Laboratory Contamination

Negative controls demonstrate the absence of laboratory contamination or sample cross-contamination. DNA extracts from nontransgenic plants, clean buffer and mastermix with no template DNA added are common negative controls that are run concurrently with the test samples in the PCR. 

Because of the ubiquitous nature of FMs in consumer products, it is critical that any analytical chemistry laboratory measuring these compounds takes extra precautions to avoid laboratory contamination of samples. Several researchers [2,11,14-17] have pointed out that likely sources of FM contamination in the modern-day laboratory include the use of consumer products and fine fragrances by laboratory workers, fragrances in soaps used to clean glassware and the laboratory, and laboratory supplies such as gloves. 

Before beginning the analysis of FMs at low concentrations, the laboratory should analyze several laboratory blank samples to assess the degree to which the laboratory is contaminated. With every set of samples analyzed, the laboratory should also analyze a laboratory and field blank sample. Laboratory workers should be advised to be aware of their personal use of fragrance-enhanced consumer products and the potential for laboratory contamination. 

The introduction of laboratory contamination is a significant but often overlooked concern in sample cleanup. The introduction of extractable materials from plastics nsed for joining tubes and the introduction of contaminated solvents are only two of the potential sources of laboratory contamination. 

Source Detected in distilled water-soluble fractions of new and used motor oil at concentrations of 38 to 43 and 15 to 23 pg/L, respectively (Chen et al., 1994). Leaching from flexible plastics in contact with water. Laboratory contaminant. 

Sample Concentration Experiments. A CLLE quality assurance blank was run by extracting 90 L of Milli-Q water with three CLLE samplers in a parallel configuration and concentrating the composited extract to 4 mL by Kudema-Danish evaporation. The 22,500-fold concentrate was analyzed by GC-flame ionization detection (GC-FID) and GC-MS. Thirty-two peaks were observed by using GC-FID analysis, but because of their low concentrations, only four contaminants were identified by GC-MS cyclohexene, 2-cyclohexen-1-one, n-butyl phthalate, and bis(2-ethylhexyl) phthalate. Cyclohexene is a solvent preservative that has been identified in commercial high-purity methylene chloride (16), and 2-cyclohexen-l-one is its air oxidation product. The phthalates are ubiquitous laboratory contaminants and have also been identified in commercial methylene chloride (17). 

In previous studies, the solubilization of hydrophobic organic contaminants using surfactants has been shown to increase the rate of contaminant desorption from soil to water (Deitsch and Smith 1995 Yeom et al. 1995 Tiehm et al. 1997). A 3,000 mg/L solution of Triton X-100 (CMC = 140 mg/L) increased the rate of desorption of laboratory-contaminated TCE from a peat soil (Deitsch and Smith 1995). However, the solubilization effect was secondary compared to the surfactant s effect on the desorption rate coefficient. Yeom et al (1995) developed a model that satisfactorily predicted the extent of polycyclic aromatic hydrocarbon solubilization from a coal tar-contaminated soil. Only at high surfactant dosages did the model fail to accurately predict the ability of different surfactants to solubilize polycyclic aromatic hydrocarbons. It was hypothesized that mass-transfer limitations encountered by the polycyclic aromatic hydrocarbons in the soil caused the observed differences between the data and the model simulations. In another study (Tiehm et al. 1997), two nonionic surfactants, Arkopal N-300 and Saogenat T-300, increased the rate of polycyclic aromatic hydrocarbon desorption from a field-contaminated soil. The primary mechanism for the enhanced desorption of polycyclic aromatic hydrocarbons was attributed to surfactant solubilization of the polycyclic aromatic hydrocarbons. 

The only contaminants usually found in equipment blanks are common laboratory contaminants phthalates, methylene chloride, acetone. 

Most often, trip blank contamination originates in the laboratory, either from common airborne laboratory contaminants (methylene chloride, acetone) or from laboratory water containing VOCs, typically methylene chloride, acetone, and toluene or water disinfection byproducts (chloroform, dichlorobromomethane, chlorodibromomethane, bromoform). Rare, but well documented sources of trip blank and associated field samples contamination are insufficiently clean sample... 

The intent of equipment rinsate blank collection as a field QC sample seems reasonable. In reality, however, equipment blank analyses rarely provide information that can be meaningfully related to the field samples because the only contaminants that are usually present in equipment blanks are common laboratory contaminants or byproducts of water disinfection process. 

The practice, however, shows that ambient blanks do not give us the information they are designed to provide because airborne ambient concentrations are usually extremely low and the exposure of the collected sample to ambient air is very short. The only contaminants typically found in ambient blanks are common laboratory contaminants. 

