Macromolecular N-Chlorosulfonamide as an Oxidant for Residual

Mar 16, 2005 - Nitrites in Aqueous Media. Romuald Bogoczek,* Elz3 bieta Kociołek-Balawejder, and Ewa Stanisławska. Wrocław University of Economics,...
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Macromolecular N-Chlorosulfonamide as an Oxidant for Residual Nitrites in Aqueous Media Romuald Bogoczek,* Elz3 bieta Kociołek-Balawejder, and Ewa Stanisławska Wrocław University of Economics, ul. Komandorska 118/120, 53-345 Wrocław, Poland

A macroporous and macromolecular product, in bead form, polystyrene cross-linked by divinylbenzene, containing pendant N-chlorosulfonamide groups, was used to oxidize nitrite to nitrate in dilute aqueous alkaline, neutral, or acidic media. The well-known sodium salt of this macromolecular oxidant was unreactive in the said conditions; however, its hydrogen form was very reactive and enabled it to complete nitrite elimination. Nitrates in wastewaters are a few hundred times less harmful than nitrites. Aqueous solutions of nitrates at the concentration in question can serve as a nutritive spray for farmlands. Introduction The content of nitrites in natural water is one of the main decisive factors indicating the class of cleanliness. A high content of these chemical compounds is always undesirable and testifies to the pollution of the aqueous environment, although they form in water as a result of natural processes: the nitrification and denitrification processes. The permissible content of nitrites in natural water, first class of purity, is very low and should not exceed 0.01 mg of NNO2-/L. Nitrites can be formed in water-supply systems as a result of nitrification bacteria activity and also in water treatment. One imputes the increasing content of nitrites in the environment to the irrational fertilization of soils with nitrogen compounds and as a consequence of their penetration via sewage into the water system. Numerous manufacturing processes using nitrites as raw materials are well-known. Dangerous, for living organisms, is the ability of nitrites to react with amino groups of albumens, leading to the formation of nitrosamines, which show mutagenic and cancerogenic properties. The removal of nitrites from natural water and industrial solutions can be carried out by chemical methods, using oxidation to nitrates, for which the permissible content in water is 5.0 mg of NNO3-/L. In this case, the use of a strong oxidizing agent is required. Chlorine or sodium hypochlorite, chlorine dioxide, ozone, or hydrogen peroxide can be used.1 Removal of the undesirable residual substances demands extensive use of a homogeneous oxidant with the result that the conditioned solution is polluted again, although with other kinds of substances. For the removal of toxic admixtures present in low concentrations in solutions, heterogeneous reagents applied in column processes can be especially useful. Numerous papers on this topic come from Emerson et al.,2-6 from Worley and co-workers,7,8 and from us.9-11 The proposed method here for the removal of NO2ions from aqueous solutions involves their oxidation with the active chlorine present in the functional groups of a reactive polymer, which has a redox character, * To whom correspondence should be addressed. Tel./Fax: +48 71 3680275. E-mail: [email protected].

showing strong oxidative properties. The reactive polymer, insoluble but swollen in water, is molecularly built from a polystyrene/divinylbenzene skeleton with a macroporous structure and has N-chlorosulfonamide functional groups where the built-in active chlorine atoms represent the +1 oxidation degree state. The concentration of active chlorine in the copolymer, wellswollen in water, is very high and attains 1.5 M. In this paper, we have used the N-chlorosulfonamide copolymer in both the sodium and hydrogen forms. We have already obtained and described elsewhere copolymers containing hydrogen-form N-chlorosulfonamide functional groups,12 but their potential use in place of sodium derivatives in oxidation processes has not been considered until now. In this investigation, the examination of the possibility of nitrite removal from aqueous solutions, where their primary concentration was tens to several hundreds of milligrams of NO2- per liter and their final concentration is less than 0.1 mg, on the basis of the following reactions was conducted.

