Bones Multidimensional Gas Chromatography

Peter Q. Tranchida , Luigi Mondello , in Separation Science and Applied science, 2020

half dozen.1.1 Flame ionization detection

The FID, especially in the get-go decade of the GC×GC history, was by far the most common detector used. The intrinsic characteristics of the FID—universal response to almost all organic compounds, low limits of detection (LoDs), high conquering frequency, wide linearity range, limited internal volume, and reduced maintenance necessities [7]—made it an obvious pick, specially in petrochemical applications [8]. Even though the production of some very circuitous GC×GC-FID chromatograms did highlight the belittling power of the multidimensional GC technology, it did as well emphasize the demand for more than data-rich detectors.

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Methods

R.A. Shellie , in Encyclopedia of Forensic Sciences (Second Edition), 2013

Flame Ionization Detector

An FID is among the most commonly used detectors; it is unresponsive to air, water, carbon dioxide, ammonia, hydrogen sulfide, sulfur dioxide, and most GC carrier gases, merely responds readily to compounds containing carbon and hydrogen. Cations and electrons are produced when the effluent of a GC column containing vapors of organic substances is combusted in a hydrogen/air flame. A collector electrode is used to collect the created ions and produce a small current. The electrical conductivity of the flame is very sensitive to the presence of organic vapors and an FID tin can respond to approximately 20   pg of each component eluting from a capillary GC cavalcade.

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Forensic Science

Ilkka Ojanperä Ilpo Rasanen , in Handbook of Analytical Separations, 2008

eleven.5.ii Detection

Flame-ionization detector (FID) has a nearly universal response to organic compounds, a low LOD and a wide linear response range (107). The FID response results from the combustion of organic compounds in a small hydrogen-air diffusion flame. Information technology is the most popular GC detector in current use. In drug screening, withal, in that location may be interference from biological background, and this may be pronounced with post-mortem samples. In the absence of reference standards, FID can be used to predict relative response factors of known structures with reasonable accurateness using the constructive carbon number concept, as shown with amphetamine-type compounds by Huizer et al. [68].

NPD is identical to FID, except that an alkali metal table salt source is placed betwixt the burner tip and the collector. Using low hydrogen flow rates, NPD is selective to nitrogen, having 10four–x5 times the response relative to carbon, and has a moderate linear response range (tenfive). Tables 11.1 and xi.2 show that NPD is the most popular detector in toxicological drug screening. Most nitrogen-containing drugs give a satisfactory response, just nitro-compounds, amides and carbamates, such as meprobamate, are less favourable. Both the selectivity and the sensitivity of the detector are dependent on experimental variables, including the source heating current, source location, jet potential, air and hydrogen flow rates and choice of carrier gas. Peculiarly the alkali bead lifetime may vary markedly depending on the individual bead and on the samples. With a workload of 30 runs per twenty-four hours in the authors' laboratory, the chaplet from a major manufacturer lasted from two weeks to four months. NPD is non uniform with silylation reagents and halogenated injection solvents such every bit dichloromethane.

Surface ionization detector (SID) is based on a like principle to NPD, but information technology is substance-selective rather than chemical element-selective. Co-ordinate to Kageura et al. [69], SID exhibited a high response for tertiary amines, a rather low response for secondary amines, no response for amides and little or no response for xanthines and benzodiazepines. Despite its potential in forensic toxicology, SID has not been used in comprehensive GC screening for drugs.

Electron capture detection (ECD) can be used for the sensitive analysis of compounds that take high electron affinities. Electrons produced from a radioactive 63Ni source are selectively captured by, eastward.g., pesticides and drugs with certain structures, such as a halo grouping or the nitro grouping, or with bottom sensitivity, the carbonyl group. ECD is normally practical to toxicological screening for benzodiazepines [34,40], but information technology produces no response with the 7-amino derivative of nitrazepam. The detector's linear response range is somewhat limited (104), which may result in a need to dilute the sample.

MS detection has, to a certain extent, replaced the detectors described above due to its unsurpassed properties in structural analysis. Still, routine target screening of fifty–200 compounds is oft more feasible using selective detectors such equally NPD and ECD. These detectors become even more attractive when comprehensive screening and simultaneous quantification are required at low concentrations in blood. In MS, the number of compounds that can be analysed in ane run using selected ion monitoring (SIM) has been restricted, and the full browse mode may in turn lack sufficient sensitivity. This dilemma may be solved past splitting the GC-MS column effluent to a second selective detector like NPD.

