Environ. sci. Technol. 1994, 28,388-393
Spectrophotometric Method for Nitroglycerine Analysis in Air Nazim 2. Muradov
Florida Solar Energy Center, 300 State Road 401, Cape Canaveral, Florida 32920
A method for the spectrophotometric analysis of nitroglycerine (NG) in gaseous effluents is developed. The procedure is based on the conversion of NG to nitrite ions by dissolving NG in an absorbing alkaline solution. Nitrite ions were analyzed spectrophotometrically by reacting the sample with hydrogen peroxide, a mixture of sulfanilamide and phosphoric acid, andN-(1-naphthy1)ethylenediamine dihydrochloride, successively. NG concentrations were determined from absorbances a t 540 nm via specially developed calibration graph. The detection limit is about 0.1 ppmv of NG in air. The selectivity of the method and the effect of NO2 presence in the sample are discussed. Estimates of NG concentrations correlate well with those obtained by chromatographic method.
Introduction One of the major environmental problems associated with the production of munitions is the extensive contamination of air, water, and soil by toxic explosives at sites and around facilities where munitions are manufactured, stored, or used. Nitrate esters, in general, and nitroglycerine (NG), in particular, are among the most widely used chemicals for the manufacture of explosives and propellants ( I ) . Current manufacturing methods to produce multibase propellants use solvents for the formation of NG, and when these solvents are removed at various processing stages, by sparging with hot air, significant levels of NG-contaminated volatile organic compounds (VOC) are emmited. NG-contaminated air emissions potentially represent an environmental problem in other areas of NG utilization, for example, in the pharmaceutical industry. Although the vapor pressure of NG is low [0.033 Pa at 20 'C ( I ) ] ,it presents a serious air pollution problem because NG is adsorbed so readily through the lipoidal surfaces of the lungs and the skin (2). The potential toxicity of NG and other nitrate esters has been well-documented ( I ). Several analytical methods for determining NG in air and other media have been developed, i.e., via GC, GC/MS, HPLC, etc. (2-6). The GC/MS method (Finnigan 4500 quadrupole MS) using a 15-m-longcapillary column has been employed by several authors ( 4 ) for the detection of explosives, including NG, in post-blast debris. Others (5) have used the GC method for airborne NG analysis; a known volume of air was passed through a glass tube packed with a porous polymer (TenaxCG) in which NG was absorbed. The sorbent was extracted with ethanol, which was then injected into a GC equipped with an electron capture detector. The minimum detectable quantity (MDQ) for NG by this procedure was about 1pg. These laboratory methods of NG analysis are costly and not always accessible to most researchers. Several spectrophotometric methods have been developed for the quantitative NG measurements in blood and urine and for the quality control determination of NG in dosage forms (7-10). For example, the xylenol procedure is based on the spectrophotometric measurement of nitroxylenol formed from the reaction of hydrolyzed 388
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organic nitrate with 2,6-xylenol(7). The method described in ref 8 involves NG degradation in alcoholic (methanol) sodium hydroxide solution with the formation of a chromophoric intermediate absorbing at 336 nm. The spectrophotometric method for the assay of individual NG tablets reported in ref 9 is based on alkaline hydrolysis of NG with subsequent colorimetric (absorbance at 550 nm) determination of the nitrite ion formed through diazotization and coupling reactions. A colorimetric method for individual tablet analysis based on the NG hydrolysis with tetramethylammonium hydroxide has been developed (10);the nitrite ion formed was used to diazotize p-chloroaniline, which was then reacted with N-(lnaphthybethylenediamine. As far as airborne NG is concerned, no spectrophotometric method for the microdetermination of NG in air has been reported in the literature. The main objective of this work was to develop asimple, reliable and inexpensive method for NG analysis in air. Principle of the Method. NG was collected by passing NG-contaminated air through an absorbing alkaline solution forming stable nitrite ions. The concentration of nitrite ions in the solution was determined spectrophotometrically by reacting the sample with a complex reagent (referred to HSPN reagent in this paper) containing hydrogen peroxide, sulfanilamide, phosphoric acid, and N-(1-naphthybethylenediaminedihydrochloride (NEDA) solutions (11).
