Identification and estimation of neutral organic contaminants in

(89) E. J. Kompass, Contr. Eng., 11,73 (1964). (90) K. Boardman, Corning Fluidics, Corning Glass Works, Corning, N.Y., private communication, 1971. (91) S. P. Cram and R. L. Wade, Abstracts 1971 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, Feb. 28-March 5 , 1971, No. 223. (92) J. W. Tanney, Instrum. Contr. Syst., 06, 3 (1969). (93) J. Van der Heyden, ibid., p 7. (94) W. S. Griffin and W. C. Cooley, ibid., p 19. (95) D. F. Folland, Instrum. Coritr. Syst., 41,537 (1968). (96) C. J. Miller, Electron. World, 79 (6), 23 (1967). (97) C. W. Woodson, Western Electronic Show and Convention, Los Angeles, Calif., Aug. 1968. (98) R. L. Wade, Ph.D. Dissertation, University of Florida, Gainesville, Fla., 1971. (99) S. P. Cram and J. E. Leitner, Abstracts 162nd National Meet-

ing, American Chemical Society, Washington, D.C., Sept. 1971, No. CHED 021. (100) D. E. Davis, ASME (Amer. SOC.Mech. Eng.) Publ. No. 70WAIFICS-7, New York, N.Y., 1970. (101) M. K. Testerman and P. C. McLeod, U.S. Patent 3,273,377 (1966). RECEIVED for review August 13, 1971. Accepted November 9, 1971. This work was presented in part by the authors a t the 22nd Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 4, 1971. The financial support of the National Science Foundation under Grant No. GP-14754 and a n American Chemical Society Division of Analytical Chemistry Fellowship sponsored by the Procter and Gamble Co. is gratefully acknowledged.

Identification and Estimation of Neutral Organic Contaminants in Potable Water A. K. Burnham, G . V. Calder, J. S. Fritz, G. A. Junk, H. J. Svec, and R. Willis Institute f o r A t o m i c Research and Department o f Chemistry, Iowa State University, Ames, Iowa 50010

A method has been developed for extracting trace organic contaminants from potable water using macroreticular resins. These resins extract weak organic acids and bases and neutral organic compounds quantitatively from water solutions at parts per billion to parts per million levels. The method has been tested with water from a well contaminated by organic compounds which produce an objectionable odor and taste in the water. The identification and quantitative analysis of the individual contaminants extracted from the well water were ascertained using a gas chromatograph-mass spectrometer combination and other spectrometric methods.

MINUTEQUANTITIES of organic contaminants can impart a disagreeable taste and odor to water and the contaminants may be potentially toxic; however, data on the organic content of water and techniques for obtaining such data are rather limited (1-3). An adequate analytical method for determining trace organic compounds in water must satisfy two criteria. First, the identity and the relative amounts of the contaminants should not be altered by the extraction procedure used to concentrate them. Second, an efficient scheme for analyzing mixtures of organic compounds must be employed, because even nominally pure water may contain a large number of organic substances in low concentration. The limitations of methods such as charcoal absorption and solvent extraction in fulfilling the first of these criteria are recognized (2, 4, 5). These methods usually require processing large volumes of water and meticulously purifying the sorbants and solvents. Furthermore, in the case of charcoal absorption, the contaminants sometimes react on (1) “Cleaning Our Environment, the Chemical Basis for Action,” The American Chemical Society, Washington, D.C., 1969, pp

152-155. (2) R. A. Baker and B. A. Malo, J. Sunit. Eng. Div., Amer. SOC. Cicil Eng., 93, 41 (1967). (3) J. B. Andelman, M. A. Shapiro, and T. C. Ruppel, Purdue Univ. Eng. Bull. Ext. Ser., 118,220 (1965). (4) J. Amer. Wurer Works Ass. 54, 223 (1962). (5) W. L. Lamar and D. F. Goerlitz, ibid., 55, 797 (1963).

the charcoal or cannot be removed from it. In solvent extraction, the distribution coefficient for the contaminants between water and an extracting solvent may be unfavorable, especially when trace amounts are involved. This report describes a procedure which involves quantitative sorption of trace organic compounds on a macroreticular resin bed, followed by selective desorption using appropriate eluents. This procedure has been used for extracting and separating a variety of model compounds from pure water in order t o test the scope and limitations. A modified procedure has been used for the extraction, separation, identification, and quantitative estimation of water from a contaminated well. Tentative identifications of the compounds in the well water were made with a gas chromatograph-mass spectrometer combination. The identifications of the major contaminants were confirmed by comparing gas chromatograph retention times and ultraviolet, infrared, proton magnetic resonance, and mass spectra with authentic samples. The quantitative analyses were based on ultraviolet spectrophotometry or gas chromatography. EXPERIMENTAL

