Detectors element selectivity

Element selective detectors Element selective detectors applicable in pesticide residue analysis include electron capture detector (ECD), electrolytic conductivity detector (ELCD), halogen-specific detector (XSD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD), pulsed flame photometric detector (PEPD), sulfur chemiluminescence detector (SCD), and atomic emission detector (AED). To cover a wider range of pesticide residues, a halogen-selective detector (ECD, ELCD, XSD) in conjvmction with a phosphorus- (NPD, FPD), nitrogen- (NPD), and/or sulfur-selective detector (FPD, SCD) is commonly used. A practical approach is to spht the column flow to two detectors that reduces the number of injections however, the reduced amoimt of analyte that reaches the detector must be considered. 

Identification of stmctures of toxic chemicals in environmental samples requires to use modern analytical methods, such as gas chromatography (GC) with element selective detectors (NPD, FPD, AED), capillary electrophoresis (CE) for screening purposes, gas chromatography/mass-spectrometry (GC/MS), gas chromatography / Fourier transform infra red spectrometry (GC/FTIR), nucleai magnetic resonance (NMR), etc. 

Screening of the samples for the presence of compounds of interest by different element selective detectors, preliminai y identification of heteroatom compounds ... 

Element-selective detectors. Many samples, e.g. those originating from environmental studies, contain so many constituent compounds that the gas chromatogram obtained is a complex array of peaks. For the analytical chemist, who may be interested in only a few of the compounds present, the replacement of the essentially non-selective type of detector (i.e. thermal conductivity, flame ionisation, etc.) by a system which responds selectively to some property of certain of the eluted species may overcome this problem. 

The principles and applications of element-selective detectors have been reviewed.74... 

D F S Natusch and T M Thorpe, Element selective detectors in gas chromatography, Anal. Chem., 1973,45, 1184A... 

The combination of an element-selective detector and MS can provide excellent information for determining the presence of an analyte or, just as important, eliminating the chance that a pesticide is present. The added selectivity gained in the use of tandem MS (MS") can also weigh heavily in confirmation of pesticide identity despite the possible lack of three ions of defined ratios. 

The most widely used element-selective electrochemical detector is the Hall electrolytic conductivity detector (HECD) [98,116,206]. This is an improved version of an earlier design by Coulson [207,208]. In both detectors the reaction products are swept from the furnace into a gas-liquid contactor trtiere they are mixed with an appropriate solvent. The liquid phase is separated from insoluble gases in a gas-liquid separator and then passed through a conductivity cell. The Coulson detector employed a... 

The FID may be operated as an element-selective detector after minor modification. The hydrogen atmosphere flame ionization detector (HAFID) can be made selective towards organometalllc... 

Table 4.8 shows some frequently used element selective chromatographic detectors (ESDs) and Table 4.9... 

Spectroscopic detectors, which measure different spectral properties (absorption, fluorescence, scattering, etc.), may be element selective, structure or functionality selective, or property selective. The most common... 

HPLC-QFAAS is also problematical. Most development of atomic plasma emission in HPLC detection has been with the ICP and to some extent the DCP, in contrast with the dominance of the microwave-induced plasmas as element-selective GC detectors. An integrated GC-MIP system has been introduced commercially. Significant polymer/additive analysis applications are not abundant for GC and SFC hyphenations. Wider adoption of plasma spectral chromatographic detection for trace analysis and elemental speciation will depend on the introduction of standardised commercial instrumentation to permit interlaboratory comparison of data and the development of standard methods of analysis which can be widely used. 

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. 

As SFC provides gaseous sample introduction to the plasma and thus near-100 % analyte transport efficiency, coupling SFC with plasma mass spectrometry offers the potential of a highly sensitive, element-selective chromatographic detector for many elements. Helium high-efficiency microwave-induced plasma has been proposed as an element-selective detector for both pSFC and cSFC [467,468] easy hyphenation of pSFC to AED has been reported [213]. 

Evaporative LC-FTIR is rapidly gaining industrial acceptance as a useful tool in low-MW additive analysis. HPLC has also been coupled with various element-selective detectors. There is significant demand for speciation information for many elements, and the separation ability of chromatography coupled to ICP-MS offers the analyst a versatile tool for such studies. It is apparent that ICP-MS is increasingly being employed for chromatographic detection. Several modes of GC, SFC, LC and CE have been hyphenated with ICP-MS for improved detection limits compared to other traditional methods of detection such as UV-VIS spectroscopy. Inorganic speciation deserves more attention. 

Atomic emission detector (AED) Atomic emission of elements 0.1-50 pg/s 4 Element selective as in atomic emission spectrometry... 

Lee SM, Wylie PL. 1991. Comparison of the atomic emission detector to other element-selective detectors for the gas chromatographic analysis of pesticide residues. J Agric Food Chem 39 2192-2199. 

Organochlorine pesticides and OPPs have been determined mainly using GC, because of the stability and volatility that most of them show under chromatographic conditions and, particularly, the availability of element-selective detectors that display high selectivity for OCPs (electron-capture detector, ECD), and OPPs (flame photometric detector, FPD, and nitrogen phosphorus detector, NPD). Mass spectrometry-based detection is also more popular in GC than in HPLC (1,2,12,16). 

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