Dear Dominik, a researcher friend, kept the samples, generating an inert atmosphere of argon. The results were good

Dear Dominik,

The USEPA has an on-line document of environmental analytical methods. Chapter 2 addresses preservation. You will be most interested in page 2-65 in the attached document or the website:   http://www.epa.gov/wastes/hazard/testmethods/sw846/pdfs/chap2.pdf.

I WOULD NOT add chloroform and this organic solvent will interfere with ion chromatography and may destroy the analytical column.  Also, nitrite and ammonia are unstable and may require a faster analysis time than the oxidized species nitrate, phosphate, and sulfate.

Nitrate , Nitrite and Ammonia in water sample are very much unstable. Based on our experimental study, it is advisable to go for spot analysis. However other parameter like Sulphate and Phosphate must be analysed within a week time without adding any component. Freezing  process may spoil the sample.Inaddition to this chloroform may not serve the purpose.

Hi,

In our lab, we use H2SO4 for sample preservation prior to analysis parameters such as phosphate, nitrate. In case of ammonia, H2SO4 changes the sample concentrations. So, just right after filtration we preserve ammonia samples at sub-zero temperatures.

According to USEPA, the best technique of sample preservation is storing at sub-zero temperatures. In cases where this is not possible, you can go for filtering to reduce algal and bacterial activity. It is also important to keep the sample as cool as possible and in the dark.

In general and as per standard sample collection guide lines, in particular for the analysis of trace elements in water samples 2 -3 drops of dilute nitric acid have been added in 100 ml sample bottle,  and this is just after collecting the water samples. The resultant pH must be 3.0 or less. Acidification minimise loss of solute by oxidation or precipitation and by adsorption to the container surface. The sample must be tightly capped polyethylene bottle.

Kindly refer : 

Method for collection and analysis of water samples for dissolved mineral and gases. Eugene brown and others, U.S. Government Printing Office, Washington.

Adding concentrated H2SO4 as a preservative will change the sulfate concentration. I would not recommend that this be done.

Don´t use sulphuric for trace metals. The recomendfation is nitric acid. Sulphates ( asnd chlorides) interferes.

For common consituentes: filter and to ice book at-10-  -20ºC.,

If not possible analyuze for nitrites and ammonia at the arrival of the sample.

Slightly acidified the water samples with sulphuric acid before 24 hours of the collection..

From my experience, immediate filtration and analysis of the sample as soon as possible will provide the most accurate results... particularly with a wastewater sample of perhaps unstable pH and unknown redox condition.

Since you will be analyzing wastewater, you need to read the regulations for your country, state, etc. You will probably find that your choice of holding time, preservation, filtration, etc. are severely constrained.

I would much agree with Dave Huebert. Proceed to filtrate as soon as possible after collecting the sample, using various filters to finish with a GF-F filter (for example), then put the filtrated in a glass o poly-carbonate bottle (http://www.qorpak.com/CatalogImages/17-212-Category_Primary_Image.jpg). Ready to go.

Thank you for all

all suggestions are very important for me.

best regards

I agree with Mr. Franklin. Filtration is important to avoid any changes to take place. You can always refer to attached USEPA's "Sample handling and preservation guide". Alternatively, you can refer to USEPA's "Handbook for Sampling and Sample Preservation of Water and wastewater" for detailed instructions regarding sampling and sample handling including sample preservation.

Best Regards,

http://www.epa.gov/region6/qa/qadevtools/mod5_sops/sample_handling_preservation/r6sample_handling_tables.pdf

nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=30000QSA.TXT

My only comment is that if you are interested in a biologically based measurement (BOD, respiration, etc) or conducting measurements of the microbial aspects of the wastewater, then you might want to have a portion of the sample with minimal chemical preservation or refridgeration.

Dear all

Thank you for all your answers! Because our waste water is quite "friendly" (water from a recirculating aquaculture with fairly moderate levels of BOD, pH, TSS, etc.) and because we mainly need to know how much bio-available P and N (i.e. mainly ortho-phosphate and nitrate) is in the water, we hope that our samples can be preserved. So we plan a little test (comparison of freezing, H2SO4, etc. over a few weeks of storage) and hopefully I can come back in a couple of weeks with some reassuring data.

Dominik, we have some experience with freezing and storing sample - in terms of nitrogen species balance. We tested storage in room, in fridge 4C and freezer -15C. The resume is that if you want to know the original NH4+ concentration you must freeze the sample. Using the fridge worked for short period of time, only.

Here is a suggestion if you want to avoid the possible precipitation while freezing - you must freeze fast! I would try freezing the water using liquid nitrogen if you have the chance... these are my thoughts on this.

Good luck.

Dear Dominic. After reading about your samples. I can add, there is quite a lot work about this, one main conclusion is that when you add any chemical, you run the risk to have interference in the analysis, your sampling preparation could become cumbersome and so on. So, please filter (GF-F) your samples, then freeze them to about -20C, as I suggested use those bottles; then when thawing take some precaution (slowly).  perhaps this paper could give you some insight. Ormaza-González F.I. y P.J. Statham (1996). A comparison of methods to determining particulate and dissolved phosphorus in natural waters. Water Research 30: 2739-2747. ISSN 0043-1354

Good luck

I think addition of chloroform or any other organic  solvent will interfere with ion chromatography and will destroy the  column. I also agree with Mr Ormaza that adding any thing will increase the risk of interference / contamination. hence fast filtration and freezing is a better option.

