Internal reference principle

The important features of the sample preparation procedure were as follows. First, the samples were acidified to dissolve normal urine precipitates and to prevent analyte loss by adsorption on the walls of the sample containers (13). Second, the procedure was kept as simple as possible so that the risk of contamination and/or loss was minimized. Third, dilute, normal, and concentrated series of solutions were used to simulate actual urine samples with a wide range of total dissolved solids. Fourth, because the rate of sample nebulization and the corresponding rate of sample introduction into the plasma can be aflFected by changes in the amount of total dissolved solids, internal reference elements were included in each sample and reference solution. The use of analyte/internal reference element net intensity ratios provided a means of correcting for possible diflFerences in sample introduction rate according to the internal reference principle (14,15). Finally, because all of the sample solutions introduced into the plasma were derived from one composite, the different series were known to have trace element concentrations which were related to each other by known dilution factors (see Table IV). 

Because the electrical circuit is closed inside the sensor, no external reference electrode is necessary and the Severinghaus-type electrode can be used for measurement in either gaseous or liquid samples. It is important to remember, however, that the potential of the internal reference electrode must remain constant. In principle, it would be possible to use a liquid junction but it would add to the complexity of the design. Because the counterion resulting from the dissociation equilibrium is the only interfering ion, and because it is present in a very low concentration, it is possible to ascertain the constancy of the reference potential by careful choice of the internal electrolyte. Thus, for example, in the CO2 electrode the internal electrolyte is O.lMNaHCOs and 0.1 M NaCl and Ag/AgCl is used as an internal reference element. 

Principle. Accurate measurement of proinsuJin has been difficult for several reasons the blood concentrations are low antibody production is difficult most antisera cross-react with insulin and C-peptide, which are present in much higher concentrations the assays measure intermediate cleavage forms of proinsuhn and reference preparations of pure proinsulin were not readily available. Therefore few accurate data are availabie in the hterature on plasma proinsulin. These problems have, to a large extent, been overcome by the availability of biosynthetic proinsulin, which has allowed the production of monoclonal antibodies to proin-sulin and provided reliable proinsulin calibrators and reference preparations. An International Reference Preparation for human proinsulin (code 84/611) is available from the National Institute of Biological Standards and Controls (Potters Bar, United Kingdom). Earlier assays may have overestimated proinsulin concentrations. ... 

The reference principle for on-line methods has to be different as compared to classic dual-inlet isotope ratio analysis, as it is not possible to introduce sample and reference gas in exactly the same maimer into the mass spectrometer. Reference gas pulses have to be set at different points during one mn, but also laboratory standards with knovm 8-values have to be analysed periodically and exactly in the same manner and under the same conditions as the samples under investigation (identical treatment principle ]13]). A general problem of on-line HPLC and GC methods in isotope ratio analysis is the lack of international reference materials suitable to fulfil the above mentioned requirements. This implies the necessity to establish suitable laboratory standards by EA (elemental analysis) or classic measurements. Meanwhile, also efforts in supplying suitable international organic standards have been overtaken by the IAEA (e.g. caffeine, glutamic acid ]176, 177]). This programme (benzoic acid reference materials with different 8 0-values) will also support the on-line EA and GC 8 0-meas-urement by reductive pyrolysis (carbon reduction) methods (standardisation problems are compiled in ]178]). 

In fact, background corrections achieved with SPD, for both types of underlying spectral backgrounds, are comparable to that achieved with the array PMT polychromator (50). The shifts in the analytical curves, visible in Figures 8 and 9 reflect the reduction in the nebulizer efficiency at the high or concomitant concentrations. This matrix effect could be eliminated by utilizing the internal reference line principle to normalize variations in the nebulizer efficiency. For this normalization procedure... 

Once the effects of inner filters and quenching are controlled, luminescene appears more promising owing to its sensitivity and selectivity. Simultaneous excitation at two wavelengths is interesting, but requires a more complex installation and demultiplexing. It is preferable to have an internal reference in the system. The incorporation of the reference signal at the op-tode by means of two copolymerized reactants and the use of the principle of fluorescence... 

These enormous achievements have been possible in part because internationally agreed principles and procedures are in place to secure high levels of safety, efficacy, and quality of vaccines. Vaccines differ from therapeutic medicines first because of the biological and thus inherently variable nature of the products themselves, the raw material used in their production, and the biological methods used to test them. Thus, special expertise and procedures are needed for their manufacture, control, and regulation. The use of appropriate standard materials and reference preparations, whenever they exist, is fundamental to the standardization and control of vaccines [9]. 

Fundamentals. Based on the functional principles of the scanning electrochemical microscope, other scanning probe methods used to determine localized surface properties of the electrode under investigation or of the solution phase adjacent to this surface have been developed utilizing suitable microelectrodes. A pH-sensitive microelectrode based on a glass capillary filled with a pH-constant buffer solution and containing an internal reference electrode that has a tip filled with a proton-selective ionophor cocktail is scanned across the surface. The potential of the internal reference electrode with respect to an external reference electrode is directly correlated to the local pH value. A schematic cross section of this microelectrode is shown in Fig. 7.18. 

Table 6>10. Common extraction columns with rotating internals. Design, principles, characteristic data and references [6.23, 6.31, 6.46, 6.52].

An ion selective electrode operates on exactly the same principles as a pH electrode (see Chapter 1). In fact, a pH electrode is a type of ion selective electrode sensitive to hydrogen ions. Just like a pH electrode, the electrode body contains a reference solution and an internal reference electrode. On to this electrode body is sealed an ion selective membrane which acts as... 

The wavelengths of the analytical lines and the estimated limits of detection for different phosphor hosts are summarized in table 37E.2. The table is not exhaustive as several investigators who have utilized the XEOL technique for the determination of trace level rare earths have not tabulated the limits of detection. Typical analytical curves that have been obtained in our studies utilizing the internal reference element principle are shown in fig. 37E.12. 

The function of reboilers has already been discussed. These components are essentially heat exchangers that are used to transfer heat to bring the liquid at the bottom of the column to its boiling point (refer also to discussions in Chapter 1). The principle types employed are jacketted kettles, simple kettle type reboilers, internal reboilers, and thermo-syphon reboilers. Examples of each type are illustrated in Figure 7. 

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