Spectrometers multi-channel

The hematite with adsorbed Co-57 or Sb-119 along with the solution was subjected to emission Mossbauer measurement at 24 1°C with the experimental setup shown in Figure 2. The absorber, Fe-57-enriched potassium ferrocyanide (0.5 mg Fe-57/cm2) or barium stannate (0.9 mg Sn-119/cm2), was driven by a Hanger 700-series Mossbauer spectrometer connected to a Tracor-Northern TN-7200 multi-channel analyzer. The Mosssbauer gamma-rays of Co-57 and Sb-119 were detected respectively with a Kr(+3% carbon dioxide)-filled proportional counter and with a 2 mm-thick Nal(Tl) scintillation counter through 65 pm-thick Pd critical absorber for Sn K X-rays. The integral errors in the relative velocity were estimated to be of the order of 0.05 mm/s by repeated calibration measurements using standard absorbers. 

If reasonable amounts of negative quarks could be had in a sample, energetic photons just above the threshold can ionize the quark to a free state with moderate kinetic energy. One advantage of such an experiment liberating photo-ionized quarks is that a high-resolution spectrometer (or related multi-channel device) can detect the well-defined X-rays emitted by the capture of the quark to a definite heavy atom (such as gold or thorium). 

The spectrum is scanned repetitively and accumulated until the signaknoise ratio is adequate. Depending on the count-rate, i.e. the strength of the source, this may take a few minutes or several hours. Accumulation is normally in a multi-channel analyser, so that the spectrum is obtained in digitized form and may be transferred directly to a computer which fits a calculated spectrum to the data points modern spectrometers are effectively PCs with built-in data processing. The fitting programme takes estimates of the parameters supplied by the user, from which a trial spectrum is calculated, and an iterative process optimizes the parameters. 

Non-dispersive systems are very compact, and potentially less expensive than dispersive spectrometers. For this reason they may be used for multi-channel instruments, measuring upto six elements almost simultaneously.39,40 Although... 

Yet, another feature that becomes available with the fast sequential mode of operation in HR-CS AAS is the use of the reference element technique, that is, the use of an internal standard. This technique has rarely been described in LS AAS [3] for a number of obvious reasons. Firstly, the technique requires a dual-or multi-channel spectrometer, and there have been only very few spectrometers of this type available commercially over the past decades. Secondly, the reference element technique is ideally suited to correct for nonspecific interferences, such as transport interferences, but it is notoriously difficult to find an appropriate reference element for element-specific interferences. Thirdly, the most successful multi-channel LS AAS equipment, the Perkin-Elmer Model SIMAA 6000, which has been available for a number of years, was designed for ET AAS only, a technique that does not typically exhibit nonspecific interferences. The number of publications using this technique is therefore very limited. 

There is a real chance of a breakthrough of Raman spectroscopy in routine analytics. Excitation of Raman spectra by near-infrared radiation and recording with interferometers, followed by the Fourier transformation of the interferogram into a spectrum -the so-called NIR-FT-Raman technique - has made it possible to obtain Raman spectra of most samples uninhibited by fluorescence. In addition, the introduction of dispersive spectrometers with multi-channel detectors and the development of several varieties of Raman spectroscopy has made it possible to combine infrared and Raman spectroscopy whenever this appears to be advantageous. 

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of most major and trace elements. The samples are fused in a Claisse semi-automatic fusion device in Pt-Au crucibles with lithium metaborate (4). The fusion product is dissolved in diluted HNO and brought to volume. For trace elements determination the sample is decomposed by HF, HNOg and HCIO. Scandium serves as an internal standard and is added to all samples and solutions. The instrument (product of Jobin Yvon, France)is calibrated using multi-element synthetic standards. The aqueous solutions are nebulized and injected into the heart of a plasma fire ball. A computerized multi-channel vacuum spectrometer has been programmed for multi-element analysis. 

Raman spectra were obtained with a Dilor-Jobin Yvon-SPEX spectrometer equipped with an optical multi-channel analyzer. The Raman spectra were excited with the 488-nm line of an Ar-ion laser. 

In routine industrial analysis, multi-channel spectrometers under computer control generally acquire, store, and update analytical curves for numerous elements simultaneously as part of a periodic check on standards. Excellent precision and accuracy can be obtained with these procedures. 

Fig. 8, Schematic of a Raman spectrometer showing the options of single-channel (scanning) and multi-channel detection. From [2].

Internal Standards. When internal standardization is used, the ratio of the signals of the analyte line and an internal standard line is measured. This technique is well known in emission spectrometry, where the internal standard is either the major element in the matrix or an added element of known concentration. In AAS, this technique may be employed when a double-channel (or multi-channel) instrument is in use and simultaneous measurements at two wavelengths are possible. This technique eliminates small variations in nebulizer and flame performance. Such variations are not corrected by double beam spectrometers. 

A multi-channel spectrometer has a light source with shutter, a sample and reference compartment, a grating polychromator and a diode array detector (Fig. 4.9). 

All spectral elements are recorded simultaneously by the array detector, i. e. the measuring time with the shutter in its open position is very short The short illumination time permits the sample and reference positions to be positioned immediately after the light source. Multi-channel spectrometers may also be constructed as double beam instruments. For special measurements, e. g. rapid kinetic investigations, when the chopper frequency is too low with respect to the rate of... 

Among wavelength-dispersive spectrometers, a distinction can be made between single-channel instruments and multi-channel spectrometers. In the former type of instrument, a single dispersive crystal/detector combination is used to sequentially measure the X-ray intensity emitted by a sample at a series of wavelengths when this sample is irradiated with the beam from a high power (2—4 kW) X-ray tube. In a multi-channel spectrometer, many crystal/detector sets are used to measure many X-ray Unes/elements simultaneously. 

Fig. 5. Schematic of a Mossbauer spectrometer working in multiscaler operating mode abreviations A - multi-channel analyzer, G - square-wave generator, J - integrator, > - amplifier D - differentiator, M - movement system, S - source, A - absorbent, D - detector and S-A single channel analyzer, respectively...

The energy spectra discussed below were obtained with a Packard Tricarb Spectrometer 3380, in combination with a Packard multi-channel analyser Spektrazoon 930. The spectra displayed on the screen of the multi-channel analyzer were photographed with a reflex Ccunera. 

Figure 7.13 Schematic drawing of a multi-channel microreactor set-upofwhich the products are scanned with a nozzle, connected to a quadrupole mass spectrometer. Reprinted from [52], Copyright 2001, with permission from Elsevier.

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