Headspace analysis benzene

Principles and Characteristics Pare et al. [475] have patented another approach to extraction, the Microwave-Assisted Process (MAP ). In MAP the microwaves (2.45 GHz, 500 W) directly heat the material to be extracted, which is immersed in a microwave transparent solvent (such as hexane, benzene or iso-octane). MAP offers a radical change from conventional sample preparation work in the analytical laboratory. The technology was first introduced for liquid-phase extraction but has been extended to gas-phase extraction (headspace analysis). MAP constitutes a relatively new series of technologies that relate to novel methods of enhancing chemistry using microwave energy [476]. 

Antoine et al. 1986 Ashley et al. 1992, 1994 Michael et al. 1980). Recent improvements in the method have resulted in excellent sensitivity (300 ppt) and acceptable precision and accuracy (Ashley et al. 1992, 1994). The purge-and-trap method has also been used to analyze breast milk for other volatile organic compounds and could be used for analyzing benzene in breast milk (Michael et al. 1980). For headspace analysis, the samples are placed in a special vial, and the gas generated above the liquid sample under equilibrium conditions is analyzed (Gruenke et al. 1986 Pekari et al. 1989). 

Screening methods are available for analysis of benzene in feces and urine (Ghoos et al. 1994) and body fluids (Schuberth 1994). Both employ analysis by capillary GC with an ion trap detector (ITD). Benzene in urine has been determined by trapping benzene stripped from the urine on a Carbotrap tube, followed by thermal desorption GC/flame ionization detection (FID). The detection limit is 50 ng/L and the average recovery is approximately 82% (Ghittori et al. 1993). Benzene in urine has also been determined using headspace analysis with capillary GC/photoionization detection (PID). The detection limit is 40 ng/L (Kok and Ong 1994). 

JiCKELLS, s. M., CREWS, c., CASTLE, L. and GILBERT, J. Headspace analysis of benzene in food contact materials and its migration into foods from plastics cookware , Food Additives and Contaminants 1990 7(2) 197-205. 

A water sample is analyzed for traces of benzene using headspace analysis. Samples and standards are spiked with a fixed amount of toluene as internal standard. The following data are obtained ... 

In instances where the chemical identity of some or all of the volatiles present in a polymer are not known it is possible to obtain the required information by the application of this technique. Thus, workers at Hewlett Packard [3] used headspace analysis mass spectroscopy (MS) to identify six volatiles in styrene-acrylonitrile-maleic anhydride teropolymer (benzene, toluene, ethylbenzene, styrene, aromatics, and maleic anhydride). 

Several approaches are used to isolate and eoneentrate volatile analytes from waste samples for subsequent measurement. Some of these based on headspace analysis involve evaporation of volatile substanees into the space above the sample (headspace) in a closed container. Method 5021, Volatile Organic Compounds in Soils and Other Solid Matrices Using Equilibrium Headspace Analysis, is used to isolate volatile organic compounds, such as benzene, bromomethane, chloroform, 1,4-dichlorobenzene, dichloromethane, styrene, toluene, vinyl chloride, and the xylene isomers, from soil, sediment, or solid waste samples for determination by gas chromatography or gas chromatography/mass spectrometry. 

The principle of headspace sampling is introduced in this experiment using a mixture of methanol, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, benzene, toluene, and p-xylene. Directions are given for evaluating the distribution coefficient for the partitioning of a volatile species between the liquid and vapor phase and for its quantitative analysis in the liquid phase. Both packed (OV-101) and capillary (5% phenyl silicone) columns were used. The GG is equipped with a flame ionization detector. 

