Carryover contamination

When bubbles accumulate at the steam-water interface, dissolved solids pass into the post-boiler steam section, and this carryover contaminates the steam and causes fouling of the system. Where the foam-... 

Tl. Thornton, C. G., Hartley, J. L., et al., Utilizing uracil DNA glycosylase to control carryover contamination in PCR Characterization of residual UDG activity following thermal cycling. Biotechniques 13(2), 180-184 (1992). 

Is there a better PCR technique Over the past few years different authors have described other 16S rDNA-based PCR methods. Spaepen et ah (1992) used a nested PCR system with great sensitivity, but the use of a second amplified cycle dramatically increased the risk of DNA carryover contaminations, van Kuppeveld et al. (1994) reported a single PCR system that seems to be very suitable to detect cell culture contamination but it requires a DNA extraction stage, which is very time consuming. Moreover, a new marked PCR method is available (Stratagene, CA). The primers used make it possible rapidly to (4-5 h) test eukaryotic cells for mycoplasma infection but this method seems to be less sensitive than our PCR technique. 

All reagents used for the PERT assay must be free of any contaminating MS 2-DNA. To avoid carryover contamination, set up at least two different rooms for work with materials before and after PCR. Use different sets of equipment, chemicals, and disposables. If possible, avoid the use of pH probes and spatula. If glass ware is used, do not have them washed in a central facility (where it can get contaminated), wash and bake it personally (at 240°C for 5 h). It may be a good idea to have a friend at a different location (where no work with MS2 is carried out) who can prepare solutions. Use only positive displacement pipetes or pipet tips with filters especially for PCR. The published recommendations in ref. 17 are useful. 

Nested PCR reactions can offer significant advantages in sensitivity and specificity yet are prone to carryover contamination of the second reaction that uses the internal primer set. Such contamination cannot be prevented by the sterilization methods described above. Future nested systems may incorporate both the external and internal primers in the same reaction, wherein intentional differences in annealing and denaturation temperatures of the respective primers or target sequences would only permit the intended target to function in primer annealing, denaturation, and synthesis (E6, Y2). 

Kit manufacturers provide instmctions on measures used to prevent and monitor potential issues during sample preparation and analysis. To prevent carryover contamination, one of the companies recommends the use of separate areas for DNA preparation, reaction setup, and amplification, encouraging that manipulation of PCR products never be performed in the PCR setup or DNA extraction dedicated labs. Also, this kit includes dUTP instead of dTTP, which allows the use of uracil A-glycosylate to prevent PCR product carryover contamination (see Section 9.5.5). 

Longo MC, Beminger MS, Hartley JL (1990). Use of uracil DNA glycosylase to control carryover contamination in polymerase chain reactions. Gene, 93 125-128. 

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. 

Steam can be contaminated with soHds even when carryover is not occurring. Contaminated spray attemperating water, used to control superheated steam temperature at the turbine inlet, can introduce soHds into steam. A heat exchanger coil may be placed in the boiler mud dmm to provide attemperation of the superheated steam. Because the mud dmm is at a higher pressure than superheated steam, contamination will occur if leaks develop in the cod. 

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. 

Dip in palladium chloride solution (this gives only modest adhesion and carries the danger of contamination of the bath by solution carryover). 

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 formation of superheater deposits in and around the superheater tube outlets and receiving header is a relatively common but serious superheater problem that may occur. These deposits are caused by contamination from BW carryover and also by gross contamination of attemperation water used to control the degree of superheat. 

Operational problems, such as BW foaming and surging (priming) all ultimately lead to BW carryover and the resultant contamination of steam and condensate lines. 

Carryover refers to the entrainment of BW (and the contaminating solids contained in the water) into the steam. Contamination of steam from entrained water may lead to deposits in superheaters, on turbine valves, and in steam traps, valves, and flash vessels. 

Higher rates of sludging also take place in the boiler vessel. In turn, this potential fouling problem requires additional maintenance time because more frequent internal surface cleaning, wash-down, and boiler vessel sludge removal usually is required. Carryover of contaminants into the steam also is more likely. 

Additional problems that may cause serious contamination of the treated MU water are those related to carryover and after-precipitation from external treatment processes. Both of these processes may result in the presence of insoluble solids in the various lines, tanks, and valve areas of the pre-boiler section. Some solids may even pass through to the boiler. 

Condensate contamination originates from several sources, including BW carryover into the generated steam, corrosion debris pickup... 

Process leaks of sugars, fats, colloidal materials, pectins, emulsions, and proteins cause stable foams in the boiler, leading to carryover and a further contamination cycle. 

Process contamination. Sticky films (LP boilers) Varnish (HP boilers) Steam discoloration FW pH fluctuations Acid corrosion Stable foams leading to carryover... 

As discussed previously, serious fouling, deposition, and corrosion problems may occur in the FW line as a result of the entry of carryover, after-precipitation, corrosion debris pickup, or oxygen and other contaminants, from either the MU or returning condensate. 

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. 

Carryover is the term for BW (containing some level of contaminant) that is entrained in the steam and passes into the steam header and main distribution lines. Carryover is always detrimental to the steam cycle process and produces problems of ... 

Process leaks from food and beverage production or wood leachates often produce sugars, colloidal materials, pectins, emulsions, and proteins that cause stable foams in the boiler. These lead to carryover and further steam-condensate line contamination. The temporary use of a demulsifier or defoamer as part of the water treatment program may be of particular benefit, but again the condensate is unsuitable for return to the boiler. Other process leaks include ... 

---