[P]-SO2NClNa + NO2- + H2O f [P]-SO2NH2 + NO3- + NaCl (1) [P]-SO2NClH + NO2- + H2O f [P]-SO2NH2 + NO3- + HCl (2) [P] stands for the copolymer styrene/divinylbenzene macroporous structure. The sodium derivative of the N-chlorosulfonamide copolymer used here is a high molecular weight equivalent of the known micromolecular oxidant, the chloramine T, which is used in analytical chemistry for the quantitative determination of NO2- ions.13-15 Materials and Methods Resins. The copolymers that had N-chlorosulfonamide groups in sodium or hydrogen form (R/Na stands for [P]-SO2NClNa, and R/H stands for [P]-SO2NClH)

10.1021/ie040267x CCC: $30.25 © 2005 American Chemical Society Published on Web 03/16/2005

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we prepared by methods published in detail elsewhere:12,16

[P]-SO3H f [P]-SO2Cl f [P]-SO2NH2 f [P]-SO2NClNa [P]-SO2NClNa + CH3COOH f [P]-SO2NClH + CH3COONa (3) As a starting material, Amberlyst 15 (produced by Rohm and Haas Co.), a commercially available sulfonate cation exchanger, was used. This is a macroporous poly(S/20% DVB) resin that contained 4.7 mmol/g -SO3H groups in the dry state (surface area 45 m2/g and average pore diameter 25 nm). The product contained 2.15 mmol/g -SO2NClNa groups (i.e., 4.30 mequiv of active chlorine/ g) and 0.70 mmol/g -SO3Na groups. The transformation of the N-chlorosulfonamide sodium groups to the Nchlorosulfonamide hydrogen groups was performed by treatment of the R/Na product with an excess of acetic acid. In stationary experiments, a sample R/Na was shaken with an excess of 0.1 M CH3COOH. After 2 h of shaking, the resin beads were separated from the solution by filtration and were washed with distilled water. The product was analyzed after drying at normal conditions to a constant weight. In dynamic experiments, the R/Na resin was placed in a glass column and was washed first with 0.05 M CH3COOH and then with distilled water. For a sample that contained 40 mequiv of active chlorine (i.e., 9.5 g of resin), 1.0 L of said acid was used. Analysis of Functional Groups in Resins. The active chlorine content in the resin (R/Na and R/H) was determined by the iodometric method. N-Chlorosulfonamide groups in the hydrogen form were additionally determined by alkalimetric pH titration. Nitrite Solutions Used for Testing. Analyticalgrade sodium nitrite was used for the preparation of the aqueous solutions containing NaNO2 alone or in a mixture with sodium hydroxide or sulfuric acid in different proportions. Solutions used in the batch regime were 0.01 M NaNO2 in water, in 0.01, 0.1, and 1 M NaOH, or in 0.05 M H2SO4. The solutions used in the experiments carried out in a dynamic regime were 0.005 M NaNO2 in water of in 0.005 M NaOH or 0.0005 M NaNO2 in water. Analysis of Solutions. The nitrite and nitrate ion concentrations were determined by colorimetric methods (Spekol 1200, Analytic Jena, Jena, Germany).17 The nitrite concentration was determined by a modified Griess-Ilsovay method. The reaction of a violet diazo dye formation of sulfanilic acid and dihydrogen chloride of N-(1-naphthyl)ethylenediamine was used. The absorbency measurement was taken at 545 nm wavelength. Nitrates were determined with sodium salicylate, where the formation of the yellow nitrosalicylic acid was used. The absorbency was determined at 410 nm wavelength. Chloride ions were estimated by argentometric titration using 0.01 M AgNO3 and the Ag/AgCl/ calomel electrode system. Redox Potentials of R/Na and R/H. Into seven separate samples of R/Na [0.24 g (∼1.0 mequiv) of active chlorine] or seven separate samples of R/H [0.21 g (∼1.0 mequiv) of active chlorine] were introduced the following increasing solution volumes of 0.01 M NaNO2, respectively: (1) 0.0 mL, (2) 12.5 mL, (3) 25 mL, (4) 37.5 mL, (5) 50 mL, (6) 62.5 mL, and (7) 75 mL. To the first (1)

Table 1. Concentration Drop of Nitrite Ions in Solution during Batchwise Contact with a Sample of R/Na (i.e., an 100% Excess of Active Chlorine in Relation to Stoichiometry) concn of nitrite ions in solution, mg of NO2-/L time, h 0 2 5 24

in 0.005 M H2SO4

alone

in 0.01 M in 0.1 M in 1 M NaOH NaOH NaOH

0.50 g of R/Na + 50 mL of 0.01 M NaNO2 460 460 460 460 85.5 450 453 453 16.9 439 450 450 2.14 418 435 440

455 453 450 441

Active Chlorine in a Sample of R/Na, mequiv before reaction 2.15 2.15 2.15 after reaction 0.96 1.85 1.80