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AIR Assay | Workplace Air

J. Yu , R.M.A. Hahne , in Encyclopedia of Analytical Science (2nd Edition), 2005

Photoionization/flame-ionization detectors (PIDs/FIDs)

PIDs and FIDs detectors are oftentimes used in situations where loftier sensitivity (sub-ppm levels) and express selectivity (broad-range coverage) are desired. The normal working range is betwixt 0.ane and 100000   ppm for FID and 0.2–2000   ppm for PID. PID/FIDs are commonly used for detecting volatile organic compounds (VOCs) such as benzene/toluene/xylene, vinyl chloride, and hexane, and provide quick response for this growing concern.

A PID operates by ionizing components of a sample stream with loftier-free energy ultraviolet UV light (while FID operates by ionizing components with high-temperature hydrogen/air flame) and detecting the resulting charged particles collected at an electrode inside the detector. Advantages of this technology include the fast response time and first-class shelf-life. PIDs endure from sensor drift and humidity effects; therefore, calibration requirements are more demanding than other mutual gas detectors.

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POLYMER ADDITIVES: SUPERCRITICAL FLUID CHROMATOGRAPHY

T.P. Hunt , in Encyclopedia of Separation Scientific discipline, 2000

Identification of Unknown Additives

FID and UV detection are sufficient for the analysis of an additive packet of known composition. The gild of the eluting peaks is determined in this case by comparing their retention times with those of the pure additives, eluted nether identical conditions; however, this process is clearly impossible for the identification of a mixture unknown additives. Hence there is a requirement for the SFC separation to be coupled with a spectroscopic technique which records sufficient structural and fingerprinting information on the eluting additive to enable it to exist identified either by deduction or past comparison with library records.

Fourier transform infrared (FTIR) spectroscopy tin can exist coupled indirectly to capillary SFC past depositing the additive on to an infrared disc or directly by passing the cavalcade outflow through a flow prison cell. The latter technique is possible because carbon dioxide exhibits but two narrow absorption bands in the about infrared spectrum. Alternatively xenon, which is completely transparent to infrared, tin can be used as the mobile phase. Both interfaces have been successfully used to place a wide range of stabilizers; even so, they lack sensitivity and quantitative measurements have non been achieved. The poor sensitivity necessitates the employ of 100   μm i.d. columns.

Carbon dioxide is a nonprotonated solvent and this makes SFC the ideal chromatographic technique to couple with aneH nuclear magnetic resonance (NMR). The relatively large dead book of the NMR probe means that it can only be interfaced with packed column SFC with flow rates >one   mL min−1 and sample loadings of xx–120   μL. This procedure has ben used to analyse phthalate plasticizers. Unfortunately, SFC-NMR signals take been constitute to be pressure-dependent and showroom increased spin-lattice relaxation times.

SFC has been virtually successfully coupled to mass spectroscopy (MS). MS detectors tin be used in several modes to give molecular ion information and structural data from fragmentation patterns which tin can exist compared with library records to identify an unknown additive. Total ion chromatograms can also exist used for quantitative analysis. Capillary SFC is interfaced directly by feeding the cease of the cavalcade into the ionization chamber of the MS. The MS betoken is non affected by the SFC pressure gradient. This has been used for the identification and quantitation of flame retardants from polyurethane foams. Several interfaces (moving belt, thermospray, particle beam) have been used to couple packed-cavalcade SFC and MS. These tend either to inhibit the range of compatible SFC atmospheric condition or upshot in the loss of volatile components. The almost promising system is currently atmospheric force per unit area chemic ionization MS which has been used with a carbon dioxide–methanol limerick gradient to place and quantify benzotriazoles and phenolic stabilizers.

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FRAGRANCES: GAS CHROMATOGRAPHY

East.R. Adlard , M. Cooke , in Encyclopedia of Separation Science, 2000

Detection

The FID is the workhorse detector for aroma analysis. Information technology has many advantages just lacks the sensitivity of some of the selective detectors which may exhibit upward to 10three times better lower limit of detection as well as giving qualitative information. Figure half dozen gives two headspace chromatograms of coffee olfactory property, i obtained with an FID and the other with a helium ionization detector with less than half the gas volume (twoscore   μL equally opposed to 100   μL for the FID) which shows the much bigger response of the latter; the tailing in the helium detector chromatogram is due to the response to a water superlative. In this instance, the helium detector clearly has dandy advantages over the FID.

