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Anal. Chem. 1986, 58, 170-175
trescine, 110-60-1;silica, 7631-86-9.
LITERATURE CITED (1) Lukacs, K. D., Thesis, University of North Carolina, Chapel Hill, 1983. (2) Jorgenson, J. W.; Lukacs, K. D. Science (Washington, D.C.,7883-) 1983, 222,266-272. (3) Kopaciewicz, W.; Regnler, F. E. Anal. Biochem. 1982, 726, 8-16, (4) Green, J. S.;Jorgenson, J. W. Pittsburgh Conference, New Orleans, 1985;paper 892. (5) Bolt, G. H. J . Phys. Chem. 1957, 6 1 , 1166-1169. (6) Stigter, D. “Physical Chemistry: Enriching Topics from Colloid and
Surface Science”; van Olphen, H., Mysels, K. J., Eds.; Theorex: La Jolla, CA, 1975;p 304. (7) Seng, H. P. Text. Prax. I n t . 1984, 39, 795-798. (8) Rlghetti, P. G.;Caravaggio, T. J . Chromatogr. 1976, 127, 1-28. (9) Malamud, D.; Drysdale. J. W. Anal. Blochem. 1978, 86, 620-647. (IO) Righettl, P. G.; Tudor, G.; Ek, K. J . Chromatogr. 1981, 220, 115-194. (11) Reijenga, J. C.; Aben, G. V. A.; Verheggen, Th. P. E. M.; Everaerts, F. M. J . Chromatogr. 1983, 260, 241-254.
(12) Knecht, L. A.; Guthrie, E. J.; Jorgenson, J. W. Anal. Chem. 1984, 56,
479-482. (13) McManigill, D.; Lauer, H. H., unpublished work. (14) Good, N. E.; Winget, G. D.; Winter, W.; Conolly, T. N.;Jzawa, S.; Singh, R. M. M. Biochemistry 1966, 5 , 467-477. (15) Good, N. E.; Jzawa, S. Methods fnzymol. 1972, 2 4 , 53-68. (16) Thormann, W. flectrophoresls (Weinheim, Fed. Repub. Ger.) 1983, 4 , 383-390. (17) Kopaciewicz, W.; Rounds, M. A,; Fausnaugh, J.; Regnier, F. E.; J . Chromatogr. 1983, 266, 3-21. (18) Hunter, R. J. “Zeta Potential in Colloid Science”; Academic Press: London, 1981. (19) Martln, M.; Guiochon, G. Anal. Chem. 1984, 5 6 , 614-620. (20) Martin, M.; Guiochon, G.; Walbroehl, Y.; Jorgenson, J. W. Anal. Chem. 1985, 5 7 , 559-561. (21) Terabe, S.; Otsuka, K.; Ando, T. Anal. Chem. 1985, 5 7 , 834-841.
RECEIVED for review June 10,1985.Accepted August 19,1985.
Reversed-Phase High-Performance Liquid Chromatographic Determination of Nitroorganics in Munitions Wastewater Thomas F. Jenkins* and Daniel C. Leggett
U S . Army Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755 Clarence L. Grant and Christopher F. Bauer Department of Chemistry, University of New Hampshire, Durham, New Hampshire 03824
Concentrations of HMX, RDX, TNT, and 2,4-DNT are determlned In munltlons wastewater. Aqueous samples are diluted wlth an equal volume of 76/24 (v/v) methanol-acetonltrlle, flltered through a 0 . 4 - ~ mpolycarbonate membrane, and analyzed by reversed-phase HPLC uslng an LC-8 column wlth 50/38/12 (v/v/v) water-methanol-acetonltrlle. The method provlded linear callbratlon curves to at least several hundred mlcrograrns per liter. Detectlon llmlts were conservatively estimated to be 26, 22, 14, and 10 pg/L for HMX, RDX, TNT, and 2,4-DNT, respectlvely, wlth corresponding standard devlatlons of f3.4, 3.3, 4.4, and 4.6 pg/L up to concentrations of 250 pg/L. At hlgher concentratlons, the percent relative standard devlatlon values were approxlmately f 2 % for HMX and RDX and f4% for TNT and DNT. A ruggedness test Involving the major manlpulatlve steps in the procedure Indicated that conslstent results required glass sample contalners, precondltlonlngof filters, and careful malntenance of sample-to-organlc solvent ratio. The method was tested wlth munition wastewater from several Army ammunltlon plants and found to perform adequately for load and pack wastewaters, wastewater from HYX/RDX manufacture, and contaminated groundwater.
