Chromatography Forum

We have a Shimadzu GCMS-QP2010 SE, and according to the Basic Operation Guide, it suggests that for samples where the concentration is greater than 10ng/L to use Split mode, but for samples less than 10ng/L to use Splitless.

In the past our method that we developed following the guidelines from Supelco who had done SPME of Odors in Drinking Water, for Analysis by GC?MS (but the sample size was 2ppt) used the Splitless mode, so that's what we did with ALL of our samples and standards. But we were never confident in any of the results we got on our samples.

However, we are beginning to follow the protocols set out in Standards Methods for 6040D, and the majority of our calibration curve standards are 10ng/L or higher (5ng/L, 10ng/L, 20ng/L, 50ng/L, 100ng/L, and 200ng/L). Should we actually use Split mode? Or stick with the Splitless? We aren't sure what the concentrations in our reservoir waters or drinking waters are going to be on a routine basis. When we have had taste and odor problems, the levels we have had tested by an outside laboratory had results of 80-90ppt in the drinking water.

Suggestions and advice welcome.

We have a Shimadzu GCMS-QP2010 SE, and according to the Basic Operation Guide, it suggests that for samples where the concentration is greater than 10ng/L to use Split mode, but for samples less than 10ng/L to use Splitless.

???

Presumably your current method is headspace SPME?

Yes Ralph, our method is SPME.

Also, I just rechecked the basic operation guide and think I figured out the answer to my own question....the operation guide actually says to use Split if the concentration is greater than 10 ng/microliter....not ng/L like I originally thought.....since my largest concentration is 200ng/L that is equal to 0.0002 ng/microliter, so all of my standard concentrations are well below 10 ng/microliter, and therefore we should use the Splitless mode.

10 ng/microlitre.

That is what I suspected and why I queried it

Glad you have it sorted

"samples where the concentration is greater than 10ng/L"

The concentration of the sample is not important, because samples can be extracted, concentrated, diluted etc. The only thing that is important is the mass of analyte that you put on the column - if you are doing liquid injections, which the guidance assumes you are, that is the injection volume times the mass/volume concentration of what you are injecting.

Since you are doing SPME the guidance as given is irrelevant. You either have to work out the mass in each peak from a calibration, which would be extra work, assume or measure an extraction efficiency from sample to fiber, or look at peak shapes and use split if they are overloaded when you use splitless, or go to splitless if the peaks are too small when you use split.

Peter