Figure half-dozen. Helium ionization detector and FID chromatograms of coffee aroma. Column: 100   thou×0.5   mm i.d. stainless steel coated with Witconol LA-23. Column temperature 60°C isothermal. Sample introduced via a gas sampling valve. (Reproduced from Andrawes FF and Gibson EK Journal of High Resolution Chromatography (1952) with permisson from Wiley–VCH.)

Every bit pointed out earlier, many olfactory property compounds comprise hetero-elements and Figure 7 shows headspace chromatograms of coffee smell obtained with an FID and the pulsed flame photometric detector in the sulfur mode, which shows the presence of a big number of sulfur compounds. This detector can too be used in a nitrogen-selective mode to reveal the presence of pyrroles, pyrazines and caffeine in the coffee aroma.

Effigy 7. Pulsed flame photometric detector (in S way) and FID chromatograms of coffee odor. (From Varian publication 03-914625-00, 1998. Past courtesy of Varian Assembly.)

The Fourier transform infrared detector (FTIR) should be extremely useful in aroma analysis considering of its ability to give a response to specific functional groups in a molecule. This detector is gradually coming into use for this type of work (see Further Reading) merely the sensitivity to different functional groups varies considerably and the capital cost is quite large. The mass spectrometer in the selective ion monitoring style probably gives the best all-circular sensitivity. Full browse mass spectra tin give sensitivities in the pg range nether favourable circumstances. Effigy eight shows a mass chromatogram and a Gram-Schmidt FTIR chromatogram of a dynamic headspace sample of the vapour above a detail variety of strawberries. The identity of the peaks is given in Table i. Although there is a general similarity between the two chromatograms, there is a considerable divergence in detailed quantitative response, with some pocket-sized peaks in the mass chromatogram giving a large FTIR response.

Figure 8. (A) Mass chromatogram of a headspace sample above strawberries; (B) FTIR chromatogram of the same sample. For peak identities encounter Table 1. (By courtesy of the Journal of High Resolution Chromatography (1997), 20: 279.)

