Measuring sample

B. W. Loo, J. M. JaMevic, and F. S. Goulding, "Dichotomous Virtual Impactors for Large Scale Monitoring of Airborne Particulate Matter," in B. Y. H. Liu, ed., Eine Particles, Aerosol Generation, Measurement, Sampling and Analysis, Academic Press, Inc., New York, 1976, pp. 311—350. 

B. Y. H. Liu, ed.. Tine Particles—-Aerosol Generation, Measurement, Sampling and Analysis, Academic Press, Inc., New York, 1976. 

Atomic Absorption Spectroscopy. Mercury, separated from a measured sample, may be passed as vapor iato a closed system between an ultraviolet lamp and a photocell detector or iato the light path of an atomic absorption spectrometer. Ground-state atoms ia the vapor attenuate the light decreasiag the current output of the photocell ia an amount proportional to the concentration of the mercury. The light absorption can be measured at 253.7 nm and compared to estabUshed caUbrated standards (21). A mercury concentration of 0.1 ppb can be measured by atomic absorption. 

Neutron Activation Ana.lysis, A measured sample activated by neutron bombardment emits gamma rays that are used to determine the mercury content by proton-spectmm scanning. Mercury concentrations as low as 0.05 ppb have been determined by this method. 

Because of water s plasticizing effect, the water content of nylon fibers and fabrics must be known and controlled when measuring physical properties. Prior to the measurement, samples are conditioned at a specified temperature and rh for at least 24 h. 

For determination of the aerodynamic diameters of particles, the most commonly apphcable methods for particle-size analysis are those based on inertia aerosol centrifuges, cyclones, and inertial impactors (Lundgren et al.. Aerosol Measurement, University of Florida, Gainesville, 1979 and Liu, Fine Paiiicles—Aerosol Generation, Measurement, Sampling, and Analysis, Academic, New York, 1976). Impactors are the most commonly used. Nevertheless, impactor measurements are subject to numerous errors [Rao and Whitby, Am. Ind. Hyg. A.s.soc.]., 38, 174 (1977) Marple and WiUeke, "Inertial Impactors, in Lundgren et al.. Aerosol Measurement and Fuchs, "Aerosol Impactors, in Shaw, Fundamentals of Aerosol Sci-... 

Reactive System Screening Tool (RSST) The RSST is a calorimeter that quickly and safely determines reactive chemical hazards. It approaches the ease of use of the DSC with the accuracy of the VSP. The apparatus measures sample temperature and pressure within a sample containment vessel. Tne RSST determines the potential for runaway reactions and measures the rate of temperature and pressure rise (for gassy reactions) to allow determinations of the energy and gas release rates. This information can be combined with simplified methods to assess reac tor safety system relief vent reqiiire-ments. It is especially useful when there is a need to screen a large number of different chemicals and processes. 

After the flov/ measurement, sample the discharge stream to a continuous Flame Ionization Detector (FID) that works as an Analyzer Indicator Transmitter CYIT). The Flow Controller (FC) reads the TCE concentration signal and adjusts the flow to keep the TCE at the set level of, say, 250 ppm. 

Several manual and continuous analytical techniques are used to measure SO2 in the atmosphere. The manual techniques involve two-stage sample collection and measurement. Samples are collected by bubbling a known volume of gas through a liquid collection medium. Collection efficiency is dependent on the gas-liquid contact time, bubble size, SO2 concentration, and SO2 solubility in the collection medium. The liquid medium contains chemicals which stabilize SO2 in solution by either complexation or oxidation to a more stable form. Field samples must be handled carefully to prevent losses from exposure to high temperatures. Samples are analyzed at a central laboratory by an appropriate method. 

None, except there are techniques that measure sample thickness... 

Fig. 7. The Hall coeffieient (left seale) and conduetance (right seale) vs temperature. R was determined using the measured sample dimensions without any eorreetion.

In the previous section it has been shown that the measured sample absorbance may be higher than the true absorbance signal of the analyte to be determined. This elevated absorbance value can occur by molecular absorption or by light scattering. There are three techniques that can be used for background correction the deuterium arc the Zeeman effect and the Smith-Hieftje system. 

