greater Pb2+-binding ability of SFA compared to WFA. However, a typical freshwater lake or river has an ionic strength much lower than that of our experiments (0.1 M). In the environment, there is less cation competition for WFA complexing sites, so that the lead(I1)-WFA conditional stability constants in a natural water will be higher than those listed in Table I. Knowing that Pb2+ binds strongly to fulvic acid much as Cu2+does, does not fully explain the behavior of Pb2+-fulvate complexes. We have observed that when precipitation begins, there is increased removal of Pb2+ from solution ( 2 2 ) .This extra loss of free Pb2+may be caused by adsorption onto the solid precipitates or entrapment within developing aggregates. The work of Hassett ( 2 3 ) shows that plant uptake of Pb2+ correlates best with how saturated a soil is with Pb2+ (the amount of Pb2+ in the soil compared to the soil’s maximum Pb2+ holding capacity) rather than with the amount of Pb2+ in the soil. The large conditional stability constants for Pbfulvate complexes indicate the potential for much lead(I1) in a soil or lake sediment to be bound to fulvic acid. Generally, the larger the excess of metal ion, the weaker the sites that the metal ion is bound to, and, hence, the more available the metal ion is for plant uptake. The same kind of Pb2+complexation likely occurs for other fractions of naturally occurring organic matter, such as humic acid (10,13).While much Pb2+in a soil may be immobilized by inorganic ions and clay minerals, the ions may well enter the solution phase before it is available to plants. Dissolved organic matter can exert its control over Pb2+ availability at this point. A complication arises, however, when Pb-organic matter aggregates form and become insoluble. Such precipitates may render some of the Pb2+biologically unavailable. Therefore, we conclude that lead fulvate precipitation joins lead(I1) precipitation by inorganic species and solution-phase ion exchange and chelation as determiners of lead(I1) mobility in soils where locally high lead(I1) and organic matter concentrations may exist. Such a situation could arise in soils used to renovate sewage sludge. Sludges commonly have high concentrations of both organic matter and heavy metals, including lead(I1). Lead(I1) fulvate precipitation is not likely to be a factor, however, in freshwaters, where lead(I1) con-
centrations rarely exceed 2.4 X ( I ) and where humic substance concentrations typically are to M using an average molecular weight of 1000 ( 2 ) .These lead(II)/organic matter ratios are much too low for precipitation to occur.
Literature C i t e d (1) . , Lovering. T. G.. Ed.. “Lead in the Environment”. Geol. Suru. Prof.
Pap. 197& No. 957. ’ 12) Reuter. J. H.: Perdue, E. M. Geochim. Cosmochim. Acta 1977, 41, 325-334. (3) Hassett, J. J. Commun. Soil Sci. Plant Anal. 1974,5, 499-505. (4) MacLean, A. J.; Halstead, R. L.; Finn, B. J. Can. J . Soil Sci. 1969, 49, 327-334. (5) Jackson, K. S.; Skippen, G. B. J . Geochem. Explor. 1978, 20, 117-138. (6) Guy, R. D.; Chakrabarti, C. L. Can. J . Chem. 1976, 54, 26002611. (7) Gamble, D. S.; Schnitzer, M. In “Trace Metals and Metd-Organic Interactions in Natural Waters”; Singer, P. C., Ed.; Ann Arbor Science: Ann Arbor, 1973; pp 265-302. (8) Hem, J. D. In “Lead in the Environment”. Geol. Suru. Prof. Pap. 1976, NO. 957, pp 5-11. (9) Schnitzer, M.; Skinner, S. I. M. Soil Sci. 1967,103, 247-252. (10) Takamatsu, T.; Yoshida, T. Soil Sci. 1978,225, 377-386. (11) Stevenson, F. J. Soil Sci. SOC.A m . J . 