Tabular array 1. Compounds in strawberry aroma identified by GC-MS and GC-FTIR

Top no. a Compound RRT (%SD, n=three) m/z λmax (cm−1)
ane Acerb acid 0.141 43 (100%), lx (M+, 83%) No data
(5.four%)
2 Methyl acetate 0.156 43 (100%), 74 (M+, xv%) 2966, 1777, 1757, 1448
(v.2%) 1372, 1240, 1048
3 Ethyl acetate 0.255 43 (100%), 61 (5%), 2992, 1769, 1755, 1373,
(3.6%) 88 (M+, nineteen%) 1238, 1093, 1052
iv Isopropyl acetate 0.310 43 (100%), 59 (6%), 2985, 2904, 1755, 1383,
(2.half dozen%) 61 (26%), 87 (ii%), 1239, 1138, 1021
102 (G+, 9%)
5 Ethyl propionate 0.393 57 (100%), 74 (12%), 2992, 2958, 1753, 1185
(one.vii%) 102 (Thousand+, 33%)
6 Methyl butyrate 0.415 43 (100%), 55 (11%), 2968, 1760, 1444,
(iii.4%) 59 (13%), 71 (28%), 1359, 1297, 1256,
74 (33%), 87 (8%), 1184, 1103
102 (M+, 12%)
seven 4-Methyl- 0.440 43 (100%), 58 (13%), 2960, 2881, 1729, 1373,
2-pentanone (1.8%) 85 (40%), 100 (M+, 26%) 1285, 1240, 1176
8 Ethyl 0.499 43 (100%), 71 (29%), 2973, 2895, 1755, 1461, 1442,
isobutryate (one.five%) 88 (14%), 116 (Thousand+, 22%) 1390, 1365, 1249,
1234, 1188, 1154, 1096
1083, 1021
9 Methyl 0.518 41 (55%), 43 (100%), 2966, 2889, 1759, 1440,
2-methylbutyrate (one.vii%) 55 (xx%), 57 (58%), 1363, 1292, 1242, 1186,
59 (25%), 69 (12%), 1112, 1017
74 (12%), 85 (20%)
88 (52%), 101 (13%),
116 (M+, 4%)
10 Methyl 0.518 41 (forty%), 43 (100%), 2969, 2896, 1757, 1466,
isobutyrate (1.5%) 57 (17%), 59 (17%), 1445, 1378, 1363, 1299,
74 (22%), 85 (9%), 1257, 1187, 1161, 1112,
101 (five%), 116 (Thou+, vi%) 1099, 1018
11 n-Hexanal 0.567 41 (100%), 44 (45%), 2940, 2885, 2811, 2714,
(1.1%) 56 (xxx%), 72 (7%), 1744
82 (16%), 99 (7%),
100 (M+, iv%)
12 Ethyl butyrate 0.567 43 (100%), 60 (10%), 2983, 1754, 1255, 1181
(1.4%) 70 (4%), 71 (45%),
88 (19%), 89 (15%),
101 (iv%), 116 (M+, 14%)
xiii Isobutyl acetate 0.587 41 (xviii%), 43 (100%), 2969, 2886, 1764, 1485,
(ane.i%)
56 (14%), 61 (21%), 1372, 1234, 1064, 1032
69 (eight%), 71 (8%),
116 (Yard+, x%)
xiv Isopropyl 0.637 41 (43%), 43 (100%), 2981, 2944, 2890, 1750,
isobutyrate (1.ii%) 71 (forty%), 89 (35%), 1468, 1376, 1238, 1184,
130 (Grand+, 2%) 1152, 1091, 1030
15 Ethyl 0.674 41 (100%), 43 (l%), 2979, 2948, 2891, 1750,
2-methylbutyrate (0.7%) 57 (67%), 69 (21%), 1466, 1377, 1248, 1182,
74 (12%), 85 (11%), 1149, 1088, 1033
115 (5%), 130 (M+, 12%)
16 Ethyl isovalerate 0.678 43 (100%), 57, (59%) 2971, 2884, 1753, 1468,
(0.8%) 69 (10%), 87 (twenty%), 1374, 1295, 1250, 1184,
130 (Thousand+, 10%) 1115, 1039
17 Hex-2(Z)-enal 0.681 41 (100%), 55 (41%), 2972, 2949, 2885, 2814,
(0.9%) 69 (18%), 83 (eleven%), 2727, 1715, 1634, 1151,
98 (Chiliad+, 14%) 1091, 1037, 981
18 Isoamyl acetate 0.712 43 (100%), 55 (24%), 2969, 2887, 1761, 1468,
(1.five%) 61 (seven%), 70 (17%), 1371, 1234, 1038
87 (4%), 130 (1000+, 4%)
nineteen 2-Methylbutyl 0.72 43 (100%), 55 (13%), 2972, 2899, 1762, 1468
acetate (1.6%) 61 (6%), 70 (12%), 1373, 1233, 1039
87 (1%)
xx 3-Methyl- 0.747 45 (100%), 55 (26%), No data
2-heptanol b (0.6%) 57 (23%), 69 (8%),
83 (7%), 92 (seven%),
112 (1%)
21 Amyl acetate 0.798 43 (100%), 55 (thirteen%), 2963, 2944, 1767, 1361,
(0.3%) 61 (25%), 70 (xi%), 1234, 1143, 1048
130 (M+, 2%)
22 Methyl 0.816 43 (100%), 55 (24%), 2963, 2879, 1760, 1440,
caproate (0.5%) 59 (21%), 69 (xiii%), 1241, 1215, 1173, 1110
74 (40%), 87 (13%),
99 (11%), 130 (M+, 13%)
23 Ethyl 3-methyl- 0.849 43 (20%), 55 (100%), 2987, 2948, 2936, 2904,
2-butenoate (1.v%) 83 (forty%), 100 (thirteen%), 1731, 1652, 1268, 1138,
113 (27%), 128 (Thousand+, v%) 1081, 1053
24 2,5-Dimethyl- 0.933 43 (100%), 55 (xxx%), No data
four-methoxy- (0.8%) 69 (10%), 85 (13%),
iii(2H)-furanone 101 (5%), 127 (4%),
142 (One thousand+, 2%)
25 Ethyl caproate 0.966 43 (100%), 55 (27%), 2969, 2943, 2882, 1754,
