Avoidance of Contamination

Earlier analytical results from the gas chromatographic analysis of fatty acids seemed to be very high. Williams [102] repeated much of the early work, using extreme care in the avoidance of contamination, and found very much smaller quantities. Papers concerned with the fatty acid content of the water column and sediment include [ 103-109]. 

Avoidance of contamination is a major operating factor, for instance the air must be sterilized. 

West C.W. and G.T. Ankley (1998). A laboratory assay to assess avoidance of contaminated sediments by the freshwater oligochaete Lumbricus variegatus. Archives of Environmental Toxicology 35 20-24. 

The single most important factor in the avoidance of contamination problems is good housekeeping. This applies to all aspects of trace residue examination procedures, and includes police vehicle interiors, custody offices, cells, sampling rooms, and sampler s premises. 

The single-use sensors have other important advantages, especially working in the field of clinical analysis, such as avoidance of contamination among samples. 

A water-insoluble lactoperoxidase, linked to CNBr-activated Sepharose beads, capable of iodinating serum albumin, is commercially available (Worthington Biochemical Corp.), and may be useful where avoidance of contamination of the product by the enzyme is important. 

There is tighter control on conditions (e.g., pH, temperature, substrate and product concentrations, dissolved 02 concentration, avoidance of contamination by foreign organisms). 

Another important consideration is how exposure to a stressor may alter natural behavior, thereby affecting further exposure. In some cases, this may lead to enhanced exposure (e.g., increased preening by birds after aerial pesticide spraying), while in other situations initial exposure may lead to avoidance of contaminated locations or food sources (e.g., avoidance of certain waste effluents or physically altered spawning beds by some fish species). 

Overall, will the samples be taken in a satisfactory manner for the work to be done - especially with regard to organisation, labelling and avoidance of contamination ... 

But first, although the importance of careful sampling of any product that is to undergo testing is self-evident, very special precautions must be taken in the case of insulating oils (ASTM D-923, IP 51), for which special techniques are recommended. Precautions that are stipulated are mainly concerned with the avoidance of contamination that would affect electrical tests. 

The separate and independent components of an effective system of aseptic manufacture overlap rather than abut against one another. Momentary failure of any one system does not necessarily compromise product sterility. Nonetheless, good assurance of avoidance of contamination can only be obtained from knowledge that each system is capable of performing as it ought to perform (validation) and that it continues to operate effectively in routine use (routine monitoring). 

Many papers have been published directed to the preparation of biological samples for analysis and to methods for avoidance of contamination. Versieck (1983) discussed errors arising from needles, vacutainers, etc, for Cr, Ni, Cd, Pb, Mn, Cu and other metals. He also discussed errors arising in neutron activation analysis. His emphasis is on problems relating to contamination. 

The literature on procedures for PbB determination is abundant. Those techniques that have been shown to provide accurate and precise PbB determinations in routine use include anodic stripping voltammetry (ASV), flame atomic absorption spectrophotometry (FAAS), discrete sampling FAAS, and graphite furnace AAS (GF-AAS). The method most widely used for routine determination is AAS in its various modifications. The relatively slow analysis rate of ASV tends to limit the application of this technique to that of a backup or reference method. Whatever the technique which is applied, it should be emphasized that avoidance of contamination, careful handling of the blood samples and frequent intra- and interlaboratory checks are more important for ensuring precision and reliability than the method itself. 

Avoidance of Contamination Causing Stress Corrosion Cracking... 

There are modifications of the above procedure which do not require the complete separation of phosphorus from silica, but depend on the preferential reduction of silicomolybdic acid to molybdenum blue in the presence of phosphomolybdic acid. In general, it is emphasized that dependable results rely on careful avoidance of contamination of the sample with silica from glassware, elimination of interference by phosphorus, and maximum sensitivity in making the colorimetric measurement (409-411). Baumann described a preferred technique for analysis of silica in blood and other biological materials (see Chapter 1, Ref. 320). 

This is probably the most sensitive technique for lead, and in very low level work the avoidance of contamination is likely to be a more major problem than the approach of the analytical detection limit. Sensitivity may be improved even further by the use of alternative electrodes (e.g. glassy carbon) in place of the commonly used hanging mercury drop. Advantages of ASV are the possibility of simultaneous determination of four metals (Pb, Cd, Cu, Zn) in one sample, and the freedom from matrix effects as a standard additions technique is always used. 

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