Hello Gilbert,

Let me backup Carol Kendall's advice to you. I really do think that it is
best if you can store your samples and carry out all the lab work back at
McGill. One trick you might try is to gently evaporate the groundwater
samples to pre-concentrate. This means that you do not have so much water to
carry or ship back to McGill. We routinely evaporate samples down to
50-100ml with no measurable effect on the delta 15-N of the dissolved
nitrate. NOTE that it is necessary to carry out the evaporation on a gentle
heat and NOT to evaporate to dryness. That will shift the isotopic
composition. Carol's advice about freeze drying is interesting and one that
we may try out. Evaporation to dryness without additional heating
(freeze-drying) sounds like a good idea.

Paul Dennis,

UEA Stable Isotope Laboratory, ENV, UEA, NORWICH, UK NR4 7TJ