Experimental Section Apparatus. The analytical system consists of three subsystems; namely, an absorber, a device for pumping and controlling the air flow, and a spectrophotometer. These subsystems are described below: Absorber. A 20-mm i.d. and 20-cm-long Pyrex test tube with leap and a gas dispersion tube with a fritted end (porosity B, 70-100 pm maximum pore diameter) was used. Alternatively, a special bubbler for sampling nitrogen dioxide can be used (12). Waste Simulation System. A SAGE Model 341B calibrated syringe pump (Orion Research Inc.) and 10250 WLglass syringes (Scientific Glass Engineering) were used for the simulation of NG-containing gaseous streams. Flow Control. An air pump, equipped with a metering valve and rotameter, capable of delivering 0.2 L/min of flow through the absorbing solution was used. Flow rates were measured also using HFM-200 Series Teledyne Hastings Raydist mass flowmeters. Spectrophotometer. Any spectrophotometer or colorimeter capable of absorbance measurement at 540 nm can be used. For example, a simple Spectronic 20 instrument with 10-mm glass cuvettes was found to be quite adequate. For precise laboratory measurments, a Spectronic-601 (Milton Roy) spectrophotometer or spectrophotometric system consisting of an Xe light source, a GM 252-40 monochromator, and an Oriel 77348 photomultiplier with a 100-mm cuvette was used. For field screening, battery-operated spectrophotometers can be used. 0013-936X/94/0928-0388$04.50/0
0 1994 American Chemical Society
Flgure 1. Experimental setup for the simulating and sampling of NG-containing gaseous streams. A, mixing manifold; B, heated and insulated part of the waste simulation system; 1, calibrated syringe pump; 2, glass syringe; 3, high-temperature septum; 4, glass wool; 5, air filter; 6, air flowmeter; 7, air heater; 8, absorber with fritted gas dispersion tube; 9, ice bath; 10, silicone tubing connection; 11, trap with glass wool; 12, valve; 13, rotameter: 14, air pump.
Reagents. All chemicals used were ACS analytical reagent grade. The absorbing solution was prepared by dissolving 4 g of sodium hydroxide in distilled water, diluted to 1000 mL. A sample of 0.2 mL of 30% hydrogen peroxide was diluted to 250 mL with distilled water. This solution may be used for a month if kept in the dark. A total of 20 g of sulfanilamide was dissolved in 700 mL of distilled water. A total of 50 mL of concentrated phosphoric acid (85%) was added and diluted to 1000 mL. The solution remains stable for a month if refrigerated. NEDA (0.5 g) was dissolved in 500 mL of distilled water. The solution remains stable for a month if refrigerated and protected from light. Spirits of 10.26 (wt %) of NG in ethanol were shipped from the Navy munitions production facility for use in this work. Procedure. Sampling. The air sampling train is depicted in Figure 1. The system consists of an absorber (containing 50 mL of absorbing solution) and an air pump connected to the unit simulating the NG-contaminated airstream. Airflow rate through the absorber was a constant 200 mL/min. An air pump with a metering valve was used for drawing the sample through a fritted bubbler at a constant flow rate of 200 mL/min for 20 min. Spirits of NG (in ethanol) of known concentrations and volumes were introduced a t a preset and steady injection rate via a heated (normally around 100 "C) manifold, through a special high-temperature septum. At the point of injection, the manifold was packed with glass wool (herbicidal grade) to allow high surface area and to facilitate the rapid
evaporation of the reagents. Preheated (100 " C ) air entered the mixing manifold a t a specified rate and mixed with NG/ethanol vapors. The entire manifold section was wrapped with a heating element and insulated to allow a uniform mixing temperature. The manifold temperature was monitored, controlled, and maintained a t a constant level by means of a type-K thermocouple, placed on the wall near the sample injection port. The temperature in the area of the junction of the mixing manifold and the absorber was maintained between 70 and 80 "C. After sampling was accomplished and the bubbler was disconnected from the experimental unit, the NG which condensed on the inner walls of the gas dispersion tube (GDT) was carefully washed out. This was done using a rubber bulb and drawing the absorbing solution through the dispersion'tube. The absorbing solution (sample A) was removed from the absorber into a beaker and allowed to remain undisturbed for approximately 30-40 min at room temperature. Analysis. A 10-mL sample of A was pipeted into a beaker, and 1.0 mL of hydrogen peroxide solution, 10.0 mL of sulfanilamide solution, and 1.4 mL of NEDA solution were successively admixed. The solution was thoroughly mixed each time the reagents were added. A blank was also prepared in the same manner using 10.0 mL of absorbing solution. After 10-15 min of color development interval, the absorbance a t 540 nm was measured against the blank background. The complete analysis usually lasts about 45 min. Safety. Efforts were made to adhere to the accepted safety guidlines for the handling and use of energetic compounds, in general, and NG, in particular. For reasons of safety and repeatability, much care has been taken in Envlron. Sci. Technol., Vol. 28, No. 3, 1994 388
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Wavelength, nnFlgure 2. Absorbance spectrum of the colored product formed from NG-containing absorbing solution mixed with HSPN reagent.
