Samples preservation

Samples from sediment traps subsampled by wet splitting techniques (e.g., v. Bodungen et al., 1991), should be filtered as described above. Flushing at the end of filtration is important. 

After filtration and flushing some air is drawn through the filters to remove most of the water. The moist filters are then dislodged from the filter holder with a pair of stainless steel tweezers and placed into a shallow cavity in a clean Plexiglass (Perspex) transport box (Fig. 17-1) which is easily made by any competent workshop. 

The transport box with filters is temporarily stored in a freezer until each cavity (usually 50) has been filled. The transport box without cover is then put into a drying oven and the filters are dried at 60 °C for 30 min. Subsequently, the cover of the transport box is screwed into place and the box is stored frozen until immediately prior to analysis. Some 20 filters of each shipment should be retained unused so that their carbon and nitrogen blank values can be determined. 

5 Sepan on of particulate inorganic carbon from particulate organic carbon 

Losses of metals from dilute aqueous solution on storage are well documented. To prevent this it is usually necessary to acidify the sample after collection and filtration to pH 1. If the sample is to be analysed subsequently by flame AAS hydrochloric acid should be used (Section III.C.2) alternatively, prior to flameless electrothermal atomic absorption analysis, nitric acid should be added to preserve the sample (IV.B). The type of storage container is also important and high-density polyethylene is the preferred material for sample bottles. Here the adsorptive losses of metals appear to be lower than on glass. To avoid container contamination of the sample the container should be leached with dilute nitric acid for several days prior to use. This will remove surface contamination from the container material. Subsequent to the acid-leach, containers are washed in distilled-deionised water and then with a portion of the sample. Storage of samples for mercury analysis requires special conditions and these will be discussed later. 

The choice of analytical procedure for the determination of metals in water using AAS is dictated by two important factors, (a) The suspended solids and organic content of the water determines whether a pretreatment is necessary, (b) The particular metal and its level of concentration in the sample decides whether a pre-concentration technique is required. In addition, this factor may be useful in choosing between employing a flame or flameless mode of analysis. 

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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. 

Sample Preservation Once removed from its target population, a liquid sample s chemical composition may change as a result of chemical, biological, or physical processes. Following its collection, samples are preserved by controlling the solu-... 

Sample Preservation Without preservation, many solid samples are subject to changes in chemical composition due to the loss of volatile material, biodegradation, and chemical reactivity (particularly redox reactions). Samples stored at reduced temperatures are less prone to biodegradation and the loss of volatile material, but fracturing and phase separations may present problems. The loss of volatile material is minimized by ensuring that the sample completely fills its container without leaving a headspace where gases can collect. Samples collected from materials that have not been exposed to O2 are particularly susceptible to oxidation reactions. For example, the contact of air with anaerobic sediments must be prevented. 

More attention to selecting and obtaining a representative sample. The design of a statistically based sampling plan and its implementation are discussed earlier, and in more detail than in other textbooks. Topics that are covered include how to obtain a representative sample, how much sample to collect, how many samples to collect, how to minimize the overall variance for an analytical method, tools for collecting samples, and sample preservation. 

Generally, sampling of waterways should be at the fastest flowing part of the stream/river, usually mid-depth unless the eontaminant is less dense than water and eould float, or is more dense and eould aeeumulate near the river bed. For lakes representative samples should be taken near to the inflow, outflow and other loeations. If two phases are present both may require sampling. Sample preservation by refrigeration, pH adjustment, elimination of light, filtration, and extraetion may be important. 

In this chapter The background of shock-induced solid-state ehemistry eonceptual models and mathematical models chemical reactions in shock-compressed porous powders sample preservation. 

In addition to the need for an adequate method for free cyanide and an adequate sample preservation method, a methodology should be developed for the differentiation of species, especially between free (HCN and CM ), metallic complexes, and organic complexes. 

Monsanto. 1981. Stability study of natural sediments samples preserved by frozen storage with attachment. Monsanto Company, St. Louis, MO. 

Ashton and Chan [ 1 ] have reviewed the techniques for the collection of seawater samples preservation, storage, and prevention of contamination are all discussed. The most appropriate measurement techniques, preconcentration and extraction, method validation, and analytical control are all covered. The apparent aluminium content of seawater stored in ordinary containers such as glass and polyethylene bottles decreases gradually, e.g., to half in 2.5 h. But if the samples are acidified with 0.5ml/l concentrated sulfuric acid the aluminium content remains constant for at least one month. Accordingly, samples should be acidified immediately after collection. However, the aluminium could be recovered by acidifying the stored samples and leaving them for at least five hours. 

One is almost forced into hoping that freezing will prove satisfactory as a method of sample preservation, since none of the usual inorganic poisons... 

Preservation of organic samples is thus still a major problem there is no general, foolproof method applicable to all samples and all methods of analysis. The most generally accepted method of sample preservation is storage under refrigeration in the dark, with a preservative. This is another area that still needs extensive investigation. 

Table 1.8. Sample preservation (from author s own files) ...

Sample preservation by pasteurisation has been applied to the preservation of nitrite and nitrate in seawater [152], Samples can be stored for several months before analysis. 

Sample Preservation, Storage, Handling and Documentation, http //denr.sd.gov/des/gw/spills/ Handbook/SOP7.pdf 04/26/2011. 

R93002 A Review of Methods for Assessing Aquifer Sensitivity and Ground Water Vulnerability to Pesticide Contamination 600483039 Addendum to Handbook for Sampling and Sample Preservation, EPA-600/4-82-029... 

Adequate analytical methods exist for the analysis of 1,2-diphenylhydrazine in environmental samples and are presented below. However, adequate methods are not available for the sampling, sample preservation, and sample preparation (extraction) of environmental media. Neither ERA nor NIOSH have standard methods for analyzing 1,2-diphenylhydrazine in any medium ... 

In conclusion, HPLC is preferred over GC for analysis of 1,2-diphenylhydrazine. Sample preservation and extraction methods need improvement. 

Sampling of these substances has been carried out following three approaches liquid absorbents [47], solid-phase microextraction (SPME) fibres [43] and filter substrates (mostly quartz fibre filters but also PTFE membranes [1, 42, 48, 49]). When filter substrates are used, atmospheric particles are collected over 24-h periods using high-volume (dichotomous or single-filter instruments [1, 48]), medium-volume or low-volume samplers (operated to ensure collection of sufficient aerosol mass [37, 50]). Samples were always stored at low temperamres (refrigerated or frozen) to ensure sample preservation. 

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