Apparatus and Equipment. A 1.5-cm diameter glass column, approximately 15 cm long, was fitted with a female hose coupling. This column could be attached to a pump outlet or water faucet for sampling large volumes of water. For some experiments, a 1.O-cm diameter conventional glass column was used. The column was filled to height of 7.0 cm with 100-1 50 mesh Rohm & Haas XAD-2 or XAD-7 resin, obtained by grinding and sieving larger mesh resin. A small plug of glass wool was placed both above and below the resin bed. Neutral compounds isolated from water were separated by gas chromatography using a 1/8-in. 0.d. X 84-in. column at 200 “C,packed with 1 5 z Carbowax 20 M on Chromosorb P. A Perkin-Elmer 270 combination gas chromatographmass spectrograph was used for gas chromatographic separations in conjunction with mass spectrographic identification

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Table I. Compounds Tested for Retentfon on XAD-2 and XAD-7 Resins ConcenRetration, tention, Resin Compound (7) PPm % Methyl isobutyl ketone XAD-2 100 100 n-Hexanol XAD-2 200 85 Ethyl butyrate XAD-2 100 100 Benzene XAD-2 100 100 Naphthalene XAD-2 0.05 100 Benzene sulfonic acid XAD-2 3.0 31 p-Toluene sulfonic acid XAD-2 9.0 23 Benzoic acid XAD-2 1.0 23 Benzoic acid (pH 3.2) XAD-2 1.0 100 Phenylenediamine XAD-2 0.9 98 2-Hydroxy-3-naphthoic acid XAD-2 39 0.6 Phenol XAD-2 45 0.4 Phenol XAD-7 0.4 86 2,4-Dimethylphenol XAD-2 0.4 100 p-Nitrophenol XAD-2 0.2 100 2-methyl phenol XAD-2 100 0.3 4,6-Dinitro-2-aminophenol XAD-2 43 0.4 Aniline XAD-7 4.0 100 o-Cresol XAD-2 100 0.3 Table 11. Separation of a Model Mixture on XAD-2 Fraction Recovery, No. Compound % 1 Benzoic acid 102 2 Phenol 94 3 o-Cresol 97 4 p-Phenylenediamine 98 5 Naphthalene 97

of peaks. Data were recorded with an oscillograph or photographic paper and processed manually. Procedures. For screening the sorptive properties of model compounds, approximately 50 ml of a very dilute solution of the compound in distilled water was passed through a 1 x 10-cm column of XAD-2 or XAD-7 at a flow rate of 2 ml/min. The sorbed compound was then eluted from the column with an appropriate solvent such as 25 ml of ethyl ether or methanol. The percentage of compound sorbed was determined by ultraviolet spectrophotometry or by quantiative gas chromatography. For separation of a mixture of model compounds, the mixture was sorbed onto a 1.5- x 7.0-cm column of XAD-2 resin. Then the column was eluted in turn with 20 ml of 0.05Msodium bicarbonate, 20 ml of 0.05M sodium hydroxide, plus an additional 50 ml of methanol to remove benzoic acid, phenol, o-cresol, phenylenediamine, and naphthalene, respectively. The p H for each fraction was adjusted so that the species would be predominately non-ionic; then each fraction was separately resorbed on the resin and eluted with ethyl ether. After evaporation of the ether, the solute was measured by gas chromatography or other means. F o r qualitative examination of well water samples for neutral contaminants, 1.5- X 7.0-cm column of XAD-2 resin was attached directly t o a pump outlet at the well, and approximately 150 liters of water was passed through the column at a flow rate of 50 ml/min (4.0 bed volumes/min). Some sand and iron oxide accumulated in the glass wool plug and the top part of the resin, but this caused n o difficulty. The iron was washed from the column with 100 ml of 1M hydrochloric acid; then any basic organic compounds were removed with 100 ml of 0.05M hydrochloric acid. Next, 100 ml of 0.05M sodium hydroxide was added to remove acidic compounds 140

(including humic acids). Neutral compounds were eluted from the column with 15 ml of ethyl ether. Finally, very weak humic acids were removed with 100 ml of methanol. RESULTS

