Flame ionization detector, general

The flame ionization detector is capable of measuring only gaseous hydrocarbons, in other words, hydrocarbons that have a low boiling point. Emission gases can, however, also contain hydrocarbons in liquid form at ambient temperature and pressure. Therefore, analyzers based on flame ionization detection are generally equipped with heating elements to keep rhe sampling line and the detector at about 200 °C. 

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. 

The flame ionization detector Is the most popular of the flame-based detectors. Apart from a reduction in sensitivity compared to expectations based on gas chromatographic response factors [138] and incompatibility with the high flow rates of conventional bore columns (4-5 mm I. 0.), the flame ionization detector is every bit as easy to use in SFC as it is in gas chromatography [148,149]. It shows virtually no response to carbon dioxide, nitrous oxide and sulfur hexafluoride mobile phases but is generally incompatible with other mobile phases and mixed mobile phases containing organic modifiers except for water and formic acid, other gas chromatographic detectors that have been used in SFC include the thermionic ionization detector (148,150], ... 

Chromatographic system. (Follow the method described in the general procedure <621 >.) The gas chromatograph is equipped with a flame ionization detector and a 1.2 m x 2 mm column packed with 3% phase G32 on support S1A. The injection port, detector, and column temperatures are maintained at about 250, 300, and 250 °C, respectively, and helium is used as the carrier gas, flowing at rate of about 50 mL/min. The relative retention times for cholestane and miconazole nitrate are about 0.44 and 1, respectively. Chromatograph the Standard preparation, and record the peak responses as directed for procedure The resolution, R, between cholestane and miconazole nitrate is not less than 2 and the relative standard deviation of replicate injections is not more than 3%. 

Gas chromatography detectors employed for the determination of volatile organics in soil are generally flame ionization detectors (FIDs), photoionization... 

For semivolatile constituents of petrolenm, the gas chromatograph is generally eqnipped with either a packed or a capillary colnmn. Either neat or dilnted organic liqnids can be analyzed via direct injection, and componnds are separated dnring movement down the column. The flame ionization detector nses a hydrogen-fneled flame to ionize compounds that reach the detector. For PAHs a method is available (EPA 8100) in which injection of sample extracts directly onto the colnmn is the preferred method for sample introdnction for this packed-colnmn method. 

With enantiomer analysis, however, a linear detector response is indispensible. Thus, for the correct determination of. say, 0.1 % of an enantiomeric impurity, linearity within a concentration range of at least three orders of magnitude is required. It is generally accepted that the flame ionization detector (FID) does fulfill this requirement, but it is recommended that the linear detector response is verified via dilution experiments31. In contrast, the linear response range of the electron capture detector is low, being only two to three orders of magnitude. 

Generally, the detector response will depend on the type of aromatic amine detected. Table I shows that response to N,N-di-methylaniline is about twice as high as the response to its primary isomer 2,6-dimethylaniline. Sensitivity for a selected number of aromatic amines was found to be increased by a factor 5-16 in comparison to a flame-ionization detector. 

The most general purpose detector for open tubular chromatography is a mass spectrometer. Flame ionization is probably the most popular detector, but it mainly responds to hydrocarbons and Table 24-5 shows that it is not as sensitive as electron capture, nitrogen-phosphorus, or chemiluminescence detectors. The flame ionization detector requires the sample to contain SlO ppm of each analyte for split injection. The thermal conductivity detector responds to all classes of compounds, but it is not sensitive enough for high-resolution, narrow-bore, open tubular columns. 

One major aspect of quantitative analysis is sensitivity and dynamic range of linearity. Such data have been reviewed (2) for the gas density, thermal conductivity, and flame ionization detectors. Since response is a function of molecular weight in the gas density detector, it is difficult to make comparisons in a simple manner. In general, however, the sensitivity of the gas density cell is about twice that of comparable thermal conductivity cells and about one-tenth that of flame ionization detectors (when bleed of the column is limiting). 

Selection of GC detectors is very crucial in chemical analysis. Flame ionization detector (FID) and thermal conductivity detector (TCD) can be used for all general purposes. The detection limits for analytes, however, are high, especially for the TCD. The latter is commonly used for gas analysis. 

The recovered lemon oil samples were analyzed by gas chromatography. A 0.5 mm i.d. x 30 m thin film (0.1 pm) SE-30 glass capillary column (Supelco, Inc., Bellefonte, PA) was used with a flame ionization detector. The temperature was programmed from 348 to 473 K. Peak identification was based on information of Supelco, Inc., A. M. Todd Company, and Staroscik and Wilson (] ). Staroscik ( ) provided us with the response values used in his work and we assumed that our detector would give proportionate responses. Staroscik found in his work that relative standard deviations of the response values were generally less than 3%. 

Many GC detectors exist, but not all are suitable for phytochemicals. The thermal conductivity detector (TCD) is considered a universal detector and is appropriate for most analytes as long as the thermal conductivity of the carrier gas is different from that of the analytes. During the early development phase of GC, TCD was an easy choice because thermal conductivity measuring devices were already in use (Colon and Baird, 2004). Ionization detection arrived with its improved trace determinations and replaced TCD in many applications. While TCD is still used for some food applications (Allegro et ak, 1997 Sun et ak, 2007) and in the past was used for phenolic acids (Blakely, 1966), currently it is not generally used for phytochemicals. Rather, the flame ionization detector (FID) is better-suited due to its selectivity for organic compounds and superior measuring ability for trace measurements. 

Detailed kinetic models almost never include all species that are known to be present in the reactor. As an example, it is well known to everyone who has used a gas chromatograph with a flame-ionization detector, that ions are present in hydrocarbon flames. However, mechanisms for methane flames do not, in general, include the reactions of ions. The fact is that implicitly reduced mechanisms are used more often than not in modelling work understanding how objectively reduced mechanisms can be generated is, therefore, of primary importance. 

Additionally, subsequent analysis of the materials for compliance to various regulations is based on solvent extraction protocols followed by GC/FID (flame ionization detector) analysis. These protocols are generally based on specific target compounds that are regulated rather than analysis for all compounds present. From our experience we have documented many problems related to such an approach. The following case studies emphasize the need for thoroughly analyzing materials for suitability early on in the developmental process. 

The flame ionization detector (FID) is the most widely used and generally applicable detector for gas chromatography. With a detector such as that shown in Figure 31-8, effluent from the column is directed into a small air/hydrogen flame. Most organic compounds produce ions and electrons when pyrolyzed at the temperature of an air/hydrogen flame. Detection involves monitoring the current produced by... 

Functional groups, such as cai bonyl, alcohol, halogen, and amine, yield fewer ions or none at all in a flame. In addition, the detector is insensitive toward noncombustible gases such as H2O, CO2, SO2, and NOf These properties make the flame ionization detector a most useful general detector for the analysis of most organic samples, including those that are contaminated with water and the oxides of nitrogen and sulfur. 

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