Urine analysis sample storage

The samples must be stored in good conditions pending analysis. The storage conditions that are appropriate will depend upon the type of sample and the determinations required. Most soil analysis, for example, is done on air-dried soil, but the nitrate content can be altered by drying, so nitrate studies are usually done on fresh soil. If the soil has to be stored, this should be at <4 °C and for no more than 48 hours. Similarly samples in which analysis of the volatile components is required, such as silage, urine and faeces, are usually kept frozen until immediately before the analysis. 

The urine is collected in polyethene bottles, and the specimens are refrigerated (up to 7 days) or deep frozen until use. Specimen collection must be carried out as described in Sec. Sampling and Sampling Storage (A. Aitio and J. Jarvisalo). Contamination must be strictly avoided. The sample preparation for the AAS analysis including standard addition... 

When one wishes to determine drug residues separately in yolk and egg white, it is also advisable to separate these compartments immediately after laying because of reported diffusion from yolk to egg white (20). As with urine samples, it is also necessary to buffer egg samples prior to analysis, because the pH of the egg white may vary between 7.6 and 9.4 depending on the storage time, although while yolk pH is always in the narrower range of 6.0-6.8 (19). 

Urine is the most common bioassay sample type because it is nonintrusive and readily available, and provides some insight into radionuclide intake, retention, and excretion, but is not ideal for all radionuclides. A preservative can be added to urine samples immediately after collection. Bioassay samples are refrigerated for prompt analysis and kept frozen for extended storage. 

The analysis of volatiles presents particular problems. First, many of the compounds of interest occur commonly in laboratories and this necessitates special precautions against contamination and interference. Second, collection, storage, and transport of biological samples must be controlled as far as practicable in order to minimize loss of analyte - quantitative work is futile if very volatile compounds such as propane are encoimtered unless special precautions are taken to prevent the loss of analyte from the sample prior to the analysis. Third, many compounds of interest are excreted imchanged via the lungs and thus blood (and/or other tissues in fatalities), and not urine, is usually the sample of choice. Finally, the interpretation of results can be difficult, especially if legitimate exposure to solvent vapor is a possibility. 

Aqueous samples such as drinking water, surface water, and waste water but also beverages and urine samples, should always be acidified with mineral acids for stabilization purposes immediately after collection. This is especially true for the prevention of desorption processes during sampling and storage of samples in the course of trace metal analysis. Acidification reduces the tendency for ions to be adsorbed onto active sites at the surface of the containment vessel, and it also inhibits bacterial growth [9]). Glacial acetic acid and... 

Hair has been also an object of analysis to detect the consumption of opium alkaloids [68, 78, 83]. This matrix has attracted a lot of attention for the easy and noninvasive sample collection and difflcult adulteration compared to the plasma, urine, and saliva specimens. In addition, hair samples are more stable in storage and can provide a wider detection time window, which can reveal the history of drug abuse. 

Tables 116-120 show results obtained by this procedure in the analysis of water, shell and human urine samples for organotin compounds. All samples were analyzed without pretreatment. Samples which were not analyzed immediately, were frozen until analysis was possible. Polyethylene bottles, 500-ml volume, were used for sample acquisition and storage. No contamination of samples by the bottles was observed and no cross contamination was noted between uses. Poly(vinyl chloride) materials must be avoided to prevent tin contamination from the organotin plasticizers used in its production. Approximately 17-60% of the total tin present was found to be in the methylated forms. The saline waters appear to have the highest percentage of methylated tin compounds, 60% of the total tin present was found to be in the methylated forms, the dimethyltin form contributes approximately half of this value.

No common statement can be given for the stability of arsenic compounds in water samples. Many different arsenic compounds have to be considered, such as the redox pair As(III)/As(V), the methylated compounds MMA (monomethylarsenic) and DMA (dimethylarsenic) (in either 3- or 5-valent forms), and arsenobetaine (AsB), arsenocholine (AsC) and the larger arsenosugars, which require different storage conditions. For example, the arsenic species As(III), As(V), MMA and DMA were found to be stable in water samples without any preservation, when analysis was carried out during the following 24 h. Urine and water containing As(V), MMA, DMA, AsB and AsC were stable when stored at —20°C. ... 

Certain precautions should be taken in handling samples for thiamin analysis. Urine should be acidified to avoid degradation and stored below —20 °C. Heparinized whole blood should be collected and immediately put on ice. For total erythrocyte TDP measurements, cells are separated from plasma within 2h when possible, washed in saline, and diluted 1 1 with saline prior to acidification. Centrifugation of the acidified mixture provides a clear extract that can be stored for no more than 5 days at 4°C or longer at <—20°C. Washed red cells are also used for the ETKL assay. Duplicate tubes of the red cells in saline suspension with and without added TDP are mixed and can be stored at —70°C prior to enzymatic analysis of ETKL activity. Even at —70°C, however, storage should be for no more than a few weeks. The ETKL apoenzyme is unstable, and even in the tubes to which TDP has been added, if mixing did not thoroughly expose all apoenzyme to the added coenzyme, deterioration will occur and results will be unreliable. 

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