Measurement methods benzene

Colorimetric methods have led to the development of visual devices for measurement of benzene concentration. These visual detection tubes have been popular since the 1960s and have provided a simple and rehable method for evaluating ambient aromatic vapor contamination. These products are available from anumber of manufacturers such as Drager (Lubeck, Germany), Gastec (Tokyo, Japan), Kitagawa (Kawasaki, Japan), DuPont (Wilmington, Delaware, USA), and 3M (St. Paul, Minnesota, USA) (85). 

Dipole-moment measurements in benzene solution on 1,4-dimethylpiper-azine and on a series of 1 -alkyl-4-tm-butylpiperazines120 show clearly that the N-alkyl groups exist predominantly in the expected position and indicate a value of 1.8 kcal mol-1 for the N-methyl group. This must now be considered a minimum value, and kinetic protonation of 1,4-dimethylpiperazine with 13C-NMR analysis of the products326 gives 2.96 + 0.05 kcal mol". An attempt312 to apply the line-broadening method failed.313... 

An example of an evaluation undertaken according to this protocol is for the measurement of benzene in ambient air by tube type samplers subject to thermal desorption (EN, 2005b) and samplers subject to solvent desorption (EN, 2005a). These standards were developed specifically to provide measurement methods meeting requirements for checking compliance with the air quality standard for benzene set by the European Ambient Air Quality Directive (Directive 96/62/EC, 1996). Evaluation of published data concerning the samplers under the test conditions enabled an evaluation of the expanded relative uncertainty of measurement at a limit value (5 pgnT3) for benzene in air and for solvent and thermally desorbed samplers a value of 13.4% was obtained. 

EN (2005a) 14662-5. Ambient Air Quality-Standard Method for Measurement of Benzene Concentrations Diffusive Sampling Followed by Solvent Desorption and Gas Chromatography, The British Standards Institution, London, UK. 

Measurement of Benzene Concentrations. Part 1 Pumped Sampling Followed by Thermal Desorption and Gas Chromatography Method, CEN. 

An alternative to the method of Problem 14.43 might be to measure the vapor pressure of the benzene stream at 25°C. Compare the two methods. Benzene and toluene form ideal solutions. The vapor pressure at 25°C is approximately 95 torr for benzene and 30 torr for toluene. 

For measurements to be practicable it is almost necessary to have some degree of conductivity in the organic liquid, which means that ions can pass, though not necessarily at a rapid rate. Therefore such adsorption potentials as are measurable will probably be transient. Measurements with benzene or paraffins as the organic liquid have not yet been made,3 on account of the difficulty of their low conductivity. Possibly a modification of the vibrating plate method described on p. 35 might be applied to the measurement of oil-water potentials when the oil has a very low conductivity. 

Few methods have been reported for measurement of benzene in foods performance data are generally lacking. 

Separate molecular weight determinations by the ebullio-scopic method using benzene and butanone as solvents provide values of 211 and 192, respectively. Inasmuch as the formula weight of [Zr(C6H702)3]Cl is 424, these values indicate that the complex is practically completely ionized. This is confirmed also by conductometric measurements in benzene and butanone and by the ready precipitation of silver chloride by silver perchlorate in acetone solution. 

Zinco-aluminosilicates having different pore volume and external surface area were synthesized and their stability in aromatization was investigated. Table 2 shows some properties of catalysts. External surface area was measured by benzene-filled pore method described by Inomata et al. [5]. Average crystal size was measured geometrically by SEM images. Stability of those catalysts was examined under the same condition as stated above, and the results are shown in Fig, 2. 

MEASUREMENT METHODS Charcoal tube ethyl acetate benzene gas chromatograph with flame ionization detection. 

MEASUREMENT METHODS Particulate filter benzene gravimetric. 

MEASUREMENT METHODS Charcoal tube benzene methanol gas chromatography with electron capture detection. 

Direct measurements of benzene solubility in mixed acids were not always possible because of the reactivity of the benzene. The following method was used to estimate the distribution of benzene between phases at reaction conditions. First, the distributions of nitrobenzene and chlorobenzene between phases were measured using mixed acids comparable in concentrations to those used in the two-phase reaction study. Nitrobenzene was unreactive in these acids and the amount of chlorobenzene that reacted (while measurements were being made) was negligible in most cases. Second, the distribution of benzene between phases was measured at conditions where reaction did not occur these measurements were made at low temperatures and/or using mixed acids much less concentrated than those used in the two-phase reaction study. The results of these measurements were then extrapolated to reaction conditions using the data for nitrobenzene and chlorobenzene as a guide. 

Following on from this work, the Bristol group have made careful measurements on benzene + glycerol-a system which was known to involve surface adsorption. The method used, which involves determining the extrapolated retention volume as a function of column loading, should serve as an example to workers in this field. The activity coefficient at infinite dilution at 323 K was found to be 2.084 0.005. 

DIN EN 14662-2, Ambient air quality - standard method for measurement of benzene concentrations part 2 pumped sampling followed by solvent desorption and gas chromatography, 2005. 

A similar circumstance is detectable for nitrations in organic solvents, and has been established for sulpholan, nitromethane, 7-5 % aqueous sulpholan, and 15 % aqueous nitromethane. Nitrations in the two organic solvents are, in some instances, zeroth order in the concentration of the aromatic compound (table 3.2). In these circumstances comparisons with benzene can only be made by the competitive method. In the aqueous organic solvents the reactions are first order in the concentration of the aromatic ( 3.2.3) and comparisons could be made either competitively or by directly measuring the second-order rate constants. Data are given in table 3.6, and compared there with data for nitration in perchloric and sulphuric acids (see table 2.6). Nitration at the encounter rate has been demonstrated in carbon tetrachloride, but less fully explored. ... 

The overall reactivity of the 4- and 5-positions compared to benzene has been determined by competitive methods, and the results agreed with kinetic constants established by nitration of the same thiazoles in sulfuric acid at very low concentrations (242). In fact, nitration of alkylthiazoles in a mixture of nitric and sulfuric acid at 100°C for 4 hr gives nitro compounds in preparative yield, though some alkylthiazoles are oxidized. Results of competitive nitrations are summarized in Table III-43 (241, 243). For 2-alkylthiazoles, reactivities were too low to be measured accurately. 

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