I'm working in a enviromental company ,we use preconcentration technic solid phase extraction ( SPE).
We use the C-18 phase as a solid phase. We measure pesticides in drinking water (Lindane, Hexachlorobenzene, Heptachlor, p-p DDT, Methoxychlor). Our problem is in poor reproducibility of the same level of concentration from one SPE column to other SPE column. I realy know, that my GC work properly, because when I measured one sample from the same SPE column e.g. five times reproducibility, is excellent(RSD15%).
Our SPE procedure is:
Column conditioning: 2column volume methanol, then 2 column volume dist.water
Sample application: Slowly aspirate 1000 ml drinking water through the column.
Column washing: 1 ml dist. water, dry column under vacuum
Elution: 1 ml hexane
I think possible reason is:
Not equal particle size of C18 sorbent.
I do not understand about this, because producer of C 18 SPE column is quaranteeing excellent reproducibility from SPE column to other SPE column.
Thank you very much for your advice.
By Anonymous on Thursday, January 23, 2003 - 08:09 am:
Not meaning to be rude, but 15% RSD on replicate injections seems a bit high to me. I used to work in an environmental lab and usually our RSDs were much smaller if I remember right. Also, you didn't tell us what the SPE column to column RSD was either.
By Anonymous on Thursday, January 23, 2003 - 10:55 am:
I agree. We are shooting for les than 3% RSD on replicate injections of the same standard. If you are getting 15 % on replicate injections, I would think there is something wrong with your GC.
By B.Buglio on Thursday, January 23, 2003 - 02:40 pm:
How are you injecting? An autoinjector should be
giving you a c.v of 1% or less.
By Anonymous on Monday, January 27, 2003 - 02:33 am:
how about use of a internal standard???