Specification limits, routine monitoring

In addition to recommendations for seawater and seafood testing, shellfish control authorities , which are entities of state or national governments, have the responsibility to determine the risks associated with specific shellfishharvesting waters based on the presence of natural toxins. As a result of routine monitoring, harvesting of seafood from these areas may be limited to certain times of the year or to specific environmental conditions. 

Since many herbicides are crop-specific, herbicide concentrations in farmer s fields are routinely monitored to determine herbicide carry-over. Residual herbicides from the previous year adversely affect alternate crops grown to be grown during the subsequent season. There has been a limited amount of literature describing the successful SFE of herbicides such as sulfonylureas, diruron, linuron, and s-triazines spiked on various solid matrices with COj and methanol modified C02 (1,8-11). Summarized here are the differences in recovery of atrazine from an actual farmer s soil sample as a function of extraction temperature and pressure using both CO2 and methanol modified COj. Also shown are comparisons of recoveries from real vs. spiked samples and also static vs. dynamic modifier addition techniques. 

Method validations and drug substance or finished pharmaceutical product specifications are intimately linked. To ensure transferability of the method and to ensure the method will operate successfully in a QC site, the method variation (from the intermediate precision) should be known and monitored. The method variation is an estimate of the variation that will be experienced in routine use of the method. More method variation will create unacceptable random failure rates, and provide no room for reasonable product variation or even minor stability changes. The method variation should be less than one-third of the interval from the mean or target (typically the midpoint of the upper and lower specification limit) value to the nearest specification limit, or one-sixth... 

One of the main goals of impurity investigations is to determine which impurities need to have specification limits for routine monitoring. 

The ability to provide accurate and reliable data is central to the role of analytical chemists, not only in areas like the development and manufacture of drugs, food control or drinking water analysis, but also in the field of environmental chemistry, where there is an increasing need for certified laboratories (ISO 9000 standards). The quality of analytical data is a key factor in successfully identifying and monitoring contamination of environmental compartments. In this context, a large collection of methods applied to the routine analysis of prime environmental pollutants has been developed and validated, and adapted in nationally or internationally harmonised protocols (DIN, EPA). Information on method performance generally provides data on specificity, accuracy, precision (repeatability and reproducibility), limit of detection, sensitivity, applicability and practicability, as appropriate. 

To improve sensitivity, selected ion monitoring (SIM) mode may be used for the detection of routine YOCs and SVOCs and in low resolution dioxin/furan analysis (EPA Method 8280). In the SIM mode, only specific ions from the analyte s spectrum are scanned for the detector s dwelling time on each ion is increased resulting in higher sensitivity. A mass spectrometer operated in the SIM mode is approximately ten times as sensitive as one in the full scan mode. The SIM mode has limitations, such as the capacity to monitor only a limited number of ions and the need to monitor multiple ions for each compound to improve the degree of confidence in compound identification. That is why typically no more than 20 compounds can be analyzed simultaneously in the SIM mode. 

MS has always been seen as one of the most conclusive techniques for positive identification of organic compounds. The availability, since the beginning of the 1980s, of benchtop GC-MS systems based on quadrupole mass analyzers (GC-Q-MS) made such an analytical tool extremely popular also for routine applications. However, when GC-Q-MS is operated in the full scan mode, limits of detection (LODs) are too high, especially in trace analysis, and its use is seldom restricted to a confirmation technique.When the selected ion monitoring mode (SIM) is employed, the sensitivity is dramatically enhanced. On the other hand, SIM implies the detection of specific analytes with the consequent loss of all other information. 

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