According to Dickson et al, 2007, the standard operating procedure says that seawater pH samples must be as soon as possible and that there is no long term storage protocol. However samples can be stored at room temperature in the dark.
My work is primarily in the tropical region and the temperatures in the summer can be as high as 30 deg Cel. Would it be advisable to store at room temperature? or would refrigeration be recommended?
Hey Michelle..
I guess most important is to make sure that you include no headspace in the storage vial, this prevents any in/outgassing or equilibration with any enclosed atmospheric air.
Storing it in a fridge close to 0°C lowers temperature and thus also potential microbial activity is minimal, which could set free CO2 by respiration or so... Freezing would even be better, but then the volume expansion of H2O will burst the vial (no headspace)...
Also, to exclude microbe contamination as good as possible, you should sterile filter the sample, e.g., with a 0.2µm syringe filter: remove piston, attach filter, fill syringe from behind to the max, plug in piston (i.e., headspace-free sampling to avoid gas exchange), discard the first mL that comes out through the filter.
. when you deliver the liquid to the storage vial, deliver it to the wall and let it slowly run into the vial. avoid dropping, strong turbulance and convection here, this also minimizes gas exchange.fill the vial until a little mountain of water is there, then close it without headspace
A lot of people toxify their samples by giving a drop of HgCl solution into the vial before sampling. The mercury will kill mostly anything, and storage for longer time (maybe 1-2 months?? maybe more??) should be possible. Of course, then the handling can get messy and dangerous for the scientists..
Hop i could help,
greetings to Goa
Sebastian
For storage and transportation of samples, completely filled and tightly closed polyethylene or glass bottles that have been rinsed with the sample can be used. Samples should be analysed as soon as possible, but can be stored refrigerated in the dark for up to 24 hours. Generally 25oC is considered as room temperature.
Dear Sebastian,
Lovely to hear from you and thank you so much for the detailed reply. I have never tried out filtering the sample, but possibly this must be worked out here as I could deal with turbid samples at some point.
Even before I raised the above question, I thought to put these storage methods through a small test. At a recent field trip, I collected the water samples (no headspace) and stored the samples in ice ( did not freeze them but the ice was used to bring the temperature down to about 5 or 6 deg C. And duplicates were stored in a carton box (dark and ambient temperature conditions- about 35 deg cel these days). The samples were brought to lab and I am pretty sure I analysed them in about 4 hours. I noted that the pH values of the ice stored samples and the ambient temperature samples were not significantly different from each other. The standard deviation between the readings was 0.0000 to 0.0050. These are the usual deviations I would report for coastal samples. So perhaps microbial activity may have not taken over as I managed to analyse the samples within 4 hours? Because if microbial activity played a role, then I would have seen a bigger standard deviation between the pH values. So possibly if the samples were left for longer hours, then one must refrigerate them?
I also had another thought....when we have dozens of samples to be analysed onboard, it could take hours to complete the analyses and at that time, we leave the samples in a water bath at 25 deg cel. We dont take an account of microbial action during those long hours. So possibly when we know that we are going to analyse the samples within 6 hours or so, then it may not be necessary to refrigerate the samples.
So also, this artificial decreasing in temperature (refrigeration) can result in the formation of a bubble in the sample container due to the volume decrease induced by lowering the temperature. But from my small test lately, since the deviations in pH values were insignificant, possibly one need not worry about the little bubble formed due to lowering of the temperature. ...cause pH does not vary significantly.
I dont feel convinced that refrigeration is a necessary step especially when the samples will be analysed soon. But the question then is...'How soon is 'soon' ? Possibly something to test. I recall reading that pH must be analysed in 6 hours...I'm not too sure!
Thanks!
Michelle
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