the selection of construction materials and in the design and fabrication of the system. All the surfaces and process lines that contact NG vapor were smooth and heated to prevent unwanted NG condensation, adsorption, and/or concentration. Most surfaces in the process train were Pyrex glass with minimal sharp turns, corners, etc. After each experiment, the sampling train was disassembled, and all of the components were washed using ethanol or acetone.
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Time, rnin Figure 3. Time dependence of the absorbance at 540 nm resulting from the mixing of NG-containing solution with HSPN reagent. I
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Results and Discussion Absorbance Spectra of NG in Alkaline Solutions. Figure 2 depicts the absorbance spectrum of the colored (pink) products produced from an absorbing solution containing NG mixed with the HSPN reagent. The sodium nitrite (NaN02) alkaline solution, after adding the same analytical reagents, reveals a similar absorbance spectrum = 540 nm, molar with the following characteristics:, , ,A absorptivity E = (2.05 f 0.02) X lo4 L mol-l cm-l. The similarity of spectra is an indication that NG hydrolysis takes place with the formation of nitrite ions when NG dissolves in an alkaline solution. Experiments were conducted to determine the optimum color development interval. Figure 3 depicts the data on the kinetics of the color-forming reactions, which were monitored by measuring the absorbance (at 540 nm) of the NG alkaline solutions after exposure to the HSPN reagent. It was shown that maximum solution absorbance was obtained after 10-min reaction time a t room temperature. Exposure to the analytical reagents for periods longer than this interval did not result in a noticeable change in absorbance. Thus, a 10-min color development interval was selected. Effect of Contact Time. It was found that the contact time of NG with absorbing solution markedly effected solution absorbance at 540 nm. Thus, we varied the contact time from 1to 120 min. After adding the HSPN reagent and allowing 10 min of color development, the absorbance of the solution was measured. Figure 4 shows the dependence of measured absorbance on the contact time. It can be seen that the contact time required for the concentration of nitrite ions in the solution to reach a plateau value is approximately 30-40 min. This value does not, in fact, correspond to complete hydrolysis of NG 390
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C o n t a c t time, min Flgure 4. Absorbance of the solution at 540 nm vs contact time of NG with the absorbing solution.
in the absorbing solution. Rather, it is an indication of the completion of the first rapid reaction step for NG hydrolysis. At room temperature, complete hydrolysis of NG occurs slowly after this initial fast reaction step and reaches completion after several days. Quantitative measurements using nitrite ion calibration graph (absorbance at 540 nm vs nitrite ion concentration) showed that after 20 min, 30 min, and 33 h of hydrolysis the molar ratio of NOz- to the initial concentration of NG was approximately 1.0,1.4, and 2.1, respectively. These experimental findings are in a good agreement with the results of other investigators on the stoichiometry of NG hydrolysis. For example, it was reported (13) that base-catalyzed NG hydrolysis resulted in approximately 2 mol of nitrite ions formed/mol of reacted NG. In other work (IO), it was shown that the hydrolysis of NG with tetramethylammonium hydroxide in nonaqueous systems also yielded 2 mol of nitrite ionimol of NG. Urbanski ( I ) in a historical summary of the alkaline hydrolysis of nitrate esters refers to Hay's early work, where the author had found a yield of potassium nitrite equal to 2 mol/mol of NG, in the course of NG hydrolysis in potassium hydroxide solution. Calibration, Range, and Sensitivity. Either of two methods of calibration may be employed: standardization with nitrite solution or with a known amount of NG in
t
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NG concentration, ppmv Figure 5. Calibration graph of the absorbanceat 540 nm vs volumetric NG concentration in the gaseous phase.