(1.6%) 60 (72%), 73 (40%), 1464, 1375, 1241, 1172,
88 (42%), 99 (37%), 1109, 1041
101 (18%), 115 (10%),
144 (Grand+, 8%)
26 ii,v-Dimethyl- 0.990 43 (seventy%), 67 (45%),
3-hydroxy- (0.1%) 83 (100%), 112 (6%), No information
4-methoxy- 129 (2%), 128 (iii%),
ii,3-dihydrofuran a 144 (Thousand+, half-dozen%)
27 Hexyl acetate 0.994 43 (100%), 55 (13%), 2966, 2942, 2871, 1762,
(0.ane%) 56 (22%), 61 (xiv%), 1369, 1234, 1060, 1030
69 (7%), 84 (v%),
144 (4%)
28 Hex-two-(Due east)-enyl 0.997 43 (100%), 55 (17%), 2969, 2942, 2883, 1762
acetate (0.1%) 67 (48%), 82 (31%), 1675, 1455, 1358, 1230
142 (Thousand+,3%) 1081 1024, 968
29 Cyclohexyl i 43 (100%), 55 (13%), 3018, 2970, 2947, 2908,
acetate 67 (xix%), 82 (35%), 2886, 1752, 1465, 1375,
83 (44%), 142 (M+, 4%) 1233, 1042
30 2-Ethyl hexenoate 1.028 41 (55), 55 (100%), 2975, 2939, 1743, 1650,
(isomer) (1.ane%) 68 (18%), 69 (18%), 1528, 1312, 1252, 1176,
73 (22%), 97 (31%), 1047, 991
142 (G+, 16%)
31 Amyl 1.054 43 (100%), 55 (29%), 2969, 2908, 2887, 1752,
butyrate (0.5%) lx (6%), lxx (27%), 1460, 1353, 1238, 1177,
71 (52%), 89 (ten%), 1096
158 (Yard+, 3%)
32 Unidentified 1.073 41 (100%), 55 (78%), 2966, 2934, 2882, 2817,
unsaturated (0.6%) 69 (42%), 83 (32%), 2738, 1787, 1716, 1623
aldehyde 93 (7%), 109 (57%),
128 (48%), 144 (50%),
33 Nona-2,four-dienal 1.155 43 (39%), 81 (100%), 2749, 1745, 1673
(isomer) (0.nine%) 95 (xix%), 138 (M+, 9%)
34 Non-2-en-1-ol ane.175 57 (100%), 67 (36%), No data
(isomer) (0.8%) 68 (18%), 69 (67%)
lxx (34%), 81 (39%),
83 (36%), 95 (13%)
96 (x%), 124 (7%),
142 (1000+, 2%)
35 Methyl caprylate 1.194 43 (100%), 55 (forty%), 2937, 2867, 1758, 1443,
(0.9%) 69 (11%), 74 (65%), 1353, 1238, 1191, 1113,
87 (25%), 101 (9%), 1045
115 (8%), 127 (11%),
158 (K+, vii%)
36 Benzyl acetate 1.244 43 (100%), 51 (nine%), No information
(1.3%) 69 (9%), 77 (14%),
79 (29%), 91 (87%),
108 (54%), 150 (Grand+, 4%)
37 Ethyl benzoate 1.267 43 (33%), 51 (15%), No data
(1.2%) 69 (10%), 77 (53%),
105 (100%), 122 (19%)
150 (M+, ten%)
38 n-Hexyl butyrate one.316 43 (100%), 56 (thirty%), 2943, 2895, 2877, 1754,
(1.ii%) 71 (54%), 84 (seven%), 1263, 1176, 1097
89 (52%), 117 (sixteen%),
172 (Yard+, 15%)
39 Hexyl isobutyrate 1.319 43 (97%), 55 (48%), 2971, 2943, 1754, 1265,
(1.1%) 71 (89%), 84 (100%), 1173, 1095, 1053, 976
89 (16%), 101 (9%),
172 (1000+, 26%)
40 Ethyl caprylate ane.322 43 (100%), 57 (35%), 2967, 2938, 2678, 1753,
(1.2%) 60 (29%), 61 (20%), 1465, 1366, 1342, 1263,
69 (28%), 81 (17%), 1188, 1167, 1107, 1042
88 (26%), 101 (13%),
115 (5%), 127 (viii%),
172 (1000+, 10%)
41 Decanal 1.339 43 (100%), 57 (78%), 2934, 2865, 2780, 2765,
(1.2%) 69 (37%), seventy (28%), 1746
83 (75%), 95 (28%),
109 (9%), 156 (G+, 2%)
42 Octyl acetate i.354 43 (100%), 55 (30%), 83 (12%), 2937, 2866, 1760, 1462,
(0.1%) 56 (17%), 57 (30%), 1369, 1233, 1038, 1018
61 (37%), 69 (28%),
70 (15%), 71 (42%),
112 (23%), 172 (One thousand+, 12%)
43 Amyl caproate ane.427 43 (100%), 55 (32%), 2967, 2907, 2880, 1753,
(1.five%) lx (8%), 70 (30%), 1466, 1369, 1239, 1194
71 (31%), 99 (8%), 1163, 1113
117 (16%), 186 (Yard+, 1%)
44 Nonyl acetate 1.511 43 (100%), 55 (31%), No information
(1.half-dozen%) 61 (thirteen%), 69 (22%),
83 (11%), 97 (9%),
186 (Thou+, 1%)
45 n-Decyl acetate 1.657 43 (100%), 55 (31%), 2936, 2982, 2865, 2846,
(four.iv%) 69 (28%), 83 (40%), 1755, 1456, 1272, 1175
97 (sixteen%), 200 (M+, 2%) 1094
46 Hex-3(Z)-en-1-ol c 41 (100%), 55 (19%), No data
67 (38%), 69 (8%),
81 (eleven%), 82 (xv%),
100 (Grand+, iii%)
a
Numbering 1–45 from Figure 1.
b
Tentative identification.
c
Reproduced with permission from Marco et al., Periodical of High Resolution Chromatography (1997), twenty: 276–278.

