Multielement detection systems

Vol. 107. Multielement Detection Systems for Spectrochemical Analysis. By Kenneth W. Busch and Marianna A. Busch... 

Figure 1. Evolutionary development of multielement detection systems...

Busch, K. W. and Busch, M. A., Multielement Detection Systems for Spectro-chemical Analysis, Wiley, New York, 1990. 

Despite the problems described above the MIP has been used for many applications. The limits of detection obtained for the system very much depend on the sample introduction technique and are best either for vapor introduction or preatomization systems. The major application of the MIP has been as a detector for GC, either in the selective mode or for determining empirical formulae with multielement detection systems. Table 1 shows the limits of... 

Busch, K.W. Busch, M.A. Multielement Detection Systems for Spectmchemical Analysis. Wiley New York,... 

Renishaw PLC, Wotton-under-Edge, Gloucester, GL12 7DH, U.K. www.renishaw.co.uk KW Busch, MA Busch. Multielement Detection Systems of Spectrochemical Analysis. Chichester Wiley, 1990, pp 423--490. 

A recent extension of the scope of SPE-GC and SPE-GC-MS concerns the use of AED detection with its multielement detection capability and unusually high selectivity. Hankemeier [67] has described on-line SPE-GC-AED with an on-column interface to transfer 100 iL of desorbing solvent to the GC. The fully on-line set-up is characterised by detection limits of 5-20 ngL because of quantitative transfer of the analytes from the SPE to the GC module. On-line coupling of SPE with GC is more delicate than SPE-LC, because of the inherent incompatibility between the aqueous part of the SPE step and the dry part of the GC system. 

The fluorescence technique combines the advantages of the large dynamic range of emission techniques with the simplicity and high selectivity of absorption techniques. Flame sources have been extensively used, however, for elements with refractory oxides, the ICP source has been found to be more satisfactory for AFS. A system for hollow cathode lamp excited ICP-AFS, as proposed by Demers and Allemand (1981), is commercially available as a modular simultaneous multielement ICP system. Although fluorescence techniques often offer two orders of magnitude sensitivity improvement over absorption, the multielement approach for AFS has not yet been commercially successful. Also promising for the future is the laser-excited furnace AFS where the detection limits for most elements are comparable to those of ICP-AES and for some elements, for eg, As, Cd, Pb, Tl, Lu, even lower (Omenetto and Human, 1984). The future for AFS techniques has been discussed by Stockwell and Corns (1992). 

In the struggle for supremacy in the area of multielement atomic emission, the recent advent of the induction-coupled plasma (1 -9 ) may result in the eventual extinction of combustion flames as spectroscopic sources. In the area of detection systems, numerous configurations have been proposed, and, at this time, it is... 

The evolution of detection systems suitable for multielement determinations has proceeded along two basic lines of development as indicated in Figure 1. One line of development is based upon dispersive systems. Dispersive systems are all multichannel devices which may be further classified as temporal or spatial devices. In the temporal approach, the measurement of intensities in different resolution elements is separated in time. The spatial approach uses detectors which are separated in space. 

Comparisons with other systems. Data presented in Table VI provide a comparison of results obtained with the image dissector with results reported by others with other systems. Results in the second column represent multielement detection limits observed in this work. Results in the third and fourth columns represent detection limits reported for single element determinations with conventional optics and a silicon vidicon (12J and a commercial atomic absorption instrument (33). 

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

Mitchell et al. describe a multielement atomic absorption system using a multielement hollow cathode source and a vidicon detection system. The monochromator is an 0.25-m grating that permits scanning a spectral range of 1680 A. 

The optical detection systems used in MIPs are the same as those used for other atomic spectrometers and can be either single or multichannel. Fourier transform-based spectrometers have also been used. Conventional optical systems are best designed if the plasma is viewed from the exit of the discharge tube, as is possible with the TMqio type cavity, rather than through the walls of the discharge tube, which become etched. The commercially available AED uses a computer-controlled silicon photodiode array detector which has multielement detection capability over segments of spectra. In recent years, MIP sources have also been investigated as ion sources for mass spectrometry. 

FFF-ICP-MS The ICP-MS is a multielement analysis tool ideally suited for direct coupling with FFF. The ICP torch is capable of vaporizing and ionizing particles in the eluent up to 10 pm, and the plasma is then fed into an MS for simultaneous detection of many elements. Quadripole, mass-sector, and time of flight MSs are now available, depending on the sensitivity, mass resolution, and response time required. FFF-ICP-MS yields element-based size distributions. Other element detection systems that have been used include ICP-AESs, electrothermal atomic absorption spectrometers, and very recently laser-induced breakdown spectrometers. 

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