gaseous mixtures. The latter method is more reliable because stoichiometric and efficiency factors are eliminated from the calculations. NG-containing standard gaseous mixtures can be prepared from NG/ethanol solutions of various concentrations using syringe pump and mixing manifold as depicted in Figure 1. NG/ethanol solutions of various concentrations were injected into the mixing manifold at a predetermined rate using calibrated syringe pump (see Experimental Section). The concentration of NG in standard gaseous mixtures covered the expected range of the sample concentrations. Calibration conditions were identical to those encountered during actual sample acquisition (i.e., 0.2 L/min of airflow, 20 min of sampling time, etc.). Using standard gaseous mixtures, absorbances a t 540 nm were measured using a spectrophotometer. The calibration graph was prepared by plotting absorbance vs NG concentration in the gas phase (in ppmv). Each point on the graph represents the average of three replicate measurements. The mean value and the standard deviation are 13.724 and 1.962 ppmv/absorbance, respectively, n = 15. Results are shown in Figure 5. We performed several experiments to verify the reliability of this method. For example, we found that using two different methods of introducing a fixed quantity of NG into the absorbing solution, Le., from gaseous streams and direct introduction from NG/ethanol solutions, gave approximately the same absorbances (with a margin of error of *5 % 1. This meant that NG was not lost during the bubbling of a gaseous mixture through the absorbing solution. With 50 mL of absorbing solution and a sampling rate of 0.2 L/min for 20 min, the range of the method is from 0.1 to 100 ppmv of NG in gaseous streams. The upper limit is determined by the vapor pressure of NG at the safe level of temperatures. The gaseous samples with NG concentrations below 0.1 ppmv resulted in the absorbances comparable with the absorbance of blank solution (due to nitrite impurities in the analytical reagents used). It should be noted that the detection limit of the method could be substantially lowered by increasing sampling time. Selectivity and Interferences. Since other nitrate esters can also yield nitrite ions in the course of alkaline hydrolysis, the spectrophotometric method for NG analysis based on this reaction is believed to be nonselective. However, our experiments as well as the results of other
researchers demonstrate that quite accurate colorimetric quantitation of NG can be performed in the presence of other nitrate esters. It is known that the alkaline hydrolysis of nitrate esters, and NG particularly, is very complex (1). In a solution of sodium or potassium hydroxides in water or alcohol, not only is the hydrolytic process simulated but also the oxidation and reduction processes accompany the formation of organic acids, nitrates, and nitrites. Thus, the products distribution and the yield of nitrite ions vary widely depending on a number of factors such as the structure of nitrate ester, base concentration, temperature, etc. We found out that the kinetics of hydrolysis of some nitrate esters in 0.4% (w) sodium hydroxide solution a t room temperature is very slow. For example, the hydrolysis of 15.3 mg of propylene glycol dinitrate (PGDN) (or methyl nitroglycol) in 100 mL of 0.4% (w) NaOH solution resulted (after addition of the HSPN reagent) in absorbances 0.002 and 0.018 after 2 and 20 h of reaction a t room temperature, respectively (comparing to the absorbance of 1.131 observed after 40 min of NG hydrolysis in approximately identical conditions). At 85 “C the rate of PGDN hydrolysis was substantially increased: the absorbance of 0.713 was observed after 2 h of hydrolysis (using the identical alkaline solution of PGDN). The solutions of triglycol dinitrate (TGDN) and methyltrimethylolmethane trinitrate (MTN) ’ (w) NaOH solutions did not result in the formation in 0.4% of an appreciable amount of nitrite ions at room temperature and, therefore, are practically “transparent” for the colorimetric determination in the mixture with NG. TGDN did not produce the appreciable amount of nitrite ions even after 3 h of hydrolysis in 0.4 % (w) NaOH solution a t 85 “C. It was reported (13) that neither 1,2- and 1,3-glycerol dinitrates nor 1-and 2-glycerol mononitrates interfere with spectrophotometric analysis of NG, which was also based on NG alkaline hydrolysis with subsequent quantitation of nitrite ions by the colorimetric determination of azo dye. Other researchers (14) observed MTN hydrolysis in a strong alkaline ([NaOHl = 0.96 M) 95 % ethanol/water solutions a t elevated temperatures (55 “ C ) ; at these conditions the yield of nitrite ions increased, gradually reaching a plateau value of about 0.5 mol/mol of MTN after approximately 