In the past few weeks I have run samples that I have collected in spring 2005 on McGill campus and at the McGill research station in Mont Saint Hilaire. Samples were surface snow from the first 10 cm of the snow pack and I have taken grab samples with pre-cleaned and sterilised equipment.
Because of the low concentrations present in the sample I am resorting to large sample volumes that I have collected in sterile HDPE bottles. So far I have had no cross-contamination from plasticisers in the container material, which is fine. The samples from these containers allow me to obtain a total sample volume of about 130 mL and still retain about the same amount for later experiments.
I melt the samples before my measurements and once melted, I keep them on ice and covered in tin foil to avoid any exposure to UV light and minimise volatilisation of compounds. I do not (yet) have tight containers of that size, so I am using a similar set-up described by Petterson (Chemosphere, 2004) with a 125 mL Erlenmeyer and a tinfoil cover after sterile transfer of the sample.
I am still crunching my data, but from I first glance I get good signals for aromatic compounds and a few halogenated substances (mostly Chlorobenzene, tetrachloroethylene in one sample). There are surprisingly many aldehydes and alcohols present (mostly with aliphatic chains attached), which I have not seen earlier in this abundance. The absence of organo-halogens is still surprising and remains to be investigated – although a lot of explanations are possible here (age of snow pack, precipitation, …)
