Detection of Trinitrotoluene in Water by Fluorescent Ion-Exchange Resins Carl A. Heller," Robert R. McBride,' and Matthew A. Ronning' Chemistry Division (Code 385), Na Val Weapons Center, China Lake, California 93555
A system is described for monitoring the effluent water from the purification apparatus of ammunition plants. This system will give warning of any colored species, but is mainly valuable for detecting trinitrotoluene (TNT) at low levels (70 ppb). The heart of the system is a fluorescent-dyed quaternary ammonium ion-exchange resin which darkens in contact with TNT. The resin is irradiated with ultraviolet radiation and the fluorescent output Is monitored by a photomultiplier.
T h e detection of T N T (2,4,6-trinitrotoluene) in effluent water from ammunition plants is necessary for controlling this pollutant (1). This paper describes a detection system which is presently usable a t 0.07 p p m a n d could be made more sensitive. T h e basis of the method is t h e absorption of T N T on a quaternary ammonium ion-exchange resin. T h e original thought was to absorb a fluorescent molecule on an ionic site a n d then t h e T N T on t h e same site. It was thought that the quenching of t h e fluorescence could be used t o measure the TNT. As i t happened, t h e fluorescence was quenched, b u t probably only in t h e trivial sense that a colored product formed on t h e resin a n d filtered both the ultraviolet exciting light and t h e emitted light. This did turn out t o be sensitive at low levels since t h e colored compounds are held on the surface of a resin bead and quickly form a n effective light filter. T h e reactions of TNT t o give colored products are well known ( 2 , 3 ) . Reactions of T N T with quaternary amines are not known and indeed we saw no reaction in aqueous solution. However, it appears likely t h a t Meisenheimer anions are formed in the resins to give the dark colored products. Several structures, including dimers of two TNT molecules, have been suggested for Meisenheimer anions. Our major new evidence involves the strong binding of these colored species in the resin. Ammunition plants purify t h e effluent water with various absorbing columns and need methods to detect breakthrough. T N T is one of t h e more toxic materials as are some of its decomposition products in the so-called "pink water". These colored breakdown products also given a signal on t h e resins. Colorless organic compounds or inorganic ions will not be detected.
EXPERIMENTAL Apparatus. The essentials of our apparatus (Figure 1) consist of the liquid flow system and an optical system for illuminating and viewing the beads immersed in the liquid system. This portion contains beads of commercial ion-exchange resin dyed with a fluorescent dye. Initially the beads glow brightly under UV irradiation and this glow is detected photometrically and registered on a strip chart recorder. T N T in the water causes the resin beads t o darken on the surface and the measured light output immediately decreases. The flow system uses a Cole-Parmer Masterflo pump in which only Viton tubing touches the solution until it reaches the Pyrex
' Present address, Harvey Mudd College, Claremont, Calif. *Present address, California Institute of Technology, Pasadena.
Calif.
U-tube containing Pyrex wool and the resin beads. Viton was the only tubing tested which did not absorb T N T from solutions. The beads clearly absorb TNT, but a t such low capacity that we can't detect any decrease of concentration spectrometrically. On the other hand, when water is recycled over beads, it picks up material which can be detected spectrometrically at 230 nm in a 10-cm path cell. The Pyrex U-tube was held in the cell compartment of a filter fluorimeter by a special holder, The fluorimeter was a Photovolt 540 using a primary filter for the mercury 365-nm light (Corning CS-7-60) and a secondary filter for fluorescein (Corning (3-3-67). A General Electric S-4 medium pressure mercury lamp was used. The output was detected with a 1P21 RCA Photomultiplier using a Photovolt 540 M Photometer and recorded using a HewlettPackard 7100A potentiometric recorder. Material. Resins of various manufacturers were tried and several quaternary salt polystyrenes gave positive results. Dowex-2, which was used for most of the work, is a cross-linked polystyrene which has been amminated on the phenyl rings. The amine is dimethyl ethanol benzyl quaternary ion with chloride as the counteranion. The exchange capacity is 3.15 mequiv g-' of dry resin which means there is an amine group on about every other unit of the polymer chain. The cross-linking varies according to the percent of divinylbenzene-we tried materials listed as X4, X8, and X10. The bead sizes varied and we separated special sizes for our own use by sieving. We also separated the spherical beads from broken material by rolling down an inclined board. We treated the beads with concentrated NaOH or NaCN to change the counterion from C1- to O W or CN-. The resin was water-washed to remove excess electrolyte. Rhodamine B was the first dye used. It gave positive results and moderate sensitivity but it was felt that this red fluorescer would be inherently less useful since photomultipliers lose sensitivity in the red. Uranine, a yellow fluorescer, was introduced quantitatively by placing beads into a aqueous uranine solution at concentrations where more than 99% was absorbed. The dye colored only an outer shell of the beads as could be observed by microscopic examination of sliced beads. The total capacity of some chloride beads was measured as 55.4 mmol g-'. The beads were dried before being loaded into the U-tubes. We used military grade a - T N T and RDX (2,4,6-trinitro2,4,6-triazacyclohexane) as available in our laboratory. Aqueous solutions of 0-TNT were made 100 pM and stored in glass bottles in the dark. The ultraviolet absorption spectra remained constant for months with only one peak a t 233 nm