Flame photometric detector , selective

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. 

The flame-photometric detector (FPD) is selective for organic compounds containing phosphoms and sulfur, detecting chemiluminescent species formed ia a flame from these materials. The chemiluminescence is detected through a filter by a photomultipher. The photometric response is linear ia concentration for phosphoms, but it is second order ia concentration for sulfur. The minimum detectable level for phosphoms is about 10 g/s for sulfur it is about 5 x 10 g/s. 

Flame Photometric Detector3 With the flame photometric detector (FPD), as with the FID, the sample effluent is burned in a hydrogen/air flame. By using optical filters to select wavelengths specific to sulfur and phosphorus and a photomultiplier tube, sulfur or phosphorus compounds can be selectively detected. 

On the other hand, if only specific GC detectors, e.g. the electron capture, nitrogen-phosphorus or flame photometric detectors, are tested, the argument of lack of GC method sensitivity is not acceptable. In most cases mass spectrometric detectors provide the sensitivity and selectivity needed. Unfortunately, tandem mass spectrometry (MS/MS) or MS" detectors for GC are still not widely used in official laboratories, and therefore these techniques are not always accepted for enforcement methods. 

The chemiluminescent reaction with chlorine dioxide provides a highly sensitive and highly selective method for only two sulfur compounds, hydrogen sulfide and methane thiol [81]. As in the flame photometric detector (FPD), discussed below, atomic sulfur emission, S2(B3S -> ) is monitored in the wave-... 

The analysis of organosulphur compounds has been greatly facilitated by the flame photometric detector [2], Volatile compounds can be separated by a glass capillary chromatographic column and the effluent split to a flame ionization detector and a flame photometric detector. The flame photometric detector response is proportional to [S2] [3-6]. The selectivity and enhanced sensitivity of the flame photometric detector for sulphur permits quantitation of organosulphur compounds at relatively low concentrations in complex organic mixtures. The flame ionization detector trace allows the organosulphur compounds to be referenced to the more abundant aliphatic and/or polynuclear aromatic hydrocarbons. 

The responses of these three detectors to a variety of organophosphorus molecules have often been compared the results seem to vary from compound to compound165,179,217,238,289. In many instruments the stream is split and passes through several detectors for parallel measurements184,187,298. The flame photometric detectors are the most selective for phosphorus, yield less extraneous peaks and make the identification work easier188. 

A flame photometric detector measures optical emission from phosphorus, sulfur, lead, tin, or other selected elements. When eluate passes through a Hrair flame, as in the flame ionization detector, excited atoms emit characteristic light. Phosphorus emission at 536 nm or sulfur emission at 394 nm can be isolated by a narrow-band interference filter and detected with a photomultiplier tube. 

Eluate from a chromatography column can be passed through a plasma to atomize and ionize its components and measure selected elements by atomic emission spectroscopy or mass spectrometry. An atomic emission detector directs eluate through a helium plasma in a microwave cavity. Every element of the periodic table produces characteristic emission that can be detected by a photodiode array polychromator (Figure 20-14). Sensitivity for sulfur can be 10 times better than the sensitivity of a flame photometric detector. 

Because the FPD responds to both aerosol and gaseous sulfur species, it has also been possible to modify these instruments to continuously measure aerosol sulfur by selectively removing gaseous sulfur compounds with a lead(II) oxide-glycerol coated denuder (55). Use of such an instrument for airborne measurements of aerosol sulfur in and around broken clouds has been reported (57). In principle, speciation between aerosol sulfate, disulfate, and sulfuric acid by selective thermal decomposition (58, 59) can also be achieved. Flame photometric detectors have also been used as selective detectors for gas chromatography. Thornton and Bandy (60) reported the use of a chromatographic system with a flame photometric detector for airborne measurement of S02 and OCS with a detection limit of 25 pptrv. 

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). 

The carboxin is extracted from the sample with acetone in a Soxhlet extraction apparatus and, after concentration of the extract, is determined via gas-liquid chromatography using a nitrogen-selective detector. The presence of carboxin is confirmed by the use of a sulfur flame photometric detector. Recoveries ranged from 73 to 80% (barley) and 73 to 78% (wheat). 

Flame photometric detector (FPD) selective to compounds containing sulfur and phosphorus... 

Selective to sulfur and phosphorus compounds more selective than NPD to compounds containing phosphorus Flame photometric detector Organophosphorus pesticides (EPA 8141) Sulfur compounds may interfere with organophosphorus pesticides. 

It is obvious from the FTIR and NMR analyses of these extracts that in order to positively identify organosulfur structures we need an analytical technique that is sulfur selective. That is, a technique that responds to sulfur uniquely. One such technique, applicable to the problem in hand, is GLC-FID/FPD where the flame photometric detector is set in the sulfur selective mode. 

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". 

The detection limits of a pulsed flame photometric detector (PFPD) are much better than those of any conventional FPD, and in addition the detector does not suffer the quenching of co-eluting hydrocarbon chemicals (45). The ability to also detect arsenic or nitrogen containing chemicals makes the PFPD very useful for the screening of CWC-chemicals. Frishman and Amiraw (46) used fast GC equipped with a short capillary column (1.5 m) and PFPD for the analysis of air samples. A complete analysis cycle time of 30 s was demonstrated. Killelea and Aldstadt (47) used PFPD in the arsenic selective mode for the analysis of organoarsenic chemicals. 

A more expensive alternative is to use standard AutoAnalyser type systems, based on multichannel peristaltic pumps, to pump samples and reagents and/or diluents at the desired rates to give automatic mixing at the desired ratio. Flame photometric detectors have been used for many years with AutoAnalysers, especially in clinical laboratories. Curiously, in the past, this approach has less often been routinely used in environmental analytical laboratories employing flame spectrometry, perhaps because an attractive feature of flame spectrometry is the speed of response when used conventionally. Over the past few years, however, there has been an increasing tendency towards fully automated, unattended operation of flame spectrometers. This undoubtedly reflects, at least in part, the improvements in safety features in modern instruments, which often incorporate a comprehensive selection of fail-safe devices. It also reflects the impact of microprocessor control systems, which have greatly facilitated automation of periodic recalibration. 

Another important means of selective detection is the flame photometric detector. 

Using a flame-photometric detector sensitive to sulphur, selective detection can be obtained at the nanogram level, with the possibility of carrying out the reaction on the micro-scale with only 50 pi of the sample. These derivatives give symmetric peaks on SE-30. 

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