1976,40, 665-672. (12) Stevenson, F. J. Soil Sci. 1977,123, 10-17. (13) Buffle, J.; Greter, F.-L.; Haerdi, W. Anal. Chem. 1977, 49, 216-222. (14) Schnitzer, M.; Hansen, E. H. Soil. Sci. 1970,109, 333-340. (15) Ramamoorthy, S.; Kushner, D. J. J . Fish. Res. Board Can. 1975, 32, 1755-1766. (16) Ramamoorthy, S.; Manning, P. G. J . Inorg. Nucl. Chem. 1974, 36, 695-698. (17) Schnitzer, M.; Skinner, S. I. M. Soil Sci. 1968,105, 392-396. (18) Weber, J. H.; Wilson, S. A. Water Res. 1975,9, 1079-1084. ( l 9 ) Wilson, S. A,; Weber, J. H. Chem. Geol. 1977,29, 285-293. (20) “Analytical Methods Guide”, 9th ed.; Orion Research: Cambridge, Mass., 1978. (21) Saar, R. A.; Weber, J. H. Can. J. Chem. 1979,57, 1263-1268. (22) Saar, R. A.; Weber, J. H. Geochim. Cosmochim. Acta 1980, in
press. (23) Hassett, J. J. Commun. Soil. Sei. Plant Anal. 1976, 7, 189195. (24) Buffle, J.; Greter, F.-L. J. Electroanal. Chem. 1979,101, 231251.
Received for review October 25, 1979. Accepted April 8, 1980. We thank the National Science Foundation for their partial support of this work through Grants OCE 77-08390 and OCE 79-10571.
NOTES
Determination of Phenolics in Coal Gasifier Condensate by High-Performance Liquid Chromatography with Low-Wavelength Ultraviolet Detection Charles M. Sparacino” and Douglas J. Minick Research Triangle Institute, P.O. Box 12194, Research Triangle Park, N.C. 27709 Methodology has been developed for the rapid determination of levels of phenol, cresols, and xylenols in coal gasifier condensates. Aliquots of condensate are injected directly onto a reverse-phase HPLC system, and the effluent is monitored by UV absorbance at 215 nm. At this wavelength, cresol isomers and xylenol isomers exhibit similar extinction coefficients, and can thus be analyzed via single calibration curves. An additional curve is employed for phenol determination. Validation was achieved by blinds analysis. 880
Environmental Science & Technology
The increasing emphasis on coal-based synthetic fuel production poses several potentially severe pollution problems. Since water is utilized or produced in all gasification processes, analytical methodology for aqueous media is required to monitor levels of hazardous materials. The organic contaminants present in greatest amounts in such waters are phenol and its alkylated homologues ( I , 2 ) ;these compounds are toxic to most organisms. Phenolic materials in water are most commonly determined by the 4-aminoantipyrine method ( 3 ) . This colorimetric
0013-936X/80/0914-0880$01 .OO/O @ 1980 American Chemical Society
procedure is general, but is lengthy and does not determine certain classes of phenols such as para-substituted ones. Although gas-liquid chromatography (GLC) has been used extensively ( 4 ) , most procedures require solvent extraction (and subsequent sample concentration) prior to analysis. The difficulty associated with the extraction of phenolics from water ( 5 )prompted the use of direct aqueous injection GLC (1,6, 7). This extraction problem is also avoided by the use of reverse-phase high-performance liquid chromatography (HPLC), wherein aqueous samples can be determined directly. The analysis of phenols by HPLC has been described in several reports (see, e.g., 8-11), using ion-exchange and reverse-phase chromatography. No quantitative results have been reported on aqueous gasification effluents. The need in our laboratory for a fast and accurate method for the determination of the major phenolic constituents (phenol, cresols, xylenols) in coal gasification condensate led to the development of the procedure reported herein.
