Detectors simultaneous

The alternative approach to detection and analysis incorporates a solid state detector and a multichannel pulse height analysis system. The crystals used are of silicon (of the highly pure intrinsic type), or the lithium drift principle (p. 463 etseq.) is utilized. All emitted radiations are presented to the detector simultaneously and a spectrum is generated from an electronic analysis of the mixture of voltage pulses produced. Chapter 10 contains a more detailed account of pulse height analysis and solid state detectors. Production of an X-ray spectrum in this way is sometimes known as energy dispersive analysis ofX-rays (EDAX) and where an electron microscope is employed as SEM-EDAX. 

Instruments are calibrated with substances of known relative molecular mass and very accurate mass measurements can be made with this type of analyser. Sensitivity is very high and there is virtually no upper limit to the working mass range. The performance of TOF instruments can be improved further by the incorporation of an electrostatic reflector (reflectron) which ensures that all ions of identical mass reach the detector simultaneously by correcting for any differences in their kinetic energies. 

They are especially attractive for analyzing weak light signals. This is because in an FTIR spectrometer all of the frequencies arrive at the detector simultaneously, so that the energy throughput is much greater than for dispersive instruments (the... 

Splitter. A fitting attached to the column to divert a portion of the flow. It is used on the inlet side to permit the introduction of very small samples to a capillary column, on the outlet side to permit introduction of a very small sample of the effluent to the detector or to permit introduction of effluent to two detectors simultaneously. 

A Single Sample Injected into One Column. Two dissimilar detectors simultaneously monitor the column effluent. The ratio of response of one compound on the two detectors can allow the chro-matographer to distinguish between one compound or another even though the two may elute at the same time from the particular column. 

The OMA technology has been recently applied to infra-red spectroscopy ( 18) as well. A pyroelectric vidicon (utilizing a triglycine sulfate as the sensor element) has been used as a thermal rather than a photon multichannel detector. Simultaneous spectral detection, in the 1-30 um spectral region, was accomplished that has proven to be particularly useful for IR pulse laser applications, Fig.12,... 

Schematic description of a TOF instrument equipped with a reflectron. = ions of a given mass with correct kinetic energy = ions of the same mass but with a kinetic energy that is too low. The latter reach the reflectron later, but come out with the same kinetic energy as before (see text). With properly chosen voltages, path lengths and fields, both kinds of ions reach the detector simultaneously.

As already mentioned, when ions fragment during their flight in a field-free region, with or without collision activation, the precursor and fragments have the same velocity and reach the detector simultaneously. If, however, they are accelerated perpendicularly to their trajectories and so pushed in the TOF mass analyser, ions with different masses will arrive at different times and will be detected separately according to their respective m/z [80]. However, owing to their initial velocities, they will reach the array detector at different places. 

Since the TDC is a time counting device, when two or more ions arrive at the detector simultaneously in one flight cycle, the system counts them as one ion. In the same way, when two ions arrive at the detector in sequence within a certain interval, the system does not count the latter ion because the TDC is unable to register another count during the period after each ion event (counting dead time). Consequently, the dynamic range of this... 

These saturation effects, resulting from the loss of ions due to the TDC dead time, can be statistically corrected by applying a correction factor [4], However, there is no effective correction when the quantity of ions increases and several ions arrive at the detector simultaneously. In conclusion, detection systems that operate in pulse counting mode are well suited to detect small quantities of ions by accumulation for a long period of time and when detection of individual ion events is important in order to obtain a good signal-to-noise ratio. 

With this type of device, the sample does not move. The source and the detector simultaneously move in opposite directions along the goniometric circle at a speed... 

Bioassays for BT toxin are sensitive because the test animals function as a concentrator and a detector simultaneously. When exposed to very low concentrations, the toxin is accumulated as the animal feeds over a period of days. Compared to immunoassays, bioassays for the BT toxins are generally 50-100 times more sensitive (Table II). As with other residue procedures, sample work-up can be employed to extend the detection limits of an enzyme immunoassay and to remove interfering materials at the same time. Such work up will be essential if immunoassays are to be as sensitive as bioassays using filter feeding organisms. 

In scintillation counting, two 511-keV photons may arrive at and be absorbed completely in the detector simultaneously and, therefore, a... 

Identified by Vitzthum and Werkhoff (1974a,b). Silwar et al. (1986) after steam distillation/extraction, used flame ionization and flame photometric detectors simultaneously for the sulfur compounds. They found contents of 0.4-0.45 ppm in arabicas and 0.65-0.70 in robustas. Tressl (1989) reported 0.5-1 and 0.8-1.5 ppm. 

Identified by Tressl et al. (1981) after distillation-extraction, separation by chromatography, preparative GC, then capillary GC with either flame ionization or flame photometric (for sulfur-selective analysis) detector. Silwar et al. (1986) after simultaneous distillation-extraction used the two detectors simultaneously for quantifying the sulfur compounds (see Q.14). They found less than 0.01 ppm of this dithiolane in arabicas as well as in robustas. 

Adsorption isotherms of cyclopentane vapours were measured at 20°c. Temperature programmed reduction profiles were measured by the continuous flow technique with a thermal conductivity detector. Simultaneous TG, DTG and DTA were carried out in an argon atmosphere at the heating rate of 10 K.min Catalytic measurements were performed in a continuous flow integral fixed bed reactor under 0.1 MPa at 200°C. The inlet C0/H ratios ranged from 0.5 to 2.0, the space velocity was... 

Since the last review by this author (1,2), an early paper in this field came to light in which Johnson and Fulmer (47) used three detectors simultaneously—FID, and FPD for both sulfur and phosphorus. The phosphorus FPD was considered especially useful for detecting the presence of contaminants of biological origin, such as vegetable oils. 

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