INDEX Flame ionization detector

Fig. 3. (a) Flame ionization detector (fid) response to an extract of commercially processed Valencia orange juice, (b) Gas chromatography—olfactometry (geo) chromatogram of the same extract. The abscissa in both chromatograms is a normal paraffin retention index scale ranging between hexane and octadecane (Kovats index). Dilution value in the geo is the -fold that the extract had to be diluted until odor was no longer detectable at each index. 

Figure 14.17 Schematic diagram of the on-line coupled LC-GC system VI, valve foi switcliing the LC column outlet to the GC injector V2, valve for switching the LC column to back-flush mode V3, LC injection valve RI, refractive index monitor detector UV, ulti avio-let monitor detector FID, flame-ionization detector.

Reversed-phase HPLC has been used to analyze the oxidation products of triacylglycerols in edible oils. The detection is often based on monitoring the conjugated dienes with an ultraviolet detector (234-235 nm). However, the UV detector provides no information about oxidation products without a conjugated diene structure, e.g., products of oleic acid. Information about these compounds is important when oils with a high oleic acid content are studied. The most common universal detector types—refractive index and flame ionization detectors—are not sensitive enough to detect small amounts of oxidation products. 

The minute quantity of adsorbate remaining on the column after weakly bound probe has desorbed is chemisorbed to strongly acidic or basic sites on the substrate. The desorption profile obtained by ramping the column temperature is an index of the range of effective bond strength between the solid and adsorbed vapor. The flame ionization detector also registers desorption of adventitious organic contaminants polytherms with no probe on the column must be obtained separately so that sorbate and contaminant desorption can be deconvolved. 

The identification of individual classes of fatty acids has relied on the use of gas chromatography (GC), equipped with a flame ionization detector. Lipids are sapoiufled after extraction and the fatty acids converted to methyl esters. The fatty acid methyl esters (FAME) are separated using GC. The use of standards ahowed for the identification of individual species of fatty acids based on retention time. The method is quite sensitive and permits the quantification of fatty acid species. The mode of detection has been enhanced with the use of mass spectrometry (MS), which allows for the detection and quantification of unknowns, thus increasing the utility of these methods. The Lipid Library section on the gas chromatography of lipids http //www.lipidlibrary.co.uk/GCJipid/01 intro/index. htm) provides a comprehensive description of these methods. 

Analysis and Characterization. Gas chromatography was performed with a Hewlett-Packard model 5880A equipped with capillary columns and a flame-ionization detector. Gel permeation chromatography was performed with a Hewlett-Packard HPLG model 1090A with a refractive index detector. Tacticity determinations were conducted with an F-19 nuclear magnetic resonance (NMR) spectrophotometer (Varian XL-100) at 94.12 MHz for triad analyses (13). Inherent viscosity measurements were performed in 2-butanone at 25.0 °C. 

Bearing in mind that the compounds forming a perfume have a low boiling point, GC has been the most widely used technique in the perfume industry. In this sense, a perfume, after appropriate sample pretreatment, is analyzed using GC with a flame ionization detector (FID), and the Kovats index (KI) for each peak is experimentally determined. The identification is carried out by comparing the... 

A good alternative can be the gas chromatography equipped with FID, that is, flame ionization detector [61] or with mass spectrometer, used in the majority of papers. Wink and coworkers [8], have studied the QAs profile of 56 species of lupin by GC-MS reporting Kovat s index and fragmentation ions of more than 100 quinolizidine alkaloids. 

Peetre and Smith used a Varian Model 1400 gas chromatograph with a flame ionization detector, and equipped with an auxiliary thermocouple and temperature guage for the retention index measurements. The temperature could be read to 0.1 and was constant within this range during a measurement. Any significant deviation of the observed temperature from the measurement temperature in the tables was corrected for. 

Sodium dodecyl sulfate present in hydrophilic ointments has been determined by TLC on silica gel with flame ionization detection, which was considered better than the colorimetric method. TLC is preferred to HPLC in this case due to the low sensitivity of the refractive index detector that makes difficult the analysis of small amounts of sodium dodecyl sulfate [284]. 

The components in a mixture separate in the column and exit from the column at different times (retention times). As they exit, the detector registers the event and causes the event to be recorded as a peak on the chromatogram. A wide range of detector types are available and include ultraviolet adsorption, refractive index, thermal conductivity, flame ionization, fluorescence, electrochemical, electron capture, thermal energy analyzer, nitrogen-phosphorus. Other less common detectors include infrared, mass spectrometry, nuclear magnetic resonance, atomic absorption, plasma emission. 

Choice of the proper detection scheme is dependent on the properties of the analyte. Different types of detectors are available such as ultraviolet (UV), fluorescence, electrochemical, hght scattering, refractive index (RI), flame ionization detection (FID), evaporative light scattering detection (ELSD), corona aerosol detection (CAD), mass spectrometric (MS), NMR, and others. However, the majority of reversed-phase and normal-phase HPLC method development in the pharmaceutical industry is carried out with UV detection. In this section the practical use of UV detection will be discussed. 

When compared to other mass-sensitive detectors such as flame ionization (FID), refractive index (RI), and mass spectrometry (MS), the ELSD can detect analytes without interference from organic modifiers and additives. The use of organic solvents in FID limits usefulness due to an increase in baseline noise, and FID cannot be used with HPLC. RI detectors, in general, are less sensitive than other detectors and are incompatible with gradient elution. Although the MS can be used with modifier gradients, ionization efficiencies... 

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