I preserved wastewater samples from rubber factories for 2-3 weeks. Samples that I need to analyse TOC, TN and COD were preserved by adding H2SO4 to lower the pH

I agree with all the answers you got. The basic principle is that the conservation procedure depends on the parameters you have to analyze. In general, apart from suitable chemical treatment or freezing, refrigeration is recommendable

I would agree with the above.  In our lab, NH4+is measured within 24 hrs.  We have done replicates on wastewater over time periods of up to 4 days when samples are stored at 4oC in a dark refrigerator.  After a day or two, ammonium concentrations decrease and nitrite can spike (stuck nitrification?).  When measured within 24 hours, NO2- has typically low concentrations.  However, we have found that stream water samples with low ammonium concentrations can be stored significantly longer without problems.  All of our samples are filtered through 0.45 micron membrane filters into nitric acid cleaned bottles.  We use an ion chromatograph to measure nitrite concentrations (and other anions) and a Turner A-10 Fluormeter to measure ammonium concentrations.

Dear Dominik, 

I agree about refrigerating the samples, rather than freezing them.  Maybe you can find useful information also in this document edited by RMB Environmental Laboratories, Inc.

 http://rmbel.info/wp-content/uploads/2013/05/Sample-Collection-and-Preservation-List.pdf

Kind regards

So, it is about time to report on what we did to learn more about storing samples:

We took samples (duplicates) from a recirculating aquaculture (Tilapia), sterile-filtered them, and measured various variables with our IC. Among them: NO3- (308.6 mg/l), PO43- (8.5 mg/l), SO42- (33.6 mg/l): We then splitted the samples and stored them as follows:

- in the fridge at 4 °C (just like that or with a drop of chloroform or with methanol)

- in the freezer at -20 °C

After 24 days we measured them again (averages, replicates were very similar):

- Fridge: NO3: 305.4 mg/l; PO4: 8.0 mg/l; SO4: 32.9 mg/l.

- Fridge with chloroform: NO3: 303.8 mg/l; PO4: 7.9 mg/l; SO4: 32.8 mg/l.

- Fridge with methanol: NO3: 249.5 mg/l; PO4: 6.5 mg/l; SO4: 27.0 mg/l.

- Freezer: NO3: 305.0 mg/l; PO4: 7.5 mg/l; SO4: 32.9 mg/l.

K+, Mg2+ and Ca2+ all remained completely stable irrespective of the treatment (we didn't include methanol here).

We struggled with NH4+, simply because it seems that NH4+ was gone before we could even measure it in the first place. I assume that keeping the sample cool and quickly add HNO3 is really important here.

So I decided to follow this protocol:

Sterile filtration, split samples and add HNO3 to one of them (the one for the cations), store in fridge. Should be fine for at least 3 weeks.

In the worst case, you underestimate PO4 by 10%, which I think is acceptable. NO3 and SO4 are more stable.

These are my 2 cents... And of course they only hold for aquaculture samples.

A big thank you to all those people that responded to my question, I am really grateful for all your comments!

Best

Dominik

Dear Dominic. For the samples you added chloroform and methanol; you should have added similar amount to calibration samples (blank and standards); did you do so? These reagents could have interference.

Good work!

@Franklin Ormaza: Yes, you are completely right. We didn't do that. I am quite confident that it didn't matter for chloroform because we added only a drop to about 10 ml sample. Not sure about methanol though.

Another thing dear Dominic; the protocols for P and N were conceived for natural waters, perhaps would also to help to clarify your horizon, is to run some spiked samples.

Regards

my dear.i agree with dr.franklik  about the protocols

Well,

Dear, in pages between 91 and 96, from the attached pdf, can be found the answer.

SINCERELY

Hello Dominik Refardt

The collected water samples were filtered using 0.45-µm pore size membrane filters and stored in polyethylene bottles that were previously washed with concentrated HNO3-. For cation and trace element measurements the samples were preserved by acidifying to pH 2 using ultra-pure concentrated HNO3- .

Dominik.... For your purpose (anions in water), keeping the samples an a frig (4o C) is enough. For other pollutants say organic matter and heavy metals the preservation procedure is different and required special additives, e.g., nitric acid for heavy metals... good luck

I agree with Mahmood

I normally use a cool box and analyse within two hours of sampling.

Maybe thymol, it is usually used for natural (rain)water samples (https://www.sciencedirect.com/science/article/abs/pii/096016869190198G)

Depend on the analysis to be performed.

First, sample must be filtered (0.45 um).

Freeze for dissolved nutrients {N, P, Si}

And what about conserving purified water samples prior to microbiological analysis ? Thanks

Ivanco Sinadinoski, I am afraid I don't understand: Once a water sample is purified, I doubt that a microiological analysis makes sense... What do you mean by purification?

On the contrary Dominik Refardt , even the water is being sterilized / distilled, still it would be perfect media for microbial proliferation whenever it comes in contact with microorganisms. Purified water is utilized primarily in pharma and cosmetic industry and is generated by couple of sequential treatments among which is De-chlorination (active carbon). At the beginning of the purification system, the oxidation properties of chlorine play a significant role in the removal of viruses and bacteria. However, as the purification system proceeds, the same oxidation properties pose a great threat to certain critical components like the RO membrane or the piping. However, besides many filters and post-treatments the PW is far from sterile and is subjected to certain criteria for microbiological purity. So, finally it comes to my query for how long such a sample could be stored in fridge prior to testing, retaining its relevant characteristics and bioburden which should be revealed?

Regards

I see. Honest answer: no idea. Practical answer: A few days at 4 °C are very likely ok. But beyond, say, one or two weeks I would begin to doubt any results.