Preserving samples

Natural crystals, synthetic crystals, and glasses often contain small bubbles that preserve samples of the fluid from which the crystals grew or of the atmosphere over the glass melt. Using a long focal length lens, the laser beam can be focused into inclusions at some depth below the crystal or glass surface. The Raman spectra then permit the identification of molecular species dissolved in the aqueous solutions or of components in the gas bubbles. ... 

Although two-dimensional features are readily apparent in the shocked and preserved samples, and study of the loading conditions indicates the need for two-dimensional studies, the influence of various powder descriptions and time scales of the events can be studied more efficiently in one-dimensional... 

If the purchaser is not satisfied with the wire rope service, he or she shall send the properly preserved sample or a sample of the rope from an unused section to any testing laboratory mutually agreed upon by the purchaser and the manufacturer, with instructions to make a complete API test, and notify the manufacturer to have a representative present. If the report indicates compliance with specifications, the purchaser shall assume cost of testing otherwise, the manufacturer shall assume the expense and make satisfactory adjustments not exceeding full purchase price of the rope. If the report indicates noncompliance with specifications, the testing laboratory shall forward a copy of the test report to the manufacturer. 

Figure 10. SEM photographs of polished, etched thin sections of fossil Acropora palmata coral (after Edwards 1988). The scale bar in a is 10 microns, a depicts sample AFS-12, a last interglacial coral from Barbados. The crystal morphology in this well-preserved sample is indistingnishable from that of a modem sample (see Fig. 9b). The scale bar in b is 100 microns, b depicts sample PB-5B, a fossil coral collected from North Point Shelf on Barbados. The crystal morphology of this sample shows clear evidence of alteration, inclnding a large calcite crystal filling in a macroscopic pore (dark area in npper right portion of photograph).

The results obtained for these four samples highlighted the usefulness of SPME to get complementary information allowing a better characterisation of resinous substances. It is indeed possible to detect many non degraded mono- and sesquiterpenes in well preserved samples such as samples 1480 and 1485 and to detect some characteristic compounds in degraded samples such as sample 1484. 

Surface and bottom water samples were collected in 500 ml, 1, or 4 litre polycarbonate bottles. Polycarbonate bottles have been shown to retain 97% of an initial spike of bis(tri-n-butyltin) oxide in seawater at a concentration of 0.5 mg/1 over a weeklong period [104]. Samples were analysed immediately after collection and transported to the laboratory, or were stored frozen at -20 °C and analysed at a later date. Frozen storage has been shown to be effective in preserving sample stability with respect to monobutyltin, dibutyltin, and tributyltin concentrations for a period of at least 100 days. 

Table 3.5 Examples of physical and chemical methods of preserving samples...

Kubeck and Naylor [2] tested four chemical preservatives (formaline, sulfite, bisulfite and a mixture of formaline/sulfite) by analysing NPEOs in river water over a period of 4 weeks. The sulfite- and bisulfite-preserved samples deteriorated drastically beginning after the first week, dropping 60-80% in NPEO concentration after four weeks. Formaline maintained the NPEO concentration within 10% of the original through at least two weeks. Formaline/sulfite mixture showed 25% loss after four weeks. 

Compounds bearing the functional groups of the present chapter are usually analyzed for the characteristic N heteroatom and less frequently for O. In this section some recent advances in the analysis of these heteroatoms are presented. A critical review appeared of the analysis of the nutrient elements C, N, P and Si, and their speciation in environmental waters, including sample collection and preservation, sample preparation and methods for end analysis5. 

ICP-MS. Ions from the plasma gas (such as Ar" and Ar ) can result in spectral overlaps with Ca and Se , respectively. Acids used to digest and preserve samples can also result in intense signals from molecular ions that can overlap with major isotopes of some elements (e.g. from... 

Storage at 4 °C or less is recommended for all samples, and storage at —20 °C or less is recommended for crude and processed extracts. The recommended containers are amber glass bottles with Teflon tops, but Teflon containers may be used for particularly corrosive samples. Stainless steel containers are not considered acceptable because of the potential for sample contamination. Additional research to address optimum storage conditions (temperature, time, and storage containers) that preserve sample integrity is recommended. This study should include research on the storage of raw samples, crude extracts, and processed extracts. 

Sample Preservation. Samples of naturally occurring organic acids are subject to both biological and chemical degradation. To avoid degradation of the sample, it is important to filter the sample immediately after collection. Filtration through a 0.45-/zm or smaller filter effectively removes organisms as small as bacteria from the sample. After filtration, the sample should be processed as soon as possible. 

