Flame photometric detection

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. 

M. De Paoli, M. Barbina Taccheo, R. Mondini, A. Pezzoni and A. Valentino, Determination of organophosphoms pesticides in fruits by on-line size-exclusion chi O-matography-flame photometric detection , 7. Chromatogr. 626 145-151 (1992). 

Boraiko C, Yoder R, Cooper J, Lieckfield R Jr, Remski M (2004) Sampling and analysis of butyltin compounds in air using gas chromatography and flame photometric detection. Journai of Occupational and Environmental Hygiene, 1 (1 ) 50-56. 

Jiang GB, Xu FZ, Zhang FJ (1999) Dioctyltin and tributyltin detection at trace levels in water and beverages by capillary gas chromatography with flame photometric detection. Fresenius Journal of Analytical Chemistry, 363(3) 256-260. 

Baynes RE, Bowen JM. 1995. Rapid determination of methyl parathion and methyl paraoxon in milk by gas chromatography with solid-phase extraction and flame photometric detection. J Assoc Off Anal Chem 78 812-815. 

Prinsloo SM, De Beer P143R. 1985. Gas chromatographic relative retention data for pesticides on nine packed columns I. Organophosphorus pesticides, using flame photometric detection. J Assoc Off Anal Chem 68 1100-1108. 

Stan H-J, Mrowetz D. 1983. Residue analysis of organophosphorus pesticides in food with 2-dimensional gas chromatography using capillary columns and flame photometric detection. J High Resol Chromatog Chromatog Comm 6 255-263. 

The presence of heteroatoms usually provides a convenient feature for improving selectivity by employing selective detection mechanisms. GC may then use flame photometric detection (FPD) for S and P atoms and to a certain extent for N, Se, Si etc. thermoselective detection (TSD) and nitrogen-phosphorus detection (NPD) for N and P atoms electron capture detection (ECD) for halogen atoms (E, Cl, Br, and 1) and for systems with conjugated double bonds and electron-drawing groups or atomic emission detection (AED) for many heteroatoms. 

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. 

Each sample was fortified with chlorpyrifos, as a reference standard, to determine the recovery during each extraction. Three portions of solvent were used, and the combined extract for each sample was dried with sodium sulfate. Analyses employed gas chromatography/flame photometric detection. Limits of detection for vegetation and animal tissues were 0.2 and 0.007 pg respectively. Recoveries from fortified samples were 82%. Diazoxon occurrence was infrequenf and at trace concentrations. 

In multi-residue analysis, an analyte is identified by its relative retention time, e.g., relative to aldrin when using ECD or relative to parathion or chlorpyrifos when using a flame photometric detection (FPD) and NPD. Such relative retention times are taken from corresponding lists for the columns used. Further evidence for the identity of an analyte is provided by the selectivity of the different detectors (Modules D1 to D3), by its elution behavior during column chromatography (Modules Cl and C2) and in some cases even by the peak form in a gas chromatogram. In a specific analysis for only some individual analytes, their retention times are compared directly with the corresponding retention times of the analytes from standard solutions. 

Oxime carbamates are not directly amenable to gas chromatography (GC) because of their high thermal instability, which often leads to their breakdown at the injection port or in the column during analysis. Analysis of oxime carbamates by GC with sulfur detection or flame photometric detection involves oxidation of the intact insecticides or alkaline hydrolysis to form the more volatile but stable oxime compound. Enzymatic techniques have been reported for the analysis of these compounds. Enzyme-linked immunosorbent assay (ELISA) has been used to determine aldicarb and its sulfone and sulfoxide metabolites and methomyl in water, soil, and sediment samples. 

Quantitation is performed by the calibration technique. Construct a new calibration curve with methomyl oxime standard solutions (0.2, 0.4, 0.6, 0.8 and 1.0 xgmL in acetone) for each set of analyses. Plot the peak area against the injected amount of methomyl oxime on logarithmic paper. As the amount of alanycarb is measured in terms of its oxime derivative, a conversion factor of 3.8 (the molecular weight ratio of alanycarb to methomyl oxime) should be applied to obtain the net amount. The injection volume should be kept constant as the peak area varies with the injection volume in flame photometric detection. Before each set of measurements, check the GC system by injecting more than one standard solution containing ca 2-10 ng of methomyl oxime. 

Frenzel, W., Schepers, D., and Schulze, G., Simultaneous ion chromatographic determination of anions and cations by series conductivity and flame photometric detection, Anal. Chim. Acta, 277, 103, 1993. 

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. 

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... 

Sass S, Parker GA. 1980. Structure-response relationship of gas chromatography-flame photometric detection to some organophosphorus compounds. J Chromatogr 189(3) 331-349. 

AAS = atomic absorption spectroscopy CdS04 = cadmium sulfate GC/ECD = electrochemical gas chromatographic detection GC/FPD = gas chromatography with flame photometric detection HC1 = hydrochloric acid H2S = hydrogen sulfide NaOH = sodium hydroxide NR = not reported PAS = photoacoustic spectroscopy... 

Radford-Knoery J, Cutter GA. 1993. Determination of carbonyl sulfide and hydrogen sulfide species in natural waters using specialized collection procedures and gas chromatography with flame photometric detection. Anal Chem 65 976-982. 

Figure 5.19. Schematic design of the NaBH4-reduction/flame photometric detection system for the determination of tin species in natural waters. Source Author s own files...

Andreae discusses each of these steps in detail [712]. A typical instrumental configuration to accomplish these steps is shown in Fig. 5.19 for the borohy-dride reduction/flame photometric detection system for tin speciation analysis. 

Garra and Muth [80] and Wasik and Brown [81] characterised crude, semi-refined, and refined oils by gas chromatography. Separation followed by dualresponse detection (flame ionisation for hydrocarbons and flame photometric detection for S-containing compounds) was used as a basis for identifying oil samples. By examination of chromatograms, it was shown that refinery... 

The sulfur compounds that are present in minor quantities in petroleum products also exhibit a typical gas chromatographic fingerprint easily obtained by flame photometric detection. This fingerprint has been introduced to complement the flame ionisation detection chromatogram with the aim of resolving the ambiguities or increasing the reliability in the identification of the pollutants [74]. 

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. 

DAGAN, S., Comparison of gas chromatography-pulsed flame photometric detection-mass spectrometry, automated mass spectral deconvolution and identification system and gas chromatography-tandem mass spectrometry as tools for trace level detection and identification, J. Chromatogr., A., 2000,868,229-247. 

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. 

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