Counter resolution

Fig. 14. a,b. The excitation and luminescence spectra in the thin solid films PIC2-6 (a), PIC2-10 (b) with two counter resolution... 

Benchtop X-ray energy dispersive analyzer BRA-17-02 based on a gas-filled electroluminescent detector with an x-ray tube excitation and range of the elements to be determined from K (Z=19) to U (Z=92) an electroluminescent detector ensures two times better resolution compared with traditional proportional counters and possesses 20 times greater x-ray efficiency compared with semiconductor detectors. The device is used usually for grits concentration determination when analysing of aviation oils (certified analysis procedures are available) and in mining industry. 

The electrical aerosol analyzer and the optical counter are used to measure particle size distributions. Describe the size range and resolution characteristics of each of these instruments. 

Most of the chiral membrane-assisted applications can be considered as a modality of liquid-liquid extraction, and will be discussed in the next section. However, it is worth mentioning here a device developed by Keurentjes et al., in which two miscible chiral liquids with opposing enantiomers of the chiral selector flow counter-currently through a column, separated by a nonmiscible liquid membrane [179]. In this case the selector molecules are located out of the liquid membrane and both enantiomers are needed. The system allows recovery of the two enantiomers of the racemic mixture to be separated. Thus, using dihexyltartrate and poly(lactic acid), the authors described the resolution of different drugs, such as norephedrine, salbu-tamol, terbutaline, ibuprofen or propranolol. 

The apparatus as modified for x-ray emission spectrograph is also shown in Figure 11-1. The proportional counter may be used alone (pulse-height analysis Section 2.13) or a curved-crystal spectrometer can be employed to achieve better resolution. Analytical results were comparable to those quoted above, but localization of the area analyzed was considerably less sharp than the micron-diameter spot achieved in differential absorptiometry. 

High performance liquid chromatography (HPLC) has been by far the most important method for separating chlorophylls. Open column chromatography and thin layer chromatography are still used for clean-up procedures to isolate and separate carotenoids and other lipids from chlorophylls and for preparative applications, but both are losing importance for analytical purposes due to their low resolution and have been replaced by more effective techniques like solid phase, supercritical fluid extraction and counter current chromatography. The whole analysis should be as brief as possible, since each additional step is a potential source of epimers and allomers. 

Solid-state detectors based on silicon- or germanium-diodes possess better resolution than gas counters, particularly when cooled with liquid nitrogen, but they allow only very low count rates. PIN diodes have also recently become available and have been developed for the instruments used in the examination of Martian soils (Sects. 3.3 and 8.3). A very recent development is the so-called silicon-drift detector (SDD), which has very high energy resolution (up to ca. 130 eV) and large sensitive detection area (up to ca. 1 cm ). The SNR is improved by an order of magnitude compared to Si-PIN detectors. Silicon drift detectors may also be used in X-ray florescence spectroscopy, even in direct combination with Mossbauer spectroscopy (see Sects. 3.3 and 8.3). 

Table 8.40 compares the main characteristics of WDXRF and EDXRF. Multidispersive XRF combines the benefits of the WDXRF technique for routine elemental analysis with the complete flexibility offered by EDXRF for nonroutine analysis. Clearly, modem XRF instrumentation is rather varied, ranging from simple benchtop EDXRF equipped with a low-power X-ray tube and high-resolution proportional counter for some key elements, to 4 kW simultaneous multichannel spectrometers with 28 fixed element channels for... 

The Sauerbrey equation predicts a mass sensitivity per unit area of 0.226 Hz cm 2 ng . For a typical crystal the exposed area is c. 0.25 cm2 and the absolute mass sensitivity is 0.904 Hz ng 1. The resolution of modern frequency counters is easily +0,1 Hz in 10 MHz, giving a theoretical mass resolution of c. 9 x 10 10 g in practice this is usually found to be closer to 2 ng. 

Sometimes requires large quantities of organic solvents poor resolution of mixtures of organic materials except by counter-current distribution which is slow. 

A counter current movement of the mobile phase and the sorbent has some unique advantages when designing separation processes for maximum economy. The efficiency requirement for the sorbent is lower compared to other chromatographic modes, since no individual column has to achieve full resolution. Instead only the pure fractions of the zones obtained are withdrawn from the system. The time-space yield in terms of productivity is enhanced considerably by the improved utilization of the sorbent capacity. The product dilution is lower, pure fractions are withdrawn with high yield and it is not necessary to consider fractions of less then the desired purity. Early on it was re-... 

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