Sample Storage
Water collection and evaluation is a major component of environmental chemistry. The way samples are stored and treated are critical to the quality of the results. A few things must be considered to ensure quality results when determining the appropriate storage technique: storage container, temperature, and treatments of sample.
There are a number of variables that can be detrimental to the quality of the water sample if not considered during the collection process. If the desired water sample is not stored in a specific type of container, the quality of the results will decrease with time. A tightly sealed bottle can prevent contamination and evaporation of the water sample. By collecting the sample in a clean, dry high-density polyethylene container, the risk of diffusion and isotopic exchange with the surroundings can be eliminated.
Appropriate environmental conditions will allow for minimal outside interference with the sample. A prompt analysis (24-48 hours) is most critical to the overall analysis of the sample. The less time involved between collection and processing will increase the accuracy and precision of the results. In order to avoid the process of ingrowth of organic material the container should be stored in a refrigerated, dark environment. However, upon refrigeration it is critical to assure the sample does not freeze because of its affect on the equilibrium of the solution. See the reference table below for specific storage conditions.
When outside conditions are not sufficient to preserve the quality of the sample, additional treatments can be added to the water. The preservation technique depends upon the desired components/analytes being studied. Analysis of certain metals often requires the use of strong acids. Nitric acid will prevent the oxidation of metal cations. All preservation techniques will adjust the accuracy of your results, and help stabilize the pH of the sample. There are countless strategies used to preserve water samples. For more information on these strategies, see the chart below:
Parameter | Container | Preservative(s) | Maximum Holding Time |
Inorganic Tests | |||
Acidity | 1 qt./gal. Polyethylene container | Cool to ≤ 6°C | 14 days |
Alkalinity | 1 qt./gal. Polyethylene container | Cool to ≤ 6°C | 14 days |
Bacteria | 4 oz. sterile glass or | Cool to 10°C, NaSO if chlorine suspected or present | 6 hours |
Chloride | 1 qt./gal. Polyethylene container | Cool to ≤ 6°C | 28 days |
Conductivity 25°C | 1 qt./gal. Polyethylene container | Cool to ≤ 6°C | 28 days |
Cyanide | 1 qt. Polyethylene container | Cool to ≤ 6°C, raise to pH of >12 | 14 days |
Fluoride | 1 qt. Polyethylene container | Cool to ≤ 6°C | 28 days |
Oil & Grease | 1 qt. Clear Glass jar with teflon-lined cap | Cool to ≤ 6°C, 2mL HSO to pH <2 | 28 days |
Nutrients | |||
Ammonia | 1 qt. polyethylene container | Cool to ≤6°C, 2mL HSO to pH<2 | 28 days |
TKN | 1 qt. polyethylene container | Cool to ≤6°C, 2mL HSO to pH<2 | 28 days |
Nitrite + Nitrate | 1 qt. polyethylene container | Cool to ≤6°C, 2mL HSO to pH<2 | 28 days |
Nitrite | 1 qt. polyethylene container | Cool to ≤ 6°C | 48 hours |
Orthophosphate | 1 qt. polyethylene container | Cool to ≤ 6°C | 48 hours |
Phosphorus | 1 qt. polyethylene container | Cool to ≤6°C, 2mL HSO to pH<2 | 28 days |
Sulfate | 1 qt./gal. polyethylene container | Cool to ≤ 6°C | 28 days |
Organic Carbon | 1 qt. polyethylene container | Cool to ≤6°C, 2mL HSO to pH<2 | 28 days |
Organics | |||
BNAs | 2-1 liter amber glass with Teflon lined cap | Cool to ≤ 6°C | 7 days to extraction, 40 days from extraction to analysis |
Herbicides | 4-1 liter amber glass Teflon lined cap | Cool to ≤ 6°C for jars 1&2 Cool to ≤6°C, Sodium Sulfite and 6 M HCL for jars 3&4 | 14 days to extraction, 30 days from extraction to analysis |
Pesticides | 2-1 liter amber glass with Teflon lined cap | Cool to ≤ 6°C | 7 days to extraction, 40 days from extraction to analysis |
PCBs | 2-1 liter amber glass with Teflon lined cap | Cool to ≤ 6°C | 7 days to extraction, 40 days from extraction to analysis |
Halocarbons | 40mL glass with Teflon lined septum seal cap | Cool to ≤ 6°C, 3mg/40ml NaSO | 14 days |
VOCs | 40mL glass with Teflon lined septum seal cap | Cool to ≤6°C, 3mg/40ml NaSO and 1:1 HCl to pH of 2.0 | 14 days |
Aromatics | 40mL glass with Teflon lined septum seal cap | Cool to ≤6°C, 3mg/40ml NaSO and 1:1 HCl to pH of 2.0 | 14 days |
References:
The EPA Handbook of sampling and sample preservation of water and wastewater.
Sample Collection and Preservation at Oregon State University.
Content on this web page authored by Robert Johnson, Jessica Bergana, Feven Welday & Katie Albanese