Preservation and Handling of Samples

Waters are susceptible to change by differing extents as a result of physical, chemical or biological reactions that take place between the time of sampling and analysis. If suitable precautions are not taken before and during transport as well as the time spent in the laboratory, then the nature and rate of these reactions are often such that concentrations determined will be different from those existing at the time of sampling. The causes of variation may include 

A summary of the preservation options and recommended maximum storage periods for various determinands is given in Table 3.1. The individual options are described below. 

High-turbidity samples can clog filters reducing the effective pore size. To avoid this, glass fibre pre-filters should be used and clogged filters changed regularly. 

It is essential that the filter is not a cause of contamination and, if applicable, filters should carefully be washed before use. If possible a portion of sample should be flushed through the filter before sample collection. In general, samples for most organic determinands should NOT be filtered highly turbid samples and all samples collected for dissolved metals SHOULD be filtered. 

The most commonly used preservatives for groundwater samples are 

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BSI (1996). Water quality. Sampling Part 3. Guidance on the preservation and handling of samples. BS EN ISO 5667-3. 

ISO (1994) Water Quality - Sampling - Part 3 Guidance on the Preservation and Handling of Samples, ISO 5667-3. International Organization for Standardization, Paris. 

ISO. Water quality—Sampling—Part 3 Guidance on the preservation and handling of samples. 

ISO (2003) Standard 5667-3 Water quality sampling, part 3 guidance on the preservation and handling of water samples... 

Trick J. K., Stuart M., and Reeder S. describe the tools available to the field sampler for the collection of groundwater samples, methods of on-site water quality analysis, and the appropriate preservation and handling ofsamples. The authors discuss the merits of different purge methodologies and show how on-site measurements such as pH, specific electrical conductance (SEC), oxidation—reduction potential (ORP), dissolved oxygen (DO), temperature, and alkalinity can be used to provide a check on subsequent laboratory analyses. Techniques for the preservation and analysis of samples and quality assurance and quality control are also presented. 

International Standards Organisation (1999) Water quality - sampling, part 15 guidance on preservation and handling of sludge and sediment samples, ISO 5667-15 1999. 

Proper sample preservation and handling in the field and at the laboratory the correct application of subsampling techniques during analysis the use of proper preparation and analysis procedures—all of these are important in maintaining the collected sample representativeness. 

Accessibility to remote areas is becoming more difficult. Post-access event reporting is required and minimally comprises taxonomic name, locality, amount and number of samples collected, sample destination and the preservation method. The level of detail is also determined by the local collaborator. Intellectual property issues are typically handled by the overseas parties in collaboration with the local partners. 

Using a spectrophotometer to measirre colour of natural objects (e.g. vegetation, soil) could be very cumbersome, because the samples need to be harvested and handled correctly before transportation to the instrument. Live specimens quickly begin to change, and, without appropriate preservation and handling, would yield inaccurate results (Foley et al., 2006 Richardson and Berlyn, 2002). 

Collection and handling of aqueous samples for low-level determination of mercury must address factors such as whether the sample is representative of the system sampled, possible interconversion processes, contamination, as well as preservation and storage of the sample before analysis. The measurement (sampling and analysis) protocol must be even more carefully designed if speciation of mercury forms in aqueous samples is intended. There have been remarkable improvements in sampling and analytical techniques that have resulted in a dramatic increase in the reliability of data for mercury levels in water samples over the past 15 years. The stability of mercury in solution is affected by many factors. These include (1) the concentration of mercury and its compounds, (2) the type of water sample, (3) the type of containers used, (4) the cleaning and pretreatment of the containers, and (5) the preservative added. 

Another aspect that must be considered subsequent to sampling is sample preservation and handling. The integrity of the sample must be preserved during the inevitable delay between sampling and analysis. Sample preservation may include the addition of preservatives or buffer solutions, pH adjustment, use of an inert gas blanket, and cold storage or freezing. 

Because of their diversity and complexity as well as the gradual internationalization of the different standards, it has proven necessary to standardize the methods of sample preservation, handling, fractionation, and analysis throughout the chain of separation and treatment. All these stages are the object of precise protocols established by official national and international organizations. They describe in as minute detail as possible the procedures employed not only for each analysis but very often giving different procedures for the same analysis in different matrices. These are the standards or standardized methods discussed in Chapter 7. 

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