Macroreticular resins, in particular Rohm & Haas XAD2 and to a lesser extent XAD-7 have been used to extract phenols, alkyl sulfonic acids, dyes, steroids, vitamin B-12, and fulvic acid from water (6). In the present work, the compounds listed in Table I were extracted from solutions in distilled water t o test further the sorption properties of these resins and t o ascertain their extraction efficiency. The following conclusions can be drawn. Both XAD-2 and XAD-7 extract many non-ionic organic compounds from dilute aqueous solution with -1OOX efficiency. Ionic solutes pass through the resins unhindered. Thus common inorganic ions, such as Naf and C1-, as well as strongly ionic compounds, such as benzene sulfonic acid, p-toluene sulfonic acid, and 4-naphthol sulfonic acid are not retained. Weakly ionic organic compounds, such as carboxylic acids, phenols, and amines are sorbed or not sorbed depending upon the p H of the solution. This dependence forms the basis for separating classes of sorbed organic compounds. The resins appear to have a somewhat lower efficiency for concentrating low molecular weight aliphatic compounds than for aromatic compounds. The retention efficiency increases with increasing molecular weight in homologous series, the very low molecular weight compounds being retained with lower efficiency. The retention of a model contaminant at high flow rates was tested by passing a 0.86-ppm aqueous solution of naphthalene through a column at 10 bed volumes/min. Ultraviolet monitoring of the effluent showed n o detectable leakage of naphthalene. Elution with ethyl ether at the same flow rate resulted in 99% elution of the naphthalene by 20 ml of the ether. An aqueous solution of five compounds was used as a model mixture to establish a general procedure for resolving mixtures. The mixture was sorbed on a 0.63- X 20-cm column of XAD-2 resin and eluted in turn at 2 ml/min with 20 ml of 0.05M sodium bicarbonate, 20 ml of 0.05M sodium hydroxide, and additional 50 ml of 0.05M sodium hydroxide, 20 ml of 0.05M hydrochloric acid, and 50 ml of methanol. The eluent fractions contained the benzoic acid, phenol, ocresol, phenylenediamine, and naphthalene, respectively. Analysis of the fractions by UV spectrophotometry resulted in the recoveries listed in Table TI. For many years the water supply of Ames, Iowa, has had a t times an undesirable taste and odor. This occurs when water from certain wells is used. The offensive materials had been tentatively identified as phenols and cresols. This conclusion was based on a marginally positive 4-aminoantipyrene color test (7) and the qualitative observation that the bad taste and odor intensified after chlorination. Analysis of the water by acidification to p H 3 and siphoning through a column as described in this paper proved that this conclusion was erroneous. The positive color test was probably an artifact caused by the presence of iron, and the effect of chlorination can be understood in terms of chlorination reactions of the contaminants that were ultimately identified. ( 6 ) “Amberlite XAD Macroreticular Absorbants,” Rohm & Haas Co., Philadelphia, Pa., 1970. (7) F. T. Snell and C. T. Snell, “Colorimetric Methods of Analysis,” Third ed. Vol. 3, D. van Nostrand, New York, N.Y., 1953, p 107.

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Examination of samples of water from contaminated wells in Ames, Iowa, gave the following results. No basic organic compounds were found. Elution of the column with sodium hydroxide to remove acidic compounds produced an odorless extract which gave negative 4-aminoantipyrene (7), nitrous acid (8), and nitrous acid-mercuric nitrate (8) tests for phenols. In addition, the ultraviolet spectrum of the eluted fraction did not exhibit the expected pH dependence that is characteristic of phenols (9). Because the compounds in this fraction were concentrated by a factor of l o 4 and all the above tests for phenols are sensitive to about 1 ppm, it was concluded that phenols are not a substantial contaminant in the Ames water. This acidic fraction was then resorbed on the resin and eluted with 0.05M solutions of the successively stronger bases, sodium bicarbonate, sodium carbonate, and sodium hydroxide. The ultraviolet absorption of the eluents was continuously monitored at 210 nm which is the characteristic absorption region for the carboxylate anion. Seven components were detected; however, the absence of any odor even upon acidification of the fractions containing them suggested strongly that the materials responsible for the offensive odor and taste of the water were neutral organic species still sorbed on the column. The ethyl ether eluent containing the neutral compounds was concentrated to about 1 ml by evaporating the ether at 0 “C in a closed vacuum system. Tests showed that negligible loss of the contaminants occurred during this evaporation. A strong tar-like odor from this concentrated fraction was clear evidence that the offending compounds has been extracted successfully. Separation of the components of this neutral fraction by gas chromatography produced a chromatogram with 40 t o 50 peaks. It would have been very difficult to identify each of these if the gas chromatograph had not been coupled to rapid scanning, quadrupole mass spectrometer. With this combination a mass spectrum of each G C peak could be scanned once every second and either displayed oscillographically or recorded photoelectrically. Not only was this instrumentation invaluable in identifying the compounds, but it was also possible to verify whether each peak consisted of a single component or a composite, by examining the distribution of mass signals in several scans made during the passage of each chromatographic peak. The major neutral compounds identified in the water and representing 16 of the gas chromatographic peaks are listed in Table 111. Many of these compounds possess characteristic mass spectra so that tentative identifications could be made solely from the mass spectral data. In some cases the identification was only narrowed to a choice of possible structural isomers. The GC effluents of $he major components were collected to aid in obtaining positive identifications. The G C retention time, ultraviolet spectrum, mass spectrum, and where possible the proton magnetic resonance and infrared spectrum were compared with authentic samples of each compound. The concentrations of the contaminants listed in Table I11 were determined by passing approximately 50 liters of water through each of three resin columns at flow rate of 1 bed vol/ min, processing the sorbed neutral fraction as described (8) F. Feigl, “Spot Tests in Organic Analysis,” 6th ed., Elsevier Publishing Co., New York, N.Y., 1960, pp 195-198. (9) R. M. Silverstein and G. C. Bassler, “Spectrometric Identification of Organic Compounds,” 2nd ed., John Wiley and Sons, New York, N.Y., 1967, p 163.

