Sample handling contamination

Field measurements provide savings in sample handling and analysis time, and they eliminate costly delays when re-sampling is required. In addition, they permit important real-time decisions by the on-scene cleanup coordinator regarding removal of sufficient contaminated soil to effect the desired cleanup while avoiding the removal of low-level contamination beyond that required. 

Similar to most Hg sampling methods, sampling sediments and soils require care in avoiding contamination artifacts due to improper sample handling. However, because Hg concentratiorrs are much higher in soUd matrices than in water, if corrrmonly accepted trace-metal protocols are used, substantial contamination artifacts should be exceedingly rare. Also, because sediment Hg concentration profiles... 

There are a number of other elements appearing from time to time in the laboratory. From these, chromium and nickel are most common. Both appear in enhanced concentrations in workers exposed to welding fumes, in galvanization processes, and in processing of ores. Prolonged exposure to Cr and/or Ni causes cancer and affects the kidney. Preferred methods of determination of Ni and Cr in urine are GF-AAS. Because of the risk of contamination of the very low concentrations in urine, extreme precautions in sample handling and analysis must be carried out. 

Sample handling and shipment 3.3.1 Prevention of cross-contamination... 

For assays of stable materials with wide ranges of tolerable error, sample handling is of little concern. For assays of labile materials, especially assays for purity or for minor components, controlled sample handling procedures need to be established. There are three potential ways in which a sample may become contaminated, namely by the sampling tools, sample containers, and degradation on storage. 

No sample handling between extraction and separation (no contamination)... 

Flow NMR has recently been eclipsed by the advent of robotic sample handling systems capable of dealing with very small sample quantities and volumes. We now have a system operating in our laboratory that makes up samples directly into 1 mm NMR tubes, using only about 8 ul of solvent. These can be run under automation and the tubes emptied back into the plate wells by the same robot. This technology offers superior performance and largely gets around the problems of contamination and recovery. 

X-ray fluorescence spectrometry was the first non-destructive technique for analysing surfaces and produced some remarkable results. The Water Research Association, UK, has been investigating the application of X-ray fluorescence spectroscopy to solid samples. Some advantages of nondestructive methods are no risk of loss of elements during sample handling operations, the absence of contamination from reagents, etc. and the avoidance of capital outlay on expensive instruments and highly trained staff. 

Another aspect to take into account is that surfactants are often ingredients in the cleaning products used in chemical laboratories. The sampling (as discussed above) and sample handling to which the samples are subjected always carries with it the risk of contamination. It is therefore necessary to process sufficient numbers of blank samples together with the real samples. Numerous samples of oceanic seawater and fossil seawater (taken from wells) have shown traces of LAS (around 1 ppb). Therefore, environmental concentrations found at similar levels should be regarded with caution. 

Modern methods of sample handling for determination of surfactants in aqueous samples are practically all based on SPE and modifications thereof. Substantial reductions in analysis time, solvent consumption, sample volume required, and number of off-line steps have thus been achieved. This has not only increased the analysts capacity and analysis price per sample, but also decreased the risk of both analyte loss and contamination during sample handling. Whether or not this has indeed resulted in an increased quality of analytical results still needs to be validated through, e.g. intercalibration exercises. This aspect is discussed in more detail in Chapter 4. 

A review article reports information regarding the preparation, handling, and storage of this important 3-carbon chiral source.9 Our experience with the compound demonstrates that it tends to polymerize and readily adds water to form hydrate 1 in aqueous solution, from which it is extracted with only difficultly. Both hydrated and polymerized aldehyde can contaminate samples and result in lowered optical rotation values, even though no racemization has occurred. The present procedure provides... 

Many analyses of organic compounds in liquid samples require selective cleanup and concentration. Direct on-line coupling of sample preparation to the analytical instrumentation minimizes sample handling and thereby the risk for contamination or loss of analyte. Also, on-line coupling makes... 

Most of the chemical analyses are performed after melting of the snow samples which subdivides the species into water-soluble and insoluble ones. The concentrations of trace species can vary by at least two orders of magnitude and the lowest values are in the range of 1-10 pg/1 for major ions such as Ca ", NH4, NOs , S04, and 10-100 ng/1 for trace metals. Thus, the snow and ice samples are particularly sensitive with respect to contamination and require special care in sample handling. 

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