-
2.6-XRENOC 3,S-XYLENOL MlXTURE(6 ISOMERS)
Approach Although the reverse-phase HPLC analysis of phenols is straightforward, the development of methods for the group quantification of such materials is more challenging. A brief examination of a high-efficiency ( N = 3000) reverse-phase column showed that, while good separation was achieved for the cresol and most xylenol isomers, group quantitation was not possible without the laborious use of multiple calibration curves and subsequent data summation. A mode of detection was then sought that would provide roughly equal response to all, or nearly all, isomers. This would permit the use of a single calibration curve for each isomeric group, and would thus enhance the speed of the analysis. With a variable wavelength UV detector, several wavelengths were examined using reference compounds to determine if similar extinction coefficients existed for all materials. These conditions were met by monitoring column effluent a t 215 nm, a wavelength compatible with most reverse-phase solvent mixtures. Absorbance spectra were recorded for all isomeric xylenols to confirm the selection of 215 nm as the wavelength of choice for HPLC analysis. Figure 1 shows the absorbance curves for two representative isomers and a mixture of all six isomers. Each curve represents equal concentrations of xylenols. With approximately equal response from all group isomers, complete separation was not needed, and a column with relatively low efficiency (N = 1000) was selected for use. Such a column is advantageous both in terms of cost and increased longevity. Solvent conditions were achieved that eluted the compounds of interest in an ,acceptable fashion. As expected, the most polar substance (phenol) eluted first, followed by cresols and xylenols, each as single peaks. An internal standard (4-isopropylphenol) was selected that eluted after the xylenol peak. Under these con(ditions, calibration curves were prepared using phenol (for phenol), m-cresol (for cresol isomers) and 2,4-xylenol (for xylenol isomers). Experimental Chromatographic System. The HPLC solvent delivery system consisted of dual reciprocating piston pumps (Waters Associates, Model 6000A) and a septumless injector (Model U6-K), Waters Associates). Detection was accomplished by UV absorption a t 215 nm (Model SF-770, Schoeffel Instruments). The stainless steel column (25 cm X 4.6 mm i d . ) contained octadecyl-bonded silica gel (Partisil-20, Whatman, Inc.) and was prepared in-house by slurry packing under pressure. The mobile phase consisted of methanol-water. High-purity solvents (Burdick-Jackson) were degassed before use; water was distilled-deionized and degassed. Quantitation of peak areas was achieved through the use of an electronic
I
I
200
225
I
250 WAVELENGTH (nm)
I
I
275
500
Figure 1. Absorbance spectra of representative xylenols
integrator (System I, Spectra-Physics). Calibration Curves. For each curve, four concentration points were utilized with triplicate determinations of each point. The standard solutions were prepared in methanol just prior to use. The internal standard was added such that a concentration of 495 ng was injected onto the system. Calibration plots were constructed by plotting area count ratio (analytehnternal standard) vs. concentration ratio (analyte/ internal standard). A linear regression (least squares) was performed to provide the working equations. Condensate Analysis. A known amount (-10 mL) of gasifier condensate is acidified to p H -5.0 with HCl (6 N). This solution is quantitatively diluted with methanol. A small 1 is removed and filtered through a 5-pm portion ( ~ mL) Teflon filter (syringe with Swinny adaptor). Internal standard is added, and 1-10 pL of this solution is injected onto the HPLC. Further dilutions are made if the amounts of phenolics are excessive, i.e., beyond the tested linear response range. After approximately every third injection, the column is washed with methanol to remove nonpolar materials present in the condensate that are highly retained under the conditions of the analysis. Results and Discussion System efficiency was determined for phenol. A plate count of N = 800 and retention value of k’ = 2.35 were obtained with a mobile phase of methanol-water (1:l).The linearity of response for each compound used for curve preparation was confirmed for the following concentration ranges: phenol, 134-804 mg/L; m-cresol, 107-624 mg/L; 2,4-xylenol, 82-492 mg/L. These ranges were tested since actual gasification condensate samples contained the phenolics in roughly these amounts. The regression equations and the degree of fit for each Volume 14, Number 7, July 1980
881
~~
Table I. Regression Equations for Phenol, m-Cresol, and 2,4-Xylenol
a
compd
regresslon equatlons a
phenol mcresol 2,4-xylenol
y = 1 . 0 6 0~ 0.0048 y = 1 . 0 0 4~ 0.0029
x =
r* b
+
y = 1 . 0 9 7 ~ 0.0084
concentration ratio; y = peak area ratio.
