Preservation of Samples

Samples that cannot be analysed immediately on board ship may be preserved by adding zinc acetate (or chloride), which precipitates the sulphide as zinc sulphide. A 1 mL aliquot of zinc acetate solution is immediately added to a 50 mL sample with a piston pipette. Samples thus preserved may be stored for long periods of time if kept in a dark place. The other reagents are later added at the home main laboratory. 

The reagents, 0.5 mL of dimethyl-p-phenylenediamine and 0.5 mL iron(///) chloride solution, are added in exactly the same way as the reagents for determining oxygen, i.e., simultaneously with piston pipettes or with dispensers. The tips of the pipettes/dispensers should touch the bottom of the oxygen bottles. No air bubbles must be trapped in the bottles. The colour develops within a few minutes. If other sizes of sample bottles are used, the amoimts 

The storage of samples during transport from the field to the laboratory, and on the laboratory shelf, has to be done with care and expertise. Major points are 

Validation should be performed on three separate days to compare precision by analyzing three replicates of reference standards under identical conditions (once again the acceptance criteria should be a prespecified coefficient of variation). 

To demonstrate that other analysts can perform the experiment with similar precision, two separate analysts should make three independent measurements (the acceptance criterion is once again a prespecified RSD). 

The limit of detection, limit of quantitation, and linear dynamic range are to be determined by serial dilution of a sample. Three replicate measurements at each level are recommended, and the acceptance criterion for calibration linearity should be a prespecilied correlation coefficient (say, an r2 value of 0.995 or greater). 

The molecular weight markers should fall within established migration time ranges for the analysis to be acceptable. If the markers are outside this range, the gel electrophoresis run must be repeated. 

Common steps in sample preservation are the use of proper containers, temperature control, addition of preservatives, and the observance of recommended sample holding time. The holding time depends on the analyte of interest and the sample matrix. For example, most dissolved metals are 

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At present, the principal thrust of shock-induced solid state chemistry rests upon preservation of samples that have been subjected to controlled, quantitative, reproducible shock loading. Such an endeavor must, of necessity, involve close, cooperative efforts between materials communities, including solid state physics, materials science, and shock-compression science. 

In order to avoid further biodegradation of surfactants after sampling or during storage, various substances have been used for the preservation of samples. So far, mainly formaldehyde and salts of copper(II) and mercury(II) [7,14] have been applied, and formaldehyde has been found to be the most effective of these, although still not sufficient for long term storage. This topic is discussed in more detail in Chapter 4.3. 

There are marry sources of variability related to the sampling, handling, transfer, and preservation of samples. The preparation, sampling, and analysis of animal feeds deserve special attention. 

The collected samples must be identified with unique sample numbers efficiently tracked in the field stored in a secure location for the preservation of sample integrity and transferred to the laboratory with the information on their identification (ID) and the requested analysis. The provisions for sample numbering, labelling, storage in the field tracking and transfer to the laboratory are set forth in the SAP. 

Difficulties have been observed in the preservation of samples for speciation of chromium. Chromium speciation in seawater was determined on board ship shortly after samples had been collected (Abollino et at., 1991). Some samples were frozen, and analysed later in a laboratory. However, significantly lower concentrations of Crvl were observed in these latter samples. Thus, sea-going analytical methods for the determination of Crm and total chromium are of particular importance (Mugo and Orians, 1993). The volatile trifluoroacetyl-acetone derivative of Crm was formed and then concentrated by extraction into toluene. Chromium was determined by means of a gas chromatograph equipped with an electron capture detector. Total chromium was determined as Cr111 after reduction. The detection limits were 0.062 and 0.255 nmol dm 3 total chromium. A useful method was described for sampling natural water in the field, and for the preservation of Crm and Crvl species for subsequent analyses in a laboratory (Cox and McLeod, 1992). Water samples were drawn through small columns packed with activated alumina, which had been prepared previously. Chromium species were retained on the columns. 

The Director-General shall have the primary responsibility for the security, integrity and preservation of samples and for ensuring that the confidentiality of samples transferred for analysis off-site is protected. The Director-General shall do so in accordance with procedures, to be considered and approved by the Conference pursuant to Article Vin, paragraph... 

Table 3.1 Techniques for the preservation of samples for analysis (simplified from BSI, 1996)... 

Preservation of samples, 114,116 Presinol, 764 Prestim, 375, 1026 Presun 4, 847 Presun 8, 340 Prethcamide, 495 Priadel, 708 Priamide, 690 Prilocaine, 920 Prilocaine hydrochloride, 920 Primachin, 921 Primaclone, 922 Primalan, 735 Primal(s), 334 Primaquine, 921 Primaquine phosphate, 921 Primidone, 25, 922 therapeutic drug monitoring, 109 Primogyn C, 596 Primogyn Depot, 831 Primolut N, 823 Primolut Nor, 823 Primoteston-Depot, 1003 Primperan, 776... 

The preservation of samples for environmental analysis is an important topic, and field methods are always an area for new methods development. Work by Martinez and Barcelo (1996) found that pesticides could be preserved on disk by passing the sample through the disk in the field, then immediately storing the disk in the frozen state until elution could be done in the laboratory. Ferrer and Barcelo (1997) found a similar result for the preservation of pesticides on cartridges. They found that samples could be stored safely for several weeks... 

The ASTM has already published a preamble to oil identification (19) and methods on preservation of samples (20), elemental analysis (21), and infrared analysis (22), in addition to the GC and FL methods (4,5) and sample preparation methods (3) previously mentioned. Widespread adoption of these carefully developed methods and their under-... 

Preservation of samples In 77% of the reports, fresh or frozen materials were extracted. In 23% of the reports, the organism was lyophilized or air-dried (two instances) prior to extraction. 

Overall, the assurance of adequate containerization and preservation of samples is a matter which needs to be built in to the preparatory planning of any environmental sampling exercise, in consultation with the receiving laboratory. 

What preservation of samples is required and are the materials available ... 

It is immediately apparent that the complete automation of this sub-stage is a difficult task. Only in a few instances (e.g. the automatic in vivo determinations described In Chapter 14 and performed with the on-line process analysers dealt with in Chapter 17) is this ideal objective affordable. Much more often, some of the above-mentioned operations involve human participation, although It is still termed automated [1]. Therefore, although many clinical analysers are classed as automatic, the blood and urine samples that they handle are collected and even treated manually before they are placed on the sampler. Such is also the case with automatic off-line water pollutant analysers, also calling for manual collection and preservation of samples. Consequently, the automated sampling concept as used here refers to the Introduction Into the analyser or instrument concerned of a definite portion of sample collected from its source and even treated manually, with the few exceptions stated above. 

Hamlin, S.N. (1989) Preservation of samples for dissolved mercury. Water Resources Bull., 25, 255.262. 

A primary criterion that governed the development of these methods was the preservation of sample morphology. To that end, we avoid subjecting the samples to damaging treatments such as protease digestion or air drying. An intrinsic requirement for in situ hybridization is that the chromosomal DNA must be... 

Preservation of samples may be necessary in individual cases. The best form of preservation of samples is a rapid investigation of the water sample after sampling. This should take place in the laboratory as far as possible no later than 2 days after sampling. During transport and until commencement of the investigation the water samples should be stored in cool conditions at around C. 

Cooling or preservation of samples is particularly important when taking... 

Depending on the purpose of the analysis, the origin of the sample, and the analytical method being used, regulations and directives are already in effect and standard procedures have been written up that describe and regulate sampling as well as the storage and preservation of samples [2-12]. The common practice... 

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