Table 111. Neutral Compounds in a Contaminated Ames, Iowa, Well Concentration, Std Name of component Identification ppb dev

Isopropylbenzene a Ethyl benzene a Naphthalene a 2,3-Dih ydroindene e 15 Alkyl-2,3-dihydroindene e,f) Alkyl benzenes e,f Alkyl benzothiophenes e,f Alkyl naphthalenes e,f, 5 Identification was verified by comparison of retention time and mass spectrum with an authentic sample. * Identification was verified by comparison of the ultraviolet spectrum with an authentic sample. c Identification was verified by comparison of the proton magnetic spectrum with an authentic sample. d Identification was verified by comparison of the infrared spectrum with an authentic sample, e Identification based on mass spectral data alone. Knowledge of the exact positional isomer was not important for this work. This could be done by proton magnetic resonance if needed.

’

above, and comparing the GC peak areas with those obtained from solutions of authentic samples at known concentration. It was assumed that the retention and elution efficiency of the resin column was 100%. The concentrations listed are the average of three separate runs. The retention efficiency of the XAD-2 column was tested by passing a well water sample through two nearly identical columns, connected in tandem. The two columns were eluted separately under identical conditions and the ether eluates concentrated t o 0.3 ml and 0.07 ml, respectively. Gas chromatography showed many large peaks for the first column but only three small peaks for the second. The peaks from the second column represent < 1 % of the concentrations of those from the first column. These results indicate that a single column efficiently removes the neutral organics from water. Although anthracene and other high molecular weight polynuclear hydrocarbons can be retained on the resin column and can be eluted by ether, they could not pass through the gas chromatograph under the conditions used in the gas chromatograph-mass spectrometer experiments. However, an ultraviolet spectrum of the concentrated ether eluent showed no absorption in the 350-500 nm region where many of these compounds absorb strongly. It is concluded that no high molecular weight polynuclear aromatic hydrocarbons are present in the Ames, Iowa, well water. The source of the contamination is believed to be residues from a coal gas plant operated in the city of Ames, Iowa, during the 1920’s. To produce a mixture of combustible gases, similar to natural gas, high pressure steam was passed over coal at about 1000 OC. Unfortunately the tar residues from this plant were buried in a pit that was connected hydrologically to the aquifer supplying the city water (IO). Al(10) M. S. Akhavi, “Occurrence, Movement and Evaluation of Shallow Groundwater in the Ames, Iowa Area,” Thesis Iowa State University, Ames, Iowa, 1970.

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though the coal gas plant ceased operation about 1930, and the tar residues were exhumed in 1959, substantial amounts of coal tar compounds could have been leached into the aquifer during the intervening 30 years. The compounds identified in the water are entirely consistent with this source of contamination.

In general, mixtures of trace organic compounds are so complicated that semi-automatic identification techniques must be employed to analyze the components. The most promising approach appears to be resin extraction followed by gas or liquid chromatography coupled with mass and infrared spectrometry of the separated effluents.

DISCUSSION AND CONCLUSIONS

ACKNOWLEDGMENT

The Rohm & Haas macroreticular resins XAD-2 and XAD-7 are efficient sorbers of a broad range of non-ionic organic compounds present in aqueous solution, even at concentrations in the parts-per-billion range. The simplicity of the extraction equipment makes it useful for field sampling as well as for laboratory experiments. Moreover, the sorption process appears to be completely reversible so that quantitative as well as qualitative results are possible.

