I want to do a time series analysis of soil and manure samples for nitrate and ammonium, will it be okay to sample and freeze for all the analysis to be done at the same time on a later date?
@ Isaac, yes you can do it to store the wet sample at 4 celsius degree if analyze within a month otherwise freeze the sample in liquid nitrogen directly in the field if analysis cannot be performed immediately.
If you do not have liquid nitrogen, I would transport the samples back to the lab in a cooled box as quickly as possible then store them in the freezer at -20 C.
You may do this in air tight condition because microbial activities might be stop under this temperature.
Defrost the frozen samples in the fridge at a temperature not higher than 4° C to prevent microbes from becoming active.
Yes, you can store it in a cold chamber to stop the microbial activities till you are ready for analysis.
If you store the samples directly in 4°C, the following extraction and analysis should be done within one week. Or the mineral N could be transformed into different forms as well as gaseous losses. I recommend to extract (e.g. with 1M KCl or 0.5M K2SO4) and filter （e.g. 0.45 um）your samples as soon as possible after sampling. The filtrates then can be stored for several weeks up to months at -20°C before analysis. In the morning of the day of analysis I usually thaw them in a fridge at 4°C, before a accomodate them to room temperature (20 to 25°C) right before analysis (exactly as Stefan Johannes Forstner advised). Good luck.
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