2.15 1.82

Chloride Ions in Solution, mmol of Clbefore reaction 0 0 0 0 after reaction 0.49 0.10 0.12 0.14 pH after reaction 4.41 9.52 12.23 13.28

0 0.16 13.74

sample of the copolymers was added only distilled water. Said increasing solution volumes of NaNO2 were needed to bring about the reduction of (1) 0%, (2) 25%, (3) 50%, (4) 75%, and (5) 100% of the functional group active chlorine. However, the last two samples for each copolymer contained (6) 125% and (7) 150% of the nitrite ion. All of these samples, in closed vessels, were shaken at room temperature. After 24 h, the electric potentials of the reaction media in the vessels were measured by means of the platinum/calomel electrode pair. Nitrite Oxidation in the Batch Scale. In all studies carried out in the batch regime at room temperature, a measured amount of the resin (ca. 0.50 g of R/Na or R/H) placed in a flask was shaken mechanically with 50 mL of 0.01 M NaNO2 (100% excess of active chlorine) or 200 mL (100% excess of nitrites). Timedependent measurements of the residual NO2- in solution were made. After the reaction, the polymeric reagent was separated from the reaction medium by filtration and was analyzed for the active chlorine content. Nitrite Oxidation in the Flow System. R/Na (9.5 g in the dry state; ∼17.5 mL after swelling in water; 40 mequiv active chlorine content) was packed into a glass column (inner diameter ∼1.15 cm; height of the package ∼17.5 cm). The resin bed of R/Na was transformed into hydrogen form by allowing first 1 L of 0.05 M CH3COOH to pass through the bed and then distilled water until neutral reaction of the outflow was achieved. Several fractions, each 100 mL, were taken and examined by titration with 0.1 M NaOH and 0.1 M Na2S2O3. Then diluted NaNO2 solutions of diverse alkalinity were passed through the bed of R/Na or R/H. The examined flow rates were from 5 to 17 bed volumes/h. Fractions (250 mL) were collected to estimate their composition in terms of pH and nitrites, nitrates, and chlorides. Results and Discussion The estimation of the entire oxidative ability of the R/Na in relation to nitrites after 24 h showed a very low reaction progress. Only a slight decrease in the concentration of nitrite, from 460 to 446 mg of NO2-/L, occurred. To investigate whether the reaction among R/Na and nitrites has taken place to any degree and whether the pH has any influence on its course, a sample of the copolymer was shaken with 0.01 M NaNO2 in different media (Table 1). It was observed that the acidic sample

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Figure 1. Alkalimetric titration curve of R/H (m ) 0.504 86 g).

showed a very large conversion of nitrites; their concentration dropped from 460 to 2.14 mg of NO2-/L. In that solution, the chloride content was in accordance with the stoichiometric nitrite dropout. In the other media of nitrite solutions (those without any additives or with an admixture of NaOH), the NO2- ion concentration drop was insignificant. After discovering that the oxidation reaction of nitrites is favored by the acidic reaction, we tried to bind the acidic functionality with the high molecular oxidant, and we succeeded using the hydrogen-form N-chlorosulfonamide copolymer. A sample of R/Na (1.202 26 g), after conversion to the hydrogen form, dried at room temperature, to a constant weight (1.064 66 g), showed a high (ca. 13.5%) weight decrease. The active chlorine content of the hydrogen-form resin was 4.80 mequiv/g. In Figure 1, the course of the potentiometric alkalimetric titration curve of the R/H resin is shown. The medium strong acid, acetic acid, is in the position to transform the weakly acidic N-chlorosulfonamide groups (pKa ∼ 7.2) from the sodium form to the hydrogen form, whereas it is not in the position to transform the residual strong acidic sulfonic groups from its sodium form to its hydrogen form also present in the copolymer. The measurement of the total oxidative capacity of R/H in relation to nitrites showed that it was 110 mg of NO2-/g of the resin. Using a sample of R/H with ca. 100% of the active chlorine excess, the kinetics of the oxidation reaction of nitrites was measured. We wished to examine how much the nitrites concentration in the solution at the given conditions would decrease. As indicated in Figure 2 (curve a), the reaction is rapid and the concentration of nitrites dropped below the level of 1.0 mg/L after 4 h. When the reaction was over, the solution pH was 3.08 and its chloride content was ca. 0.48 mmol. The copolymer contained ca. 50% of the initial active chlorine. The curve b in Figure 2 illustrates the run with the R/Na during an analogous reaction route. This reaction occurs only to a small degree; after 4 h, the analytically observed decrease of nitrites was only 5%. To find out why the N-chlorosulfonamide copolymer in the hydrogen form oxidizes nitrites, while that in the sodium form does not, the normal redox potential of the copolymers in both forms was measured. An acknowledged special method was used because the reaction ran too slowly because of the fact that the reagents were in different phases. The redox potential of the R/H resin follows from curve a in Figure 3. It was ca. +800 mV.

