GC Calibration

[IrishMike]

Hello all..


I'm new to this game and have been landed with a problem that I need to resolve ASAP.

I work in a lab that analyses hazardous waste where 95%+ is organic solvent waste containg some or all of the following MeOh, EtOh, acetone, ETAC, Chex, MTBE, toluene, THF, IPA and sometimes DCM and others.
To date we have been analysisng just to see what is in there and have managed to seperate all of the above however we now need to be able to quantify these....

We are using a wax column, injecting 0.5 microlitre and running under the following:
35 C (1 min) - 90 C@ 4 C /min (1.25 min)

Can anyone suggest suitable standard prep for calibration??

Oh yeah...samples can vary in concs. from 0-100 % solvents in water..

Thanks

Mike

[JGK]

Given your statement that the concentrations in unknowns can vary between 0 and 100%.

If that refers to each individual component the you'll have to run a calibration for each component (individually) over that range.

If that refers to total organic content, then it's a bit more complicated. Chances are you'll still end up having to run the individual calibration as the design of combined STD s will be a nightmare

[AICMM]

IrishMike,

I would propose the following. Do a pretty big split, maybe 100:1, shoot 1/2 uL, and add an internal standard that you are confident will not co-elute and calibrate for the list of compounds at say 10%. Establish relative response factors to the internal standard and rely on the FID to be linear over the range of most of the concentrations you are facing. If you get bad chromatography or weird results, dilute the sample by factor of 4 and run it again. The key is the high split ratio which will limit the amount of material getting to the detector and keep the detector in its linear range. It will also really help flash the sample even with high water content. Crude but I will bet you effective. Of course, trace analysis in this scenario is out of the question but that does not sound like the problem at hand here anyway.

Best regards.

[chromatographer1]

I would propose you run standards of combined solvents each at 0.1%, 1%, 5%, and 10% in water to get an idea of the linearity of your test and the accuracy of your analysis.

The lower amounts would also determine if large water content on the wax column affects your analysis of the organic solvents.

You could also run 20% of common high concentration solvents and check for linearity.

Otherwise, run 100% samples of each solvent and use that area to determine the lesser amounts of each solvent.

best wishes,

Rod

[IrishMike]

Hi

Sorry for not being clearer, the samples could be something like 40% h2O, 30% ETAC, 20% MeOh, 10% Chex or you could have a mix of solvents with low water...anything goes really!!

I was thinking of basing the method on ASTM 5830..

My plan was to make 3 stds. 0.1%, 0.5% and 1% and then diluting the samples 1:200 to get the components within the calibration range..

I was gonna use DMSO or CS2 as diluent...

Any thoughts??

[chromatographer1]

I would avoid DMSO or CS2 unless they are going to be in your samples routinely.

Use DMAc if need be as a balance to measure the more volatile solvents at lower levels. Be aware that DMAc and DMSO, and CS2 can contain or produce trace early eluting impurities.

A solvent of Diethylene glycol to be the balance might be an option.

best wishes,

Rod

[IrishMike]

Thanks all...

I'll let you know how I get on...