288
Anal. Chem. 1982, 54, 286-289 Imln
,
A
Flgure 4. Typical signal profiles: (A) open-tube coil, length 1.0 m, SO,(g) 10 ppm (v/v), sample volume 0.80 mL, flow rate 4.0 mL/min; (B) single-bead string reactor, length 0.5 m, SO,(g) 7.5 ppm (v/v), sample volume 0.80 mL, flow rate 4.0 mL/min; (C) impinger, volume of reagent 2.0mL, SOdg) 6.0 ppm (v/v), sample volume 10.0 mL, flow rate 10.0 mL/mln.
determination to sub-part-per-million levels of S02(g)in air. As shown in Table 111, however, a sacrifice in the number of samples which can be processed per hour has to be expected when using the midget impinger setup. Working Curve, Limit of Detection, and Sensitivity. The three different types of reactors discussed in this paper have different performance characteristics as can be seen in Table III. Typical signal profiies for the three types of reactors evaluated in this work are presented in Figure 4. Conclusions. The possibility of determining gaseous species in gaseous samples by sample intercalation in a continuous liquid flow system has been demonstrated. Three systems of different geometric characteristics were compared; the single-bead string reactor is recommended when samples contain 2.0 or more ppm of SO2 in air. Otherwise the midget impinger setup should be used. The successful removal of excess gas after reaction of SO2with the dinuclear iron(II1) complex of 1,lO-phenanthrolineby means of a specially designed debubbler permits monitoring of the ferroin accumulated in the gas-liquid interface located at the tail of the gas sample plug. LITERATURE CITED (1) RUtIEka, J.; Hansen, E. H. ”Flow InJectlon Analysls”; Wlley: York, 1981.
New
(2) Mottola, H. A. Anal. Chem. 1981,53, 1312 A-1316 A. (3) Wolff, Ch-Mlchel; Mottola, H. A. Anal. Chem. 1978,50, 94-98. (4) Ramasamy, S. M.; Iob, A,; Mottola, H. A. Anal. Chem. 1979,51, 1637-1639. (5) Ramasamy, S. M.; Jabbar, M. A. A.; Mottola, H. A. Anal. Chem. 1980,52, 2062-2066. (6) Izuml, T.; Nakamura, K. J. Phys. E . 1981, 14, 105-112; Chem. Abstr. 1981,94, 144622t. (7) Weber, D.; Oslen, K. B.: Ludwlck, J. D. Talsnta 1980,27, 685-1368. (8) Alder, J. F.; Kargosha, K. Anal. Chlm. Acta 1979, 1 1 1 , 145-153. (9) Zepeck, R. WLB, Wasser, Luft Betr. 1980,24, 46-47; Chem. Abstr. 1981,94, 70396~. (10) Sandronl, S.; De Grot, M., Atmos. Envlron. 1980, 1 4 , 1331-1333. (11) Woods, P. T.; Jolllffe, 8. W.; Mark, B. R. Opt. Commun. 1980, 33. 281-288; Chem. Abstr. 1980,93, 2445201. (12) Frazler, C. D. Ion Chromatogr. Anal. fnvlron. Pollut. 1979,2 , 211221; Chem. Abstr. 1980,93, 30944~. (13) Bruno, P.; Caselli, M.; Della Monica, M.; Di Fano, A. Talanta 1979,26, 1011-1014, (14) Laskover, B.; Kolbe, W. F. Report 1978, LBL-7986, CONF-781033-34, Lawrence Berkeley Laboratory: Berkeley, CA; Chem. Abstr. 1980, 92, 10478a. (15) Adamowicz. R. F.; Koo, K. P. Appl. Opt. Ig79, 18, 2938-2946. (16) Klockow, D.; Teckentrup, A. Int. J. fnvlron. Anal. Chem. 1980,8 , 137-1 48. (17) Fernandez, T.; Garcia, L. A.; Garcia, M.F. Analyst (London) 1980, 105, 317-327. (16) U.S.E.P.A. Fed. Reglst. 1981,46 (26 Jan) 8352-8364. (19) Hansen, E. H.: RuiiEka, J. J. Chem. Educ. 1979,56, 677-680. (20) Chlapowski, E. W.; Mottola, H. A. Anal. Chlm. Acta 1975, 76, 319-328, (21) Ramasamy, S. M.; Mottola, H. A. Anal. Chlm. Acta 1981, 127, 39-46. (22) Jacobs, M. 8. “Analytical chemistry of Industrlal Polsons, Hazards, and Solvents”, 2nd ed.; Interscience: New York, 1949; pp 314-315. (23) Attari, A.; Iglelskl, T. P.; Jaselskls, B. Anal. Chem. 1970, 42, 1262-1285. (24) Schllt, A. A. “Analytical Applications of 1,lO-Phenanthroline and Related Compounds”; Pergamon Press: New York, 1969; pp 166-168. (25) Stephens, B. G.; Lindstrom, F. Anal. Chem. 1969, 36, 1308-1312. (26) Begg, R. D.Anal. Chem. 1971,4 3 , 854-857. (27) RelJn,J. M.; van der Llnden, W. E.; Poppe, E. Anal. Chlm. Acta 1981, 123, 229-237.