Thiocyanate is a monovalent polyanion that has the formula SCN-. This anion is rarely found in wastewaters. However, cyanide-containing wastes or waters on contact with sulfides can form thiocyanates. On chlorination, thiocyanate could react with chlorine to form highly toxic cyanogen chloride, CNC1. Thiocyanate in water may be analyzed using 1. colorimetric method and 2. spot test. The latter method is a rapid spot test that can give semiquantitative results. Preserve samples at pH below 2 and refrigerate. 

To reduce the loss of contaminants from the collected samples due to volatilization and bacterial degradation, the majority of environmental samples must be preserved by storage within a temperature range of 2-6 °Celsius (C). Samples collected for VOC analysis are particularly susceptible to such losses even at slightly elevated temperatures. Preserved samples represent the sampling point conditions at the time of sampling, and that is why proper preservation upon sample collection is necessary to assure the collected sample representativeness. 

If preserved containers for water samples are not available, we should obtain small quantities of preservation chemicals from the laboratory and preserve samples in the field immediately after they have been collected. Only laboratory-grade, high purity chemicals, which have been certified as free of contaminants of concern, should be used as preservatives. 

Preserve samples collected for metal analysis with 5 ml of 1 1 nitric acid solution. 

Familiarize yourself with shipping regulations and shipping container labelling requirements as you may be personally liable for improper shipment of hazardous materials (i.e. acid and base-preserved samples or PCBs). 

Option 5. Preserve two soil samples per either one of the four above-described options transfer the third sample into a vial with 10 ml of purge-and-trap grade methanol store at 2-6°C analyze methanol-preserved samples within 14 days of collection. 

Preserving soil with methanol is the most efficient way to arrest bacterial activity and to prevent VOC volatilization. Methanol is also a much more efficient extraction solvent than water, and VOC concentration data obtained from the methanol-preserved samples are higher in values than the data obtained from soil/water slurries of the same samples (Vitale, 1999). 

The laboratory will store the containers with methanol-preserved soil at 2-6°C. The holding time for analysis is 14 days as defined by EPA Method 5035. ASTM Standard D 4547-98 indicates that methanol-preserved samples do not exhibit VOC losses for a period of time of up to two months (ASTM, 1998). The state of Alaska Department of Environmental Conservation (ADEC) Method AK101 for gasoline analysis of methanol-preserved soil samples specifies a holding time of 28 days (ADEC, 1999). 

When sampling for dissolved metals, filter the sample directly into a preserved sample container. 

Preservation chemicals and disposable pipettes, if preserved sample containers are not available... 

Slowly discharge the water from the bottom check valve into preserved sample containers. To minimize turbulence and exposure to air, let the water flow down the side of the sampling container. 

Assemble the filtration apparatus. Pour sample into the filter funnel and filter the water by creating a vacuum in the collection flask with a hand pump. If the filter becomes clogged with sediment, release the vacuum, replace the filter, and continue filtering. Transfer the filtrate into a preserved sample container. 

Pour a small volume of the preserved sample into the container lid or into a paper cup and take a pH measurement by dipping a pH paper strip into the lid or cup and comparing it to the color scale. 

Collect samples directly into the sample containers by lowering them under the water surface. Sample containers in this case should not contain preservatives. Preserve samples as appropriate after they have been collected. 

Retrieve more water from the same sampling point transfer the water from the dipper into preserved sample containers cap the containers. 

Transfer the water into preserved sample containers cap the containers. 

The protocols for sampling of industrial wastewater require that the pH of preserved samples be verified immediately upon sampling to assure proper preservation (APHA, 1998). The basis for this requirement is the fact that some of the industrial wastewater streams have a high basic pH or contain acid-reactive chemical components, which may neutralize the acids added to samples for preservation. For this reason, the pH of preserved wastewater samples is always measured during sampling and is adjusted, if necessary, to bring it into required range of values. 

In wipe sampling, the same area cannot be sampled twice. To sample the same sampling point for a different class of contaminants, we delineate an adjoining area and wipe it with a chemical appropriate for the target analyte. To thoroughly cover the sampled area, the wiping motion inside the template is performed in two directions, horizontal and vertical, as shown in Figure 3.12. We place the used wipe into a preserved sample container and submit it to the laboratory for analysis. 

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