One detector specific to olfactory property/perfumery studies is the man nose. The effluent from the GC is split between a conventional detector such equally the FID and a sniffing port which is purged with humidified nitrogen. Considering the ability to recognize the presence of an odour varies considerably from one individual to another it is necessary to select a panel from people who have been shown to possess a keen sense of scent and to train them to recognize the odour of particular compounds. Although it is e'er stated how insensitive the homo nose is compared to those of animals, nevertheless information technology is still a highly sensitive organ. Information technology is possible, apparently, for trained panellists to indicate the emergence of an odoriferous compound from a GC column in parts of the chromatogram where no signal is obtained from conventional detectors. Under these circumstances the procedure is to use small scale preparative GC and to collect fractions at the points indicated past the panel; these fractions are and so re-run under analytical GC conditions.

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CHROMATOGRAPHY: GAS | Detectors: General (Flame Ionization Detectors and Thermal Conductivity Detectors)

D. McMinn , in Encyclopedia of Separation Scientific discipline, 2000

The Flame Ionization Detector

The FID was adult in 1958 by McWilliam and Dewar in Australia and virtually simultaneously by Harley, Nell and Pretorius in South Africa and rapidly became the detector of choice in commercial instrumentation. As an ionization detector, the FID responds readily to compounds that contain carbon and hydrogen and to a lesser extent to some compounds containing only carbon. It is unresponsive to h2o, air and most carrier gases. Because of its broad applicability and relative ease of operation, it is probably the nigh common detector in GC systems. The FID responds quickly and tin be constructed with a pocket-size internal volume, which makes it especially well suited for capillary GC.

Response of an FID is due to the sample being burned in a fuel-rich mixture and producing ions. In the same process, electrons are produced. Either ions or electrons are collected at an electrode and produce a pocket-sized current. Since there are nearly no ions present in the absenteeism of sample, the baseline is stable and the current is easily converted to a voltage and amplified to produce a indicate. The response to most hydrocarbons is about 0.015   C   g−1 carbon.

