Internal standard, 158 also

During a single run, which may take all day if a large number of samples are to be analyzed, the instrument may drift from its optimum settings. To detect this drift in solution-based techniques, and also to compensate for some matrix effects, a known amount of an element may be added to each sample before analysis. This internal standard (also called a spike) is added to all the samples and blanks, with the exception of the instrument blank (which is defined as zero concentration for all elements see below). It is important that the element (or isotope) chosen as the spike is not an element which is to be determined in the samples, and preferably which does not occur naturally in the samples. It must not be an element which will cause, or suffer from, interference with the other elements to be determined. In solution ICP-MS,... 

On-line analysis of the hydrocarbons in the vent gas was done on a 20-ft Porapak Q column with an internal standard. In many cases, the internal standard also allowed calculation of hydrogen by difference. A Beckman 3AM3 gas density balance provided a check on the vent gas analysis and the necessary parameter for calculating mass flow rates from orifice pressure drop data. Mass balance closure was typically better than it 2%. 

There are currently no commercially available 13C-labeled PCN congeners and therefore 13C-labeled PCBs are frequently used as internal standards also for PCN analysis. It should however be noted that the major hexaCNs in tech-... 

The yields were determined by GC analyses using internal standard. Also l,l-bis(4-tolyl)pent-l-ene 0.06%. Also 2-methyl-l,l-bis(4-tolyl)prop-l-ene <0.06%. Also 2-phenyl-l,l-bis(4-tolyl)ethene... 

Proper selection of an internal standard also allows the internal standard to correct for extraction efficiency. The internal standard is chosen to be similar in structure, generally a structural analog to the analyte, so that they have similar... 

X-ray fluorescence has been found to be useful in the quantitation of titanium oxides, with internal standards also being used [35]. The methods all make use of the Ti Ka emission at 2.750 A, and differ in their choice of internal standards. 

From earlier discussions we can gather knowledge about various methods for hazard analysis systems, and implication of these methods from international standards. Also details about safety instrumentation system (SIS) and safety integrity level (SIL) have been covered. From previous discussions it is quite clear that the essence of a safety system can be described by Ref. [2] ... 

Note According to the enormous usage of isotope dilution, H- (D) and Relabeled standards [56] are commercially available for a wide range of applications. Often, a methyl is exchanged for a trideuteromethyl as this safely avoids overlap with isotopic peaks of the analyte. It is also inportant not to select corrpounds with acidic hydrogens exchanged for deuterons. Other restrictions for internal standards also apply. 

Flow measurements using tracers are performed in all piping systems carrying oil, gas or water including separators, compressors, injector systems, and flares. Calibration of elsewhere difficult accessible flow meters is regularly performed by the tracer methods, which are based on international standards. Tracer flow measurements are also well suited for special purposes... 

When possible, quantitative analyses are best conducted using external standards. Emission intensity, however, is affected significantly by many parameters, including the temperature of the excitation source and the efficiency of atomization. An increase in temperature of 10 K, for example, results in a 4% change in the fraction of Na atoms present in the 3p excited state. The method of internal standards can be used when variations in source parameters are difficult to control. In this case an internal standard is selected that has an emission line close to that of the analyte to compensate for changes in the temperature of the excitation source. In addition, the internal standard should be subject to the same chemical interferences to compensate for changes in atomization efficiency. To accurately compensate for these errors, the analyte and internal standard emission lines must be monitored simultaneously. The method of standard additions also can be used. 

Determination of the potency of Factor VIII is also difficult. This is normally measured by the abiUty of the sample to correct the clotting time of plasma deficient in Factor VIII. A number of methods and practices have evolved for this purpose (231), but these give very different results, particularly when activation of products may also occur (232). International standards have been used, but further standardization of the analytical method and harmonization of working standards is underway (233,234) under the auspices of the ISTH and the EC. 

The International Standards Organization 9000 (ISO 9000) standard, developed by the European Economic Community (EEC), also impacts manufacturers implementation of LIMS systems. ISO 9000 is a set of standards which are required for manufacturers selling products to the EEC. The 9000 standards are credited with playing an important part in the impetus to greater computerization of laboratory information management (9). 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

A 165-MW-class gas turbine/generator has been introduced by another manufacturer. This machine, also developed by scaling up a proven design, features a simple-cycle efficiency of 37.5% a turbine inlet temperature of 1235°C a pressure ratio of 30 1, up from 16 1 on the previous generation and an output of 165 MW for gas fuel firing under International Standards Organization (ISO) conditions (101 kPa, 15°C (14.7 psia, 59°F)). A combined-cycle facihty based around this machine could achieve efficiencies up to 58% or a heat rate of about 6209 kj/kWh (5885 Btu/kWh). 

Industrial resistance thermometers are also the subject of a number of national and international standards, which describe both cahbration constants and classes of accuracy and interchangeabihty. lEC pubhcation 751 was revised in 1976 to conform to ITS-90, and national standards will be revised to conform to this document. lEC 751 uses the fixed-poiat values of ITS-90 with the simpler algorithm of IPTS-48 ... 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

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