Chromatography Forum

Afternoon to everyone

I have been trying to calibrate a method for analysing Volatile Petroleum Hydrocarbons using headspace(Single Ion Monitoring) on a Bruker Scion SQ GC-MS, with an Rxi-5Sil MS column. The standard I am using is a Restek one, WA VPH Standard(1 000 ug/mL). The standard has 15 components in it and the problem I am having is that the regression is bad(as each component has its own linear curve), for the BTEX components in the standard the regression is closer to 1 but still off by about 8-20%. Then the rest of the components like the aliphatics have a coefficient of determination that is way below, like 0.079 which then either over-recovers the actual prepared concentration or under-recovers.

Has anyone ever worked with this standard or had a similar problem? How unstable can these standards be?

Kind regards
Gugu

Hi Gugu

Unless you tell us your methods nobody can do anything except guess.

The more you don't tell us, the more we can't help you.

Peter

Hi Gugu

Unless you tell us your methods nobody can do anything except guess.

The more you don't tell us, the more we can't help you.

Peter

Hi Peter

I developed a method combining modified(by me) EPA method 8015 for analysing Total Petroleum Hydrocarbons and EPA method 5012A for Volatile Organic Compounds, with the purpose of analysing Total Petroleum Hydrocarbons.

Anything else I left out?

Gugu

Hi Gugu

The EPA numbers mean something only to people who use EPA methods. I don't so you haven't told me anything.

Peter

The standards for petroleum hydrocarbon methods tend to be very stable. For extracted samples/standards in DCM by 8015 (our diesel range) for example, our calibrations are good for a year or so and the standards don't go bad unless mistreated. If you are having reproducibility issues I would start with your headspace unit.

The standards for petroleum hydrocarbon methods tend to be very stable. For extracted samples/standards in DCM by 8015 (our diesel range) for example, our calibrations are good for a year or so and the standards don't go bad unless mistreated. If you are having reproducibility issues I would start with your headspace unit.

Hi Steve

Thanks. That's what I needed to know.

Kind regards
Gugu