As shown in Figure 1, the most oft used configuration has the jet tip at approximately 200   V relative to the collecting electrode. For use with capillary columns, a smaller jet tip (c. 0.3   mm i.d. rather than the 0.5   mm used with packed column configurations) is utilized in order to increase detector sensitivity. The capillary cavalcade is usually inserted through the ferrule and so a few centimetres are broken off and discarded. Ideally, the column is positioned within 1–2   mm of the jet tip and column effluent enters the detector and mixes with hydrogen (fuel) and make-up gas without undue contact with metal surfaces. This mixture is combusted in an excess of air and the organic components are decomposed into ions. The ion chemistry of the improvidence flame has been studied by mass spectrometry. It appears that the ultimate positive charge carrier is H3O+ (or clusters of this with h2o molecules) resulting from charge transfer reactions from the initially formed ions (principally CHO+). Thus the detector is frequently referred to as providing an 'equal per carbon response'.

Figure 1. Cross-sectional diagram of a flame ionization detector.

This response to hydrocarbons allows one to quantify mixtures, for example from petroleum samples, without necessarily identifying each of the components individually nowadays. With compounds other than hydrocarbons, the response is decreased when partially oxidized carbon atoms are present. This requires corrections to be made when the compounds contain, for example, oxygen, nitrogen or halogens. Either pure sample compounds or compounds of similar structure are used to institute advisable response factors. Alternatively, the concept of effective carbon number has been updated to provide a model for the quantification of components in a complex organic mixture if they can be assigned to general functional grouping categories.

When used with narrow capillary columns, the FID usually requires a brand-up gas for maximum sensitivity. The wider (530   μm) columns can be operated at a higher carrier gas menstruation charge per unit and may often be used without the additional make-up gas. For virtually operations the total menstruation charge per unit (column+make-up) volition be 20–sixty   mL   min−1. The fuel and air flow rates are maintained close to that recommended by the manufacturer – oftentimes 30–40   mL   min−1 for the hydrogen fuel and well-nigh 10-fold college for the air. Under these conditions, the minimum detectable amount (MDA) of organic compounds is approximately 10–100   pg, depending on the structure. In addition, response is ordinarily linear from the MDA to a concentration some 107 times as nifty. (This higher limit is often beyond the loading capacity of narrow-diameter capillary columns.) Flows to the detector can be adjusted while using standard samples containing the components of interest in order to obtain maximum response.

Water is a product of the combustion process producing the ions. Thus, the detector assembly must be kept hot in order to prevent condensation. A convenient guide is to take the detector twenty–l° greater than the upper column temperature, merely in no case lower than 150°C. So water vapour, along with the other combustion gases, is swept out of the detector body. With virtually instruments, once the thermal environment of the detector has stabilized, temperature fluctuations are pocket-size and easily tolerated.

The FID is oftentimes described every bit a 'forgiving' detector since acceptable results are obtained even when the gas flows and other conditions are not optimized. None the less, some circumspection must be taken to avoid baseline drift, loss of sensitivity and the presence of spurious peaks. It is of import to ensure that the gases employed are gratis from hydrocarbon impurities. Filters are available for this purpose. The flame itself is quite small and invisible, so checking for the presence of water vapour is the best approach to ensure that flame ignition has been successful. This can be done by belongings a common cold mirror in a higher place the outlet of the detector and observing condensation of the water vapour. Deterioration of functioning of a properly operating FID is oftentimes the result of having used chlorinated solvents. Soot particles and the presence of HCl somewhen lead to loftier and noisy baselines. The jet tip and collector electrode may have to be cleaned or, if badly corroded, replaced. Some spiking may exist observed if portions of the polyimide blanket are burned off the end of the capillary column.

The FID is mass flow-sensitive, meaning that the area response for a compound does not change as menstruation rate is varied. For quantitative work, appropriate response factors must be obtained, particularly if a split up injection manner is employed. When properly configured, a FID can respond to approximately 20 pg of each component eluting from a loftier resolution capillary column.

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GAS CHROMATOGRAPHY | Terpenoids

K. Mansoor , G.B. Lockwood , in Encyclopedia of Separation Science, 2007

Detection and Characterization of Terpenes

The flame ionization detector (FID) is the nigh widely used detector for detection and quantification of terpenoid compounds, although the photoionization detector and surface ionization detectors have been used for investigation of monoterpenes in the atmosphere, and detection of mixtures of terpenes.

Separated constituents have traditionally been identified by co-chromatography with standards, but identification of mono- and sesquiterpenes can be carried out by comparison with Kovats retention indices (RI). The RI data from two GC columns of different polarity, allows reliable identification of large numbers of terpenes.