where the molecular absorbance was t = 19600 M-' cm-l. Procedures. Three chemical forms of the resin were tried-the original chloride, the hydroxide, and the cyanide. Many physical configurations of the beads in various tube shapes were tried. The final and best material was with cyanide counterions using 35-60 mesh beads of Dowex-2 X10 with 50 Fmol g-' of uranine. The U tubes (Figure 1)were made of 3-mm 0.d. standard wall Pyrex. The U was 68 mm long with one arm bent outward 45" for the upper 20 mm. The ends were flared to hold the Viton tubing. The tubes were reinforced a t the bottom and top with epoxy resin to prevent breakage. Loading was in the straight arm using Pyrex glass wool a t the bend, then beads for about 10 mm, and then another wool plug. Water was run into the straight arm. The tube was constricted a t the bottom bend to prevent the glass wool plug from being moved by the water. Water or solutions were pumped through the Viton tubing and U tube at rates of 10-50 mL min-'. The fluorescence was monitored on the strip chart recorder Solutions were changed ANALYTICAL CHEMISTRY, VOL. 49, NO. 14., DECEMBER 1977
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n
UV
A
LAMP
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SAMPLE61 FILTER
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FILTER
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RADIOMETER
RECORDER
PHOTOMULTIPLIER
Figure 1. Schematic of apparatus 3M0
I
I
I
I
I /
ADD 03pM TNT
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Table I. Summary of TNT Concentration and Flow Rate Runs Flow, Run mL 01,pA ’.’ !Fb No. min-’ m i x l a TNT,pm min 23A 13 0.7 10 1000 23B 30 12 5 2800 23C 14 48 2.1 890 23D 30 15 0.82 236 33 0 23F 10 1800 2 3G 30 14 10 2000 23H 30 7 5 1000 231 34 8 2.1 260 235 31 9 0.82 320 2 3K 25 16 0.3 186 29-1 43 4.2 9 741 29-2 30 4.2 9 1060 a 01 is the slope with distilled water running a t the flow rate indicated. 0 is the slope with TNT solution running at the same flow rate. Table 11. Radiometer Readings TNT,,uM I o : mA I-,b mA t, hour 0 5 900 5 100 24 5 1 2 000 50 3 20 7 500 400 3 50 6 5 000 8 000 3 a I , = Initial reading. I , = Reading after reaching lower plateau. In another run, a low concentration of T N T (0.82 pM) was passed over the beads for 20 min. Then a higher concentration (2.1 pM) caused a clear break in t h e slope. When periods of water flow were intermixed with sections of T N T solution flow, there were flat portions for the water while the T N T curves looked like portions of an unbroken curve. Sometimes there was a slight upward recovery during the water flow period but this never approximated the original light level although the resin seemed to “wash out” more when the T N T periods were very short, i.e., when the products were “fresh”. T h e runs with rhodamine B are of interest since i t is a cationic dye. T h e fluorescein dianions of uranine can be associated with the cations of the resin at least up to the 3.15 mequiv g-’ level. The rhodamine cations must be located in t h e neutral portions of t h e polymer chains. T h e fluorescein anions can be displaced by Meisenheimer anions and presumably would give higher sensitivity. Some efforts t o determine this effect were unsuccessful. Chemical Experiments. T o learn more about t h e chemical reactions, resin beads without fluorescer were reacted with T N T solutions. They start out looking amber, turn red, and then black. Attempts t o take absorption spectra by immersing the beads in solutions of matching index of refraction were unsuccessful. Reacted beads were sliced and viewed through a microscope which showed t h a t only an outside shell was colored. Beads were stirred with T N T solutions for several days and only about 25% of the reactive sites had taken u p T N T . Hoffsummer ( 4 ) tells us that he observed the same thing when he tried to use resin beads to clean u p T N T from water. He also observed t h a t RDX, an equally large molecule, did seem t o penetrate resin beads to react with an OH- counteranion. In our work the uranine molecules penetrate completely when a t high concentration; perhaps t h e Meisenheimer anions formed from T N T block the pores of t h e resin. I t should be noted t h a t the initial reaction is very fast, as shown in Figure 2. T h e outer surface darkens very rapidly. We followed the uptake of T N T by 35-60 mesh beads for
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several days. The curve of uptake starts rapidly and becomes very slow. T h u s reaction 1 must be very rapid, but diffusion is very slow for some reason. A point of interest is t h a t quaternary amines which are soluble in water do not give colored products with TNT. We tested benzyl triethyl ammonium chloride and benzyl dimethyl ethanol ammonium chloride with TNT-saturated water and obtained no visible reaction. The environment in the polymer beads must shift the reaction equilibrium toward the colored species. Interferences. Any colored anion, organic “dye” or dark particulate matter will give a signal. We obtained signals with “pink water” from T N T photolysis and from rusty tap water. For the intended use, this is not a drawback since any of these in t h e purified water is a reason t o make adjustments in the purification system. Batch analytical methods exist to separate and identify the impurities ( 5 ) . Most noncolored organic or inorganic materials will not give a signal. We specifically tested RDX, NH4N03,and two sulfonated dinitro toluenes formed from (3- and y - T N T plus sodium sulfite (6). T h e really bad case would be any poisons which lowered t h e sensitivity to T N T without darkening the resin. RDX, a likely contaminant, did not do this. Since the water is generally low in other contaminants after passage through a carbon or resin column, we think this danger is low, but it can be checked periodically by adding known T N T solutions or can be taken care of by replacing the beads daily.
