Specimen cross-contamination

In a few patients, backflow from blood tubes into veins occurs owing to a decrease in venous pressure. The dangerous consequences of this occurrence may be prevented if only sterile tubes are used for collection of blood. Backflow is minimized if the ai m is held downward and blood is kept from contact with the stopper during the collection procedure. To minimize problems if backflow should occur and to optimize the quality of specimens- especiaUy to prevent cross contamination with anticoagulants—blood should be collected into tubes in the following order (1) blood cul-... 

Appropriate specimen collection and transport conditions are critical to ensure nucleic acid integrity, especially for quantitative methods, and to prevent cross-contamination of specimens. The appropriate specimen type, timing of... 

Common to all analytical procedures (manual, automatic, etc.) is the initial careful measurement of a volume of fluid (in clinical chemistry usually blood, serum, plasma, or urine) as well as volumes of standardizing solutions the accuracy and precision of this single operation are probably the factors that most affect the reliability of the whole procedure for any particular type of analysis. Several different sorts of error may be introduced at this stage the absolute volume of sample measured for each of a batch of replicate analyses may be incorrect the variation from one member of a batch to another in respect of the volume of sample taken may be outside the limits acceptable for the analysis and, when batches of specimens are analyzed, there may be cross-contamination of one specimen with material remaining in the system from the analysis of another specimen. 

Another issue with sampling is possible cross contamination of adjacent specimens or specimen carry-over. At least two options exist The instrument must wash or clean the probe between specimens, a sometimes fallible procedure because large wash volumes must be used if a low enzyme activity specimens follows one with tremendous activity. Alternately, a new pipette tip or probe is used with each specimen as is done on the Kodak Ektachem 700 avoiding the problem of contamination but adding the cost of pipette tips. 

B. Sample/Specimen Collection. Sample/specimen collectors should use full protective gear. If the specimen or sample is to be tested for biological agents, it must be marked as such. Great care should be used to prevent cross-contamination of one sample/specimen by another. Routine medical sampling procedures will be modified so that proving and documenting the BW attack occurred. Contact TAML, USAMRIID, the unit s Chemical Officer and Technical Escort for additional help. 

We present these data on PE crystals as being qualitatively representative of the tensile properties of such crystals but recognize that the quantitative information must be regarded as preliminary. Not only must more accurate knowledge of the specimen cross-sectional area be obtained, but we must make certain the crystal surface is not contaminated with residue suflScient to affect the mechanical properties. 

The TEM specimen is usually thinned by ion-milling crushing will fracture the sample along GBs. This thinning process has been shown to result in cross-contamination of the specimen and in the formation of a groove at the interface. The degree of contamination depends on a large number of factors ... 

Hot-Air Test Tiibe Aging. In this method (ASTM D 865), specimens are heated in air but confined within individual test tubes. This prevents cross-contamination of compounds due to transfer of volatile materials (e.g., antioxidants, curatives, plasticizers, degradation products, and so on) from one sample to another. Thus, this test is free of some of the complications that can occur when numerous compounds are aged in the same enclosure. As before, hardness and tensile mechanical properties are measured before and after aging. 

Corrosion specimens may be unacceptable if they are not prepared properly. One of the major problems is cross contamination during specimen fabrication. Examples of contaminated surface areas of several Grade 702 zirconium specimens from different suppliers are given in Table 1. The specimen preparation can contaminate specimen surface as well when certain operations, such as bending and grinding, are employed. Tools should be clean in specimen-making processes. Surface condition plays an important role in corrosion and is particularly important to zirconium. 

No analytical service can operate efficiently without the internal procedures which can be lumped together under the heading of good housekeeping." Such procedures are basically commonsense routines that ensure that both personnel and instruments function smoothly and reliably, that proper records are kept and kept up-to-the-minute, that specimens are not mislaid, mishandled or cross-contaminated, that reports are compiled and sent on time, that customers are always fully informed, that safety standards are being met. etc. The volume will have much to say about the esoteric aspects of surface and interface analysis. It must always be borne in mind, however, that attention to detail is at least as important to the final outcome. 

Many corrosion specimens from either of the origins described above may contain a plethora of chemical elements when subjected to surface or microanalysis. Some of these could be considered to be contaminants because they arose from processes having little or nothing to do with the corrosion. For example, the internal walls of high-pressure autoclaves are ready sources of cross-contaminants from previous experiments, particularly alkaline and heavy elements. Similar elements precipitate in many industrial heat transport circuits from sources as varied as valve packing to water treatment columns. In the case of the controlled experiment, it is best to remove the source of the contamination and then repeat the run. No such option is available with most failure specimens. 

Contaminating antibodies in the negative control serum are cross-reacting with proteins from the specimen tissue. Replace the negative reagent control serum repeat staining protocol. 127-130... 

The test procedure of lEC Publication 112-1979 refers to the relative resistance of solid electrical insulating materials to tracking up to 600 volts when the surface is exposed under electric stress to water with the addition of contaminants. A horizontal specimen at least 3 mm in thickness and 15x 15 mm plane area is loaded by two platinum electrodes with cross-section of 5 x 2 mm at 1 0.05 N (Fig. 3.116). During the test procedure, the surface between the electrodes is dampened by a liquid droplet 20 3 mm every 30 s. The following standard solutions are used ... 

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