RECEIVEDfor review July 13,1981. Accepted October 20,1981. This work has been supported by a grant from the National Science Foundation (CHE-7923956). This paper was presented at the 182nd National Meeting of the American Chemical Society, New York, NY, Aug 25, 1981.
Field Detection of 2,4,6=Trinitrotoluenein Water by Ion-Exchange Resins Carl A. Heller, Sterling R. Greni,l and Eric D. Erlckson” Chemistry Division, Research Department, Na vai Weapons Center, China Lake, Caiifornia 93555
A rapid, on-site detector Is described for the detection of trinitrotoluene (TNT) In effluent water from the purlflcatlon apparatus of ammunition plants. The tube detector utilizes a basic oxide section to convert the TNT to its Melsenhelmer anions, followed by an alkyl quaternary ammonium chloride Ion exchange resin which collects the colored anions. The length of the resultant stain Is proportional to the concentration of TNT In the water.
2,4,6-Trinitrotoluene (a-TNT) is a blood and liver toxin which can be absorbed through the skin, lungs, or gastrointestinal tract (1). In addition, photochemical degradation of dilute aqueous solutions of a-TNT results in a phenomenon Current address: South D a k o t a School of Mines and TechnoloCity, SD.
gy, R a p i d
aptly called “pink water”. In order to reduce these undesirable effects and to meet regulatory standards, ammunition plants fiiter their effluent water through columns of strong absorbers such as activated carbon or diatomaceous earth (2). These columns will not extract unlimited quantities of contaminants. It is therefore desirable to determine when breakthrough occurs in order that the column be replaced. At the present time, breakthrough is determined by collecting a sample of the effluent from the columns and analyzing it by a laboratory method. Techniques for the detection of TNT in aqueous samples which are presently employed include: oxidation followed by colorimetricdetermination of the nitrate content (3); extraction into an organic phase followed by electron capture gas chromatographic analysis; or reversed-phase high-pressure liquid chromatography. Detection has also been reported by measuring the fluorescence quenching of a-TNT trapped on a fluorescent ion-ex-
Thls artlcle not subject to US, Copyrlght. Publlshed 1962 by the Amerlcan Chemical Society
ANALYTICAL CKMISTRY. VOL. 54, NO. 2, FEERUARY 1982
207
TNT in the solution of interest. By comparison of the stain length with that obtained from standards, the concentration of the unknown can be estimated.
b
-."
.
.I
..
1 ".*1 ".
""-."
I ,I."s..n,
Flgu~e1. Apparatus fa tM detection of TNT.
