Detectors thermionic

Among the various detectors specific for nitrogen, the NPD (Nitrogen Phosphorus Thermionic Detector) we will consider, is based on the following concept the eluted components enter a conventional FID burner whose air and hydrogen flows are controlled to eliminate the response for hydrocarbons. 

Other Detectors Two additional detectors are similar in design to a flame ionization detector. In the flame photometric detector optical emission from phosphorus and sulfur provides a detector selective for compounds containing these elements. The thermionic detector responds to compounds containing nitrogen or phosphorus. 

SPME has been utilized for deterrnination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-siUca fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). EuU automation can be achieved using an autosampler. Eiber coated with 7- and 100-p.m film thickness and a nitrogen—phosphoms flame thermionic detector were used to evaluate the adsorption and desorption of four j -triazines. The gc peaks resulting from desorption of fibers were shown to be comparable to those obtained using manual injection. 

One great advantage of GC is the variety of detectors that are available. These include universal detectors, such as flame ionization detectors and selective detectors, such as flame photometric and thermionic detectors. The most generally useful detectors, excluding the mass spectrometer are described in the following sections. 

EC = electrical conductivity detector ECD = electron capture detector FPD = flame photometric detector GC = gas chromatography HPLC = high performance liquid chromatography NPD = nitrogen phosphorus detector TID = thermionic detector UV = ultraviolet spectroscopy... 

Analysis of methyl parathion in sediments, soils, foods, and plant and animal tissues poses problems with extraction from the sample matrix, cleanup of samples, and selective detection. Sediments and soils have been analyzed primarily by GC/ECD or GC/FPD. Food, plant, and animal tissues have been analyzed primarily by GC/thermionic detector or GC/FPD, the recommended methods of the Association of Official Analytical Chemists (AOAC). Various extraction and cleanup methods (AOAC 1984 Belisle and Swineford 1988 Capriel et al. 1986 Kadoum 1968) and separation and detection techniques (Alak and Vo-Dinh 1987 Betowski and Jones 1988 Clark et al. 1985 Gillespie and Walters 1986 Koen and Huber 1970 Stan 1989 Stan and Mrowetz 1983 Udaya and Nanda 1981) have been used in an attempt to simplify sample preparation and improve sensitivity, reliability, and selectivity. A detection limit in the low-ppb range and recoveries of 100% were achieved in soil and plant and animal tissue by Kadoum (1968). GC/ECD analysis following extraction, cleanup, and partitioning with a hexane-acetonitrile system was used. 

Hewlett-Packard Model 6890 gas chromatograph with capillary split/splitless inlet with HP5973 mass-selective detector equipped with an autosampler Shimadzu GC17A gas chromatograph with capillary split/splitless inlet with flame thermionic detector equipped with an AOC-17 autoinjector... 

Shimadzu GC-7A gas chromatograph with flame thermionic detector Pyrex spiral column packed with 3% OV-1 on Gas Chrom Q (80-100 mesh), 1 m X 3-mm i.d. 

Gas chromatograph equipped with a flame thermionic detector High-performance liquid chromatograph... 

To improve the detectability of silyl ethers, silylation reagents containing an electron-capturing group [443,449-451,468] or cyano group for thermionic detection [469] have been prepared, the 2-cyanoethyldimethylsilyl derivatives are only marginally aore sensitive (ca. 5 fold) to the thermionic detector than to the flame ionization det ftpr which Units their usefulness. The... 

Shinohara et al. [299] have described a procedure based on gas chromatography for the determination of traces of two, three, and five-ring azarenes in seawater. The procedure is based on the concentration of the compounds on Amberlite XAD-2 resin, separation by solvent partition [300], and determination by gas chromatography-mass spectrometry with a selective ion monitor. Detection limits by the flame thermionic detector were 0.5-3.0 ng and those by gas chromatography-mass spectrometry were in the range 0.02-0.5 ng. The preferred solvent for elution from the resin was dichloromethane and the recoveries were mainly in the range 89-94%. 

NPD nitrogen-phosphorus detector (also known as a thermionic detector)... 

In both systems the flow of helium carrier gas through the columns was 0.7-0.8 ml min-1, with a septum purge of 0.5 ml min-1 and a split valve flow of 4-4.5 ml min-1. The injection ports were maintained at 260°C and the detector ovens at 240° C. The detector employed was either a flame ionisation or a nitrogen-specific NPD-40 thermionic detector (Erba Science (UK) Ltd) and the output was recorded on a HP 3390 integrator (Hewlett Packard Ltd, Wokingham, UK). 

Carlsson H, Robertsson, G, Golmsjo. 2001. Response mechanisms of thermionic detectors with enhanced nitrogen selectivity. Anal Ghem 73 5698. 

Hewitt, A. D., T. F. Jenkins, and T. A. Raney. Field Gas Chromatogra-phy/Thermionic Detector System for On-site Determination of Explosives in Soils. U.S Army Corps of Engineers, Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory Technical Report ERDC/CRREL TR-... 

Kale, endive, carrots, lettuce, apples, potatoes, strawberries Extraction of crops with ethyl acetate and granular sodium sulfate, filtration, concentration with K-D. Sweep codistillation cleanup for GC. Florisil partition chromatography for polarographic confirmation. GC/KCI thermionic detector or GC/FPD polarographic confirmatory method No data for GC polarographic 0.2 ppm based on 1 g crop in 1 mL cell No data AOAC 1990... 

Numerous non-fatty crops Extraction with acetonitrile and partition into petroleum ether. Concentration using K-D and purification using Florisil column chromatography. GC/KCI thermionic detector identifications by combinations of gas, thin layer, and paper chromatography No data >80 AOAC 1990... 

MS, Mass spectrometry El, electron impact Cl, chemical ionization MID, multiple ion detection PICI, positive-ion chemical ionization NICI, negative-ion chemical ionization SIM, selected ion nmonitoring TSP, thermospray PPINICI, pulsed positive ion-negative ion chemical ionization ECD, electron-capture detector NPD, nitrogen/phosphorous detector NSTD, nitrogen-selective thermionic detector FT-IR, Fourier transform infrared spectrometry. 

A phosphorus-specific thermionic detector was also adapted from GLC (See Section III.3.b) for use with small-bore HPLC columns208,307,330,334. Based on an electrically heated rubidium salt bead, it permits detection limits of 0.2-0.5 ng of phosphorus and its response is linear with the amount of phosphorus over several orders of magnitude. This detector yields good results with phosphates which cannot be detected by UV spectrophotometry or by fluorescence measurements. 

However, by no means are microbore HPLC columns nonoptimal when sample volumes are limited. Because of the substantially reduced mobile-phase volumes necessary to carry out a given separation, microbore columns are more easily interfaced to many useful detection systems, for example, electron-capture detectors, nitrogen-specific thermionic detectors, and mass spectrometers. 

Figure 14. Chromatograms of organophosphorus pesticides obtained from a small-bore fused silica column (0.2 mm i.d., 1 m long) packed with 5-pm Spherisorb ODS. A, UV detection at 254 nm and B, dual-flame thermionic detector. Peaks correspond to 1, solvent containing phosphorus impurities 2, guthion, 89 ng of phosphorus 3, zolone, 71 ng of phosphorus and 4y ethion, 144 ng of phosphorus. Mobile-phase conditions 15% water and 85% methanol (v/v) at a flow rate of 1.6 pL/min. (Reproduced from reference 58. Copyright 1983 American Chemical Society.)...

ALKALI FLAME IONIZATION DETECTOR (AFID)/THERMIONIC DETECTOR (TID)... 

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