I am a PhD candidate analyzing the concentrations of ammonia, nitrate, nitrite, phosphate, zinc, iron, and chloride in water samples. Unfortunately, the equipment that I have been using is now failing to meet the certified standards. I have ordered new equipment, however, it is not expected to arrive until October 11th (23 days from now). I am collecting my next sample set on September 23rd. Are there any methods that would allow me to preserve these samples long-term (i.e., for 18 days) until the new equipment arrives?
The joke is to fix the samples with nitric acid. Doesn't interfere with nitrate analysis at all.
Commonly, you can freeze samples, or fix with hydrochloric acid or sulfuric acid and then freeze. But you'll have to check for these particular constituents.
Obviously you can't use nitric acid or hydrochloric acid with what you're analyzing samples for. Unless you split samples.
Freezing is probably fine for the length of time you're considering. I don't have a great reference, though. Standard Methods for the Examination of Water and Wastewater will probably be the authoritative reference for this.
If you do use acidification, be sure to see if this interferes with your chemical analysis. Sometime you need to buffer samples back to a neutral pH. And you may need to account for the extra volume of liquid added to the sample.
If you freeze samples, you may need to return samples to room temperature for chemical analysis.
Store the water sample in well sealed polythene bottles and keep in dark and cool place.
Thank you. I am currently looking at freezing as an approach to preserving my samples for two weeks. Does anyone know of any protocols or literature backing up this approach so I can support this decision when I write up my dissertation?
There are couple of references below that should be available.
But Standard Methods for the Examination of Water and Wastewater is really the best reference, especially if you are publishing in a high-quality journal.
Avanzino, R.J. and Kennedy, V.C. 1993. Long-term frozen storage of stream water samples for dissolved orthophosphate, nitrate plus nitrite, and ammonia analysis. Water Resources Research 29(10):3357–3362.
[VEPA] Environmental Protection Authority, Victoria. 2009. IWRG701: Sampling and Analysis of Waters, Wastewaters, Soils and Wastes. State Government of Victoria, Australia. www.epa.vic.gov.au/about-epa/publications/iwrg701.
earlier collected samples, keep in well sealed polythene bottles and keep in dark and cool place. In particular For trace elements Zinc and Iron keep the sample in small glass bottles.
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