Element selective detection

Many different combinations, separation -i- element-selective detection, have been attempted but HPLC in conjunction with ISP-MS has emerged as one of the best combinations. HPLC is a versatile technique, which due to the vai iety of sepai ation mechanisms developed, can be applied to a great vai iety of medically important analytes. 

GC-AAS has found late acceptance because of the relatively low sensitivity of the flame graphite furnaces have also been proposed as detectors. The quartz tube atomiser (QTA) [186], in particular the version heated with a hydrogen-oxygen flame (QF), is particularly effective [187] and is used nowadays almost exclusively for GC-AAS. The major problem associated with coupling of GC with AAS is the limited volume of measurement solution that can be injected on to the column (about 100 xL). Virtually no GC-AAS applications have been reported. As for GC-plasma source techniques for element-selective detection, GC-ICP-MS and GC-MIP-AES dominate for organometallic analysis and are complementary to PDA, FTIR and MS analysis for structural elucidation of unknowns. Only a few industrial laboratories are active in this field for the purpose of polymer/additive analysis. GC-AES is generally the most helpful for the identification of additives on the basis of elemental detection, but applications are limited mainly to tin compounds as PVC stabilisers. 

Separation technique Element-selective detection techniques... 

Although the focus of many tests is analysis of the hydrocarbon constituents of naphtha and other petroleum fractions, heteroatoms compounds that contain sulfur and nitrogen atoms cannot be ignored, and methods for their determination are available. The combination of gas chromatography with element-selective detection gives information about the distribution of the element. In addition, many individual heteroatomic compounds can be determined. 

AED combined with GC x GC was first reported by van Stee et al. [21 ] for element-selective detection in petrochemical samples. The AED used in this study had a maximum data acquisition rate of 10 Hz, which when applied to the detection of GCxGC peaks of base width of 100-300 ms, will not achieve the required minimum of 5-10 data points per peak. In order to meet this criterion, peak widths need to be broader, with necessary widths of400-1- ms required. Deliberate broadening of second... 

Eisert R, Levsen K, Wuensch G. 1994. Element-selective detection of pesticides by gas chromatography atomic-emission detection and solid-phase microextraction. J Chromatogr 683(1) 175-183. 

Fig. 11. Vanadium elution profiles from SEC-HCLP with element selective detection (a) Morichal crude, (b) residual oil, (c) porphyrin fraction (Biggs et al., 1985).

N. P. Vela, J. A. Caruso, Element selective detection for supercritical-Buid chromatography, J. Biochem. Biophys. Meth., 43 (2000), 45 D58. 

Zybin A., Schnurer-Patschan Ch. and Niemax K. (1995) Wavelength modulation diode laser atomic absorption spectrometry in modulated low-pressure helium plasmas for element-selective detection in gas chromatography, J Anal At Spectrom, 10 563-567. 

The advantage of combined systems of separation modules and element selective detection modules is the extended scope and broad applicability. Disadvantages are seen in increased complexity and thus in a risk of poorer detectivity of the systems. Besides, species equilibria can be drastically altered during separation due to dilution, separating partners in chemical equilibrium, etc.. Species transformation and destruction are likely consequences (Morrison 1989 Mota and Simaes-Goncalves 1996). The total separation time therefore must be short compared to the transformation rates of species. 

Element selective detection should be linked to quality control by use of an element-certified certified reference material (CRM). 

Table 3 GCxGC applications involving the use of FID and element-selective detection [83]...

In closing this section, it should be emphasized that element selective detection in HPLC is an area now undergoing very rapid exploration and development, and significant Improvements in HPLC-ICP/ DCP detection limits with resultant practical applications should be realized in the near future. If a then relatively inexpensive element selective spectroscopic detector could be developed for conventional or microbore HPLC, with a successful Interface providing low MDLs, this could result in a more widespread acceptance and application of both the overall Instrumentation and final techniques. 

The use of large-volume filter-based samplers for the collection of atmospheric particulates has also been combined with IC for the determination of absorbed metal species. Collected samples are extracted from the filters and desorbed from the particulate matter using acidic solutions prior to analysis by IC combined with elemental selective detection such as ICP-MS. Hexavalent chromium, platinum, and palladium have been determined in this way, as have many other transition and heavy metal ions. 

Luffer, D.R. Novotny, M. Element-selective detection after supercritical fluid chromatography by means of a Surfatron plasma in the near-infrared spectral region. J. Chromatogr. 1990, 517, 477 89. 

The combination of separation techniques on-line with element selective detection methods is resulting in hyphenated systems. These on-line systems have many advantages, especially in routine applications, due to easier operation, higher sample throughput with faster results of better quality than off-line modules, and the risk of contaminations or losses is reduced. 

The major advantage of element selective detection, in particular of ICP-MS, is that the detector response is far less compoimd and matrix... 

Nischwilz V, Berthele A, Michalke B. Rapid size fractionation of metal species in paired human serum and cerebrospinal fluid samples using ultrafiltration with off-line element selective detection. J Anal At Spec 2010 25 1130-7. 

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