Journal of Analytical Chemistry, Vol. 58, No. 5, 2003, pp. 485–488. Translated from Zhurnal Analiticheskoi Khimii, Vol. 58, No. 5, 2003, pp. 542–545. Original Russian Text Copyright © 2003 by Evgen’ev, Garmonov, Belov, Tsekhmister, Druzhinin.

ARTICLES

Test Method for the Determination of Toxic Irritants in Air M. I. Evgen’ev*, S. Yu. Garmonov*, P. E. Belov*, V. I. Tsekhmister**, and A. A. Druzhinin** *Kazan State Technological University, ul. Karla Marksa 68, Kazan, 420015 Tatarstan, Russia **Military University of Radiation, Chemical, And Biological Defense, Brigadirskii per. 13, Moscow, 107005 Russia Received March 12, 2002; in final form, July 9, 2002

Abstract—It is shown that 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine can be determined with the use of indicator tubes containing 4-chloro-5,7-dinitrobenzofurazan and its N-oxide immobilized on silica gel. The conditions for the determination of these substances in air are determined. The following effects are studied: the nature, particle size, and layer thickness of the support; the nature and concentration of the analytical reagent in the chemisorption layer; the rate and time of air aspiration through the indicator tube; and various components of the sample matrix. The limit of visual detection of the toxic substances is 0.05 mg/m3.

Irritants 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine are highly toxic [1–3]. Therefore, simple, rapid, and sensitive procedures based on the test methods of chemical analysis [4, 5] should be developed for the field determination of these substances. One of the most effective methods for the determination of toxic substances in air is the use of indicator tubes with corresponding fillers [6]. The visual determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine in air with the use of indicator tubes is commonly performed through the formation of colored compounds with mercury salts or as diazo derivatives [2, 6, 7]. However, these analytical reactions exhibit low selectivity and sensitivity and are multistep. These factors complicate the procedures and test tools and make each individual determination longer. Previously, we showed that chlorodinitrosubstituted 2,1,3-benzoxadiazoles can be used for the selective and sensitive determination of some aromatic amines and hydrazines in air and water by test methods with visual and spectrophotometric detection of the analytical signal and in automated gas analysis [8, 9]. The goal of this paper is to study the possibility of the selective determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine as their dinitrobenz-2,1,3-oxadiazole derivatives in air. EXPERIMENTAL We used commercial 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine. The organic solvents were purified when necessary according to the known procedures [10, 11]. 4-Chloro-5,7-dinitrobenzofurazan and 7-chloro-4,6-dinitrobenzofuroxan were synthesized according to the procedures [12, 13].

We used ShSM silica gel activated by boiling in nitric and hydrochloric acids and calcined at 250°C. Gas mixtures of the target compounds were prepared by evaporating their methanol solutions in a 90-L airtight container. Homogeneous substance distribution was achieved by air stirring. The analyte concentrations in the gas mixtures were determined according to the standard procedures with the use of Richter’s absorption vessels. To prepare indicator tubes, standard glass tubes with a 4 mm i.d. for the length-of-stain determination of various toxic substances in chemical warfare reconnaissance and monitoring [6, 7] were used. An EA-30 electric aspirator and a PPKhR semiautomatic device for chemical warfare reconnaissance were used as air flow boosters. RESULTS AND DISCUSSION The reactions used in test methods should proceed with a rather high rate in dynamic conditions. A high contrast of the resulting colored derivatives as compared to the initial color determines both the possibility and the sensitivity of visual determination. Therefore, only reactive substances that give intensively colored products with the analytes can be used as the reagents. When indicator tubes are used for the determination, the concentration of the toxic substance can be found from the length and intensity of the stained layer of the indicator powder containing the reagent. The very high reactivity of chlorodinitrosubstituted 2,1,3-benzoxadiazoles facilitates the derivatization of 10-chloro-9,10-dihydrophenarsazine, which exhibits only slight nucleophilic reactivity. 10-Chloro-9,10-dihydrophenarsazine interacts with the reagent (4-chloro-5,7-dinitrobenzofurazan) on the support to give a blue product (λmax = 590 nm).

1061-9348/03/5805-0485$25.00 © 2003 åAIK “Nauka /Interperiodica”

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NO2

As

NH

N O+ N

NO2

As

Cl

NO2

Cl

N N O N NO2

In the case of dibenz[b, f][1,4]oxazepine, the reaction proceeds after the acid hydrolysis of the analyte in the chemisorption layer of the indicator tube to give

primary aromatic amine. The latter reacts with 7-chloro-4,6-dinitrobenzofuroxan to give a red product (λmax = 500 nm). O

