Oxygen flame ionization detection

The most common detection method used in gas chromatography is FID. The nitrogen-phosphorus detector (NPD) can be used to identify nitrogen-containing compounds (Stashenko et al., 1996). Another possibiUty is the use of oxygen flame ionization detection (O-FID) for the selective determination of oxygenates (Betts, 1994 Schneider et al., 1982). Mass spectrometry is a very useful tool for detecting complex terpene mixtures. 

In GC, FID is the most common detection method used. Nitrogen-containing compounds can be identified by nitrogen-phosphorus detection (NPD) [46]. Another possibility is the use of oxygen flame ionization detection (0-FID) for the selective determination of oxygenates [47,48]. This application seems to be particularly useful for the analysis of small sample volumes commonly associated with tissue cultures or oil glands. 

D5599 Determination of Oxygenates in Gasoline by GC and Oxygen Selective Flame Ionization Detection 60 m X 0.25 mm x 1.0 Xm BPl... 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

For FID detection, hydrogen is mixed with the carrier gas, and the column effluent stream is burned in air. The FID measures the ionization of the sample stream, which is proportional to the mass of the sample in the gas. Flame ionization detector has high sensitivity (MDL is lO g/sec), but it has two main disadvantages FID cannot detect compounds that do not produce ions in a hydrogen-oxygen flame (e.g., H2O, CO2, CO, CS2, N2, H2S, formic acid, and nitrogen oxides). Further, FID destroys the sample material in the detection process. Therefore, if the gas effluent is to be examined further, an effluent splitter is required prior to the FID detector. 

In earlier work [23] the method for converting of non-detectable into detectable compounds was extended by using multi-step chemical conversions, which makes the method more widely applicable to compounds whose molecules lack carbon atoms. To determine oxygen there has been proposed a method of two-step quantitative conversion of oxygen into an equivalent amount of methane, which is then detected by a flame-ionization detector. Oxygen is first converted into carbon monoxide, which is then reduced to methane in a flow of hydrogen on a nickel catalyst. 

C to hydrogenate the preadsorbed CO. After 30 minutes of reaction time, the entire contents of the reactor are flushed directly into a Varian 3400 GC and the concentration of CH4 is analyzed with a flame ionization detector. No higher hydrocarbons or oxygenated hydrocarbons were detected. The amount of methane was quantified by comparing the integrated area of the methane in the reactor gas to Ae integrated areas of methane samples admitted fi om a calibrated volume sample loop. 

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