Filter sampling method for atmospheric sulfur dioxide at background concentrations

Abstract

0.2mM were stable and sufficiently concentrated to give quantitative results. The thiocyanate concentration was found to be important in driving the reaction to completion and affected the rate of complex formation. Low absorbances observed at concentrations less than about 0.2M might, in part, result from the decomposition of I(SCN)zto form the non-absorbing ISCN (IO).Hydrogen ion concentrations were about 1M in all cases.Lower concentrations caused a slight decrease in stability and higher concentrations (above 2-3M) led to the decomposition of thiocyanic acid (9).Absorbance measurements on thirty separately prepared solutions are shown in Table I. Precision of replicate measurements is good and the overall accuracy has a range of about f3%. A linear least squares fit to the data gives a slope of 41100 f 200 1. mol-' cm-l and a y-intercept of Possible interferences from extraneous ions were examined. Table I1 summarizes these observations. In each case, two solutions of identical iodide concentrations were compared with an extraneous ion added to one. These were carried through the procedure in parallel.Clearly, chloride presents no serious interference at the levels examined and bromide lowers the absorbance only a few percent. The fact that the chloride interference does not change with chloride concentration suggests that the 2% difference in absorbance may be a measurement error rather than an interference. Sulfate, a frequent interference in iodide analyses, causes a small decrease in absorbance.The transition metal ions interfered to varying extents. Since thiocyanate complexes form with these cations, interferences are to be expected.-0.003.

Sampling for chemical analysis

“…Although only indirectly related to sampling, descriptions of the treatment of the data in both papers are useful. Methods for sampling sulfur dioxide (29,152,224,241,503) and nitrogen dioxide (82,105) have been described. Husar and co-workers provided a good discussion of the sampling designs and equipment required when sampling for sulfur dioxide and sulfate particulates from an aircraft (224).…”

Evaluation of metallic foils for preconcentration of sulfur-containing gases with subsequent flash desorption/flame photometric detection

“…Therefore, quantitative measurements of atmospheric sulfur-containing gases at these ultratrace levels require an efficient sample preconcentration step prior to the actual detection phase. These sample enrichment techniques have included various types of chemically impregnated filters (1)(2)(3)(4)(5), solid adsorbents (6)(7)(8), metal-coated glass beads (9,10), and cryogenic traps (11)(12)(13)(14).…”

Personal monitoring method for nitrogen dioxide and sulfur dioxide with solid sorbent sampling and ion chromatographic determination

“…In each test, one sample was analyzed immediately; the others were capped and stored at room temperature. Results in Table II indicate that less than 10% of N02 and S02 was lost in the sample after 4 days.…”