Flame photometric detection method

The continuous methods combine sample collection and the measurement technique in one automated process. The measurement methods used for continuous analyzers include conductometric, colorimetric, coulometric, and amperometric techniques for the determination of SO2 collected in a liquid medium (7). Other continuous methods utilize physicochemical techniques for detection of SO2 in a gas stream. These include flame photometric detection (described earlier) and fluorescence spectroscopy (8). Instruments based on all of these principles are available which meet standard performance specifications. 

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. 

The most common final separation techniques used for agrochemicals are GC and LC. A variety of detection methods are used for GC such as electron capture detection (BCD), nitrogen-phosphorus detection (NPD), flame photometric detection (FPD) and mass spectrometry (MS). For LC, typical detection methods are ultraviolet (UV) detection, fluorescence detection or, increasingly, different types of MS. The excellent selectivity and sensitivity of LC/MS/MS instruments results in simplified analytical methodology (e.g., less cleanup, smaller sample weight and smaller aliquots of the extract). As a result, this state-of-the-art technique is becoming the detection method of choice in many residue analytical laboratories. 

Methods exist for determining levels of diisopropyl methylphosphonate in air, soil, and water. These methods include separation by GC coupled with FID and flame photometric detection (FPD), determination by infrared and Raman spectroscopy, separation by ionization mass spectrometry, determination utilizing piezoelectric crystals, and determination by gas-sensitive microsensors. Table 6-2 summarizes the methods that have been used to analyze environmental samples for diisopropyl methylphosphonate. 

Valkirs et al. [105] have conducted an interlaboratory comparison or determinations of di- and tributyltin species in marine and estuarine waters using two methods, namely hydride generation with atomic absorption detection and gas chromatography with flame photometric detection. Good agreement was obtained between the results of the two methods. Studies on the effect of storing frozen samples prior to analysis showed that samples could be stored in polycarbonate containers at - 20 °C for 2 - 3 months without significant loss of tributyltin. 

Muller [76] has described a gas chromatographic method for the determination of tributyltin compounds in sediments. The tributyltin compounds are first converted to tributylmethyltin by reaction with ethyl magnesium bromide, and then analysed using capillary gas chromatography with flame photometric detection and gas chromatography-mass spectrometry. Tributyltin was found in samples of sediment and these results demonstrated that the technique has detection limits of less than 0.5pg L 1. 

Diazinon was determined in bovine liver and rumen content by GC/flame photometric detection (FPD) by Holstege et al. (1991) using a method with a limit of detection (LOD) reported to be 0.01-0.05 pg/g using a 5 g sample. Recoveries were reported to be 95% from rumen content and 88% from liver. In another study, diazinon was determined by GC/FPD and GC/mass spectrometry (MS) in avian liver and kidney using a method with a LOD of 0.02 ppm and 100% recovery at the 0.05 ppm level. Brown et al. (1987) used GC/FPD to determine diazinon in animal fat. No data were reported for the LOD, but the recovery was stated to be 90% (6% RSD) at 0.4 ppm. 

Clark and Lesage [76] have described a method for the determination of elemental sulfur in soils using gas chromatography with flame photometric detection after the sulfur is reacted to form Ph3PS. 

Basic techniques for speciation analysis are typically composed of a succession of analytical steps, e.g. extraction either with organic solvents (e.g. toluene, dichloromethane) or different acids (e.g. acetic or hydrochloric acid), derivatisa-tion procedures (e.g. hydride generation, Grignard reactions), separation (gas chromatography (GC) or high-performance liquid chromatography (HPLC)), and detection by a wide variety of methods, e.g. atomic absorption spectrometry (AAS), mass spectrometry (MS), flame photometric detection (FPD), electron capture detection (ECD), etc. Each of these steps includes specific sources of error which have to be evaluated. 

Valkirs, A.O., Seligman, PF., Olson, G.J., Brinckman, F.E., Matthias, C.L. and Bellama, J.M. (1987) Di- and tributyltin species in marine waters. Inter-laboratory comparison of two ultratrace analytical methods employing hydride generation and atomic absorption or flame photometric detection. Analyst, 112, 17-21. 

Berijani, S., Y. Assadi, M. Anbia, M.-R. Milani Hosseini, and E. Aghaee. 2006. Dispersive liquid-liquid microextraction combined with gas chromatography-flame photometric detection Very simple, rapid and sensitive method for the determination of organophosphorus pesticides in water. J. Chromatogr. A 1123 1-9. 

Matthias et al. [216] have described a comprehensive method for the determination of aquatic butyltin and butylmethyltin species at ultratrace levels using simultaneous sodium borohydride hydridisation, extraction with gas chromatography-flame photometric detection and gas chromatography-mass spectrometric detection. The detection limits for a lOOmL sample were 7ng L 1 of tin for tetrabutyltin and tributyltin, 3ng L 1 of tin for dibutyltin and 22ng L 1 tin for monobutyltin. For 800mL samples detection limits were l-2ng L 1 tin for tri- and tetrabutyltin and below lng L 1 tin for dibutyltin. The technique was applied to the detection of biodegradation products of tributyltin in non saline waters. 

D.R. Killelea and J.H. Aldstadt, Solid-phase microextraction method for gas chromatography with mass spectrometric and pulsed flame photometric detection studies of organoasenical speciation, J. Chromatogr. A, 918, 169-175 (2001). 

Gas Chromatography. Gas chromatography is one of the "workhorse methods used for oil identification. The newly approved ATSM Method D3328-78 (4) incorporates simultaneous flame photometric detection along with flame ionization detection. Such dual detection, using a high-resolution SCOT column is the routine method employed by COIL for Coast Guard analyses. 

Lestremau, F., Desauziers, V., Roux, J.-C., and Fanlo, J.-L., Development of a quantification method for the analysis of malodorous sulphur compounds in gaseous industrial effluents by solid-phase microextraction and gas chromatography-pulsed flame photometric detection, J. Chromatogr. A, 999, 71-80, 2003. 

Braman et al. achieved LODs of 0.1 ppt v/v for H2S after enrichment on gold and detection with flame photometric detection. The method s potential was limited by the carrier gas helium, because reduction was detected for mercaptanes, CS2, and COS. 

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