Determination of Styrene

The readings of the freshly degassed sample solutions are taken as described next. 

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HS-GC methods have equally been used for chromatographic analysis of residual volatile substances in PS [219]. In particular, various methods have been described for the determination of styrene monomer in PS by solution headspace analysis [204,220]. Residual styrene monomer in PS granules can be determined in about 100 min in DMF solution using n-butylbenzene as an internal standard for this monomer solid headspace sampling is considerably less suitable as over 20 h are required to reach equilibrium [204]. Shanks [221] has determined residual styrene and butadiene in polymers with an analytical sensitivity of 0.05 to 5 ppm by SHS analysis of polymer solutions. The method development for determination of residual styrene monomer in PS samples and of residual solvent (toluene) in a printed laminated plastic film by HS-GC was illustrated [207], Less volatile monomers such as styrene (b.p. 145 °C) and 2-ethylhexyl acrylate (b.p. 214 °C) may not be determined using headspace techniques with the same sensitivities realised for more volatile monomers. Steichen [216] has reported a 600-fold increase in headspace sensitivity for the analysis of residual 2-ethylhexyl acrylate by adding water to the solution in dimethylacetamide. 

Applications Radiotracer measurements, which combine high sensitivity and specificity with poor spatial resolution, have been used for migration testing. For example, studies have been made on HDPE, PP and HIPS to determine effects of manufacturing conditions on migration of AOs from plastic products into a test fat [443]. Labelled antioxidant was determined radio-analytically after 10 days at 40 °C. Acosta and Sas-tre [444] have used radioactive tracer methods for the determination of styrene ethyl acrylate in a styrene ethyl acrylate copolymer. 

F.C. Y.Wang and P.B. Smith, Quantitative analysis and structure determination of styrene/ methyl methacrylate copolymers by pyrolysis gas chromatography, Anal. Chem., 68, 3033 3037(1996). 

Varner, S.L., Breder, C.V. and Fazio, T. (1983). Determination of styrene migration from food-contact polymers into margarine, using azeotropic distillation and headspace gas chromatography, J. Assoc. Ojf. Anal. Chem., 66, 5, 1067-1073. 

Electrochemical measurements are useful for determining concentrations of electroactive species in solution. Playing the role of solvent, the monomer studied in this chapter is styrene. One of its most remarkable characteristics is the low dielectric constant (e=2.43 at 298.0K) compared with that of water (e=78 at 298.0K). A solvent with a low dielectric constant is a highly resistive medium, in which voltammetric measurements are not evident. Voltammetric measurements in styrene as solvent have not been described before. Papers describing an electrochemical method for the determination of styrene in more polar organic solvents can be found in the literature13-17. 

Another example of the PA-FTIR analysis of a rubber is the determination of % styrene in SBR. A typical PA-FTIR spectrum of an emulsion SBR is shown in Figure 2.9. 

The method of Rossli and Marek (1977) uses GC determination of styrene after isolation by co-distillation with water and continuous extraction of the distillate with hexane. 

Nerin, C. Rubio, C. Cacho, J Salat ranca, J. 1996. Determination of Styrene in Yogurt by an Automatic Purge and Trap System Coupled to GC-MS. Presented at ILSI International Symposium Food Packaging Ensuring the Safety and Quality of Foods Budapest, Hungary. 11-13 September. 

Kotiaho, T., Gylling, S., Lunding, A. and Lauritsen, F.R. (1995) Direct determination of styrene and tetrachloroethylene in olive oil by membrane inlet mass spectrometry. J. Agric. Food Chem., 43, 928-930. 

Figure 4. Calorimetric determination of styrene oxide In 1(2 dlchloroethane In the presence of various acids. Reaction conditions 6 ml of styrene oxide, 50 mL of 1,2 DCE, and 50 mg of catalyst. Starting temperature 20 C.

Figure 5. Calorimetric determination of styrene oxide reactivity In the presence of "methyldlsulfone" as a function of solvent. Note activation as the reaction proceeds. Reaction conditions ...

In a number of instances it is important to increase the sensitivity of determination. The most frequently used technique for this purpose is to convert substances into compounds detected with high sensitivity. Determination of styrene in 1 10 g amounts is a problem of practical importance in air pollution studies. Hoshika [118] proposed a simple, selective and sensitive method for determining trace amounts of styrene, based on converting styrene into a corresponding dibromide by reaction with bromine, followed by chromatographic separation and determination of the bromine derivative using an BCD. 

The following values for the pharmacokinetic parameters were scaled up from vitro determinations of styrene monooxygenase and epoxide hydratase activities in mouse liver (15). 

Crompton and co-authors [76] have described a UV spectroscopy method for the determination of styrene monomer in chloroform. 

