Phosphorus-specific detector

Abel et al. [389] determined simazine in estuary water by adsorption on a Ci8 SPE cartridge followed by determination by HR-GC using a nitrogen-phosphorus specific detector. 

Durand and Barcelo [390] carried out a study of the interferences in the analysis of chlortriazines in seawater using GC-MS secondary ion monitor spectrometry and by GC using a nitrogen-phosphorus specific detector C39. 

Generally, a nitrogen phosphorus-specific detector is used in the determination of organophosphorus insecticides in soil [316-318]. Use of an acetone-n-hexane extraction solvent led to recoveries of 54-83%. 

Verwej et al. [175] have described a procedure for the determination of PH3-containing insecticides in surface water. In this procedure the insecticide is hydrolysed to methylphosphonic acid, and the acid is concentrated by anion exchange and converted to the dimethyl ester. After clean-up on a microsilica gel column the ester is analysed by gas chromatography using a thermionic phosphorus-specific detector. Detection limit is lnmol L 1. 

A Rapid Gas-Liquid Chromatographic Determination of Serum Lidocaine Using a Nitrogen-Phosphorus Specific Detector... 

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. 

The pesticides included in this study were fenvalerate, chlordecone (kepone), chlorothalonil, and chlorpyrifos. Fenvalerate is a synthetic pyrethroid insecticide used, for example, for mites on chickens. Its chemical name is cyano(3-phenoxyphenyl)-methyl 4-chloro-alpha-(1-methylethyl)benzeneacetate. Chlordecone is an insecticide, no longer used, and has a chemical name decachloro-octahydro-l,3,4-metheno-2H-cyclobuta(cd)=pentalen-2-one. Chlorothalonil is fungicide used on tomatoes whose chemical name is 2,4,5,6-tetrachloroisophthalonitrile. Chlorpyrifos is an insecticide with a chemical name 0,0-diethyl 0-(3,5,6-trichloro-2-pyridyl)phosphorothioate. Chlorpyrifos is the U. S. Food and Drug Administration chromatographic reference standard since numerous specific detectors (electron capture, flame photometric in both sulfur and phosphorus modes, alkali flame, nitrogen phosphorus, and Hall detectors) are sensitive to it. 

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. 

The alkali flame ionization detector (AFID) or thermionic detector (TID) is a specific detector used primarily in the trace analysis of pesticides particularly those containing phosphorus. 

Barrio et al. [137] used pyrolysis-gas chromatography to study organic matter evolution in sewage sludge-amended soils. Nitrogen-phosphorus specific flame ionisation and mass spectrometric detectors were used. 

The most popular thermionic detector (TID) is the nitrogen-phosphorus detector (NPD). The NPD is specific for compounds containing nitrogen or phosphorus. The detector uses a thermionic emission source in the form of a bead or cylinder composed of a ceramic material impregnated with an alkyl-metal. The sample impinges on the electrically heated and now molten potassium and rubidium metal salts of the active element. Samples which contain N or P are ionized and the resulting current measured. In this mode, the detector is usually operated at 600-800°C with hydrogen flows about 10 times less than those used for flame-ionization detection (FID). 

Most OP insecticides may be determined directly by GC using the phosphorus-selective flame photometric detector (FPD) which helps to minimize clean-up. However, it must be emphasised that the FPD is only a "selective" detector for phosphorus (at 540 nm) or sulphur (at 394 nm) and not an "element specific detector". 

Gas chromatography (GC) analysis with element-specific detectors, for example, a nitrogen-phosphorus detector (NPD), a flame photometric detector (FPD, in sulfur or phosporus mode) and/or an atomic emission detector (AED) ... 

Specific detectors respond to a particular type of compound or a particular chemical group. An example of a specific GC detector would be NPD that responds specifically to compounds containing nitrogen and phosphorus. In LC the fluorescence detector would be a typical specific detector that responds only to those substances that fluoresce. 

The response of a GC detector can be general or specific. A detector with a catholic response such as the FID is used widely in routine analysis. The specific detector, such as the nitrogen-phosphorus detector (NPD), is extremely useful for measuring particular types of compounds such as herbicides and pesticides, where the compounds of interest are not eluted discretely but mixed with a number of other contaminating compounds. Examples of this type of application will be given when the NPD is discussed in detail. 

The nitrogen phosphorus detector (NPD) (sometimes called the thermionic detector) is another sensitive, but, in this case, a specific detector, that is based on the FID. Physically the sensor appears to be similar to the FID but, in fact, operates on an entirely different principle. A diagram of an NPD detector is shown in figure 9. 

In trace analysis of contaminant substances, one can use specific detectors for certain compounds, such as a nitrogen-phosphorus detector (NPD), thus gaining detection ability for nitrogenated and phosphorylated compounds the electron-capture detector (ECD) shows excellent performance for chlorinated substances and the flame photometric detector (FPD) is the most widely used for sulfur-containing compounds. 

Two other types of element-specific detector for nitrogen currently in use coupled to SFCs are the nitrogen phosphorus detector (NPD) and the thermal energy analyzer (TEA). The NPD uses a hot, catalytically active solid surface immersed in a layer of dissociated H2 and O2 to form electronegative N and P ions which are detected on a nearby electrode [2]. NPD has been shown to have broad application in SFC, especially in the agrochemical industry [3]. The TEA, as described by Fine et al. [4], uses low-temperature pyrolysis, followed by ozone-induced chemiluminescence, for the detection of compounds containing NO2 groups. The TEA has been used for the determination of tobacco-specific nitrosamines and explosives [5]. Both of these detectors require spedlic standards of the analytes of interest for quantitation... 

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