Source sampling

Even while Raman spectrometers today incorporate modem teclmology, the fiindamental components remain unchanged. Connnercially, one still has an excitation source, sample illuminating optics, a scattered light collection system, a dispersive element and a detechon system. Each is now briefly discussed. 

Sample introduction system. A system used to introduce sample to a mass spectrometer ion source. Sample introduction system, introduction system, sample inlet system, inlet system, and inlet are synonymous terms. 

Automated analyzers may be used for continuous monitoring of ambient poUutants and EPA has developed continuous procedures (23) as alternatives to the referenced methods. Eor source sampling, EPA has specified extractive sampling trains and analytical methods for poUutants such as SO2 and SO [7446-11-9] sulfuric acid [7664-93-9] mists, NO, mercury [7439-97-6], beryUium [7440-41-7], vinyl chloride, and VOCs (volatile organic compounds). Some EPA New Source Performance Standards requite continuous monitors on specified sources. 

Source sampling of particulates requites isokinetic removal of a composite sample from the stack or vent effluent to determine representative emission rates. Samples are coUected either extractively or using an in-stack filter EPA Method 5 is representative of extractive sampling, EPA Method 17 of in-stack filtration. Other means of source sampling have been used, but they have been largely supplanted by EPA methods. Continuous in-stack monitors of opacity utilize attenuation of radiation across the effluent. Opacity measurements are affected by the particle size, shape, size distribution, refractive index, and the wavelength of the radiation (25,26). 

The purpose of source sampling is to obtain as accurate a sample as possible of the material entering the atmosphere at a minimum cost. This... 

Brenchley, D. L., Turley, C. D., and Yarmac, R. F. "Industrial Source Sampling." Ann Arbor Science Publishers, Ann Arbor, Ml, 1973. 

FIGURE 10< 108 The procedure to measure the capture efficiency by the tracer gas method, aj The measurement of the reference concentration in the duct, when the tracer is released direcdy into the duct, fb) The measurement of the concentration in the duct, when the tracer is released from the source, / -= sampling point, 2 = pump, J = analyter, 4 - injection of tracer, 5 = tracer gas flow meter, 6 = tracer gas cylinder. 

Source sampling The testing and measurement of an emission at its point of generation. 

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of... 

Taniguchi and Ninomiya [273] and Ninomiya et al. [274] have reviewed TXRF as an inherently surface-sensitive, nondestructive and cost-saving method in the analysis of trace elements and other microcomponents in polymers and other materials. An overview of sources, samples and detectors for TXRF is available [275]. 

Repeated measurements of the same measurand on a series of identical measuring samples result in random variations (random errors), even under carefully controlled constant experimental conditions. These should include the same operator, same apparatus, same laboratory, and short interval of the time between measurements. Conditions such as these are called repeatability conditions (Prichard et al. [2001]). The random variations are caused by measurement-related technical facts (e.g., noise of radiation and voltage sources), sample properties (e.g., inhomogeneities), as well as chemical or physical procedure-specific effects. 

The most satisfactory mechanism used to date to convert the acetylene gas into graphite-like carbon has been electrical dissociation. The apparatus is shown in figure 9. The efficiency of the mechanism of dissociation is strongly dependent upon gas pressure, and after experimentation a pressure of about 10 torr has been selected as optimum. At this pressure, a hard black carbon deposit is observed on the substrate with a thickness of more than 0.1 mm. In the current source, samples produce several microamperes after about 1 hour of running, and this current remains very steady for several hours of operation. 

Excitation of sample atoms by primary radiation from a high-intensity broad spectrum or element selective source. Samples atomized in a chemical flame using a circular burner. Optics to isolate emission line and photomultiplier to measure its intensity. 

In point source sampling, consideration of the topography, in this case (Figure 7.6) the slope and soil type, will be important. Discussion of soil types and sampling is presented in the next section. 

---