Flame ionization detection principle

A total hydrocarbon analyzer used by the auto industry uses the flame ionization detection principle to identify specific hydrocarbons in auto exhaust. 

Following the separation of pyrolysates, the detection can be done using common procedures for GC such as thermal conductivity detection, flame ionization detection (FID), etc. However, nonselective detectors without the identification capability are less common than mass spectrometric detection. While a GC separation with FID detection can provide only a fingerprint chromatogram for a specific polymer pyrolysate, mass spectrometry allows, at least in principle, the identification of pyrolysate components. 

Method 21 monitoring is conducted to quantify the fugitive VOC leaks and identify components (illustrated in Figure 4), which are candidates for repair. Qatargas utilizes a Toxic Vapor Analyzer (TVA) which utilizes flame ionization detection (FID) principle to measure the VOC leak concentration. The equipment is fully compliant with the monitoring requirements of Method 21. 

As an alternative, Lindstrom et a. [16] used a Fourier transform infrared (FTIR) spectrometry with flame ionization detection to determine the sum of hydrocarbons in the gas phase as NMHCs (non-methane hydrocarbons). The best result for diesel slip indicates a background signal of 10 ppmv corresponding to 120-200 ppmv carbon. A higher accuracy of lOOppbv for each Cy fraction leads to the best case conversion of 99.9966%. TOC measurements in the range 0.5-2 mgl are definitely more accurate. Conversion higher than 99.99966% demands a TOC lower than 1.75 mg 1 or a residual amount of carbon in the gas phase of 0.77 ppmv. In principle, accuracies in the ppb range are possible with specialized GC techniques [21, 22]. 

From a practical point of view, SFC may allow the use of many different detection principles, including both typical LC detectors (UV-absorbance, fluorescence) and typical GC detectors (flame ionization, mass spectrometry). Also, capillary SFC seems to be well within the posssibilities of current technology, while capillary LC is not. 

Organic compounds ionize when burned in a hydrogen air flame. If two electrodes at a potential difference of approximately 150 V are inserted into this flame, differences in conductivity of the flame can be measured as the solutes elute from the column and are burned. This isthe principle on which the flame ionization detector is based. In the usual flame detector, the column effluent ismixed with hydrogen. This mixture is fed into the flame jet of the detector. The jet is a thin-walled stainless steel tube that also acts as one electrode. The other electrode is a fine platinum wire held above the jet. The response of this detector is practically instantaneous. It is not affected as much as the thermal conductivity detector is by changes in temperature and carrier gas flow rate. It is very sensitive and can detect approximately 10 °-10 mol solute. 

Several commercial evidential breath alcohol measurement devices are available. The principle of measurement is either infrared absorption spectrometry (most common), dichromate-sulfuric acid oxidation-reduction (photometric), GC (flame ionization or thermal conductivity detection), electrochemical oxidation (fuel cell), or metal-oxide semiconductor sensors. A list has been published of DOT-approved breath alcohol devices.Some of these devices are approved for screening only. In this case, the second or confirmatory breath alcohol determination must be performed with an approved evidential breath alcohol analyzer. Breath alcohol devices may also be used for the medical evaluation of patients at the point of care (e.g., emergency department). A Fourier transform infrared point-of-care breath analyzer capable of measurement of... 

The carbon monoxide gas is carried by the carrier gas passing the probe to a gas analyzing unit, which continuously measures the carbon content of the gas. The carbon monoxide is converted by catalytical hydriding to form methane, which is then determined by means of a flame ionization detector. This principle is applied in the Harwell carbon meter At 550 °C the sensitivity of such a probe allows the detection of a chemical activity of carbon in sodium in the level of = 10. This activity corresponds to a concentration of about 10 wppm carbon in sodium. 

Mass detector. The liquid chromatographer s demand for a universal detector which overcomes some of the problems encountered with the RI detector, (such as poor sensitivity and temperature instability) led to the development about ten years ago of the mass detector described here. The transport detectors of the 1960s detected the solute by means of a flame ionization detector after removal of the solvent from the eluent stream. They were abandoned, owing to lack of sensitivity and mechanical problems associated with the moving belt or wire. The new mass detector is similar in principle, but here the eluent leaves the column and is pumped into a nebulizer, assisted by an air supply. The atomized liquid is passed into a heated evaporation column where all the solutes less volatile than the solvent are carried down the column as a cloud of fine particles. A light source and photomultiplier arranged at the bottom of the column, perpendicular to the flow, detect the cloud of particles. The output from the photomultiplier, which is proportional to the concentration, can be amplified and directed to a recorder or data system. 

Obviously, the chromatographic principles are the same in process and laboratory GCs and they are built up in a very similar way. Standard detectors are in each case the thermal conductivity detector (TCD), which is a universal detector for all components, and the flame ionization detector (HD), which is a specific detector for hydrocarbons. To detect sulfur gases selective detectors like an electrochemical detector, chemiluminescence detector and, most important, flame photometric detector (FPD) are used. Gaseous fuels hke natural gas, synthetic gases, and blends are complex mixtures that cannot completely be separated in a single column. Two or more different columns must be combined. To monitor the fuel quality a quasi-continuous analysis is necessary this means that very short cycle times must be realized. To do so, high-boiling components are removed... 

Gas Detection Principles. Some of the more common gas detection principles used in toxie gas monitoring include electroehemistry, electro-optical detection, solid state detection, mass spectrometry, moleeular (or flame) emission speetrometry,irrfrared speetrophotometry, ionization teeh-niques, and thermal conduetivity. Brief deseriptions of several different gas detection technologies are deseribed below. 

Of the available standard detection principles, thermal conductivity (TCD), flame ionization (FID) and electron capture (ECD), FID has been the most widely used, owing to its response to most organic compounds, its good linearity and detection limits. In contrast, the ECD is only effective when electron-capturing groups are present in the molecule. For example, it is... 

Finally, we would like to mention a derivative of OG spectroscopy, which is conducted not in a discharge cell but in a (hot) flame the technique is often referred to as laser-enhanced ionization (LEI). The technique is used for sensitive detection of trace atoms and molecules. The excitation of the species under investigation populates high-lying energy levels the thermal heat of the hot flame is sufficient to ionize the species out of their excited levels. Electrodes placed around the flame detect the charge carriers generated in this way. Further details on the principles and applications of OG spectroscopy and LEI can be found, for example, in Stewart et al. (1989). 

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