Chromatography Forum

Hi,

I am currently facing some problems with the quantitative analysis of total petroleum hydrocarbons (tph)- diesel.

I used to run analysis on the GC-FID for TPH diesel by injecting a range of standards prepared from DRH-TX-002-D-40X . The samples are then quantitated from the calibration levels based on their peak responses integrated under the C10-C28 range. However recently my colleagues sent the same sample to other laboratory for the same analysis and while I detected something in the sample, the other laboratory did not.

I hope that’s someone who is familiar with such analysis can give me a helping hand as to what did I do wrong. The standard checks are fine and surrogates (o-terphenyl) recovery is 100%.

Sorry for this lengthy post and thank you for the answers and help.

Regards
Hts123

Did you detect diesel? Did the other lab report a non-detect for diesel? Did they detect something obliviously not diesel?

Can you provide more details? Specifically:
1) What's your calibration range? (Our lab is 200-10,000 ug/mL off instrument with a 20:1 hot split injection)
2) What level was the diesel fuel hit in the extract? Was it just over your detection limit and the other lab had a hit just under?
3) How do you define your quant range C10-C28? We verify ours using an n-hydrocarbon standard containing these compounds to ensure our quant range is accurate.
4) Do you verify your calibration using a second source standard?
5) What's the nature of the sample, soil? water? Is it homogenous? Is it extracted and concentrated in MeCl2 per some determanitive method?