Contamination and Carryover

This prevents syringe contamination and carryover from the initial injection. 

Amplified DNA is identified by solution hybridization of two nonisotopically labeled oligonucleotides to one strand of the amplified DNA. Following hybrid formation DNA is bound to a solid phase and detected by enzyme-labeled specific antibodies. Because only one strand is used for detection, the other one is washed off and constitutes the main source of laboratory contamination and carryover. Take precautions to avoid the spread of these molecules to other rooms (e.g., work in a chemical fume hood, decontaminate used wash buffer with acid or sodium hypochloride, and so on). 

It is crucial in quantitative GC to obtain a good separation of the components of interest. Although this is not critical when a mass spectrometer is used as the detector (because ions for identification can be mass selected), it is nevertheless good practice. If the GC effluent is split between the mass spectrometer and FID detector, either detector can be used for quantitation. Because the response for any individual compound will differ, it is necessary to obtain relative response factors for those compounds for which quantitation is needed. Care should be taken to prevent contamination of the sample with the reference standards. This is a major source of error in trace quantitative analysis. To prevent such contamination, a method blank should be run, following all steps in the method of preparation of a sample except the addition of the sample. To ensure that there is no contamination or carryover in the GC column or the ion source, the method blank should be run prior to each sample. 

The frequency and types of tests employed should, of course, bear some relation to the type of facility being considered. If steam and condensate are not tested, carryover, corrosion, contamination, and other potential problems may be missed, which undoubtedly will have a deleterious impact in other parts of the overall boiler plant. 

Additionally, comparison of MU water usage and steam production with chemical treatment supplied, fuel consumption records, and flue gas analysis will provides early warning signs of deposit formation. Water analysis records can indicate problems of process contamination, BW carryover, and inadequate oxygen scavenging (and therefore the potential for corrosion). 

Simple sample preparation Samples for TLC separation often involve fewer cleanup steps because every sample is separated on fresh stationary phase, without cross-contamination or carryover. Even strongly absorbed impurities or solid particles in samples are not of much concern. This would be a disaster for HPLC separation, leading to column buildup, decay, and eventually destroying the performance. 

Other systems and areas that require cleaning are chromatographic columns and surfaces in the facilities, especially cleanrooms. A rigorous cleaning program has to be implemented to minimize potential product contamination. This includes a limit being set for the maximum carryover of contaminants and validated by the validation process (Exhibit 9.7). 

The insidious nature of the contamination problem is illustrated by the fact that some contamination fails to be detected by the canonical controls. We (A. Cooper, M. H8ss, and S. PMbo, unpublished observations, 1990) have observed PCR experiments where controls did not show any traces of contamination and the ancient extract gave a clearly visible band. Yet these products proved (on sequencing) to be the result of carryover from a previous amplification. Even multiple controls failed to reveal traces of contamination, and this phenomenon has been observed on several occasions in different laboratories. These observations are consistent with either very low levels of contamination or ancient extracts serving as carriers for low-level contaminants that are not detected in the controls. One control that may be of use is to include an extract of unrelated ancient tissue for... 

Finally, contamination of sample spectra can also occur by cross-contamination during sample preparation and by carryover of residual analyte from a sample analyzed earlier in the run.172 173 Essentially, any component of the assay that is reused for each sample or batch of samples can be a source of cross-contamination or carryover. These include, for example, evaporators, pipettors, automated liquid handlers, recycled sample vials, and LC and GC autosamplers. Care needs to be taken in the selection of appropriate wash solvents that will readily solubilize the sample and analytes. This will usually be a combination of high percentage of organic solvents that may include a volatile acidic or basic modifier (e.g., formic acid or aqueous ammonia). Failure to properly wash all sample components from a chromatographic column can result in late eluting components appearing in the next, or later, analytical runs. 

In addition, the use of sippers, transfer tubing, and injectors (manual or otherwise) is not practical or reliable enough for these data collection rates. The complex equipment contains numerous moving parts that can malfunction and cause sampling errors. In addition, these systems are prone to dilution-related errors, contamination, sample carryover, leaks, and blockage by air bubbles and particulate matter. 

Reliable exclusion of cross-contamination (between samples) and carryover (between successive printing processes)... 

Other aspects that should be checked throughout development include matrix interferences (Section 9.6.3), contamination (either general laboratory sources or arising within the sample preparation process itself) and carryover (Section 9.7) all of these can be evaluated by appropriate use of extracts of analyte-free control matrix. 

The fundamental components of a bioanal5dical validation (and aU validations in general) are selectivity sensitivity accuracy precision range of reliable response and linearity and reproducibility. Other characteristics of the method that should be addressed are stability carryover and control of lab contamination and matrix effects, including interferences from metabolites in incurred samples or other co-extracted compounds, as well as ionization suppression. 

Analyze a field blank at the beginning of the set of analyses and every 10 field samples to confirm the absence of contamination and/or carryover effects. 

In the event of contamination or carryover effects, check the source (s) of contamination by running a fiber blank and eventually a column blank (see Section 29.1). 

As the water evaporates into steam and passes on to the superheater, soHd matter can concentrate in a boHer s steam dmm, particularly on the water s surface, and cause foaming and unwanted moisture carryover from the steam dmm. It is therefore necessary either continuously or intermittently to blow down the steam dmm. Blowdown refers to the controHed removal of surface water and entrained contaminants through an internal skimmer line in the steam dmm. FHtration and coagulation of raw makeup feedwater may also be used to remove coarse suspended soHds, particularly organic matter. 

Kinetics of Pesticide Biodegradation. Rates of pesticide biodegradation are important because they dictate the potential for carryover between growing seasons, contamination of surface and groundwaters, bio accumulation in macrobiota, and losses of efficacy. Pesticides are typically considered to be biodegraded via first-order kinetics, where the rate is proportional to the concentration. Figure 2 shows a typical first-order dissipation curve. 

Fig. 12. Ray diagram of carryover coefficients of salts and metal oxide contaminants in steam (6). To convert MPa to psi, multiply by 145.

Condensate Polishing. Ion exchange can be used to purify or poHsh returned condensate, removing corrosion products that could cause harmful deposits in boilers. Typically, the contaminants in the condensate system are particulate iron and copper. Low levels of other contaminants may enter the system through condenser and pump seal leaks or carryover of boiler water into the steam. Condensate poHshers filter out the particulates and remove soluble contaminants by ion exchange. 

Steam Purity. Boiler water soHds carried over with steam form deposits in nonreturn valves, superheaters, and turbine stop and control valves. Carryover can contaminate process streams and affect product quaHty. Deposition in superheaters can lead to failure due to overheating and corrosion, as shown in Figure 6. 

Ammonium Nitrate Plant 7. Prill lower reduce microprill formation and reduce carryover of fines through entrainment. 8. Materials handling where feasible use covers and hoods on conveyors and transition points. Good cleanup practices must be in place to minimize contamination of stormwater mnoff from the plant property. 9. Granulators reduce dust emissions from the disintegration of granules. 

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