Showing papers by "Purnendu K. Dasgupta published in 1981"

Fluorometric determination of atmospheric sulfur dioxide without tetrachloromercurate(II)

Abstract: 1-Naphthylammonium chloride is substituted for pararosaniline hydrochloride for a fluorometric version (excitation 342 nm, emission 442 nm) of the Schiff reaction used for the determination of sulfur dioxide. The sensitivity is 2 orders of magnitude better than the colorimetric method; in all other aspects the two methods are analogous.

Determination of atmospheric sulfur dioxide without tetrachloromercurate(ii): Further refinements of a pararosaniline method and field application

Abstract: Results are presented for the field application of a pararosaniline method which determines sulfur dioxide by utilizing a nontoxic thermally stable dilute formaldehyde absorber buffered at pH 4. Parallel results by the Federal Reference Method are reported. Further refinements of the pararosaniline procedure including dye reagent purification and inclusion of a trichloroacetic acid buffer system are described. Merits and limitations of direct and reverse reagent addition are discussed.

A new method of generation of gases at parts per million levels for preparation of standard gases. Comments.

Abstract: SIR: The article “A New Method of Generation of Gases a t Parts per Million Levels for Preparation of Standard Gases” (ES&T 1980 1 4 , 4 1 3 ) describes a simple method for generation of test gases a t low levels. I t should be pointed out that, for three out of the five systems described (NO2, SOz, and HzS), the solute is subject to oxidative degradation and it is unlikely that a constant concentration of the desired gas will be maintained in the effluent stream over a long period of time. This is, of course, what Figure 7 shows when NazS03 is used as a solute: the SO2 concentration decays rapidly with time. In this context, the authors consider the greater oxidizability of S032-, as opposed to HS03-, to be responsible. Yet, the legend associated with the figure states that both the NaHS03 and Na2S03 solutions were maintained a t pH 5 . If the buffer employed had had sufficient capacity to maintain a constant pH, it would have mattered little whether Na2S03 or NaHS03 was put in solution insofar as the relative distribution of S032-/HS03is concerned. The S032-/HS03ratio is uniquely governed by the final pH of the solution and not by the form of the salt used; S0a2is reportedly protonated with a rate constant of 1011 L mol-1 s-1 ( I ) . There are other problems associated with NO, generation by this technique. Nitrous acid is sufficiently stable in the vapor phase to constitute an appreciable fraction of what is being measured as NO,. In our studies with vaporand aerosol-phase nitrous acid, we encounter a very similar problem; HNOz is measured totally as NO2 by the Saltzman procedure and it decomposes to NO and NO2 in the chemiluminescence-type analyzers. The reliability of the data presented in Figure 4 is, therefore, open to question. The method is, however, attractive for situations where chemical instability, either for the solute in the solution or for the gas in the effluent stream, is not a problem. If fresh solution is pumped in with a peristaltic pump a t an adequate rate, constant solution composition and thus constant gas composition in the effluent stream can be assured. Oxidative degradation may, of course, be eliminated by using N2 instead of air.