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Analyses of Selected Analytical Methods
Of these methods, the two that most often require measurements of multiple components (Courier-type, wavelength dispersive, catalytic) are GC-C and GC-MS, both examples of the new chemistry introduced by the 2002 ASEAN Guidelines. As discussed in Section 7.1, the measurement uncertainties are larger for GC-C, so it is important to collect data to improve the accuracy of the measurement methods if the uncertainty in some or all the analyte concentrations is important. For GC-MS, since the analytes are ionized and detected together, the uncertainty in the ionization efficiency and detection limits, not unlike those discussed in Section 6.2, apply. Furthermore, since GC-MS is the most expensive of the methods, it is important to collect data to optimize conditions and determine whether there are significant differences in performance among instruments and operators.
The Guidelines also introduced a category of analytes that include elements, many important environmental parameters, and radioactive elements. With concentrations as low as parts per trillion, the uncertainties in these measurements are substantial, but they may be important when trying to understand the impacts of low level contaminants, and the effects of concentrations that are too low to measure with precision. Because of the large number of analytes in this category, they are unlikely to become the focus of attention by interested users, and most manufacturers are unlikely to collect data on them.
There are also a number of environmental parameters that have the same concentration as concentrations found in the atmosphere or oceans, and thus no baseline values have been measured, and thus there is no uncertainty in their measurement. For example, the concentrations of the four most abundant gases in the atmosphere are constant. Without a measurement, there is uncertainty in the values being measured; for example, there is no uncertainty in the value of 1013 molecules, but there are uncertainties associated with uncertainties in the values of the other components of 1013 molecules. Therefore, although these parameters are essential for understanding the processes and phenomena in the environment, they will not be the focus of the research in this group of analytes, and no measurements have been taken by most manufacturers, so there are no detailed data to provide values that are better than those provided by the national standards.
There are also a number of analytes where be359ba680
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