1 h. The comparison spectrophotometric measurements performed on the NG sample and the mixture of NG, PGDN, and MTN (1:l:lby weight, fromethanolsolutions, using the same concentrations of NG in the sample and in the mixture) showed about 5 % discrepancy between the absorbances resulting from the sample and the mixture. There is an indication in the literature (3)that the initial step of NG alkaline hydrolysis involves a-elimination at the secondary nitrate group, as thereaction on the primary nitrate group is slower and becomes more important with the increasing hydroxide ion concentration. This fact offers a satisfactory explanation of the observed experimental results in that mono-, di-, and some trinitrate esters do not interfere with colorimetric determination of NG using dilute alkaline solutions. Thus, the analytical procedure developed in this work demonstrates the potential for the selective spectrophotometric analysis of NG. If NO2 is present in the sample, provisions must be made to account for its interference with NG analysis, as it dissolves in alkaline solution it also produces nitrite ions. Environ. Sci. Technoi., Vol. 28, No. 3, 1994 391
The difference in the physical properties, particularly, vapor pressures of NO2 and NG, made it possible to separate the analysis of these two components in the gaseous stream. NO2 is a gas at normal conditions [boiling point 21.2 "C at the atmospheric pressure (15)1,while NG is a heavy oily liquid [boiling point 180 "C at 6.66 kPa (16)l. The procedure described above was modified to allow the separation of the contributions of NO2 and NG to total nitrite ions formation in the alkaline solutions. This was done by keeping the absorbing solution immersed in an ice bath, during the entire sampling period, and maintaining the absorbing solution at a temperature as close to 0 OC as possible. Caution must be exercised, after the sampling absorber has been disconnected from the experimental unit and GDT has been removed, not to allow the absorbing solution to enter into the GDT. The solution remaining within the bubbler was then used for NO2 analysis colorimetrically, using the method recommended by the EPA (17). GDT was then washed out, to remove condensed NG, using 50 mL of fresh absorbing solution. This solution was then allowed to remain undisturbed for approximately 30-40 min and used for NG analysis. It should be noted that NO2 adsorption on the inner wall of GDT may influence NG analysis, resulting in an overestimation of NG in the effluent, especially a t low NG and high NO2 concentrations in the gaseous effluents. It was experimentally found that the absorbance due to the adsorbed NO2 did not exceed 0.01 f 0.004 in the range of NO2 concentrations up to 20 ppmv. Thus a t the level of NG concentrations 10 ppmv and higher, the absorbance due to adsorbed NO2 would not exceed 5% of the absorbance due to NG. However at lower NG concentrations and high ( > l o ppmv) NO2 concentrations, the interference factor should be accurately estimated and the necessary corrections incorporated. For example, the correction curve (absorbance due to the adsorbed NO2 vs the absorbance due to NO2 passed through GDT) could be constructed to account for this effect. It was found that NO and N2O gases did not interfere with NG analysis from the gaseous phase since they do not result in nitrites in the alkaline solution. Application to Environmental Samples and Correlation with Other Methods. The spectrophotometric methods have been successfully used for the determination of NG in gaseous streams produced in the processes of the photocatalytic destruction of airborne NG in the presence of VOCs (ethanol and acetone). The results of these studies have been published elsewhere (18). In these experiments, airborne NG in a wide range of concentrations (1-15 ppmv, which simulates NG contaminated air emissions) and flow rates (0.2-28 L/min) was introduced into special photoreactors that use a UV radiation source and an immobilized titania photocatalyst to accomplish NG destruction. The spectrophotometric method described in this paper was used for the simultaneous analysis of NG and NO2 in the gaseous effluents of the photoreactors. The gaseous samples were drawn by a pump through the absorber with a constant flow rate (0.2 L/min) for 20 min. The absorber with 50 mL of the absorbing solution was immersed in an ice bath. After sampling, the absorber was disconnected, and both unreacted NG and NO2 (the major product of NG decomposition) were quantified in accordance with the above-described procedure. Since the concentrations of NG and NO2 in the effluent were below 10 and higher 392
