Special Sampling Techniques

Each case may provide features which influence the olfactometric measurements, often demanding special sampling techniques and interpretations. In the following some of the problems and experiences will be pointed out by means of examples from sewage treatment and fish meal plants, showing the use of olfactometry for obtaining satisfactory odour reducing results. 

Testing for Legionella requires special sampling techniques and usually requires a period of 14 working days from receipt of the sample to obtain a result. A positive result will include an identification of the Legionella species, and typically also of the serotypes 1 to 6, plus a determination of the number of the bacterium per milliliter of the original sample. 

Testing for low levels of silica, iron, copper, etc. may require special sampling techniques (for example, no glass bottles for silica the addition of a small, known volume of HC1 to the sample bottle, when testing for soluble Fe and Cu, prior to taking the sample no metal lids used). 

In the future, complicated structures which are difficult to be analysed will remain. Further development of this field will require more accurate measurements of diffraction data, consideration of disorders, special sampling techniques, new devices and ideas for analysis of individual samples. 

To prevent trace level contamination, the EPA established special sampling techniques for trace elements in ambient water in Method 1669 (EPA, 1996c). The EPA also provided the guidance for clean room laboratory analysis and for documentation and evaluation of trace element data (EPA, 1996d EPA, 1996e). 

Several special sampling techniques should be mentioned. Many analyses are simplified by taking a sample from the vapor over the liquid sample. This procedure is known as headspace analysis.61 Another method known as purge-and-trap is used to concentrate a sample to improve detection limits. It is very popular in pesticide residue and drinking water analyses. 

The classical Raman effect produces only very weak signals. There are two techniques which very successfully enhance this effect. The resonance Raman spectroscopy RRS is making use of the excitation of molecules in a spectral range of electronic absorption. The surface-enhanced Raman spectroscopy SERS employs the influence of small metal particles on the elementary process of Raman scattering. These two techniques may even be combined surface-enhanced resonance Raman effect SERRS. Such spectra are recorded with the same spectrometers as classical Raman spectra, although different conditions of the excitation and special sample techniques are used (Sec. 6.1). 

To obtain surface enhanced Raman spectra from adsorbates, special sample techniques are required to produce surface roughness or small clusters either isolated in solution or as powders at surfaces. Several techniques have been described in detail in the literature (see for example Cooney et al., 1982 Cotton, 1988). 

Measurements using two samplers that had different upper range particle-size cutoffs indicated that during rain and fog the airborne salt shifts from aerosol-sized particles to droplets of approximately SO-jitm diameter (upper range of fog droplets) or greater. Consequently, the determination of the total concentration of atmospheric salt would require special sampling techniques to deal with both wet and dry particles of all sizes. 

In all work on the determination of whole blood concentrations of manganese, stainless steel needles seem to have been used. Since the concentration of manganese in whole blood is at least 10 times greater than in serum, the effect of contamination will be proportionally smaller. Nevertheless if reliable values for manganese in whole blood are to be achieved, the use of special sampling techniques would seem to be necessary. 

A special sampling technique often applied for infrared studies of biological systems is attenuated total reflection spectroscopy or ATR spectroscopy. With this technique, the infrared beam is guided through a transparent medium of high refractive index (plate, often crystalline material) in such a way that several total reflections take place at the surfaces. Ideally, if the surfaces are clean, the infrared beam is not attenuated. However, if an infrared absorber is deposited onto the surface, the infrared... 

A bubble formed at the interface of the two polyetherimide filinis. A special sampling technique was employed and gas chromatographic analysis of the bubble performed. The sampling technique consisted of placing the coated specimen into a flask which was connected to a gas chromatograph equipped with a thermal conductivity detector. 

Internal column diameters for fused silica range from 100 to 530 micrometers (0.10-0.53 mm). Some glass capillaries have even larger internal diameters. One-hundred micrometer columns, row one of Table 6.2, have limited sample capacity, and are not well suited for trace analysis. Ease of operation is also limited because of the very limited sample capacity. These small i.d. columns have very good efficiency and produce fast analyses (see Fig. 6.6), but special sampling techniques and high-speed data systems are required to realize their full potential. 

Other topics that are covered briefly are the separation of chiral compounds, some special sampling techniques (headspace and solid phase microextraction) and derivatization. 

Concentration inhomogeneities may be caused by mixing different materials or the same type of materials with different concentrations. If the inhomogeneities are in a macroscopic scale comparable to the sample cuvette size or the volume of the optical cell in which the measurement occurs, the local concentration variation will affect the measurement. Beyond the concentration variation of the sample, the optical physical characteristics of the sample also have a profound effect on the result therefore, special sampling techniques must be developed. 

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