change resin (4). All of these analytical methods are timeconsuming and require extensive technical training. A distinct advantage to the above methods would be to utilize a field detector which is portable, provides a rapid analysis, utilizes small sample volumes. ia free of interferences, yields d t a which are easily obtained, requireslittle technical training to use. and presents no health hazards to inexperienced technicians. Thin paper describes such a method based on abeorption of the colored Meisenheimer anion onto an alkyl quaternary ammonium chloride ion exchange resin. EXPERIMENTAL SECTION Apparatus. Essentially, our apparatus (Figure 1)consints of an indicator tube, a fitting, and a syringe. Initially all experiments were performed by hand, hut more recently a Sage Syringe Pump. Model 341A. has been used to provide better control of the flow rates. The syringes used are 10 cm3, 21 g, l'/* Luer-Lok tip avringea m a n u f a c t d by Becton, Dicldnson and Co.(catalog no. W).The fitting is prepared by silver soldering a stainless s t e l Luer-Lok needle to a Swage-Lok fitting. This is attached to the indicator tube with the aid of Teflon ferrules. The indicator tube consists of a glass tube (4 mm i.d., 6 mm 0.d.. and 10 cm in length) containing a basic oxide section and an anion exchange resin indicator section separated and held in place by glass wool plugs. Materials. Anion exchange resins from several manufacturers were used. Strongly basic anion exchange resins that were lightly colored yielded the best results. Most of the work was done by using the chloride form of Dowex 1x10. This is a strongly basic polystyrene resin whose active g r o u p are of the form PhCHzN+(CHd3CI-.The 5C-100 mesh size range was utilized for mcet of this work Smaller main beads tended to create tm much back-pressure while larger beads tended to have too much color to s t a r t with. Glass beads. used in the basic oxide d o n to improve flow characteristics, were type SL (0.7-1.2 mm) manufactured by PCR, Inc. For our standards we used military grade a-TNT (mp 80.2 "C). recrystallized in benzene and stored in the dark All other reagents were reagent grade as found in our stockroom. P d u r s s . A 10-em3aliquot of the solution of intereat in drawn up into the plastic syringe. The concentration of a 10 ppm TNT standard did not change measmhly after b e i i left in the plastic syringes for 4 days. After fastening the indicator tube and fitting it to the syringe, the solution of interest is pamed through the tube a t a constant rate. The function of the basic oxide section of the indicator tube in to convert the a-TNT to its highly colored Meisenheimer anion. This anion strongly attaches to the cations of the anion exchange resin forming a reddish discoloration of the resin, the length of which is proportional to the concentration of
RESULTS AND DISCUSSION Basic Oxide Pretreatment. Any base which is strong enough to react with a-TNT to form the colored anion could be used in this method. Bases which have been successfully used include NaOH, CaO, and MgO. Bases which reacted slowly with the a-TNT and therefore are not as useful include AIZO3and CaC03. Early experiments were performed by adding 1M NaOH to the solution of interest, waiting about 15 min for reaction to occur, and forcing the resulting solution through the exchange column. Although these results were promising, the addition of a highly caustic solution could conceivably cause problems when performed by untrained technicians in the field. In addition, the long period of waiting for the reaction to Occur defeats the objective of rapid analysis time. To overcome these problems, the anion forming section was placed in the indicator tube. A solution of NaOH was evap orated onto glass wool. A section of this basic glass wool was placed into an indicator tube over a main bed. Passing a TNT solution through the tube resulted in a faint discoloration of the entire length of the resin. This was caused by the in situ formation of the colored TNT anion on the resin, rather than in the prenection, due to the large solubility of NaOH in water. Teats were conducted with CaO in the preaection; this was preferable to NaOH because of its low solubility in water (0.131 g/100 cm3 a t 10 "C). This yielded a discoloration of the anion exchange resin whose length was proportional to the flow rate. concentration. and volume of the solution tested. However, fine particles of CaO in the presection increased back-pressure in the system cawing le&. This reduced the ability to maintain constant volumes and flow rates between testa Attempts to shorten the length of the presection reduced b a c k - p m m but a h increased stain lengths and made them lesa clearly defined. Similar results were obtained with a MgO preaeetion except that a slight variation in the color of the stain was noticed. Attempts with the weaker bases, CaC03and AI2O3,produced only a slight discoloration of the resin. To remove the preaection, we prepared indicator tubes with anion exchange resin mixed with 1.625% CaO. Forcing a 1.0 ppm solution of a-TNT through the indicator tubes p r e duced approximately the Bame stain length for all concentrations of CaO. Channeling and an increase in the backpressure were observed with increasing CaO concentrations. The stain lengths obtained in this manner were longer than those obtained with a CaO section; however, they were not as clearly defined. To increase the porosity of the presection and thereby reduce the back-pressure, we coated glass beads (0.7-1.2 mm in diameter) with CaO. This was done by add- enough water to a mixture of CaO and glass beads to form a paste. Drying the paste in a vacuum oven yielded glass beads which were uniformly coated with CaO. Varying the concentration of CaO in the preaection did not alter the stain length obtained from a 1.0 ppm a-TNT standard. Altering the mass and therefore the length of a 0.6% CaO presection resulted in long but undefined stains for massea under 0.3 g. Over 0.3 g, the length remained constant, but a marked increase in back-pressure waa observed. These results indicate that large concentrations of CaO are not newnary to provide optimum stain lengths. One only needs to provide enough contact time to convert the TNT to ita anion. Indicator. The indicator seetion consists of an anion exchange resin which is lightly colored, to permit visual ob-
288
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
servation of the collected anion. Also, the colored TNT anion must be strongly absorbed by the resin. The best results were obtained with an alkyl quaternary amine chloride exchange resin. The proposed chemical reactions in the indicator tube are given in eq 1 and 2.
