Altering instrumental

Extensive applications experience has shown that most particulate materials can be analyzed without any consideration of the refractive index. This is generally true because most practical materials have a high index, or are somewhat absorbing. In the exceptional case in which refractive index corrections must be applied, the values of the real and complex indices must be determined carefully. Arbitrary use of index corrections to arbitrarily alter instrument calibration may produce highly erroneous results. Table I serves as a guide to the effects of the refractive index on small particle measurements. 

The most notable applications are the determinations of Na, K. Ca and Mg in body fluids and other biological samples for clinical diagnosis. Simple Alter instruments generally provide adequate resolution for this type of analysis. The same elements, togetlier with B, Fe, Cu and Mn, are important constituents of soils and fertilizers and the technique is therefore also useful for the analysis of agricultural materials. Although many other trace metals can be determined in a variety of matrices, there has been a preference for the use of atomic absorption spectrometry because variations in flame temperature are much less critical and spectral interference is negligible. Detection limits for flame emission techniques are comparable to those for atomic absorption, i.e. from <0.01 to 10 ppm (table 8.6). Flame emission spectrometry complements atomic absorption spectrometry because it operates most effectively for elements which are easily ionized, whilst atomic absorption methods demand a minimum of ionization (table 8.7). 

Valdes and Summers (49) reported NIR determination of fat and protein in poultry. Whole carcasses from 3-week-old broilers and from 7-week-old broilers were ground, and NIR spectra were determined (19-wavelength Alter instrument). The prediction errors were reported to be 2.0-2.6% for fat and 1.0-2.0% for protein. Windham et al. (51) report a study with a fat range from 1% to 65%, giving SEP values from 0.38% to 0.84% fat. 

Sucrose Cake mixes InfraAzer 400R, Alter instrument, reflectance HPLC 38... 

The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

Apart from the need for a specialized instrument, sample preparation before analysis is extremely important for reliable results. The sample preparation must not itself alter the ratios of isotopes in the samples under investigation. 

The bot-wire anemometer consists essentially of an electrically heated fine wire (generally platinum) exposed to the gas stream whose velocity is being measured. An increase in fluid velocity, other things being equal, increases the rate of heat flow from the wire to the gas, thereby tending to cool the wire and alter its electrical resistance. In a constant-current anemometer, gas velocity is determined by measuring the resulting wire resistance in the constant-resistance type, gas velocity is determined from the current required to maintain the wire temperature, and thus the resistance, constant. The difference in the two types is primarily in the electric circmts and instruments employed. 

These are auxiliary CTs, and are sometimes necessary to alter the value of the secondary of the main CTs. They help to reduce the saturation level and hence the overloading of the main CTs, particularly during an overload or a fault condition. They are used especially where the instruments to which they are connected are sensitive to overloads. They have to be of wound primary type. So that the main CTs are not overburdened they have a VA load that is as low as possible. Figure 15.20 illustrates the application of such CTs and their selection is made on the following basis ... 

In addition to cleanliness (contamination effects), surface morpholt and the alteration of composition during specimen preparation can cause serious artifacts in microanalysis. In some older instruments, the microscope itself produces undesirable high-energy X rays that excite the entire specimen, making difficult the accurate quantitation of locally changing composition. Artifacts also are observed in the EDS X-ray spectrum itself (see the article on EDS). 

Many accidents have occurred because instrument readings or alarms were ignored (see Sections 3.2.8, 3.3.1, and 3.3.2). Many other accidents, including Bhopal (see Section 21.1), have occurred because alarms and trips were not tested or not tested thoroughly, or because alarms and trips were made inoperative or their settings altered, both without authority. These and some related accidents are described below. 

By the use of suitable shunts, the basic moving-coil movement can be adapted to measure m almost unlimited range of currents. Figure 10.46 illustrates a direct-indicating instrument with shunt, to measure current up to 5 A d.c. To ensure that the resistance of the circuit is not materially altered by the insertion of an ammeter, it is usual to install either a shunt or the meter itself (usually a moving-coil meter with internal shunt) permanently in the circuit. Ammeter shunts are normally of the four-terminal type, to avoid contact resistance errors, i.e. two current terminals and two potential terminals, as shown, in fig. J0.46. 

Application of Beer s Law. Consider the case of two solutions of a coloured substance with concentrations c, and c2. These are placed in an instrument in which the thickness of the layers can be altered and measured easily, and which also allows a comparison of the transmitted light (e.g. a Duboscq colorimeter, Section 17.5). When the two layers have the same colour intensity ... 

Flammable atmospheres can be assessed using portable gas chromatographs or, for selected compounds, by colour indicator tubes. More commonly, use is made of explos-imeters fitted with Pellistors (e.g. platinum wire encased in beads of refractory material). The beads are arranged in a Wheatstone bridge circuit. The flammable gas is oxidized on the heated catalytic element, causing the electrical resistance to alter relative to the reference. Instruments are calibrated for specific compounds in terms of 0—100% of their lower flammable limit. Recalibration or application of correction factors is required for different gases. Points to consider are listed in Table 9.10. 

Meteorites on Mars. Meridiani Planum is the first Iron meteorite discovered on the surface of another planet, at the landing site of the Mars Exploration rover Opportunity [359]. Its maximum dimension is 30 cm (Fig. 8.38). Meteorites on the surface of solar system bodies can provide natural experiments for monitoring weathering processes. On Mars, aqueous alteration processes and physical alteration by Aeolian abrasion, for example, may have shaped the surface of the meteorite, which therefore has been investigated intensively by the MER instruments. Observations at mid-infrared wavelengths with the Mini-TES... 

When developing or routinely using an analytical method, quality control (QC) fortifications can be added to each sample at critical points in the procedure to ensure that sensitive steps in the method were conducted properly and to pinpoint where problems occurred if results are less than satisfactory. For example, if the QC fortification samples for detection and cleanup were to show acceptable results in a batch of samples, but the extraction QC spike gave low recovery and/or high variability, then the analyst could modify instrument conditions or altering cleanup parameters immediately. Likewise, if the QC spike added just before analysis gives poor results, then instrument maintenance could be done and the samples merely re-analyzed rather than re-extracted. 

Force the solution through the Alter cartridge into a clean glass vial with a TeAon-lined lid for storage. Just prior to analysis, this Altered extract is diluted 1 1 (v/v) with internal standard solution. The combination of exAact with internal standard solution may be made directly into the instrument autosampler vial. 

Attach a 25-mm Acrodisc nylon Alter carAidge to the LuerLok Atting of a 10-mL disposable syringe, and transfer approximately 1.5 mL of extract to the syringe barrel. Force the solution through the Alter carAidge directly into a clean instrument autosampler vial. 

All MC-ICPMS instruments are equipped with a multiple Faraday collector array oriented perpendicular to the optic axis, enabling the simultaneous static or multi-static measurement of up to twelve ion beams. Most instruments use Faraday cups mounted on motorized detector carriers that can be adjusted independently to alter the mass dispersion and obtain coincident ion beams, as is the approach adopted for MC-TIMS measurement. However, some instruments instead employ a fixed collector array and zoom optics to achieve the required mass dispersion and peak coincidences (e.g., Belshaw et al. 1998). 

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