Figure 2. Decrease of nitrite from the aqueous solution in a batchwise reaction: (a) 0.50 g of R/H + 50 mL of 0.01 M NaNO2; (b) 0.50 g of R/Na + 50 mL of 0.01 M NaNO2.

Figure 3. Redox titration curve of (a) R/H and (b) R/Na by 0.01 M NaNO2.

In the case of R/Na (curve b), one does not observe any reaction; the curve is approximately a straight line. The sodium-form N-chlorosulfonamide copolymer is a poor oxidant in relation to nitrites, which themselves belong to very weak reducers. We explain the difference in behavior of copolymeric sodium- and hydrogen-form sulfonamides by the electronic effects taking place in the -N ¨ ClNa and -N ¨ ClH groups. The free electron pair at the nitrogen atom is attracted much more easily by the hydrogen atom than alternatively by the sodium atom. As a consequence, the chlorine atom is less powerfully held by nitrogen in the hydrogen-form sulfonamide group than in the sodium-form sulfonamide. That is why the hydrogen-form sulfonamide is a more powerful oxidant, and that is also why its redox potential is higher. The dynamic (column) method investigation began by letting a 0.005 M NaNO2 solution pass through the column filled by R/Na. A flow intensity of 10-15 bed volumes/h was applied. It was discovered that the concentration of nitrites in the effluent was nearly equal to their concentration in the influent, which was, on average, 225 mg of NO2-/L. This led to our statement that the sodium-form N-chlorosulfonamide copolymer is not able to oxidize the nitrites even in dynamic conditions. In the next phase of research, the resin in the column was transformed into the hydrogen form by passing a

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active chlorine in the resin bed). Analyzing the chloride content in the denitrited fractions (up to V/V0 ) 170), we observed that their concentration is a little lower than anticipated and is ca. 0.004 M, instead of 0.005 M. Likewise, the content of nitrates was also lower and was, on average, 250 mg of NO3-/L. Thus, the probable course of the gas-evolving side reactions, known from elsewhere, was as follows:

Figure 4. Acetic acid breakthrough curve for R/Na in the column process: influx, 0.05 M CH3COOH; flow rate, 10 bed volumes/h.

Figure 5. Nitrite breakthrough curve for R/H in the column process: influx, 0.005 M NaNO2 in (a) water and (b) 0.005 M NaOH; flow rate, 15 bed volumes/h.

0.05 M CH3COOH solution. As seen in Figure 4, which shows the breakthrough curve, the required acid quantity was ca. 900 mL, and thus the entire Na/H capacity of the resin bed was ca. 21 mmol. This corresponds to the active chlorine content in the column. Because the hydrogen-form N-chlorosulfonamide copolymer was not applied as yet as an oxidant in a column process, its stability is unknown in those conditions, so far. What is its ability to keep the active chlorine in the functional groups? This is why fractions in the preceding stage (resulting from washing of the resin bed in the column with acetic acid) were additionally analyzed iodometrically for an active chlorine presence. No oxidative reaction was observed in any of the fractions. The starch indicator decolorized after the introduction of 1-2 drops of the 0.1 M Na2S2O3 titrant. During the column experiments, a gassing phenomenon was observed, which requires an explanation. When the NaNO2 solution passed through the column of the R/H copolymer, a considerable increase of acidity of the solution was observed (pH 2.85-3.6); we stated the unfavorable occurrence of a gas evolution in the column. Gas locks made it difficult to pass the solution down the column at the given speed. The evolved colorless gas was scentless. From Figure 5, which shows breakthrough curves, it follows that the quantity of nitrites removed from the processed solution is 23.75 mmol (ca. 18% greater than the initial quantity of the

HCl + NaNO2 f NaCl + HNO2

(4)

3HNO2 f HNO3 + 2NO + H2O

(5)