Triacetone triperoxide (TATP) is a powerful explosive manufactured in clandestine laboratories and used by terrorists. As TATP subHmes easily, analysis was performed by SPME trapping of its vapor, using polydimethylsiloxane/divinyl benzene (PDMS/DVB) fiber, followed by desorption into a GC/MS injector [10]. Figure 6 shows the TIC, mass chromatogram and the El mass spectmm of headspace from a debris sample containing TATP [11]. The El mass spectmm contains a molecular ion at m/z 222 and several fragment ions. In the chemical ionization mass spectmm of TATP [12], the m or ions were at m/z 223 (100%), 222 (20%), 133 (20%), 117 (40%), 115 (20%), 103 (75%) and 100 (50%). 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

The radical "OH in surface waters is quickly consumed by organic compounds, bicarbonate, carbonate, and nitrite. It has a typically low steady-state concentration of around 10"16 M. For this reason it cannot be directly detected, and quantification in laboratory experiments is usually carried out by means of reactions of known kinetics. The formation of phenol from benzene, of 4-hydroxybenzoic from benzoic acid, and the disappearance of nitrobenzene are suitable systems if intermediate monitoring is carried out by liquid chromatography, while the disappearance kinetics of butyl chloride is suitable for headspace sampling and gas-chromato-graphic analysis [64]. 

Figure 8.13 Analysis of o-xylene and BTEX (in water) using solid-phase microextraction (a) direct SPME fibre mode (b) headspace SPME fibre mode (c) results obtained for o-xylene using mode (a) (d) results obtained for BTEX using mode (b) , no stirring IH, with stirring , with stirring, plus salt , benzene , toluene a, ethylbenzene , m-, p-xylene(s) x, o-xylene [4] (cf. DQ 8.11).

Eromberg, A., Nilsson, T., Larsen, B. R., Montanarella, L., Facchetti, S., and Madsen, J. Q., Analysis of chloro- and nitroanilines and -benzenes in soils by headspace solid-phase microextraction,... 

The flame ionization detector is the most commonly used for GC. It is considered an economical detector. The gas used for the detector is hydrogen and air. Signal out put of the flame detector is very sensitivity, Ipg/s, however the sensitivity also depends upon the sample preparation and the GC instrument. For example for benzene with the headspace GC-FID of one model is 0.02 ppm and 0.06 ppm for detection and quantitation limits, respectively which is more sensitive than the other model of the same manufacturer (Agilent technology, 2007). In quantitative analysis of a known compound by a GC, a MS detector can be used but usually avoided for routine analysis due to the running cost. 

Headspace sampling is an excellent technique for the analysis of compounds that produce, odors in many commercial products, such as plastics, rubbers, paints, resins, etc. Interfacing of a headspace GC with a mass spectrometer provides valuable information for the identification of such components. Figure 9 shows the output from head space-GC analysis of residual benzene and toluene in polymeric material. 

Figure 9 GC chromatogram trace analysis of benzene and toluene in polymer by headspace GC-FID.

Almeida, C.M.M. and Vilas Boas, L. Analysis of BTEX and other substituted benzenes in water using headspace SPME-GC-FID method validation. Journal of Environmental Monitoring 2004, 6 (1), 80-88. 

Mass spectrometry and chemometric methods cover very diverse fields Different origin of enzymes can be disclosed with LC-MS and multivariate analysis [45], Pyrolysis mass spectrometry and chemometrics have been applied for quality control of paints [46] and food analysis [47], Olive oils can be classified by analyzing volatile organic hydrocarbons (of benzene type) with headspace-mass spectrometry and CA as well as PC A [48], Differentiation and classification of wines can similarly be solved with headspace-mass spectrometry using unsupervised and supervised principal component analyses (SIMCA = soft independent modeling of class analogy) [49], Early prediction of wheat quality is possible using mass spectrometry and multivariate data analysis [50],... 

How then do the techniques differ For this, the terms recovery and sensitivity must be defined. For both methods, the recovery depends on the vapour pressure, the solubility and the temperature. The effects of temperature can be dealt with because it is easy to increase the vapour pressure of a compound by raising the temperature during the vaporization step. With the P T technique, the term percentage recovery is used. This is the amount of a compound which reaches the gas chromatograph for analysis relative to the amount which was originally present in the sample. If a sample contains 100 pg benzene and 90 pg reach the GC column, the percentage recovery is 90%. In the static headspace technique, a simple expression like this cannot be used because it is possible to use a large... 

Abbreviation for the analysis of the benzene, toluene, ethylbenzene and xylene isomers group of aromatics, mostly by headspace sample analysis. 

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