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than 15 ppmv, respectively, the correction curve was used to account for NO2 interference. Ozone at the level of concentrations produced by low pressure mercury lamps (LPML) did not effect markedly the results of the spectrophotometric analysis. The reproducibility of measurements was satisfactory. For example, four replicate determinations of NG in gaseous effluents of the NG (initial concentration 13.1 ppmv) photocatalyzed (TiO2, Degussa P25) destruction using LPML at residence time 5.5 s resulted in the following NG concentrations: 5.5,5.4, 5.5, and 5.7 ppmv (standard deviation is 0.13 ppmv). The spectrophotometric method compared favorably with the G U M S method for the NG analysis in airstreams. The gaseous samples of the photocatalytic experiments were drawn by pump (flow rate 0.2 L/min) for 20 min through a "U"-shaped Pyrex tube (33 cm X 4 mm) immersed in an ice bath. Unreacted NG condensed on the inner wall of the tube was washed out with 5 mL of ethanol. One microliter of this solution was injected into the Varian-Saturn I1GC/MS instrument (detector: Saturn I1 ion trap, E1 mode). The ion mass mle = 46 (NO2+) provided an excellent analytical marker for the identification and quantification of NG. Analytical standards for NG were prepared from Parke-Davis Nitrostat NG tablets dissolved in ethanol. The amount of NG (in pg) obtained from GC/MS measurements were then converted into NG concentrations (in ppmv). The following represents the estimates of NG concentrations (in ppmv) in gaseous effluents of three photocatalytic experiments at different residence times obtained by spectrophotometric and GC/MS (in parentheses) methods, respectively: 0.3 (0.34), 0.5 (0.54), and 1.2 (1.25). Conclusions A special spectrophotometric method has been developed for NG analysis in gaseous effluents. The procedure involves NG collection in an absorbing alkaline solution in the form of nitrite ions, which is assayed spectrophotometrically (absorbance a t 540 nm) by reacting with the HSPN reagent (aqueous solutions of H202, sulfanilamide/ phosphoric acid, and NEDA). The detection limit is about 0.1 ppmv of NG in air. The optimum contact time of 30-40 min for NG with the absorbing solution has been determined experimentally. The alkaline hydrolysis of other nitrate esters was studied, and the selectivity of the method was demonstrated. The potential interference of NO2 in air was also investigated. The spectrophotometric method compared favorably with the chromatographic (GC/MS) method of NG analysis. The method developed has been successfully used in a bench-scale experimental unit to study the photocatalytic destruction of NG in gaseous streams. Acknowledgments The author would like to acknowledge the financial support provided by the US.Department of Navy, Naval Surface Warfare Center, Indian Head Division, Maryland, and US.Army, Production Base Modernization Activity, Picatinny Arsenal, NJ (Dr. Chester Clark and Messrs. Chuck Painter and Robert Goldberg). He also thanks Dr. Ali T-Raissi for performing GC/MS analysis of NG and Drs. David Block, Kirk Collier and Clovis Linkous of Florida Solar Energy Center for their support and contribution to this work.
Literature Cited (1) Urbanski, T. Chemistry and Technology of Explosives; Pergamon Press: Oxford, 1965; Vol. 2 (2) Di Carlo, F. J. Drug Metab. Rev. 1975, 4 (l), 1. (3) McNiff, E. F.; Yap, P. S.;Fung H.-L. In Analytical Profiles of Drug Substances; Florey, K., Ed.; Academic Press: New York, 1980; Vol. 9, p 519. (4) Tamiri, T.; Zitrin, S. J. Energ. Mater. 1986, 4, 215. ( 5 ) Lodge, J. P. Methods of Air Sampling and Analysis; Lewis Publishers Inc.: Chelsea, MI, 1989; p 669. (6) Camera, E.; Pravisani, D.; Ohman, V. Explosivstoffe1965, 9, 237. (7) Andrews, D. W. Analyst 1964, 89, 730. (8) Fung, H.-L.; Dalecki, P.; Tse, E.; Rhodes, C. T. J . Pharm. Sci. 1973, 62 (4), 696. (9) Bell, F. J. Pharm. Sci. 1964, 53 (7), 752. (10) Wells, C. E.; Miller, H. M.; Pfabe, Y. H. J.Assoc. O f f .Anal. Chern. 1970, 53 (3), 579. (11) Jacobs, M.; Hochheiser, S. Anal. Chem. 1958, 30, 426. (12) ACE GLASS Inc. Catalog 900, item 7530.
(13) Lim, J. K. J.Pharm. Sci. 1979, 68 (9), 1197. (14) Hoffsommer, J.; Glover, D.; Burlinson, N. J. Org. Chem. 1983, 48, 315. (15) CRC Handbook of Chemistry and Physics, 69th ed.; Weast, R. C., Ed.; CRC Press: Boca Raton, FL, 1988. (16) Belayev,A.; Yusefovich, N. Dokl. Akad. Nauk SSSR. 1940, 27, 133. (17) U.S. Environmental Protection Agency. Fed. Regist. 1971, 36 (228), 22396. (18) Muradov, N. Z.; Linkous, C. A.; T-Raissi, A. Presented at The First International Conference on Ti02 Photocatalytic Purification and Treatment of Water and Air, London, Ontario, Canada, 1992. Received for review May 3, 1993. Revised manuscript received October 22, 1993. Accepted October 29, 1993."
* Abstract published in Advance ACS Abstracts, December 1, 1993.
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