Highly selective to halogenated and oxygenated compounds Electron capture detector EDB, DBCP (EPA 8011) Acrylamide (EPA 8032) Phenols (EPA 8041) Phthalates (EPA 8061) Organochlorine pesticides (EPA 8081) PCBs (EPA 8082) Nitroaromatics and cyclic ketones (EPA 8091) Haloethers (EPA 8111) Chlorinated herbicides (EPA 8151) CLP SOW for organic analysis Interferences from Elemental sulfur (S8) Waxes, lipids, other high molecular weight compounds Phthalate esters, which are common laboratory contaminants Oil in PCB analysis... 

Among manmade interferences are the phthalate esters, the oxygenated compounds that are ubiquitous laboratory contaminants. 

The primary source of data interpretation error in elemental analysis is laboratory contamination affecting the method blank and the samples. Method blank is a volume of analyte-free water prepared and analyzed in the same manner as the samples. Method blank is also called analytical blank or preparation blank. 

Human error is always a significant factor in elemental analysis. Inadequately trained, inexperienced or simply inattentive analysts may not be able to recognize a developing problem with a potential for blank and sample contamination and to handle it correctly. Unskilled analysts may cause laboratory contamination or cross-contamination between samples due to poor laboratory technique. There is no substitute to proper training and experience for the recognition and prevention of laboratory contamination in the trace level elemental analysis. 

Establishes that laboratory contamination does Prepared with every preparation batch of up not cause false positive results to 20 field samples for all organic, inorganic,... 

Laboratory blanks are batch QC checks used to demonstrate that laboratory contamination or residual contamination in the analytical system (memory effects) does not cause false positive results. Laboratory blanks include calibration, instrument, and method blanks. 

Sample results for common laboratory contaminants are qualified by elevating the PQL to the concentration found in the sample if sample concentration is less than 10 times the blank concentration. These contaminants include methylene chloride, acetone, 2-butanone, cyclohexane in VOC analysis and phthalates in SVOC analysis. 

The chemist will pay particular attention to samples, which were diluted in the course of analysis. The concentrations of laboratory contaminants that may be present in the samples, as indicated by contaminated instrument or method blanks, will be magnified by the multiplication by the dilution factor and create false positive results of high concentration values. 

If compounds that are not contaminants of concern are present in the blanks and in the samples, then field or laboratory contamination may have taken place. The sample data are nevertheless, representative of the sampled matrix. 

If the concentrations of contaminants of concern in the samples are greater than the concentrations in any of the blanks by a factor of 5 (or 10 for common laboratory contaminants), then the sample data are representative of the sampled matrix and may be used. 

DEHP is a widely used chemical that enters the environment predominantly through disposal of industrial and municipal wastes in landfills and, to a much lesser extent, volatilization into air (from industrial and end uses of DEHP), carried in waste water from industrial sources of DEHP, and within effluent from municipal waste water treatment plants. It tends to sorb strongly to soils and sediments and to bioconcentrate in aquatic organisms. Biodegradation is expected to occur under aerobic conditions. Sorption, bioaccumulation, and biodegradation are likely to be competing processes, with the dominant fate being determined by local environmental conditions. When DEHP is present in the environment, it is usually at very low levels. It is very difficult to determine these low levels accurately since DEHP is a ubiquitous laboratory contaminant, and laboratory contamination may cause false positives to be reported in the literature. 

When DEHP is present in the environment it is usually at very low levels. It should be noted that it is very difficult to determine these low levels accurately since DEHP is a ubiquitous laboratory contaminant. Laboratory contamination might cause false positives to be reported in the literature. Laboratory contamination often undermines the credibility of the data and, therefore, reported concentrations of DEHP in environmental samples must be carefully reviewed. 

Laboratory contamination is a sigpificant issue -when measuring DEHP in biological materials and care must be taken to address this concern, as discussed in the introduction to Chapter 7. 

Low Count Rates in Blanks. Radioactive contamination in a blank should be zero, or constant and extremely small. A procedure blank is a deionized water sample that is processed through the complete analysis. Carrier is added, every step is performed to the end of the analysis, and the final form is counted. Blanks are processed as part of each sample batch to check the quality of the analysis with regard to laboratory contamination for this batch. 

We observed that only a small fraction of the adsorbed mass would desorb even after a number of successive desorption steps. The investigation on laboratory contaminated soil showed a biphasic behavior, namely an easily desorbed fraction and a desorption resistant fraction. Both field contaminated and aged soils also showed the same behavior. The first stage involved a loosely bound fraction and the second stage involved a tightly bound fraction. The desorption constants calculated or estimated for the two fractions were em-... 

The original mold observed and preserved by Alexander Fleming was a strain of Penicillium notatum, a common laboratory contaminant. Later, cultures of Penicillium chrysogenum were found to be better producers of penicillin, and the present industrial strains have been derived from this species. The original strains produced the antibiotic only by surface fermentation methods and in very low yields. Improved media and productive strains under submerged aerobic fermentation conditions led to dramatic yield increases. Subsequent improvements, principally in culture selection and mutation, further improved yields, reaching 20-30 g/L. 

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