The most widely used arrangement for qualitative analysis is GC-MS, but GC-IR or GC-FTIR have also been employed. The latter differs from GC-MS in that it can provide solute identification in cases where the mass spectra from isomers are unsufficiently unlike.

GC tin can be coupled with either quadrupole or ion trap mass spectrometers. GC-isotope ratio MS (GC-IRMS) involves use of an IR mass spectrometer, and measures ratios of stable carbon isotopes 13C/12C for each eluted acme. This can be used to make up one's mind the origin of enantiomeric pairs.

Sniff testing, GC-olfactometry (GC-O), is widely used to discover volatile terpenes with pronounced olfactory property. Odor extract dilution analysis (AEDA) allowing identification of depression levels of flavor constituents using sequential dilution until the odour tin no longer be detected, gives further information concerning the qualities of specific terpenoids.

Characterization of the higher terpenes also involves the apply of FID plus a range of tandem techniques. A number of databases of RIs of the mono- and sesquiterpenes have been published; some list RIs for particular temperature program ramps, and there is also a database that includes information derived from iii commonly used temperature ramps. Principal component analysis has been carried out on a number of volatile terpenes in specific matrices.

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Natural Product Biosynthesis by Microorganisms and Plants, Function A

Steven R. Garrett , ... Paul East. O'Maille , in Methods in Enzymology, 2012

2.7 GC–MS instrument and run parameters

GC flame ionization detector (FID) is ideally suited for quantitative studies given that analyte combustion is insensitive to chemic structure. The indicate measured on GC–MS instruments derives from chemical compound ionization and may vary for different chemical structures. Therefore, authentic standards are important for instrument calibration and determining the ionization efficiency. While adult for the GC–MS, the methods listed beneath can readily be adapted for employ with a GC-FID.

A generic GC–MS method for sesquiterpene analysis has been developed using a Hewlett–Packard 6890 gas chromatograph (GC) coupled with a 5932 mass selective detector (MSD) outfitted with a 7683B series injector and autosampler and equipped with an HP-5MS capillary column (0.25   mm i.d.   ×   xxx   m with 0.25   μm picture) (Agilent Technologies). The standard sampling depth places the needle position 3.6   mm above the vial lesser by default (considered position   =   0 by the instrument). For these experiments, needle-sampling depth was prepare to 7   mm (10.6   mm above the vial lesser), placing the needle in the heart of the organic layer (almost the 750   μL level in the 2-mL glass vial). This should, however, exist validated as this may vary between machines and autosamplers. The GC was operated at a He flow rate of 2   mL   min−   1, and the MSD was operated at 70   eV. Splitless injections (four   μL) were performed with an injector temperature of 250   °C. The GC was programmed with an initial oven temperature of eighty   °C (1   min concur), which was then increased twenty   °C   min−   1 up to 140   °C (1   min agree), followed past a vii   °C   min−   1 to 180   °C (2   min hold) and finally an increase of 100   °C   min−   1 until 300   °C (1   min agree). A solvent filibuster of 6   min was allowed prior to the acquisition of MS data.

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Detection of Ignitable Liquid Residues at Fire Scenes

Eric Stauffer , ... Reta Newman , in Fire Debris Assay, 2008

B/ Flame Ionization Detector

The flame ionization detector is a very mutual detector used in gas chromatography. The performance principle of this detector is shown in Figure 8-21. The sample is brought to the detector via a pumping activity, and it is burned in a flame. The flame usually is generated with hydrogen and air. When a chemical chemical compound is burned, it produces ions and electrons. These electrons are located between two electrodes to which a divergence of potential of a few hundred volts is applied. As a result, the newly produced ions generate a current that can be recorded. The intensity of the current is directly proportional to the amount of analytes (ions) nowadays in the detector. The operating principle of the overall unit of measurement closely resembles what was presented in Effigy five-v.

This type of detector is sensitive to near all compounds, mostly combustible ones [15]. At that place are, notwithstanding, a few compounds to which the detector has very little, if any, sensitivity. These include O2, N2, CS2, HtwoS, SO2, NO, N2O, NO2, NH3, CO, CO2, and H2o. The insensitivity to these compounds is an reward in the burn droppings assay application.

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