The rates of reactions of ClzP atoms with methane, and with a series of substituted methanes, have been measured using mass spectrometric analysis of molecular reactant consumption in the presence of excess Cl atoms, with pseudo first order kinetic analysis ; this approach minimizes secondary reactions and the problem of reaction stoichionietries. The following rate constants were obtained for CI + RH reactions : l~g~~( k c~~/ c m~ molecule-' s-I) = (-10.294+0.043)-(778k 16) KIT, 300-686 K ; l o g l o ( k~~s~i / c m 3 molecule-' s-l) = (-9.673 k 0.087) -(776 & 30) K / T , 300-604 K ; l~g~~( k c~~~i~/ c m~ molecule-' s-I) = (-10.078 k0.074)-(629& 26) K / T , 298-621 K ; l~g~~( k c~~~~/ c m~ molecule-' s-I) = (-10.480+0.051)-(599k 19) KIT, 297-652 K ; l~g~~( k c~~c i~/ c m~ moIecuIe-' s-I) = -12.64+ 0.08, 652 K. The correlations of these results with data from competitive chlorination studies are discussed in relation to the uncertainty surrounding the Arrhenius parameters for the primary reference reaction, Values for the kinetic isotope (H/D) rate constant ratios, (~C H J~C D~) and ( k c~c i~ /~C D C I~) , were C1+ HZ+HCl+ H. measured over wide ranges of temperature : loglo(kCHs/kCD4) = (-0.155f0.024)+(384+ 12) K / T , 298-1018 K ; 298-1006 K. lOglo(kCHCl~/kCDC13) = (-0.014+0.020)+(167If:9) K / T , These results are in agreement with the predictions of the semi-empirical BEBO (bond-energy-bond order) method.Chlorination reactions with molecules RH, involving abstraction of an H atom, and leading to formation of HCl and a radical R, constitute one of the largest series of elementary reactions for which relative (although not absolute) rate constants have been measured. These kinetic data have provided some of the most extensive results for the testing of theories of absolute reaction rates, including kinetic isotope effects. Examples include the reactions : Cl+H,, D2, HT l * ; Cl+ CH4, CD4, CzH6, CzD6.2 However, surprisingly few direct measurements of absolute values for rate constants are a~ailable.~ All the reactions in the series C1+CH4, CH,Cl, CH2C12, CHC13, have activation energies less than 20 kJ f110l-l,~ whilst the values for -AU,",, in these exothermic reactions gradually increase in this series from about 4 kJ mol-l for Cl+ CH4, to about 42 kJ mol-1 for C1+ CHC13.4 Measurements of the ratios of rate constants (ICR*H/ICR"H) for reactions of this type have been carried out using competitive methods, with C1 atoms generated either thermally or photolytically from C12 : kWH Cl + R'H+R' + HCI, C1+ R"H+R" + HCl. 1547 7kRttn9

A direct differential scanning infrared spectrophotometric method is described for the determination of crystalline silica in respirable-size atmospheric dust samples from a wide range of industrial environments. The test atmosphere is drawn through a cyclone elutriator, fitted with a membrane filter, at 1.9 I min-1 for, typically, 1-4 h. The filter, without further preparation, is scanned from 1500 to 400 cm-1 and the atmospheric concentration of crystalline silica determined from the intensity of the quartz (799, 780 and 695 cm-I), together with, when present, cristobalite (796 and 621 cm-1) absorption bands. Generation of standard crystalline silica atmospheres using a portable dust chamber is described. The effect of particle size variation on the absorbance intensity, together with sample re-radiation and mineral interference effects, are examined.

Reactions of F(2P) atoms generated by a 2.45 GHz discharge in dilute F2 + He mixtures have been studied mass spectrometrically with a beam inlet system from a fast flow reactor. F atom concentrations have been measured from the consumption of Cl2 in the simple and extremely rapid bimolecular reaction 1[Formula: see text]k1 was determined to be (1.1 ± 0.3) × 10−10 cm3 molecule−1 s−1 at 300 °K.Rate measurements for the reaction 2, which forms CF3 radicals, are reported, over the range 301 to 667 °K,[Formula: see text][Formula: see text]A less detailed survey of the rates at 298 °K of a series of reactions of F with H2, CH4, CH3Cl, CH2Cl2, and CHCl3, is also given; in these cases, the source of F was a discharge in CF4 + Ar, and [F] was measured by titration with ClNO.

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of Contents I nt rod uct ion The Need for Improved Quality Analytical Methodology Reference Materials Conclusions References

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A high-performance liquid chromatographic (HPLC) method for the determination of both aliphatic and aromatic isocyanates was first devised by Dunlap et al. using N-(4-nitrobenzyl)propylamine as the urea-forming reagent (nitro reagent). Subsequent w 0 r k ~9 ~ indicated serious disadvantages associated with the use of this reagent, including oxidation of the reagent both during and after sampling, deterioration of the HPLC column packing by excess of reagent in the samples and its unsuitability for sampling in a reducing atmosphere. These disadvantages appear to stem from the presence of the aromatic nitro group in this secondary amine.

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