The main reaction (2) is accompanied by the emission of hydrogen chloride, which acidifies the processed solution; in the reactive space (inside the beads), nitrous acid can be formed. This acid, being unstable, decomposes through a disproportionation reaction, producing the colorless, barely water-soluble gas NO. The nitrites that reacted as the result of the above reactions (we estimate it at ca. 15%) did not use up the active chlorine. Thus, the breakthrough curve is “longer” than one might anticipate. The resin bed admitted more of the NaNO2 solution to undergo the oxidation than what follows from the stoichiometry of the main reaction (2). Applying the hydrogen form of the N-chlorosulfonamide copolymer in the column processes, to counteract the evolution of gaseous products, we tried to control the acidity of the solution using a partial neutralization in situ. The idea was to neutralize the strong hydrochloric acid, leaving unchanged the weak acidic -NClH group. As follows from curve b in Figure 5, the breakthrough curve became considerably shorter. The oxidative ability of the resin bed was much lower than that in the preceding column process. The conclusion is that the added alkalinity transformed the hydrogen-form sulfonamide groups back again to the sodium form prior to the HCl neutralization. This shows that in the grainlayer column the evolution of HCl (and so the oxidation reaction of nitrites to nitrates) comes later (lower in the column) than the neutralization reaction:

[P]-SO2NClH + NaOH f [P]-SO2NClNa + H2O (6) As long as the effluent reaction was acidic, gas products appeared in the column (although considerably less intensively than previously). The analysis of the postreaction copolymer showed that it had mixed functional groups: -SO2NH2 and -SO2NClNa. Because the controlled alkalinization of the influent, as a method for limiting the evolvement of the gas products, proved ineffective, we decided to check how the process would run when the concentration of NaNO2 as the column influent was lower. In that case, the reaction medium would become less acidic, and so the acid-dependent side reactions should undergo limitation. Therefore, up to breakthrough, 30 L (over 1700 bed volumes) of the 0.0005 M NaNO2 solution with a flow intensity of 17.0 bed volumes/h was passed through the resin bed in the column prepared as before. No evolution of gases in the column could be observed; the column process ran without any disturbance. The pH of the effluent remained at a level of ca. 3.75. The concentration of chlorides compatible with the anticipated value was 0.0005 M. This showed that the nitrites oxidation

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reaction proceeded quantitatively. The concentration of nitrates in the effluent was nearly 30.0 mg of NO3-/L. Conclusions When a diluted NaNO2 aqueous solution is brought into contact with a sodium-form N-chlorosulfonamide copolymer, no oxidation reaction to NO3- could be observed, either in a batch or in a column process. This is different from that in the known cases of oxidation processes of cyanides, thiocyanates, and sulfides, which seem to be better reductants than nitrites are.9-11 As we have discovered, the oxidation of the toxic nitrite ion to the 100-fold less toxic nitrate ion can be performed by the N-chlorosulfonamide reactive copolymer in the hydrogen form. Functional groups of the sodium-form N-chlorosulfonamide copolymer can be transformed into its hydrogen form by contacting the reactive copolymer with the solution of a medium strong acid, e.g., of acetic acid. The hydrogen form of the N-chlorosulfonamide copolymer is a stable product and thus can be successfully applied as an effective redox exchanger in both batch and column processes. In this work, the reactive copolymer has been used to remove nitrite ions from aqueous media by their oxidation to nitrate ions. It has been shown that this copolymer in the hydrogen form is especially suitable for the removal of nitrites from very diluted solutions, in the concentration order of tens of milligrams of NO2- per liter. In more concentrated solutions, say several hundreds milligrams of NO2- per liter, in addition to the reaction of oxidation, a number of disadvantageous consecutive reactions occur, resulting from the excessive acidification of the reaction medium. In this case, evolving gaseous byproducts create some difficulties in a column process. It should be taken into consideration here that the oxidation of nitrites to nitrates by the N-chlorosulfonamide copolymer, according to its stoichiometry, is very effective. The oxidative ability of the hydrogen-form N-chlorosulfonamide copolymer amounts to ca. 110 mg of NO2-/g of the copolymer. The reaction of nitrites oxidation by means of this water-insoluble, heterogeneous oxidant runs at a favorable speed, as can be seen from the large flow intensities in the column experiments. Nitrites are poor reducers, so their oxidation is by no means easy. The utilization here of the strong oxidative redox copolymer, thanks to its high redox potential, yielded the desirable good results. In the process investigated the postreaction solution contains HCl instead of nitrites. This does not seem to be a large obstacle to the environment because the pH of the postreaction solution is 3.75 and the chlorides in this concentration are not a danger to the environment. Very dilute aqueous HCl can be used as a secondary raw material in the reactive copolymer preparation of the main macromolecular reagent in this paper. In case the aqueous solution should be applied as nutritive spray for farmlands, neutralization with ammonia water is recommended.

