Environmental tests with instrumentation

Next, the zero-gap reference position (the contact point where the stator and the rotor just touch) should be set using the software routines for bringing rotor and stator into contact. After this, the gap used for the test itself can be set. Generally, the zero-gap referencing procedure should be done at the temperature of interest for testing. Some instruments control temperature using an environmental chamber or oven, whereas others will heat or cool the stator. If the latter is the case, then for temperatures that are well away from ambient, the gap can be referenced at ambient and the temperature of interest set with the sample in place to aid thermal conductivity. This is reasonable if the instrument has a gap temperature compensation factor. Most autogap instruments will have this facility built into the firmware that controls the rotor position with respect to the stator. 

Over time, a large number of traditional laboratory instruments have been morphed to meet industrial needs for QC applications. Example applications include raw material, product QC and also some environmental testing. In such scenarios laboratory instruments appear to work adequately. Having said that, there are issues the need for immediate feedback and the need for smaller, cheaper, and more portable measurements. There is a growing interest in the ability to make measurements in almost any area of a process, with the idea that better production control can lead to a better control of the process and of the quality of the final product. The cost of implementation of today s (2004) process analyzers is still too high, and it is impractical to implement more than a couple of instruments on a production line. Also, there is growing concern about the operating environment, worker safety, and environmental controls. 

Mass spectrometer (MS) [S] sales have always been high, especially since MS is the principal detector in a number of hyphenated techniques such as GC-MS, MS-MS, and LC-MS. The GC — MS combination accounts for about 60% of MS sales since it is used widely in drug and environmental testing. Innovations in interface technology such as inductively coupled plasma (ICP)-MS, FC-MS and thermospray or particle beam interfaces for LC-MS have both advanced the technology and expanded the interest in applications. Recent introductions of lower cost MS instruments with automated sampling and computerized data analysis have added to the attraction of the technique for first-time users. 

Atomic emission spectroscopy (AES) and atomic absorption spectroscopy (AAS) are In a manner similar to our discussion of molecular spectroscopy, where we compared UV absorption with UV excitation and subsequent fluorescence, these two determinative approaches are the principal ways to identify and quantitate trace concentration levels of metal contamination in the environment. As the need developed to quantitate increasing numbers of chemical elements in the Periodic Table, so too came advances in instrumentation that enabled this to be achieved at lower and lower IDLs AES and AAS techniques are both complementary and competitive. Atomic fluorescence spectroscopy (AFS) is a third approach to trace metal analysis. However, instrumentation for this has not as yet become widespread in environmental testing labs and it is unlikely that one would see atomic or what has become useful x-ray atomic fluorescence spectroscopy. Outside of a brief mention of the configuration for AFS, we will not cover it here. 

On the simplest type of instrument (an explosimeter) only one scale is provided, usually with readings from 0 to 100% LEL. However, the detectable changes produced by combustion are too small to be measured accurately in the presence of the low concentrations of contaminants usually encountered in evaluating potential health hazards. For example, the LEL of even the most explosive gas is of the order of 1 %, or 10,000 ppm, which is well in excess of the toxic limit for any gas. Therefore, explosimeters or combustible gas indicators which have only a 0-to-l(X)% LEL explosive scale are not suitable for environmental health testing in the ppm range. More sensitive instruments, including the type used in sampling for environmental health purposes, have a dual scale, in which the second, more... 

Some tanks are installed with permanent leak identification sensors, which can check for leaked fuel vapor or liquid as it comes into contact with the sensors.21 However, these, as well as all the environmental sign tests (visual or instrumental) may be triggered by a spill instead of a leak. The success of external systems depends on the sensitivity of the sensor, the ability of the sensor to distinguish the stored chemical from other chemicals, the ambient background noise level of the stored chemical, the migration properties of the chemical, and the sampling network. 

Level 1 sampling provides a single set of samples acquired to represent the average composition of each stream. This sample set is separated, either in the field or in the laboratory, into solid, liquid, and gas-phase components. Each fraction is evaluated with survey techniques which define its basic physical, chemical, and biological characteristics. The survey methods selected are compatible with a very broad spectrum of materials and have sufficient sensitivity to ensure a high probability of detecting environmental problems. Analytical techniques and instrumentation have been kept as simple as possible in order to provide an effective level of information at minimum cost. Each individual piece of data developed adds a relevant point to the overall evaluation. Conversely, since the information from a given analysis is limited, all the tests must be performed to provide a valid assessment of the sample. 

As for the second condition, usually the spectral response, which is provided by the instrument manufacturers, is used. For the erythemal broadband detectors, it has been demonstrated that regular testing of their spectral sensitivity is needed, in addition and prior to their absolute calibration. This is because their spectral sensitivity is determined fiom a series of optical filters and other components (e.g. the phosphor layer) that may degrade with time or with environmental conditions (e.g. humidity), changing therefore its characteristics. 

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