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Analysis of Halogens in geochemical samples Cl- , Br- and ... (3 replies)

Maya Rothman
11 months ago
Maya Rothman 11 months ago

I have been trying to analyse halogens (five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)) in soil & sediment samples at LLDs 0.5 ppm for iodine, 15 ppm for chlorine. I am able to get reproducible results for iodine above 1.5ppm & in case of chlorine reproducible results are observed in samples having concentration 50ppm or more. In case of pellets of samples having chlorine concentration less than 50 ppm enhancement of signal/concentration was observed with every exposure untill the pellet gave a value of 50ppm, thereafter it remained stable.  I am using methyl acrylate in acetone(5% solution) as binder.

Helena Russell
11 months ago
Helena Russell 11 months ago

Analysing chlorine in pressed pellets by using of wet binding material often gives erroneously high results, because soluble in water chlorine concentrated on the surface of pellet during drying of the pellet. Enhancement of the signal in repeated exposure to x-rays may have similar reason.

Alan Carter
11 months ago
Alan Carter 11 months ago

For the pellets, is the loss of chlorine due to exposure to the x-rays, or due to exposure to moisture in the air? I would suggest that you may want to try using a fairly high concentration of a liquid polymer binder to "seal" the powder particles from the environment. It may also help to contain the chlorine in the sample if the loss is due to exposure to x-rays.

11 months ago
JohnnyD 11 months ago

Your results are perfectly reasonable given the calculated LLD's you reported for your set up( instrument, application set up , sample prep etc.) Typically reproducible results can be obtained at 3-5 times higher concentration than the LLD, which is about what you are reporting. Remember that the LLD is not the LOQ, but where the analyte peak disappears into the background. Its all about counting statistics of the counts above background. That is not to say that your application could not be improved to obtain better the levels of quantification, but all else equal you are obtaining the reasonable results based on the your LLD's.