Contamination background

The most challenging aspect of measuring PFCs in environmental samples is background contamination. In fact, contamination at every step of the analysis. .. is a common problem [93]. Sources of this contamination are not completely characterized, but can include sampling, instmmental and analytical/procedural sources. This serves to highhght the importance of field, matrix and reagent blanks [94]. 

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The minienvironment approach to contamination control has been increasing in use. A minienvironment is a localized environment created by an enclosure that isolates the product wafer from contamination and people (48). Another approach is using integrated processing, where consecutive processes are linked in a controlled environment (32). Both requite in situ sensors (qv) to measure internal chamber temperatures, background contamination, gas flow rates, pressure changes, and particularly wafer temperature (4). 

Check exposures routinely by personal dosimetry or following accidents (in the UK dosimetry services must be approved) and keep records (e.g. in UK for at least 50 years). Notify the relevant employees and authorities as appropriate. Monitor background contamination periodically using equipment that has been checked by qualified persons and keep records of levels (e.g. for 2 years). 

Long-lasting measurements of the environmental background contamination (particulate matter and air in areas far away from cities and industry) and analytical data of food and biota prove that the transport into the environment is slowly decreasing. The actual emissions in Europe decreased from 500 Mg/year (1990)... 

Berset JD, Ejem M, Holzer R, Lischer P (1999) Comparison of different drying, extraction and detection techniques for the determination of priority polycyclic aromatic hydrocarbons in background contaminated soil samples. Anal Chim Acta 383(3) 263-275... 

One of the major problems associated with trace level analysis of perfluori-nated acids is background contamination in the analytical blanks. Because of the contamination in blanks, the limits of detection (LOD) of perfluoro-chemicals in water samples are high, in the range of several tens to hundreds of ng/L to a few pg/L (11-15). 

In chromatography the quantitative or qualitative information has to be extracted from the peak-shaped signal, generally superimposed on a background contaminated with noi%. Many, mostly semi-empirical, methods have been developed for relevant information extraction and for reduction of the influence of noise. Both for this purpose and for a quantification of the random error it is necessary to characterize the noise, applying theory, random time functions and stochastic processes. Four main types of statistical functions are used to describe the tosic properties of random data ... 

Soil samples at the epicentre of the nuclear bomb explosion site in Semipalatinsk93 were measured with ESR. Although the dependence on the distance from the epicentre was not presented, ESR will be potentially useful for tooth enamel of residents nearby the accident and the high background contaminated area. It must be noted, however, that the high dose-rate effect will appear in the case of direct A-bomb radiation leading to lower dose estimation than real one. Radiation effect from the contamination, which is the case for residents, may be estimated if artificial dose rate is around 100 Gy/h or less. 

Several effects, like instrumental mass bias, isobaric interferences, instrumental background, contamination of the solution introduction system and the sampler and skimmer cone and lens... 

Commercial standard solutions for flame atomic absorption are not necessarily suitable for plasma and furnace analyses. The latter methods require purer grades of water and acids for standard solutions and, especially, for dilutions. For the most sensitive analyses, solutions are prepared in a dust-free environment (a clean room with a filtered air supply) to reduce background contamination that will be detected by your instruments. 

This consideration of the principles of diffusive sampling identifies a range of factors which may influence the performance of a diffusive sampler for monitoring VOC concentrations in indoor air. These factors will potentially be a source of error in such measurements and add to the overall uncertainty of the result given by the measurement procedure. In addition the amount of uncertainty will be influenced by other factors including amount and consistency of background contamination of sorbents, repeatability of analytical determination, formation of artifacts, stability of analyte on the sorbent, recovery of analyte during analyses and presence of interferents. 

Reference values are intended to characterize the upper margin of a current background contamination of a pollutant at a given time. For contaminants in the indoor environment reference values may be calculated applying the procedure as for environmental toxins in body fluids (Ewers et al., 1999). Reference values for pollutants in house dust were reviewed recently by Butte (2003). It has to be emphasized that a reference value has no health meaning nor regulatory implication. 

PCBs collected on the filter or adsorbed onto the florisil are now desorbed with 5 mL hexane. The filter, the front section, and the back section of the florisil and the media blank are analyzed separately by GC-ECD under the chromatographic conditions as described above. The results are added up to determine the total PCBs. Also, a media blank is run to determine the background contamination. Correction is made for ary PCBs found in the media blank. 

Ironically, those pressures of the last 13 years or so have generated more information about the environmental toxicology of chlorinated insecticides than we may ever gain about other classes of pesticides or environmental contaminants. As a side-benefit, we now know that some xenobiotics may be transferred into global areas they were never intended to reach and we have developed the methodology needed to measure these low level contaminations It is also doubtful whether the extensive background contamination by PCB would have come to light so quickly without the widespread concern about OC ... 

A second type of control could be provided by national baseline data. Such data indicating the levels of ambient or background contamination usually encountered in different types of demographic settings could help clarify the significance of environmental measurements near a hazardous waste site. 

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