In order to indicate the accuracy that can be obtained from a capillary pipette, one may refer to the so called Sahli pipette, which is approximately 80 mm from mark to tip. This pipette is used as a washout pipette and can measure samples which are readily reproducible to 1 part in 80, since it is a relatively simple thing for the eye to see 1 mm. On the other hand, if one places a bulb in the tube, and cuts the bore down at the mark by 30%, then this would decrease the error by a factor of 4. It is thus practicable to sample from a micropipette, which is used as a washout pipette, with greater accuracy than one can sample from a conventional macro pipette, which delivers 1 ml by blowout, or to deliver. Figures5 and 6 illustrate various designs of micropipets (13,14). 

For these reasons, the plastic tip, or the siliconed glass tip have been used for micro measurements. With a plastic tip, there is no limit to the size of the specimen which may be sanq>led. For example, it is possible to sample amounts of the order of nanoliters, provided one resorted to a micromanipulator. While the clinical chemist has not availed himself generally of this technique, the physiologist, has for many years, been measuring samples from within a single cell, or from perhaps, a renal tubule, so that the sample can then be subsequently analyzed. It awaits only an intelligent manufacturer to adapt the micromanipulator as a routine tool in the Pediatric... 

At present, several of the instruments which are being utilized for enzyme analysis, such as the centrifugal analyzers (15), have been measuring samples of the order of 5 pi. 

Other early alpha spectrometry studies examined U-series disequilibria in East Pacific Rise (EPR) samples. Newman et al. (1983) measured samples from the RISE study area (21°N EPR) finding significant variations in Th/U and ( °Th)/( U) (Fig. 2B). Rubin and Macdougall (1988) measured ( °Th)/( U) and ( Ra)/( °Th) for samples from both the northern ( 10-12°isn and southern (-20-25°) EPR (Fig. 2C,D). This study was first to document large disequilibria in young MORB and interpreted the... 

The use of direct UV spectrophotometry to measure sample concentrations in pharmaceutical research is uncommon, presumably because of the prevalence and attractiveness of HPLC and LC/MS methods. Consequently, most researchers are unfamiliar with how useful direct UV can be. The UV method is much faster than the other methods, and this is very important in high-throughput screening. 

Only in a few cases are test samples measurable without any treatment. As a rule, test samples have to be transformed into a measurable form that optimally corresponds to the demands of the measuring technique. Therefore, sample preparation is a procedure that converts a test sample into a measuring sample. Whereas test samples represent the material in its original form, measuring samples embodies a form that is able to interact with the measuring system in an optimum way. In this sense, measuring samples can be solutions, extracts, pellets, and melt-down samples, but also definite surface layers and volumes in case of micro- and nanoprobe techniques. 

Measuring samples are considered as being composed of the analyte (Prichard et al. [2001]) and the matrix. The term matrix summarizes all the sample constituents apart from the analyte. The relationships between the amounts of sample, analyte, and matrix are given by ... 

Sample preparation is directed to the conversion of test samples in a physically and chemically measurable form. The measuring sample can require a definite state (gaseous, liquid, or solid) or form (aqueous or organic solution, melt-down tests, and pellets). In other cases, measuring samples have to become diluted or enriched to get an optimum concentration range. It may also be necessary to remove interfering matrix constituents which disturb the determination of the analyte. 

Measuring sample of organic [Pg.53]

Fig. 2.10. Composition of a test sample of wine (schematic representation in the middle the size of each area symbolizes the relative amount of the respective component or sort of constituents) and of the measuring samples of inorganic and organic components, respectively (left and right diagrams)...

Sometimes it is necessary to apply two (or more) variants of sample preparation to get different measuring samples from only one test sample. This is the case if various problems have to be solved, e.g. determination of major- and ultra trace constituents, comparison of depth- and surface profiles, or analysis of inorganic and organic trace components in the same test sample. An example is shown in Fig. 2.10 where in a test sample of wine both inorganic and organic trace constituents have to be determined and, therefore, different measuring samples must be prepared. 

Fig. 2.11. Elastic and inelastic interactions between energy and measuring sample... 

The interactions to which the measuring samples are exposed can be of elastic or inelastic type (in the physical sense). Figure 2.11 shows schematically the difference between elastic and inelastic interactions. 

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