One of the Army’s most serious water pollution problems is the disposal of wash waters used to clean equipment and interior surfaces at munition manufacturing and demilitarization facilities. It has been estimated that up to 2 X lo6 L of this type of wastewater is generated daily from a single production line (1). Current practice is to collect wash water from these processing operations in a holding tank and periodically pump it through a carbon adsorption column prior to discharge to
surface streams. These point discharges are subject to state and federal NPDES permits that generally limit the acceptable concentrations of T N T and RDX (2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-l,.3,5-triazine). Although carbon adsorption technology can reduce TNT and RDX to low part per billion levels, which meet present discharge limitations, these carbon columns have finite lifetimes. Eventually breakthrough occurs and regeneration or replacement is necessary. T o satisfy permit requirements and to check on system performance, daily monitoring of effluent from the carbon adsorption columns is necessary during manufacturing operations. Current monitoring requires separate determinations of TNT and RDX, the two most common explosives used by the U.S. Army. Additionally, monitoring for HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), also an Army explosive and a common impurity in RDX, and DNT (2,4dinitrotoluene), a low-level impurity in TNT, may also be required in the near future. At present no standard analytical method is available for TNT, RDX, or HMX. Hence, individual Army installations have developed their own procedures, which differ widely in detection limits, specificity, and precision. This work was undertaken to develop a suitable method for analysis of munitions wastewaters at U.S. Army facilities. The major requirements for the method were (a) it must have detection limits sufficiently low to satisfy monitoring requirements, (b) it must be rapid to enable quick action if levels are in excess of discharge limits, (c) it should be free of interferences from common impurities and decomposition products in munitions waste streams such as TNB (trinitrobenzene), SEX (l-acetyloctahydro-3,5,7-trinitro-1,3,5,7-tetrazocine), TAX (l-acetylhexahydro-3,5-dinitro-1,3,5-triazine), 2,6-DNT (2,6-dinitrotoluene), 2Am-DNT (2-amino-4,6-dinitrotoluene), 4Am-DNT (4-amino-2,6-dinitrotoluene), 2,6-
0003-2700/86/0358-0170$0 1.50/0 0 1985 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 1, JANUARY 1986
DAm-NT (2,6-diamino-4-nitrotoluene),2,4-DAm-NT (2,4diamino-6-nitrotoluene), 2,4,5-TNT (2,4,5-trinitrotoluene), and cyclohexanone, and (d) it should be inexpensive to implement. Methods that have been used to determine these analytes in aqueous media include colorimetry (2-5), thin-layer chromatography ( 6 4 , gas-liquid chromatography (3, 9-15), differential pulse polarography (16),conversion to nitrate (In, and high-performance liquid chromatography (1, 18-22). Reversed-phase HPLC (RP-HPLC) was particularly attractive because aqueous solutions can be analyzed directly without solvent extraction, good detection limits can be achieved without sample preconcentration, and problems with thermal instability of HMX and RDX are avoided. Consequently, RP-HPLC was the method of choice. EXPERIMENTAL SECTION Apparatus. All HPLC measurements were conducted on two sets of instrumentation. The first was a Perkin-Elmer Series 3/LC-65T equipped with a variable-wavelength UV detector set at 254 nm and a Rheodyne 7125 sample loop injector. The second utilized the Perkin-Elmer Series 3 pump with a Rheodyne 7125 loop injector and a Spectra-Physics SP8300 fixed wavelength 254-nm UV detector. Depending on the experiment, peak heights were measured manually or peak areas were obtained with HP3390A Integrators. In all cases a 100-pL sample loop was used. All analyses were conducted on Supelco 25 cm X 4.6 mm LC-8 columns ( 5 pm) using a mobile phase flow rate of 1.5 mL/min. Column efficiencies averaged about 5000 theoretical plates. Materials. All analytical standards for TNT, RDX, HMX, 2,4-DNT, 2,6-DNT, Tetryl, and TNB were prepared from Standard Analytical Reference Materials (SARM) obtained from the US. Army Toxic and Hazardous Materials Agency, Aberdeen Proving Ground, MD. Standards were dried to constant weight in a vacuum desiccator over dry calcium chloride in the dark. Standards for the aminodinitrotoluenes,the diaminonitrotoluenes, SEX, and TAX, used for retention time confirmation, were obtained from David Kaplan at the US. Army Natick laboratory and used without further purification. Methanol, acetonitrile,and water used in the mobile phase were Baker HPLC grade. They were combined in a volume ratio of 38/12/50 and vacuum filtered through a solvent-washed 0.4-pm Nucleopore filter to remove particulate matter and degas the solvent. Fresh mobile phase was prepared daily. Procedures. Stock standard solutions of HMX, RDX, TNT, and DNT were carefully prepared by weighing solid materials to the nearest 0.1 mg and diluting to volume with either methanol or methanol-acetonitrile solution. Addition of acetonitrile speeded the dissolution of RDX and HMX.Eight dilute combined-analyte standards were prepared in 50/38/12 (v/v/v) water/ methanol/acetonitrile by dilution in volumetric flasks. Concentrations of HMX, RDX, TNT, and DNT ranged from 11to 5580, 12 to 6200, 9 to 4300, and 6 to 3200 pg/L, respectively. These combined standards were analyzed in triplicate and linearity of calibration curves was evaluated by means of regression analysis using unweighted data. This required first establishing that error variances were constant over the working range according to Bartlett's test (23). For the estimation of detection limits by the Hubaux and Vos procedure (24),target limits were three times the standard deviation of the noise level at the retention time corresponding to each analyte. These values were 26, 27, 15, and 13 pg/L, respectively, for HMX, RDX, TNT, and DNT. Standards were prepared at 0.5, 1, 1.5, 2,5, 10, and 20 times these values. These standards were analyzed in quadruplicate in random order on each of four days. Ten milliliters of each standard was diluted with 10 mL of methanol-acetonitrile solution. The mixtures were allowed to stand at least 15 min prior to filtration through a 0.4-pm Nuclepore polycarbonate fiiter. The fiist 10-mL portion of filtrate was discarded and the second 10-mL portion taken for analysis. To test for the possibility of particulate adsorption of analytes, five different types of water were selected: (a) Connecticut River water from Hanover, NH, (b) Hanover, NH, tapwater, (c) gqundwater from a deep well in Canaan, NH, (d) water from a stagnant pond in Lebanon, NH, and (e) Milli-Q water. Total suspended solids (TSS),pH, and total organic carbon (TOC) were
171
Table I. Total Suspended Solids (TSS), pH, and Total Organic Carbon (TOC) in Waters Used for Recovery Study sample
TSS, mg/L
pH
TOC, mg/L
Mili-Q groundwater tap water Connecticut River pond water