Literature Cited (1) White, G. C. Handbook of Chlorination and Alternative Disinfectants; John Wiley & Sons: New York, 1999. (2) Emerson, D. W.; Shea, D. T.; Sorensen, E. M. Functionally Modified Poly(styrene-divinylbenzene). Preparation, Characterization, and Bactericidal Action. Ind. Eng. Chem. Prod. Res. Dev. 1978, 17, 269. (3) Emerson, D. W. Polymer-bound Active Chlorine: Disinfection of Water in a Flow System. Polymer Supported Reagents. 5. Ind. Eng. Chem. Res. 1990, 29, 448. (4) Emerson, D. W. Slow Release of Active Chlorine and Bromine from Styrene-Divinylbenzene Copolymers Bearing N,NDichlorosulfonamide, N-Chloro-N-alkylsulfonamide, and N-bromoN-alkylsulfonamide Functional Groups. Polymer Supported Reagents. 6. Ind. Eng. Chem. Res. 1991, 30, 2426. (5) Emerson, D. W. Chlorine Dioxide Generated by Reaction of Sodium Chlorite with N-halosulfonamide or N-alkyl-N-halosulfonamide Groups on Styrene-Divinylbenzene Copolymers. Ind. Eng. Chem. Res. 1993, 32, 1228. (6) Zhang, Y.; Emerson, D. W.; Steinberg, S. M. Destruction of Cyanide in Water Using N-chlorinated Secondary Sulfonamide Substituted Macroporous Poly(styrene-co-divinylbenzene). Ind. Eng. Chem. Res. 2003, 42, 5959. (7) Chen, Y.; Worley, S. D.; Kim, J.; Wei, C.-I.; Chen, T. Y.; Santiago, J. I.; Williams, J. F.; Sun, G. Biocidal Poly(styrenehydantoin) Beads for Disinfection of Water. Ind. Eng. Chem. Res. 2003, 42, 280. (8) Chen, Y.; Worley, S. D.; Kim, J.; Wei, C.-I.; Chen, T. Y.; Suess, J.; Kawai, H.; Williams, J. F. Biocidal Polystyrenehydantoin Beads. 2. Control of Chlorine Loading. Ind. Eng. Chem. Res. 2003, 42, 5715. (9) Kociołek-Balawejder, E. A redox copolymer having Nchlorosulfonamide groups for cyanide ion decomposition in dilute aqueous solution. React. Funct. Polym. 1997, 33, 159. (10) Kociołek-Balawejder, E. A macromolecular N-chlorosulfonamide as oxidant for thiocyanates. React. Funct. Polym. 1999, 41, 227. (11) Kociołek-Balawejder, E. A copolymer with N-chlorosulfonamide pendant groups as oxidant for residual sulfides. React. Funct. Polym. 2002, 52, 89. (12) Bogoczek, R.; Kociołek-Balawejder, E. Cation exchangers having chlorinating, oxidative and bacteriological properties. Vysokomol. Soedin., Ser. A 1987, 29, 2346; Chem. Abstr. 1988, 108, 38845. (13) Deshmuth, G. S.; Murthy, S. V. S. S. Amperometric determination of nitrite with chloramine T. Indian J. Chem. 1963, 1, 316. (14) Agterdenbos, J. The volumetric determination of nitrite with chloramine T. Talanta 1970, 17, 238. (15) Agraval, A.; Nahar, S.; Hussain, Z.; Sharma, P. D. Kinetics and mechanism of chloride ion catalysed oxidation of nitrite with N-chlorotoluene-p-sulphonamide (chloramine T) in aqueous acid perchlorate medium. Oxid. Commun. 1993, 16, 80. (16) Bogoczek, R.; Kociołek-Balawejder, E. N-Monohalogenoand N,N-dihalogeno(styrene-co-divinylbenzene)sulfonamide. Polym. Commun. 1986, 27, 286. (17) Williams, W. J. Handbook of Anion Determination; Butterworth: London, 1979.

Received for review October 26, 2004 Revised manuscript received January 28, 2005 Accepted January 31, 2005 IE040267X