NH2 CH

N CH H+

O NO2

O NH2 CH

N NO2 Cl

NO2 N

–HCl

O+ N

O

O O

O N

NO2 NH

O

O CH

O

We assessed the efficiency of the reagents for modification of the support by the length and intensity of the stained layer in the indicator tube, the rate of the color rise, and the color stability with time. The nature and structure of the support has a noticeable effect on the results. We tried the following supports for color reagents: glass, alumina, silica gel, porcelain, and zeolites. It was found that the best visualization of the analytical signal is achieved with the use of silica gel activated with acids. These results agree with the earlier data that the rate of heterogeneous reactions of amines with chlorodinitrosubstituted 2,1,3-benzoxadiazoles increases on a silica-gel surface [8, 14]. This is probably connected with the ability of silica gel to give πcomplexes with aromatic compounds, which results in the increase in the basicity of the analytes and the increase of their nucleophilic properties [15]. On this support, the reactions of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine are completed in 1–2 min to give an intense contrast stain of the chemisorption layer in the indicator tube. The particle size of the porous support affects smearing of the stained zone of the indicator powder. It is found that the best particle size for the determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine is 0.1–0.3 mm at the aspiration rate of 0.5–2.0 L/min under the studied conditions.

With larger particles, the breakthrough of the analytes and nonuniform stain of the indicator powder are observed. At the same time, with smaller support particles, the length of the stained zone decreases because of the higher mass-transfer resistance. The best length of the indicator powder layer in the tube (15–20 mm) was found by experiment. Changing the length of the layer causes smearing of the stained zone and impairs visual determination results. We tried different methods to modify the support for acid hydrolysis of dibenz[b, f][1,4]oxazepine. One of the methods consists in that a support layer (silica gel or glass) impregnated with hydrochloric, acetic, or sulfuric acid is placed in the indicator tube ahead of the layer with the immobilized color reagent. However, the best combination of the hydrolysis conversion, on the one hand, and intensity, stability, and reproducibility of the product color, on the other hand, is achieved when the support modified with the color reagent (7-chloro4,6-dinitrobenzofuroxan) is immediately impregnated with glacial acetic acid. The support surface is impregnated with nonaqueous (acetonitrile or alcoholic) solutions of the color reagents (4-chloro-5,7-dinitrobenzofurazan or 7-chloro-4,6-dinitrobenzofuroxan) with further evaporation of the solvent. The ratio between the support weight, the volume of the impregnating solution, and the concentration of

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Influence of various components on the results of the test determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b,f][1,4]oxazepine in air. The substances under determination were introduced in concentrations of 0.5 mg/m3 (n = 4, P = 0.95) Concentration of the interfering component in vapor-air mixture, mg/m3

Compound to be determined

Ammonia (20) Ammonia (150) (indicator tube with barbituric acid) Methylamine (2) Acetone (400) Chloroform (500) Methanol (300) Acetic acid (25) Ammonia (15) Ammonia (130) (indicator tube with barbituric acid) Dimethylamine (2) Acetone (350) Trimethylamine (5)

Dibenz[b,f][1,4]oxazepine ″ ″ ″ ″ ″ ″ 10-Chloro-9,10-dihydrophenarsazine ″ ″ ″ ″

the reagent in it was kept constant. The best mass concentration of the reagent in the indicator tube is 1–2%. The experiments show that the conditions in which the reagent is applied to the support are of great importance. The natural evaporation of a large volume of the solvent (acetonitrile) at room temperature or during heating results in the partial deactivation of the reagent and loss of sensitivity. This can be attributed to the high electrophilicity of 4-chloro-5,7-dinitrobenzofurazan and 7-chloro-4,6-dinitrobenzofuroxan, which can interact with a weak base as water. Obviously, the characteristics of the chemisorption layer deteriorate under the natural evaporation of the solvent from water during the preparation of the indicator powder because of the adsorption of water vapor and hydrolysis of the reagent. Therefore, the selective layers were prepared by vacuum evaporation of the minimum amount of the organic solvent at 15 mm Hg residual pressure. Highboiling solvents (glycerol, dibutyl phthalate, etc.) used for support impregnation cause smearing of the stained zone in the tube. The degree of packing of the indicator powder was monitored by its mass and the length of the support layer in the tube at a constant inside diameter. When the indicator powder is tightly fixed by glasswool plugs, the packing density has no effect on the determination. In the field application of indicator tubes, the stability of the selective layer under various storage conditions is of great importance. The selective layers retain their properties when stored sealed or tightened with plastic plugs for at least six months. When the indicator powder is stored open, the characteristics of the selective layer deteriorate, which is also connected with the hydrolysis of the reagents. The determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine should be optimized taking into account the reactivity of the reagents. 7-Chloro-4,6-dinitrobenzofuroxan is more reactive with JOURNAL OF ANALYTICAL CHEMISTRY

