Sample cross-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. 

Sample management error improper sample storage analysis of samples that have reached the end of their holding time misplaced or mislabeled samples sample cross-contamination... 

The purpose of trip blanks is to assess the collected sample representativeness by determining whether contaminants have been introduced into the samples while they were handled in the field and in transit, i.e. in coolers with ice transported from the site to the analytical laboratory. A possible mechanism of such contamination is the ability of some volatile compounds, such as methylene chloride or chlorofluor-ocarbons (Freons), to penetrate the PTFE-lined septum and dissolve in water. Potential sources of this type of contamination are either ambient volatile contaminants or the VOCs that could be emanating from the samples themselves, causing sample cross-contamination. To eliminate ambient contamination, samples must not be exposed to atmospheres containing organic vapors. Cross-contamination is best controlled by such QA measures as sample segregation and proper packaging. 

Storage blanks (40 mL vials with analyte-free water) are placed in cold storage with samples for VOC analysis. Regular analysis of storage blanks enables laboratories to detect whether sample cross-contamination may have taken place in cold storage. 

Inadequate glassware cleaning procedures may produce false positive results due to sample cross-contamination. 

Sample cross-contamination in cold storage and in preparation... 

A single microchannel has been used for sequential MS analysis of multiple samples. In this case, no sample cross-contamination has been reported. For instance, no sample crossover was observed for 10 iM cytochrome c versus 10 iM ubiquitin [943], and tryptic digests of [3-lac, CA, and BSA [776]. In another report, sequential infusion of tryptic digests of CA (290 nM) and BSA (130 nM) into ESI-ITMS was achieved using EOF. No cross-contamination resulted when a central flow of buffer confined the other samples in the reservoir and channel by precise voltage control [801]. 

Selenium has also been investigated extensively with ICP-MS. It can be efficiently introduced into the plasma by hydride generation in order to improve detection limits. The analyte is efficiently transported into the plasma as a gas and the sample matrix is left behind. The hydride generator design can influence interferences and sensitivity [258]. Sample cross-contamination was eliminated when the air bubble normally entrained between samples was removed [258]. Isotope dilution can be used to obtain high accuracy. 

Hiac ABS-2 automatic bottle sampler is a pressure sampling device used for batch analysis of volatile or viscous fluids. The ABS-2 delivers liquid to the sensor at flow rates of 10 to 200 ml min T A check valve in the sample introduction line eliminates backflow and minimizes sample cross contamination, and an automatic drain mechanism allows unattended sample analysis of multiple runs. The sampler has a built-in pressure/vacuum chamber that subjects samples to pressures up to 60 psi, accommodating viscosities up to 80 centistokes. In addition, vacuum levels of 23 psi are used to degas samples which contain entrained air. 

Fregeau, C., Yensen, C., Elliott, I, and Foumey, R. (2007) Optimized configuration of fixed tip robot liquid handling stations for the elimination of biological sample cross contamination. Journal of Laboratory Automation, 12, 339 354. 

Due to the better performances and the versatility olfered by the design, the modular interface, based on the use of commercially available Picotip emitters, was used in the final setup. The modular integration allows the replacement of the spraying tips, independently from the more expensive chips, as often as required to avoid sample cross-contamination. More importantly, the microreactors can be easily replaced, oflering the possibility to study a wide variety of chemical reactions as demonstrated, for example, in the qualitative and quantitative determination of the binding strength of supramolecular interactions as well as the study of the kinetics of NBDPZ. 

To increase throughput and eliminate sample cross contamination, which is common when analyzing cells sequentially, Munce et al. [22] developed a microfluidic device with four parallel CE channels. Calcein-labeled acute myeloid leukemia cells were selected and transported with optical tweezers to injector structures at the entrance of each channel, as shown in Fig. 3a. Once loaded, the cells were lysed by the combined action of an applied electric field and the reduction in channel cross section (Fig. 3b). The injector design also enabled stepwise lysis of the cell, shown in Fig. 3c, where only the cytoplasmic material (containing calcein AM in green) was injected into the capillary, while the nucleus (stained blue with Hoechst 33342) remained in the injector structure. This selective lysis is especially useful to separate the cytoplasm from the... 

Samples were collected utilizing a sampling kit that featured individually sealed collection tools to avoid sample cross-contamination. For the CBDE exercise, samples were collected by personnel in full protective gear. The different sample types included soils, liquids, and swipes from a CW pilot plant. These samples were collected near or from chemical storage tanks and suspect CW production equipment. Using a "chain of custody" protocol, the samples were processed at the sample work-up station for analysis. 

It is important to note at this point that cell sorting performance should not be judged solely on speed. Conventional flow cytometers are very expensive to purchase and operate, and are therefore only found in large research facilities or hospitals. Microfluidics has demonstrated that cell sorting, in multiple formats geared for tailored applications, can become available to all researchers and clinicians since these devices can be made cheaply and configured with commercially available instrumentation. In addition many of the microfluidic technologies allow for disposability which reduces the problem with sample cross-contamination, sterility, and biosafety (when... 

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