. I have a velocity concentrator/EST 8100 autosampler/6890 GC with 5975MS. The trap type is the K type - I purge as a soil with a 5mL sample size, 1 min desorb and 1 min dry purge. Column is DB624 20m
We are not an environmental lab although we do follow some of the methods loosely and I am running drinking waters.

[James_Ball]

Trichloroethylene/Tetrachloroethylene or Trichloroethane/Pentachloroethane?

If it is the latter you need to make sure you have the sample acidified. If you lose pentachloroethane look to see if tetrachloroethylene is high, if so it is breaking down by losing a Cl and forming a double bond which is common.

When you lost almost all of the compounds the first time, it could be that you were not getting a good seal at the vial when running as a soil, either the septa not sealing around the needle or against the vial itself. I had problems one time when there was a small chip in the rim of the vial that caused a leak.

Trichloroethylene/Tetrachloroethylene loss is not as common, but can happen. This is usually due to active sites the adsorb somewhere along the flow path.

In volatiles purge and trap you usually don't loose analytes due to dirty source or inlet liner unless you foam a nasty waste water and it makes it through the system. I normally don't even clean my source or inlet except about every 18 months after I finally blow a filament.

[chloesabrina]

Trichloroethylene/Tetrachloroethylene - This is a mix for regulated volatiles and all the others are close to the assigned value. On cleaning the source - I don't run wastewaters or foaming samples but I do run some samples very high in flavors and fragrances.

[James_Ball]

Trichloroethylene/Tetrachloroethylene - This is a mix for regulated volatiles and all the others are close to the assigned value. On cleaning the source - I don't run wastewaters or foaming samples but I do run some samples very high in flavors and fragrances.

Was Pentachloroethane, 1,1,1,2-Tetrachloroethane and 1,1,2,2-Tetrachloroethane present in both the calibration standards and the proficiency sample?

If you are getting breakdown of the -ane compounds into the -ene compounds then that can cause the -ene compounds to appear low when the -ane compounds are proportionately lower in the sample versus the calibration standards.

In other words, if you are getting a quantative breakdown in the calibration standards, then your curves will still look ok but samples will be inaccurate.