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- Posts: 47
- Joined: Fri Sep 07, 2007 12:39 am
- Location: Adelaide, Australia
We are experiencing issues with obtaining linearity of chloroform, even over a very small range (i.e. 80% to 120% of 60 ppm) which for our sample preparation is a concentration range of 1.5 µg/mL to 2.3 µg/mL.
Our instrument is Agilent 7890B GC-FID with 7697A headspace sampler. We are using a DB-624 column, 60 m x 0.53 mm x 3 μm film thickness.
All samples are prepared in 100% DMSO.
Headspace parameters are:
- Oven 90°C
Loop 100°C
Transfer Line 105°C
Vial Equilibration 30 minutes
Pressurize Time 0.2 minutes
Inject Time 0.5 minute
With GC oven program being:
- Oven at 40°C hold 10 min -> Ramp 100°C/min to 200°C hold 15 min.
Inlet at 220°C with split ratio of 1:1.
Colum at constant flow of 5.0 mL/min
Detector at 220°C
When we run our linearity solutions for Chloroform our peaks are all over the place. It is also not reproducible i.e. not always the same solutions which have the unexpected peak areas. For example one analysis the solutions at 100% look ok but at lower levels are bad but then the next analysis the solutions at 100% do not look ok but lower levels look ok. Note: performed with freshly prepared solutions.
We are not sure what is going on. When we analyse a standard and samples, we obtain reproducible results with Peak Area RSDs of 0.0%.
Does anyone have any advice on what could be happening? We have noticed that we also do not have an increase in peak area when we use a higher level of sample.
At the higher concentrations is my sample not getting onto the column because my inlet split is not correct?
Is there interactions between DMSO and Chloroform? Would I be best to try using DMF?
We have not looked closely at the other solvents yet as the linear range required for acetone and ethyl acetate is significantly higher than for chloroform
TIA.