OH-
t a-TNT
RN+R~CI-
-
OZN&NOp
(1)
+ o
z
N
~
N
o
z
After experimenting with the anion-exchange resins of several manufacturers, it was decided that Dowex 1 was well-suited for the indicator tube. To aid in preventing the T N T anion from attaching to interior sites of the resin and thereby decreasing the linearity of the relationship between concentration and stain length, a high degree of cross-linkages were required. The commercially available X10 and X8 forms were used. Decreasing the size of the resin beads produces a corresponding increase in the back-pressureobserved. The Dowex 1beads of the largest size commercially available (20-50 mesh) are orange while other size ranges are yellow. The optimum size range for visual detection was determined to be in the 50-100 mesh range. The syringe pump can operate with higher pressures which makes the 100-200 mesh size range more desirable. Flow Rate. Forcing a-TNT solutions through the indicator tube at different flow rates produces differences in the appearance of the stain. Slower flow rates make the stain shorter in length and much more deeply colored. Faster flow rates produce stains that are longer but not as easily discernible. This is due to the fact that the anion exchange resin is porous and contains active sites on the inside as well as on the outside of the beads. The longer a TNT anion remains in the vicinity of a bead, the greater the possibility of it diffusing to a cation site inside the bead rather than moving down the tube. This occurs in the case of low flow rate% At flow rates, a high probability exists for T N T anions to make it past the first few beads and get trapped further down the column. Varying the flow rate from 0.74to 1.5 cm3/min of a 1.0 ppm TNT solution produced a stain whose length was approximately the same. Above 1.5 cm3/min the stain length increased and the end point became less discernible. At a flow rate of 0.08 cm3/min a very sharp band of red was present at the beginning of the resin, but the length was so short as to prevent the observation of minor variances caused by differing concentrations. Sample Volume. The sample volume which may be passed through the indicator tube is limited by the amount and the solubility of the base in the presection. After all the base is in solution, the TNT anion is no longer formed. In addition, increasing the sample volume also increases the time necessary to perform the analysis. Sample volumes of 5-50 cm3have been used successfully.
At a flow rate of 1.5 cm3/min, a 5-cm3sample volume yields results in 3.3 min. However, the stain length produced is so small as to make it difficult to discern small differences in concentration. This problem is alleviated by using a 50-cm3 sample volume. However, this sample volume takes 33 min to obtain results and defeats the goal of rapid analysis time. A compromise sample volume of 10 cm3is routinely used. This volume provides results in 6.7 min and improves the ability to discern small differences in concentration. Increasing the sample volume produces a corresponding increase in the stain length. A 50-cm3sample of a 0.1 ppm a-TNT solution produces approximately the same stain length as 10 cm3 of a 0.5 ppm solution. Interferences. Substances which cause a change in the color of the resin or the stain will interfere with the determination of a-TNT. Colored waters can make the stain difficult, if not impossible, to discern. In some resins, the chloride form is yellow while the hydroxide form (which can be formed during the test from the basic oxide section) is orange. Exposure to light for extended periods of time causes the colored TNT anion to decompose, changing the color of the stain. This change makes it difficult to ascertain the stain length. Substances which alter the rates of formation of the TNT anion or the TNT-resin complex will interfere. Acidic waters will remove the basic presection preventing the formation of the TNT anion. They also cause the decomposition of any TNT anion formed. Substances which adhere more strongly to the ion-exchange resin than does the TNT anion will remove sites for the reaction to occur. Waters which have a high solid content will plug sections of the indicator tube and cause channeling to occur. No discoloration of the resin was observed from tap water, RDX, NaOH, C2H50H, CH3COCH3, CBH5CH3,NaN02, NaN03, NaC1, CaO, CaOH, MgO, Al,03, NH4CI,or NH4NOB. One molar solutions of NaCl did