Problems with TMH analysis...

[ninja]

I am currently validating a GC-MS for Trihalomethanes as per USEPA8260B but am facing a couple of issues...
I am able to run a good calibration but am having issues with a tendancy of some of the compounds withing the QC standard to read higher than expected...
I am using a 20ppb mix standard containing
Bromoform (mean result 26.2 SD 2.4)
Chloroform (mean result 23.8 SD 2.2)
Bromodichloromethane (mean result 23.4 SD 4.1)
Chlorodibromomethane (mean result 33.2 SD 6.5)
Thanks in advance as I would welcome any ideas or input in resolving this issue...

[AICMM]

ninja,

Same vendor for the calibration standards and the QC standard? If not, what happens when you run the level 3 calibration standard as a sample? Same water source in both cases?

Best regards.

[Bigbear]

Try another mix, or prep one yourself if you have any neat compounds available. It seems as if one or the other mixes you are using are questionable.
Is your purge trap ok? For the Vocarb 3000 type traps, the brominated compounds fall out first.