T
0.998 0.996 0.996 r =
correlation coeffi-
cient.
Table II. Concentration of Phenolics from Gasifier Condensates concn, ppm, tor condensate samples
phenolic species
1
2
3
phenol cresols xylenols
3594 1832 317
1031 657 123
1214 1666 250
curve, expressed as the square of the correlation coefficient, are shown in Table I. The high linearity and near-zero intercept indicate very acceptable HPLC behavior for these compounds. * To test the efficacy of the procedure, particularly with regsrd to the feasibility of using single representatives for the quantitation of cresols and xylenols, blind samples were prepared and analyzed. In addition to phenol, all three cresol isomers and five xylenol isomers were used for blind sample preparation. In each case the appropriate compound or compound group was analyzed to within 10%of actual values. The average errors based on quadruplicate analyses were: phenol (8.6%), cresols (7.9%), and xylenol (2.0%). Analytical precision was very acceptable for this analysis; the area ratio value for all replicates produced a maximum standard deviation of 7.2%. The results of the analysis of gasifier condensate (obtained from an in-house laboratory scale unit) are shown in Table
TIME (MIN.1
Figure 2. Chromatogram of gasifier condensate; conditions as described in text
chromatographic columns are inexpensive and long lasting. The overall speed of analysis (-20 min) renders the method comparable to direct aqueous injection GLC; the longevity of the columns and the simplicity of separation offer an advantage over GLC methods.
Literature C i t e d (1) Ho, C . H., Clark, B. R., Guerin, M. R., J . Enuiron. Sci. Health, 7,481-9 (1976). (2) Sharkey, A. G., Shultz, J. L., “Symposium Proceedings: Process Measurements for Environmental Assessment”, EPA-600/7-78-168, Research Triangle Park, N.C., Aug 1978, p p 211-5. (3) “Standard Methods for the Examination of Water and Wastewater’’, 14th ed., Part 510, American Public Health Association, Washington, D.C., 1975, pp 574-92. (4) Grob, R. L., Ed., “Chromatographic Analysis of the Environment”, Marcel Dekker, New York, 1975, p 418.
11.
( 5 ) Webb, R. G., “Isolating Organic Water Pollutants: XAD Resins, Urethane Foams, Solvent Extraction”, EPA Report No. EPA600/4-75-003, Corvallis, Oreg., June 1975. (6) Baker, R. A., Malo, B. A., Enuiron. Sci. Technol., 1, 997
The HPLC chromatogram for a typical analysis is shown in Figure 2. Base-line separation of all groups of components is easily achieved. Results from a number of gasification runs to date in which GC-MS analyses were carried out as well indicate that, as expected, a significantly larger concentration of phenolics is determined by HPLC. In summary, a reverse-phase HPLC method has been developed for the direct analysis of phenolics from coal gasification condensate. The method is fast, simple, and accurate. Since direct aqueous injection of the condensate is utilized, problems associated with extraction of phenolics from aqueous media are circumvented. The apparatus is simple, and the
Receiued for reuiew September 29,1979. Accepted April 4,1980. T h e support of the Industrial Environmental Research Laboratory, Environmental Protection Agency, Research Triangle Park, N.C., under Grant R804979-02 is gratefully acknowledged.
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Environmental Science & Technology
(1967). (7) Bartle, K. D., Elstub, J., Novotny, M., Robinson, R. J., J . Chromatogr., 135,351-8 (1977). ( 8 ) Bhatia, K., Anal. Chem., 45,1344-7 (1973). (9) Wolkoff, A. W., LaRose, R. H., J. Chromatogr., 99, 731-43 (1974). (10) Jolley, R. L., Pitt, W. W., Thompson, J. E., paper presented a t the 23rd Annual Technical Meeting of the Institute of Environmental Sciences, Los Angeles, Calif., April 23-27, 1977. (11) Raghavan, N. V., J . Chromatogr., 168,523-5 (1979).
