P.T. Weiss, A.J. Erickson, J.S. Gulliver, R.M. Hozalski, O. Mohseni, and W.R. Herb
Proper sample handing is essential for representative samples. Some constituents undergo rapid reaction, such as degradation (e.g., BOD), degassing (e.g., oxygen), adsorption to the walls of bottles (many metals and organics) and coagulation (e.g., turbidity). Without proper handling, sample contamination can occur and result in inaccurate results for some analyses, most notably phosphorus and some metals. It is also important that sample handing procedures are documented and that personnel collecting samples are properly trained.
Prior to sampling, sample bottles, filtration apparatuses, filters, and other equipment must be cleaned appropriately. Bottles used for collection and storage of samples containing nutrient or metals often need to be cleaned with special detergents and acid rinses. Details are provided in Standard Methods (A.P.H.A. 1998b).
Some analyses require that samples undergo some process prior or during storage, such as filtration or preservation. An extensive list of sample handing requirements is presented in Table 1060.1 in Standard Methods (A.P.H.A. 1998b). For example, samples to be analyzed for dissolved constituents should be filtered within a few hours of collection.
Some dissolved gases (e.g., dissolved oxygen and total dissolved gas) are readily measured in situ, using field instruments. If laboratory analysis is necessary, samples must be analyzed within a few minutes or collected in sample bottles that are filled completely with water (no gas bubbles) and sealed tightly to avoid contamination by gas exchange.
Many types of samples require preservation, such as refrigeration, acidification, or reaction to form stable samples for storage. Even with preservation, acceptable holding times vary from a few hours to a few months. Analysis requirements for storage containers, cleaning, filtration and preservation vary significantly and therefore it is possible for several samples to be collected at one time, or for samples to be split into many subsamples, for each type of analysis.
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