not remove a previously deposited stain. Solutions which were 0.5 M in NaCl or NaNO, and contained 1.0 ppm a-TNT were passed through the indicator tubes. A faint purplish stain resulted. This was the same effect as was seen without a basic presection. These salts were therefore preventing the formation of the TNT anion, possibly interfering with the solubility of the CaO. These results make the indicator tubes useless in their present form for the detection of TNT in seawater. Concentrations of 0.01 M NH4N03and NH4Clin 1.0 ppm solutions of TNT prevented the formation of any discoloration of the ion-exchange resin. Solutions which were 0.5 M in NH4N03removed previously deposited stains. The NH4+ion is probably responsible for a decomposition of the TNT anion. In order to determine the effect of “pink water” on the stain length, we exposed 10.0 ppm a-TNT solutions to sunlight over a weekend. Reverse-phase liquid chromatography showed that up to 80% of the TNT had photolytically decomposed. These solutions were diluted to a final concentration of 1.0 ppm TNT. The stain lengths obtained from these solutions were identical with that obtained from a 1.0 ppm a-TNT standard. Solutions of 1.0 ppm a-TNT at temperatures between 2.3 and 46 OC were passed through the indicator tubes. No differences were detected among stain lengths at various temperatures. TNT Detection. As finally adopted, this method passes a 10-cm3sample volume through an indicator tube at 1.5 cm3/min. The indicator tube’s presection consists of a 0.3-g section of 0.6% CaO-coated glass beads. The indicator section consists of 0.3 g of the chloride form of Dowex 1x10 anion exchange resin. As shown in Figure 2, different concentrations of a-TNT produce different stain lengths. An estimate of the TNT
ANALYTICAL CHEMISTRY. VOL. 54, NO. 2. FEBRUARY 1982
289
needed to differentiate between two concentrations. Figure 3 illustrates the reproducibility of the method using a 1.0 ppm standard. The relationship between stain length and concentration ia nonlinear. This is due largely to mass transfer which exists between the TNT and the ion exchange resin. One should theoretically be able to improve u p n the linearity by phyaicallv or by using- a pellicular anion . Dlunaina . - the resin Dores . -. exchange resin. Health Effects. The DH of water in the basic oxide D I section waa determined tobe about 13. The pH of the solukon exiting the indicator tube was neutral. This indicates that excess OH- ions are exchanged with the CI- ions in the resin. Species exiting the tube should be h a r t exclusivelyaqueous solutions of CaCI,. Whereas CaCI, is not a significant health hazard, the major hazard to the health of inexperienced technicians is expected to be from the possibility of cuts from broken glass tubes.
__
Fkan 2. Resparse Of ~ t c f ~ t o ~ ccncenmh. T N T Coxantrstlonsfrmn top to bottom are Mank. 0.1 ppm. 0.5 ppm. 1.0 ppm. and 5.0 ppm.
rril
CONCLUSIONS The indicator tube described in this paper is useful for determining the presence of a-TNT in fresh water systems. An estimation of the concentration can be obtained by comparison with a standard. In this manner, one can detect concentrations as low as 0.1 ppm TNT. These tubes meet the requirements of a field detector for a-TNT. Smaller bore tubing or larger sample volumes will enable the detection of T N T concentrations lower than 0.1 ppm. ACKNOWLEDGMENT The authors thank Donald Moore, Thomas Grifith, Joseph Johnson, and Christine Young for their assistance in the preparation and testing of the indicator tubes. Discuaaiona with John Nelson, Dwight Fine, William Norris, Ronald Henry, and Eugene Martin were very helpful. LITERATURE CITED
npuv 3.
Rspmducibnty of lndlcator tubes ushg 1.0 ppm TNT
concentration is obtained by comparing the stain length of the unknown to that of a standard. The smallest a-TNT concentration which ean be reproducibly detected and distinguished from a blank ia 0.1 ppm. This could be improved by using smaller bore t u b w or a larger sample volume. With a 10-cm3sample volume, a difference of a t least 0.3'ppm is
(1) MchlaW. W. D. " T o x ~ Irdusblal ; MsdkMe: Chlcago. IL. 1937. (2) '"Achlevh~a Put.% EnvtowmW: Iowa Army ArnmnmMl Plant hW dlalon. I A . RCS DDH(LE(Al1289. 1977. (3) Laggsn. D. C.Anel. Chsm. 1977. 49. 880. (4) Heller, C. A,; McBrlde. W R.; Ronnlng. M. A. Anel. chem.1977, 49.
2251.
R m m for review August 18.1981. Accepted October 13, 1981.
~
