Benzene sampling

Tobias et al. [665] have described a method in which the GC effluent is passed into a combustion furnace to convert the organic hydrogen content into water, which is then selectively reduced to hydrogen in a reduction furnace containing Ni metal. The final stream is transmitted to the IRMS via a heated Pd filter, which passes only hydrogen isotopes to the ion source. For a benzene sample a precision of < 5 %o was obtained for <52HSMOw> which approaches the performance of off-line techniques and the requirements for studies of natural variability. This already meets requirements for analysis of D-labeled compounds used in tracer studies [666,667]. 

Figure 4.22. Permeation profiles for 1 mL of a 500-ppb benzene sample at an eluent (gas or liquid) flow rate of 1 mL/min. (Reproduced from Ref. 66, with permission from the American Chemical Society.)...

The solubilization results reported here were obtained with an automated vapor pressure apparatus described previously (21). Benzene samples, from an external reservoir at 50 C, were added incrementally to the main measuring system by means of a 6-port HPLC valve. Successive increments of benzene are allowed to flash from the valve into the main solution reservoir these samples contain 2.907 x 10" moles of benzene, with a reproducibility better than 1 part in 6,000 or 7,000 (22). 

The radical bromination of alkyl benzenes is a useful reaction because the resulting benzylic halide can serve as starting material for a variety of substitution and elimination reactions, thus making it possible to form many new substituted benzenes. Sample Problem 18.7 illustrates one possibility. 

Figure 3.67. The proton sensitivity test for a 0.1 % ethyl benzene sample recorded on a 400 MHz spectrometer equipped with a dual H C inverse probehead.

Knoll, J. E., Penny, W. H., Rodney, M. The Use of Tedlar Bags to Contain Gaseous Benzene Samples at Source-Level Concentrations, NTIS order no. PB-291569 (1978)... 

A simple and sensitive gas-liquid chromatographic method (28) has been developed for the quantitative determination of clonidine and some structurally related imidazolidines in rat brain tissues. The aqueous brain homogenates are first purified and then extracted into benzene. Samples are injected directly to GLC column (2 m x 2 mm I.D.) packed with 3% OV-17 on chromosorb 750 (80-100 mesh) was used at an oven temperature of 200-270 and an injector temperature of 280 the carrier gas was helium flow rate 30 ml/min. 

A significant increase in F can be obtained by using a Teflon vial with a benzene sample size larger than 3 ml. 

The prototypical sample used in /data obtained in a benzene sample at an applied field of 0.2 T is shown in Figure 3A. The precession... 

Sample Blank—Take a 100-mL portion of the CdCL washed and filtered benzene sample (prepared in accordance with the procedure in 11.1). Transfer to a 250-mL separatory funnel. Add 10 mL of ferric sulfate-sulfuric acid solution, stopper, and shake for 2 min 15 s. Allow the two phases to separate and draw off the lower H2SO4 layer into a 50-mL volumetric flask. Add 10 mL of H2SO4 to the separatory funnel and shake for 30 5 s. Again draw off the lower H2SO4 layer into the 50-mL volumetric flask containing the first extract. Dilute to volume and mix. Repeat with each specimen. 

Fig. 2.8 HD-OKE signal from iodo-benzene sample at 273 K. In the inset we show the fast relaxation time scale, where several signal oscillations take place...

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