Sampling systems flame ionization detectors

Figure 14.8 Schematic diagram of the natural gas analyser system SL, sample loop VI, two-way valve to block the sample lines V2, ten-port valve V3, V4 and V5, six-port valves R, restriction TCD, themial-conductivity detector FID, flame-ionization detector.

Selecting an approach Off-flavors are typically due to volatile compounds present at extremely low levels. (Flavor is sensed more by the olfactory system than the tongue, which senses only 5 flavors, sweet, sour, bitter, salty, and umami). GC is ideal for detecting low levels of volatile components. In this case, headspace GC will allow you to treat the plastic directly. Since the off-flavor is suspected to be derived from the polypropylene packaging material, you decide to compare different samples ( good vs. bad ) of the material using headspace GC with both a flame ionization detector (FID) and a sniff port. These chromatograms are shown in Fig. 21.9. 

The amount detected by this system (0.3pg on column) was below the level which could have been determined using a flame ionization detector. Initial indications show that the photoionization detector may be a very useful detector for people who wish to get to lower levels on the supercritical fluid chromatography and cannot concentrate their sample. 

GC is most commonly used to determine residual solvents since these compounds are volatile. For example. Figure 1.6 [15] illustrates the use of GC to measure ICH Class 2 solvents. The solvents are dissolved in DMF and heated at 80°C for 60 min, and a sample of the headspace is injected into a capillary GC system fitted with a flame ionization detector. 

For the quantitation of chromatograms, the development condition found by the conventional TLC was transferred to another TLC system which uses a thin quartz rod coated with silica gel of 75 p thickness and may be called thin-layer-FID chromatography . The TLC system is equipped with a flame ionization detector (FID) and commercially available as a complete set (Iatron thinchrograph model TFG-10, Iatron Co., Ltd., Tokyo). The principle of sample scanning and device for FID are almost the same as those worked out by Padley57), Szakasits et al, and... 

Sensitivity. This property of the gas chromatographic system largely accounts for its extensive use. The simplest thermal conductivity detector cells can detect 100 ppm or less. Utilizing a flame ionization detector one can detect a few parts per million with an electron capture detector or phosphorous detector parts per billion or picograms of solute can easily be measured. This level of sensitivity is more impressive when one considers that the sample size used is of the order of a microliter or less. 

TPR of the samples in flowing He or H2 were performed in a Pyrex flow system which was also used for catalytic reactions. Acid properties of the samples were probed by TPD of NH3 preadsorbed at RT. The analysis of gaseous products was made by an on-line mass spectrometer or a thermal conductivity detector. Reactions of n-hexane in the presence of excess H2 were carried out at 623 K and atmospheric pressure. A saturator immersed in a constant temperature bath at 273 K was used to produce a reacting mixture of 6% n-hexane in H2. Reaction products were analyzed by an online gas chromatograph (HP-5890A) equipped with a flame ionization detector and an AT-1 (Alltech) capillary column. 

Experimental (simplex and window diagram). The chromatographic system consisted of a Model 501 supercritical fluid chromatograph (Lee Scientific, Salt Lake City, Utah) with the flame ionization detector (FID) set at 375°C. The instrument was controlled with a Zenith AT computer. A pneumatically driven injector with a 200 nL or a 500 nL loop was used in conjunction with a splitter. Split ratios used were between 5 1 and 50 1, depending on sample concentration and the chosen linear velocity, while the timed injection duration ranged from 50 ms to 1 s. We found that the variation of both the split ratio and injection time allowed greater control over the... 

Figure 14.4 Schematic diagram of the chromatographic system used for the analysis of very low concentrations of sulfur compounds in ethene and propene CP, pressure regulator CF, flow regulator SL, sample loop R, restriction to replace column 2 VI, injection valve V2, three-way valve to direct the effluent of column 1 to either column 2 or the restriction column 1, non-polar capillary column column 2, thick-film capillary column SCD, sulfur chemiluminescence detector FID, flame-ionization detector.

Chromatographic System (See Chromatography, Appendix HA.) Chromatographic conditions may vary depending on the type of headspace unit used. Use a gas chromatograph equipped with a headspace sampler, flame ionization detector, backflush valve, 1-mL gas sample loop, and a 1-m x 3.2-mm (id) nickel precolumn and a 6-m x 3.2-mm (id) nickel analytical column, or equivalent, containing 60- to 80-mesh... 

Chromatographic System Use a gas chromatograph equipped with a flame-ionization detector and a 2-m x 4-mm (id) borosilicate glass column, or equivalent, packed with 2% to 5% methylpolysiloxane gum on 80- to 100-mesh acid-washed, base-washed, silanized, chromatographic diatoma-ceous earth, or equivalent materials. The column should have a glass-lined sample-introduction system or on-column injection. Maintain the column isothermally between 240° and 260°, the injection port at about 290°, and the detector block at about 300°. Use a dry carrier gas with the flow rate adjusted to obtain a hexadecyl hexadecanoate peak approximately 18 to 20 min after sample introduction when using a 2% column, or 30 to 32 min when using a 5% column. 

For GC analysis of a sample by a GC system equipped with a capillary column and flame ionization detector (FID) (Note 7), the minimum amount of a constituent that can be detected by a FID is, on the average, approximately 1 ng. Conservatively, the solute concentration of a GC sample should be approximately 50 ng/1 solvent [=0.05mg/ml] per major constituent. Thus, for a sample with ten major constituents, the sample concentration would be approximately 1 mg/ml solvent (=10mg/10ml) after taking into account the presence of minor constituents. The sample solution thus prepared is usually divided into two equal parts. One part is used for determination of the optimum conditions for GC analysis of the sample, i.e., optimum conditions for GC-MS analysis. After the identity of the major constituents of the sample has been established, the remaining half of the solution is used for the quantitative determination of the major constituents. 

Gas chromatography (GC) is another widely used analytical technique for phytochemical determination. Similar to HPLC, GC requires sample preparation, which may include lipid extraction and/or extraction of phytochemicals. Once the sample is prepared, it enters the inlet system, flows through the column, and then reaches the detector. In the case of phytochemical analysis, the detector is often a flame ionization detector, which is suitable for all organic particles, or more commonly, the sample passes through the column directly to a mass spectrometer, which serves as the detector. 

Determination of Nerve Agents In contrast to those rather unusual methods, GC coupled to diverse detection systems, e.g. flame ionization detector (FID), nitrogen-phosphorus detector (NPD), flame photometric detector or mass spectrometer, as well as liquid chromatographic (LC) methods, represent the most common techniques for OP determination especially for biological samples. These methods offer high resolution, sufficient limits of detection, good reproducibility, and robust hardware devices. For more detailed information readers are referred to recent review articles (Hooijschuur et al, 2002 John et al, 2008). 

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