Cross-contamination, sampling system

Wilson and McGregor [2S] concluded that it is appropriate to use robotics for grinding materials for geological samples. Studies deahng with cross contamination revealed that even samples containing levels of Ph, Zn or Cr above 1% did not pose a problem, provided that 2S g of sand is used to clean the system prior to the next sample analysis. 

Carryover. Small amounts of analyte may get carried over from the previous injection and contaminate the next sample to be injected [10]. The carryover will affect the accurate quantitation of the subsequent sample. The problem is more serious when a dilute sample is injected after a concentrated sample. To avoid cross-contamination from the preceding sample injection, all the parts in the injector that come into contact with the sample (the injection loop, the injection needle, and the needle seat) have to be cleaned effectively after the injection. The carryover can be evaluated by injecting a blank after a sample that contains a high concentration of analyte. The response of the analyte found in the blank sample expressed as a percentage of the response of the concentrated sample can be used to determine the level of carryover. Caffeine can be used for the system carryover test for assessing the performance of an injector and serves as a common standard for comparing the performance of different injectors. 

Existing systems fail to prevent the loss of evidence from the most significant areas during the period between apprehension and sampling, as well as providing many opportunities for cross contamination to occur. If one could prevent the loss of evidence and confine any contamination risk to the initial arrest procedures, the advantages would be enormous. 

Microchip laboratories have many advantages. They require only tiny amounts of sample. This is especially advantageous for expensive, difficult-to-prepare materials or in cases such as criminal investigations, where only small amounts of evidence may exist. The chip laboratories also minimize contamination because they represent a closed system once the material has been introduced to the chip. The chips also can be made to be disposable to prevent cross-contamination of different samples. 

The fourth major simplification of the procedure is to inject directly from the crimped vial to the HPLC system without a separation step. Fig. 12.3 shows the HPLC injection needle immersed in the aqueous phase sampling through the octanol phase without cross-contamination. 

The premises for the various laboratories should be designed to suit the operations to be carried out in them. Sufficient space should be available to avoid mix-ups, contamination and cross-contamination. There should be adequate and suitable storage space for samples, standards, instruments, equipment, solvents, reagents and records. There should be an alarm system and an adequate system to monitor the temperature of the critical stage and storage areas. If there is an automatic alarm system, it has to be tested regularly to ensure its functionality. Daily temperature records should be kept and all the alarm checks should be documented. 

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. 

With the ever-increasing need to improve quality and productivity in the analytical pharmaceutical laboratory, automation has become a key component. Automation for vibrational spectroscopy has been fairly limited. Although most software packages for vibrational spectrometers allow for the construction of macro routines for the grouping of repetitive software tasks, there is only a small number of automation routines in which sample introduction and subsequent spectral acquisition/data interpretation are available. For the routine analysis of alkali halide pellets, a number of commercially available sample wheels are used in which the wheel contains a selected number of pellets in specific locations. The wheel is then indexed to a sample disk, the IR spectrum obtained and archived, and then the wheel indexed to the next sample. This system requires that the pellets be manually pressed and placed into the wheel before automated spectral acquisition. A similar system is also available for automated liquid analysis in which samples in individual vials are pumped onto an ATR crystal and subsequently analyzed. Between samples, a cleaning solution is passed over the ATR crystal to reduce cross-contamination. Automated diffuse reflectance has also been introduced in which a tray of DR sample cups is indexed into the IR sample beam and subsequently scanned. In each of these cases, manual preparation of the sample is necessary (23). In the field of Raman spectroscopy, automation is being developed in conjunction with fiber-optic probes and accompanying... 

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