We wish to acknowledge the cooperation and advice given by Harris Seidel, Director, Water and Pollution Control, Ames, Iowa. RFCEIVED for review June 7, 1971. Accepted November 4, 1971. Work was performed in the Ames Laboratory of the U S . Atomic Energy Commission. Partial support of this work was supplied by the Ames Water Department.

Low-Temperature Electrochemistry 1. Characteristics of Electrode Reactions in the Absence of Coupled Chemical Kinetics Richard P. Van Duyne’ and Charles N. Reilley Department of Chemistry, Uniuersity of North Carolina, Chapel Hill, N.C. 27514 Electrochemical experiments such as cyclic voltammetry and the potentiostatic relaxation techniques, chronoamperometry and chronocoulometry, can be performed in cryogenic environments (>-130 “C). Low-temperature electrochemical cells have been designed to perform these experiments with reasonable facility. A variety of solvent/supporting electrolyte systems have been evaluated for low-temperature use and butyronitrile/O.lM TBAP appears to be the best “all-purpose” low-temperature medium. Although the use of a low-temperature environment in electrochemistry results in some time response degradation, the electrical double layer can still be charged in less than 0.001 sec under all conditions tested. Double potential step chronoamperometry and chronocoulometry have the special advantage for low-temperature work that their characteristic ratio responses, L/k and Q b / Q f , respectively, are temperature independent in the absence of coupled chemical reactions. Similar temperature independent ratios are formulated for other two-step electrochemical techniques.

STUDIES OF THE STRUCTURE, thermodynamics, and kinetics of neutral and ionic free radicals generated by a variety of methods (viz., chemical redox, electrochemical redox, photolytic, and radiolytic) have received considerable attention in recent years (1-6). The widespread use of low-temperature Present address, Department of Chemistry, Northwestern University, Evanston, Ill. 60201 (1) “Radical Ions-,” E. T. Kaiser and L. Kevan, Ed., John Wiley and Sons, New York, N.Y., 1968. (2) R. N. Adams, “Electrochemistry at Solid Electrodes,” Marcel Dekker, New York, N.Y., 1969. (3) M. E. Peover, “Electrochemistry of Aromatic Hydrocarbons and Related Substances,” in “Electroanalytical Chemistry,” Vol. 2, A. J. Bard, Ed., Marcel Dekker, New York, N.Y., 1967, pp 1-51. (4) P. W. Atkins and M. C. R. Symons, “The Structure of Inorganics Radicals,” Elsevier Publishing Company, New York, N.Y. 1967. 142

environments for the observation of these highly reactive or inherently unstable species by optical spectrometry ( I , 7), magnetic resonance spectrometry ( I , 7), and, more recently, mass spectrometry (8) has proved to be of considerable value in the elucidation of their role as intermediates in chemical reactions. In contrast, comparatively little attention has been directed toward low-temperature studies of the intermediate species formed at the electrode/solution interface during an electrochemical reaction, perhaps because of the difficulty of finding satisfactory low-temperature electrolyte systems. Although no systematic studies of the low-temperature behavior of electrochemically generated radicals and their associated decay chemistries have been undertaken, several papers have appeared in which sub-ambient temperatures have been utilized in evaluating heterogeneous electron transfer kinetic parameters (9-13, conducting electrochemical

( 5 ) J. T. Richards and J. K. Thomas, Trans. Faraday Soc., 66,

621 (1970). (6) ~, M. Szwarc. “Carbanions. Living Polymers, and Electron Transfer Processes,” Interscience Publishek, John Wiley and Sons, New York, N.Y., 1968. (7) A. M. Bass and H. P. Broida, “Formation and Trapping of Free Radicals,” Academic Press, New York, N.Y., 1960. (8) J. Holzhauer and H. A. McGee, Jr., ANAL.CHEM.,41 (ll), 24A (1969). (9) B. E. Conway and M. Salomon, J. Chem. Phys., 41, 3169 (1964). (10) B. G. Dekker, M. Sluyters-Rehbach, and J. H. Sluyters, J. Electroanat. Chem., 21, 137 (1969). (11) B. E. Conway and D. J. MacKinnon, J. Electrochem. SOC., 116, 1665 (1969). (12) P. A. Malachesky, Ph.D. Thesis, University of Kansas, Lawrence, Kan.. 1966. (13) G. J. Hoijtink, Surface Sci., 18,1 (1969). (14) R. Dietz and M. E. Peover, Discuss. Faraday SOC.,45, 154 (1968). (15) J. Chambers, Ph.D. Thesis, University of Kansas, Lawrence, Kan., 1964.

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