Blanks, field quality control sampling

At least 10 % of the samples should be quality control samples. Blank sampling cartridges should be taken to the field and returned to the laboratory for analysis however, they should not be exposed to the air. Spiked sampling media may also be similarly transported as field controls. 

Once sampling is completed, sampling media should be placed immediately in appropriate clean, sealed containers and placed on ice or dry ice for return or shipment to the laboratory. The sealed containers should be placed in a freezer maintained at -20 °C or lower until extracted. Media should not be stored for more than about two weeks. Frozen extracts may be safely stored for 90d or more. At least 10% of the samples shonld be quality control samples. Blank media should be taken to the field, briefly removed from the containers to air, and then retnmed to the laboratory for analysis. 

Apart from these samples, some other quality control samples such as duplicate samples and equipment field blanks are used by different laboratories. Duplicate samples are taken from the same collection site to determine the variability of results for the same sample after the AMS analysis. Generally, one duplicate sample should be collected for every 20 samples. Equipment blanks are collected using laboratory-provided water, which has been run over the decontaminated soil sampling equipment. These samples are used to determine the efficiency of cleaning procedures for soil sampling equipment. 

The types and amount of quality control used during the field component of a study can vary depending on the data requirements of the stu. At a minimum, field blanks should be used to identify any contamination either through direct contact or airborne exposure of the sample. Other quality control samples to be considered include equipment blanks, if the same sampling equipment is repetitively used, trip blanks (contaminant-free water samples which accompany the field collected samples from the field to the laboratory but are not exposed to the air), and positive control... 

Examples of quality assurance protocols that are considered standard practice in any data collection scheme include the use of both internal control samples (e.g. use of field blanks and spikes6) and external quality assurance samples (e.g. duplicate samples of known concentrations sent to different laboratories) to determine the extent of intra- and interlaboratory variation. Ensuring that the data have not been compromised or corrupted may also require setting up accessible data archives of original paper or electronic records so that the accuracy of summaries of the data published in documents and articles can be verified. 

Quality control procedures are generally established to provide checks on the data that have been collected to evaluate whether in fact the quality assurance procedures were followed and whether the data meet agreed-upon norms. Otherwise, it is difficult for the user to judge the integrity of a data set per se, because there may be few ways to tell that procedures were not followed or values properly recorded. Quality control measures can be linked to the quality assurance procedures. In the example given above for use of field blanks, spikes and duplicate samples, laboratories must provide evidence that their analysis of these samples meets acceptable statistical guidelines for accuracy and precision. Quality control can also simply involve careful analysis of a data set to determine whether it is internally consistent. 

Quality control procedures (5-7) in the field included semiannual audit visits. These procedures were employed to maximize capture of uncontaminated samples, to identify and document them, to preserve their integrity until their arrival at the laboratory, to obtain dynamic blanks and to determine each site s precision and accuracy of pH and conductivity measurement. (The field measurements were used as a quality control to determine if precipitation samples had degraded between the field and laboratory measurements.)... 

A set of quality control parameters includes field blank, field fortified blank, md field fortified sample. 

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