Alkali flame ionization

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

AFID = alkali-flame ionization detection FID = flame ionization detection FPD = flame photometric detection GC = gas chromatography IGEFET = interdigitated gate electrode field-effect transistor ITMS = ion trap mass spectrometry MIMS = multiphoton ionization mass spectrometry MS = mass spectrometry... 

Determination of caffeine in soft drinks was undertaken using the aerosol alkali flame ionization detector.24 Soft drinks studied were Coke, Diet Coke, Pepsi, Diet Pepsi, Dr. Pepper, and Mountain Dew. A sample clean-up and concentration procedure is employed followed by GC separation with alkali flame ionization detection. Results showed that Coke, Diet Coke, Pepsi, Diet Pepsi, Dr. Pepper, and Mountain Dew contained 41 2, 52 2, 43 4, 35 9, 46 6, and 60 15 mg caffeine per 355-ml serving. These values compared favorably with levels reported in the literature. 

Alkali cellulose, 4 716 Alkali earth metal nitrides, 17 206-207 Alkali flame-ionization detector (AFID), gas chromatography, 6 381 Alkali-gravity-viscosity (AGV) charts, for silicate glasses, 22 462, 463 Alkali halide disk method, 14 229 Alkali-immobile compounds, dye release from, 19 288... 

AFID = alkali flame ionization detector ECD = Electron capture detection EPA = Environmental Protection Agency FPD = flame photometric detection GC = gas chromatography GPC = gel permeation chromatography HRGC = high resolution gas chromatography NPD = nitrogen- phosphorus detection SPE = solid phase extraction device... 

GC/AFID Gas chromatography/alkali flame ionization detector... 

ALKALI FLAME IONIZATION DETECTOR (AFID)/THERMIONIC.. . 269... 

The alkali flame ionization detector (AFID) or thermionic detector (TID) is a specific detector used primarily in the trace analysis of pesticides particularly those containing phosphorus. 

Binding Study. Concentrations of soy and diffusate were equivalent to ground beef fortified with 5-20% hydrated soy protein. The diffusate/soy mixtures were heated under the same conditions and generated pyrazines were separated and quantitated by gas chromatography with an alkali flame ionization detector (afid). Triplicate results were averaged for each level of vegetable protein and the concentration of pyrazines generated in the presence of soy proteins was determined relative to the control, diffusate heated neat. 

Figure 12. (A) Standard of dichloroacetyl-ETU (4.0 ng) (B) blank apple juice extract (C) apple juice extract spiked with 1 ppm ETU after extractive derivatiza-tion with DCAA. Conditions 6 X 2 mm i.d. glass column with 3% OV-330 on 80-100 mesh Chromosorb 750 flow rate, 30 mL/min helium oven, 200°C NP alkali flame ionization detector.

The thermionic or alkali flame ionization detector (FID) is a variant of the FID that has enhanced sensitivity to nitrogen (N) and phosphorous (P) containing compounds. It is essentially a hydrogen flame around a pellet of an alkali metal salt with an electric potential across the flame. Organic compounds in the air are drawn into the flame and ionized. The alkali metal enhances the response to N and P-containing compounds and, since many chemical agents contain N and P, it is selective for their detection. This detector is rarely used without prior separation by GC. 

TID) or nitrogen/phos (NPD) or alkali flame ionization Photoionization (PID) chemical ionization electric or flame heated UV lamp causes Aromatics 24... 

The method is not only applicable to the EU-official aqueous and fatty food simulant but also to foodstuffs such as beverages and soft margarine. Indeed the collaborative trial included fruit juice, wine and sunflower oil. The level of migrated acrylonitrile is determined by headspace gas chromatography, preferably with automated sample injection and using a nitrogen specific detector, for instance an alkali flame ionization detector (AFID). This gives the method the necessary sensivity to meet the... 

Nene S, Anjaneyulu B, Rajagopalan TG (1984) Determination of diethylcarbamazine in blood using gas chromatography with alkali flame ionization detection. J Chromatogr 308 334-340... 

The alkali flame-ionization detector, sometimes called an NP or nitrogen-phosphorus detector, contains a thermionic source, such as an alkali-metal salt or a glass element containing rubidium or other metal, that results in the efficient ionization of organic nitrogen and phosphorus compounds. It is a selective detector that shows little response to hydrocarbons. 

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