This baseline correction technique can obviously be applied to the determination of styrene monomer in PS only if any other UV absorbing constituents in the polymer extract (e.g., lubricant, antioxidants) absorb linearly in the wavelength range 288-300 nm. If the polymer extract contains polymer constituents other than styrene with non-linear absorptions in this region, then incorrect styrene monomer contents will be obtained. An obvious technique for removing such non-volatile UV absorbing compounds is by distillation of the extract followed by UV spectroscopic analysis of the distillate for styrene monomer as described next. 

Table 2.12 Comparison of direct UV and distillation/UV methods for the determination of styrene monomer ...

Both polystyrene samples contained an ester and a mineral oil type of lubricant together with a phenolic antioxidant. The lubricants have little absorption in the 280-300 nm region and do not interfere in either method of analysis at the 5-10% concentrations at which they are used in polystyrene formulations. The absorption spectrum of the phenolic antioxidant, however, shows a sharply decreasing non-linear absorbance in the 280-300 nm region and contributes significantly to the background absorption of the test solution in the direct UV spectroscopic method. This invalidates the baseline correction procedure and leads to erroneous styrene monomer values. In the distillation procedure, however, the test solution used for spectroscopy does not contain the phenolic antioxidant and there is no interference in the determination of styrene monomer. 

Pfab and Noffz [53] have described two methods, both based on GC, for the determination of styrene monomer and other volatiles in polystyrene. In one method an or /70-dichlorobenzene solution of the polymer is distilled to isolate volatiles as a concentrate in the distillate. The ortho-dichlorobenzene used to dissolve the polymer contains a known amount of toluene which is used as an internal standard. The distillate is chromatographed on a polyethylene glycol column using helium as a carrier gas and a katharometer detector. 

One infrared spectral method used for the determination the monomer units of SBR is known as Hampton s method [63]. This method utilizes the characteristic monosubstituted aromatic band intensity at 699 cm (A ) for the determination of styrene unit composition, and the scheme defined as Morero s method (see seetion on polybutadiene and polyisoprene) is used to determine the butadiene moiety. As noted in the section on polybutadiene, the 1,4-cw, 1,4-trans, and 1,2-addition components appear in the IR spectrum at 724, 965, and 910 cm . ... 

Smith, P. B., Quantitative Analysis and Structure Determination of Styrene/ Methyl Methacrylate Copol5mers by Pyrolysis Gas Chromatography, Anal. Chem. 1996 68(17) 3033-3037. 

Quantitative Determination of Styrene-7, 8-oxide in Blood by Combined Gas Chromatography-Multiple Ion Detection Mass Fragmentography J. Chromatogr. 196(2) 314-318 (1980) ... 

Poisoning. X. Determination of Styrene in Biological Material by Gas Chromatography Sangyo Igaku 22(5) 368-371 (1980) ... 

Structure Determination of Styrene-n-Butyl Acrylate Copolymers... 

Determination of Styrene Copolymer Sizing Agents in Paper... 

PGC has been applied to the determination of styrene copolymer sizing agents [104]. PGC using a multi-detector on the gas chromatograph has been nsed to determine end-group functionality in PMMA. 

In a similar way styrene and vinylacetate monomers can be determined in polymerization reactions.In the determination of styrene the reaction mixture containing maleic anhydride is boiled under reflux for 3 hr. The unreacted maleic anhydride is hydrolysed to maleic acid and determined (in the determination of styrene) in aqueous solutions of pH 3-0 or (in the determination of vinylacetate) in benzene solutions. 

Evans and co-workers [28] described techniques employing Py-GC, proton NMR and carbon analysis for the determination of styrene and methacrylate units in styrene-methylmethacrylate and styrene-n-butyl methacrylate copolymers with an accuracy of 2%. Agreement between the three independent methods is excellent. The comparison stresses the complementary nature of all three methods. The Py-GC method possesses advantages such as simplicity and rapidity. 

Steele D.H., Thorburg M.J., Stanley J.S., Miller R.R., Brooke R., Cushman J.R., Cruzan G. Determination of styrene in selected foods. Journal of Agricultural and Food Chemistry, 42 1661-1665 (1994). 

Similar effects to these were also observed with polystyrene containing other ultraviolet absorbing additives. Thus, the influence of a mixture of 0.4% w/w tris-(nonylated phenyl phosphite (Polygard) and 0.2% w/w 2,6-di-tert-butyl-p-cresol (lonol CP) on the determination of styrene monomer is shown in Table 1.8. 

Table 1.6 - Comparison of Direct Ultraviolet and Distillation/Ultraviolet Methods for the Determination of Styrene Monomer... 

Table 1.7 - Influence of Phenolic Antioxidant on the Determination of Styrene Monomer by Direct Ultraviolet and by Distillation/Ultraviolet Methods...

Titrimetric methods (Method 56) have been described for the determination of styrene and acrylonitrile monomers in styrene-acrylonitrile. These methods unfortunately have the disadvantage of being more subject to interference than the polorogrs hic method described above. 

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