Bromine, detection estimation

Evidence for the contribution of the CIO + BrO interaction is found in the detection and measurement of OCIO that is formed as a major product of this reaction, reaction (31a). This species has a very characteristic banded absorption structure in the UV and visible regions, which makes it an ideal candidate for measurement using differential optical absorption spectrometry (see Chapter 11). With this technique, enhanced levels of OCIO have been measured in both the Antarctic and the Arctic (e.g., Solomon et al., 1987, 1988 Wahner and Schiller, 1992 Sanders et al., 1993). From such measurements, it was estimated that about 20-30% of the total ozone loss observed at McMurdo during September 1987 and 1991 was due to the CIO + BrO cycle, with the remainder primarily due to the formation and photolysis of the CIO dimer (Sanders et al., 1993). The formation of OCIO from the CIO + BrO reaction has also been observed outside the polar vortex and attributed to enhanced contributions from bromine chemistry due to the heterogeneous activation of BrONOz on aerosol particles (e.g., Erie et al., 1998). 

The corresponding sodium salts, which are cheaper, serve equally well. Excess of potassium bromide and hydrochloric acid is added to a solution of the substance to be estimated and the bromate, in the form of a volumetric solution (usually N/5), is run in. The end point (shown by the presence of free bromine) is detectable, quite sharply, by spotting on starch-iodide paper as external indicator. Alternatively the end point may be determined by adding a known amount of bromate in excess, then potassium iodide, and titrating the liberated iodine with thiosulphate. 

Furthermore, acetylene concentrations decayed faster than expected from removal by OH and Cl, indicating the presence of bromine atoms with mixing ratios of l-2pmolmol . The corresponding BrO mixing ratios in the range of several tens of pmol moP should cause loss of ozone by —90% per day by the BrO-BrO reaction cycle. Estimated concentrations of chlorine atoms were —1,000 times smaller than those of bromine (Jobson et al., 1994). There are some tentative indications of substantial concentrations of CIO radicals, similar to those of BrO, 21 12 pmol mol , at a detection limit of 20pmolmol per individual measurement. 

The use of gas-liquid chromatography for the identification and estimation of potato glycoalkaloids has been described. The glycosides were rendered sufficiently volatile by conversion into their permethyl ether derivatives. Solasodine and soladulcidine in admixture may be conveniently estimated by thin-layer chromatography after bromination of the former. The detection of steroidal alkaloids on t.l.c. plates and a colorimetric method for the estimation of solasodine have been discussed. 

The isotopic ratio is particularly useful for the detection and estimation of the number of sulfur, chlorine, and bromine atoms in a molecule because of the large contribution they make to the (M -i- 2) (see Table 20-3), For example, an (M a- 2) that is about 65 i of the M peak is strong eviticnee for a molecule-containing two chlorine atoms an (M 2) peak of 4%. on the other hand, suggests the presence of one atom of sulfur. 

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