Benzene measurement

In 1971 the OSHA standard for benzene (20 CFR, Part 1910.0000) adopted a permissible exposure limit (PEL) of 10 ppm benzene measured as an 8-h TWA. In October of 1976 NIOSH updated its earlier criteria document on benzene and recommended that OSHA lower the benzene exposure standard from 10 to 1 ppm. This proposed implementation was blocked by the United States Supreme Court iu 1980 on the basis of iusufficient evidence linking benzene to cancer deaths. By the mid-1980s convincing evidence of the carciuogenicity of benzene appeared through animal studies which justified reconsideration of the 1 ppm PEL (130). 

To fully characterize and categorize the solute selectivities of GC stationary phases, Rohrschneider and McRe5molds pioneered one of the earliest characterization methods [5,6]. The Rohrschneider-McReynolds system is the oldest and widely accepted stationary phase classification systems that is based on the retention of five probe molecules namely, benzene, bufanol, 2-penfanone, nifropropane, and pyridine. Each probe molecule is used to represenf a disfincf or a combination of interactions with the stationary phase. Benzene measures dispersive interactions with weak proton acceptor properties butanol measures dipolar interactions with both proton donor and proton acceptor capabilities 2-pentanone measures dipolar interactions with proton acceptor but not proton donor capabilities nitropropane measures weak dipolar interactions and pyridine measures weak dipolar interactions with strong proton acceptor but not proton donor capabilities. 

Figure 1. Linewidlhs of different rotational transitions in the 14q1q vibronic band of benzene measured with Doppler-free two-photon absorption. The observed strong dependence on the quantum number J of the rotational angular momentum is evidence for a rotationally dependent intramolecular coupling process. (Taken from Ref. 3.)...

Recrystallization of the achiral oxo amide /V,/V-diisopropylphenylglyoxylamide (la) from benzene gave colorless chiral prisms [1], Each crystal is chiral and shows a CD spectrum in Nujol mulls (Fig. 1). One type of chiral crystal shows a (+)-Cotton effect and the other type shows a (-)-Cotton effect (Fig. 1). Crystals of (+)-la and (-)-la can easily be prepared in large quantities by seeding with finely powdered crystals of (+)-la or (-)-la during recrystallization of la from benzene. Measurement of the CD spectrum of chiral crystals as Nujol mulls is now well established [2],... 

The clinical and epidemiological evidence is summarized below. The deficiencies in the studies include the lack of appropriate sampling techniques, exposure determinations, mortality standards, and other aspects of experimental design or methodology. Additionally, intermittent exposures to benzene made it difficult to assume that the average concentrations of benzene measured in a workplace actually indicated the true exposure experienced by each worker (Goldstein 1985). A cause-effect relationship between benzene and leukemia is sufficiently clear however, there are few data from which dose-response relationships can be established. 

The amount of benzene measured in mainstream smoke ranged from 5.9 to 73 pg/cigarette (Brunnemann et al. 1990). Larger amounts of benzene were found in sidestream smoke, ranging from 345 to 653 pg/cigarette (Brunnemann et al. 1990). 

Table 4 Indoor concentrations of benzene measured and modelled (all values /tgm-3) after ref. 56...

Although recovery of total oil as measured by IR analysis appears to be satisfactory, the extraction efficiency of the resin columns with respect to individual components is still in question, since alkylbenzenes are relatively soluble in water (21) and thus might be expected to adsorb poorly on the XAD resin. Therefore, a direct comparison was made between the quantities of toluene, C2-benzenes, and C3-benzenes measured by both helium extraction and by XAD-2 adsorption. The results of this intermethod comparison are presented in Table II. 

The spectrum of benzene, measured in natural abundance, under high resolution shows long-range coupling through... 

Activity tests were run on the reduced nickel-alumina system. The reaction chosen was the hydrogenation of benzene. Measurements were restricted to the nickel-alumina series because quantitative reduction of nickel-magnesia and of nickel-rutile proved to be impossible. 

Figure 8.6 shows the X-ray structure of Fe(NCS)2(bpp)2 2(benzene) measured at 223 K. It proved that iron was coordinated by four N atoms of bpp and two N atoms of NCS in the trans position, as observed in Fe(NCS)2(bpp)2. There is one crystallographically independent iron ion that is, the conformers of bpp were anti-gauche and anti-gauche. In enclathrated benzene molecules, carbon atoms have a high temperature anisotropy and 12 atoms per molecule were observed, showing 30° rotation. The host framework has ID chain structure, and benzene molecules are located at the interstitial space located between two ID chains. The spin state of iron showed temperature-independent high-spin Fe" state. 

Fig. 1.28. Gas phase contours of absorption bands of acetylene, acetonitrile, tri-methylamine, and benzene measured in a 10-cm cell with a rock salt prism, (a) Acetylene at 81 mm pressure. The parallel and perpendicular bands are marked. The perpendicular band has a central peak which is absent in the parallel bands. There is partial resolution of some rotational fine structure, (b) Acetonitrile at 67 mm Hg pressure. The moment of inertia about the symmetry axis is relatively small. The perpendicular band has a round contour with some fine structure resolved. The parallel band is a triplet, (c) Trimethylamine at 27 mm Hg pressure. The parallel bands are a little wider than the perpendicular bands and show a more distinct central peak. The triplet bands are asymmetrical because of centrifugal distortion, (d) Benzene at 26 mm Hg pressure. The parallel and perpendicular bands are not very different. The references cited refer to the band assignments the spectra shown were obtained by the authors of this text.

Garcia Vicente, I. Garcia-Lisbona, N. Velasco, I. Otin, S. Munoz Embid, J. Kelnaian, II. V. Excess enthalpies of 1 -chloroalkanes + benzene. Measurement and analysis in terms of group contributions (DISQUAC) Fluid Phase Equilib. 1989,49, 251-262... 

Prepare 1400 mL of thiophene-free benzene. Measure the absorbance of this material by the procedure outlined in 10.2 and 11.2. The absorbance should be no greater than 0.01. 

The described theory has been verified on the adsorption isotherms of benzene measured mainly gravimetrically on three typical samples of micro-porous solids. The zeolite NaX and the microporous active carbon (a.c.) (industrially steam activated beech wood carbonaceous products) represents the samples No 36 and 29 of our found of probes, respectively. The isotherms on a.c. 29 have been overtaken from "(ref. 10)" and also analysed early... 

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