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Found analyte, mg/m3 0.5 ± 0.1 0.4 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.4 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.5 ± 0.1

primary amines as compared to 4-chloro-5,7-dinitrobenzofurazan. However, in reactions with N-arylamines, the reactivity of these electrophilic reagents usually reverses [8]. Tests of the indicator tubes showed that 4-chloro5,7-dinitrobenzofurazan is advisable for the determination of 10-chloro-9,10-dihydrophenarsazine, because the color of the layers based on 7-chloro-4,6-dinitrobenzofuroxan is rather unstable and indistinct. The indicator layers based on 4-chloro-5,7-dinitrobenzofurazan ensure good determination results under these conditions. At the same time, a higher contrast of the colored dinitrobenzofuroxan derivatives makes its use advisable for the determination of primary arylamines. Therefore, we used 7-chloro-4,6-dinitrobenzofuroxan for the determination of the primary arylamine derivative of dibenz[b, f][1,4]oxazepine. It should be noted that the indicator layer in the determination of the toxic substances begins to stain during air aspiration through the tube. The color completely develops in 3–5 min. The resulting color is stable up to one year, which is important for the documentation of the results. The limits of the visual determination of 10-chloro9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine in air are as low as 0.05 mg/m3 during 10 min of air aspiration (n = 5). The selectivity of the determination of 10-chloro9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine was studied in the presence of various components of air. It was found that hydrocarbons, acetone, halocarbons, and alcohols do not interfere with the determination at any concentration. Ammonia interacts with the color reagents to give the corresponding amino derivatives. However, its interference with the determination of 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine, resulting in smearing of the stained zone, appears at more than 20 mg/m3 of ammonia. Interference from ammonia can be eliminated by

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using a filter indicator tube containing barbituric acid, which binds ammonia. The use of the filter tube makes it possible to determine 10-chloro-9,10-dihydrophenarsazine and dibenz[b, f][1,4]oxazepine at up to 200 mg/m3 ammonia. The advantages of the proposed test methods also include their group selectivity for irritants, because other classes of toxic substances do not interfere with the determination. REFERENCES 1. Franke, S., Lehrbuch der Militärchemie, vol. 1, Chemie der Kampfstoffe, Berlin: Deut. Militärverlag, 1967. Translated under the title Khimiya otravlyayushchikh veshchestv, Moscow: Khimiya, 1973, vol. 1. 2. Franke, S., Franz, P., and Warnke, W., Lehrbuch der Militärchemie, vol. 2: Analytic Chemischer Kampfstoffe, Berlin: Deut. Militärverlag, 1969. Translated under the title Khimiya otravlyayushchikh veshchestv, Moscow: Khimiya, 1973, vol. 2. 3. Aleksandrov, V.N. and Emel’yanov, V.I., Otravlyayushchie veshchestva (Poison Gases), Moscow: Voennoe Izd., 1990. 4. Zolotov, Yu.A., Khim. Prom-st., (Moscow), 1997, no. 6, p. 48. 5. Zolotov, Yu.A., Vestn. Ross. Akad. Nauk, 1997, vol. 67, no. 6, p. 508. 6. Chebotarev, O.V., Druzhinin, A.A., Pashinin, V.A., and Sinitsin, A.N., Zh. Ros. Khim. O-va im. D.I. Mendeleeva, 1994, vol. 38, no. 2, p. 69.

7. Rukovodstvo po rabote v avtomobil’noi radiometricheskoi i khimicheskoi laboratorii AL-4M (Manual for an AL-4M Radiometric and Chemical On-Car Laboratory), Moscow: Voennoe Izd., 1988. 8. Evgen’ev, M.I., Garmonov, S.Yu., Evgen’eva, I.I., Goryunova, S.M., Nikolaeva, N.G., and Levinson, F.S., Zh. Anal. Khim., 1998, vol. 53, no. 2, p. 175. 9. Evgen’ev, M.I., Garmonov, S.Yu., and Medvedev, V.V., Zavod. Lab., 1996, vol. 62, no. 3, p. 8. 10. Weissberger, A. and Proskauer, E.S., Organic Solvents. Physical Properties and Methods of Purification, Riddick, J.A. and Toops, E.E., Eds., New York: Interscience, 1955. Translated under the title Organicheskie rastvoriteli, Moscow: Inostrannaya Literatura, 1958, pp. 302, 308. 11. Gordon, A.J. and Ford, R.A., The Chemist’s Companion: A Handbook of Practical Data, Techniques and References, New York: Wiley, 1972. Translated under the title Sputnik khimika, Moscow: Mir, pp. 439, 440. 12. Sharnin, G.P., Levinson, F.S., Akimova, S.A., et al., USSR Inventor’s Certificate no. 657025, Byull. Izobret., 1979, no. 14. 13. Bailey, A.S. and Case, J.R., Tetrahedron, 1958, vol. 3, p. 113. 14. Evgen’ev, M.I., Evgen’eva, I.I., and Levinson, F.S., J. Planar Chromatogr., 2000, vol. 13, no. 3, p. 199. 15. Styskin, E.L., Itsikson, L.B., and Braude, E.V., Prakticheskaya vysokoeffectivnaya zhidkostnaya khromatografiya (Practical High-Performance Liquid Chromatography), Moscow: Khimiya, 1986.

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