colored compound is immobilized from the flowing water and held in front of the detector, thereby increasing the sensitivity. This method might be used as a semicontinuous monitoring system by flowing distilled or t a p water 99% of the time with samples of effluent water for 50 out of every 100 s. The sudden break in t h e record could be monitored visually or with an electronic system. The beads will become less sensitive once T N T is initially detected but the beads are inexpensive and easily replaced. Different batches of beads have given similar responses to T N T so a semiquantitative estimate of concentration is possible although sim.ple detection may be all t h a t is needed.
ACKNOWLEDGMENT Discussions with Ronald Henry, William Norris, Eugene Martin, and Donald Moore were very helpful. Ronald Henry and Taylor Joyner also supplied us with several chemicals not easily available elsewhere.
LITERATURE CITED (1) D. H. Rosenblatt, M. J. Small, and J. J. Barkley, Edgewood Arsenal Report No. 73-07 USAMEERU, AD-912752 (June 1973). (2) C. A. Fyfe, C. D. Malkiewich. S. W. H. Damji, and A. R. Norris, J . A m . Chern. SOC..98, 6983 (1976). (3) C . F. Bernasconi, J . Org. Chern., 36, 1671 (1971). (4) J. C . Hoffsummer, Naval Surface Weapons Center, White Oak, Md., personal communication. (5) J. C. Hoffsummer and J. M. Rosen, Naval Ordnance Laboratory, Technical Report 71-151 (1971); J. C. Hoffsummer. J . Chromatogr., 51, 243 (1970). (6) T. Urbanski, “Chemistry and Technology of Explosives”, Macmillan, New York, N.Y., 1964, Vol. I, pp 332-333.
CONCLUSIONS A sensitive method for detecting T N T in water has been found. A reaction to form a colored material is used as has been used elsewhere ( I ) . However, in the present case, the
RECEIVED for review July 14, 1977. Accepted September 12, 1977. R.R.M. and M.A.R. were work experience students from Burroughs High School, Ridgecrest, Calif.
Separation of Hydroaromatics and Polycyclic Aromatic Hydrocarbons and Determination of Tetralin and Naphthalene in Coal-Derived Solvents J. F. Schabron and R. J. Hurtubise” Department of Chemistry, University of Wyoming, Laramie, Wyoming 8207 7
H. F. Silver Mineral Engineering Department, University of Wyoming, Laramie, Wyoming 8207 1
Tetralin and naphthalene in a coal liquefaction recycle solvent were determined by high performance liquid chromatography (HPLC) with a p-Bondapak CI8 stationary phase and a methanokwater mobile phase. Initially two fractions were collected from an aluminum oxide open column. The first fraction contained tetralin and the second naphthalene. The standard addition method was employed to determine tetralin and naphthalene. The standard deviation was 0.024% for tetralin and 0.035 % for naphthalene. Several aromatic and hydroaromatic compounds were Identified by their chromatographic behavior and by their fluorescence excitation and emission spectra. A correlation factor which relates the log k’ values for polycyclic aromatic hydrocarbons (PAH), alkyl-substituted aromatic hydrocarbons, and hydroaromatics to certain structural features was developed. The results from this work show the possibllity of developing an overall separation and characterization scheme for complex mixtures of aromatic and hydroaromatic compounds.
Table I. Precision of the Method with F - 3
Sample weight, mg 97.92 97.92 97.92 96.67 86.67
Tetralin, %
-
.y=
Naphthalene,
WIW
~
6.08 6.13 6.10 6.10 6.14 6.11
s = 0.024
rc
WIW
6.36 6.40 6.38 6.31 6.34 _2 = 6.36 s = 0.035
95% confidence level tetralin: 6 . 1 1 L 0.030% naphthalene: 6.36 i 0.043% There are a variety of methods currently in use for the separation and characterization of cornponents in coal liquids. Most involve fractionation into various classes of compounds ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
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