In addition to the above results, some interesting preliminary data have been obtained by chromatographing some of the samples of concentrated polluted water on high-resolution amino acid analyzers and carbohydrate analyzers. Several chromatographic peaks were obtained on both analyzers, and indicate an additional area for research.
Literature Cited (1) ACS Subcommittee on Environmental Improvement, “Cleaning Our Environment, The Chemical Basis for Action,” pp 105-55, American Chemical Society, 1969. (2) Skrinde, R. T., “Analytical Methods-Chemistry. Organics,” J . Water Pollut. Control Fed., 44,911 (1972). (3) Tyckman, D. W., Irvin, F. W., Young, R. H. F., “Trace Organics in Surface Waters,” ibid., 39,458 (1967). (4) Garrison, A. W., Keith, L. H., Walker, M. M., “The Use of Mass Spectrometry in the Identification of Organic Contaminants in Water from the Kraft Paper Mill Industry,” Proc. 18th Annual Conference on Mass Spectrometry and Allied Topics, pp B205-13, San Francisco, Calif., June 14-19, 1970. (5) Jolley, R. L., Pitt, W. W., Jr., Scott, C. D., “High-Resolution Analyses of Refractory Organic Constituents in Aqueous Waste Effluents,” Proc. 19th Annual Technical Meeting of the Znstitute of Environmental Sciences,. DD 247-52, Anaheim, Calif., April 2-5, 1973. (6) Katz. S., Pitt. W. W., Jr.. Scott, C. D., Rosen. A. A., “The Determination of Stable Organic Compounds in Waste Effluents a t
__
Microgram per Liter Levels by Automatic High-Resolution Ion Exchange Chromatography,” Water Res., 6,1029 (1972). (7) Scott, Charles D., “Analysis of Urine for Its Ultraviolet-Absorbing Constituents by High-pressure Anion Exchange Chromatography,” Clin. Chem., 14,521, (1968). (8) Scott, C. D., Jolley, R. L., Pitt, W. W., Johnson, W. F., “Prototype Systems for the Automated, High-Resolution Analyses of UV-Absorbing Constituents and Carbohydrates in Body Fluids,” Am. J . Clin. Pathol., 53,701 (1970). (9) Mrochek, J. E., Butts, W. C., Rainey, W. T., Jr., Burtis, C. A,, “The Separation and Identification of Urinary Constituents Using Multiple-Analytical Techniques,” Clin. Chem., 17, 72 (1971). (10) Katz, S., Pitt, W. W., Jr., “A New Versatile and Sensitive Monitoring System for Liquid Chromatography: Cerate Oxidation and Fluorescence Measurement,” Anal. Lett., 5 (31, 177-85 (1972). (11) Jolley, R. L., “Chlorination Effects on Organic Constituents in Effluents from Domestic Sanitary Sewage Treatment Plants,” PhD Dissertation, University of Tennessee, Knoxville, Tenn., 1973. (12) Jolley, R. L., “Determination of Chlorine-Containing Organics in Chlorinated Sewage Effluents by Coupled 36Cl TracerHigh-Resolution Chromatography,” Enuiron. Lett., 7 (41,32140 (1974). (13) Gehrs, C. W., Eyman, L. D., Jolley, R. L., Thompson, J. E., “Effects of Stable Chlorine-Containing Organics on Aquatic Biota,” Nature, 249,675 (1974). Receiued for reuiew September 20,1974. Accepted July 28,1975
NOTES
Comparative Atomic Absorption Spectroscopic Study of Trace Metals in Lake Water Terry Surles,’ John R. Tuschall, Jr., and Theodore T. Collins Limnetics, Inc., 6132 W. Fond du Lac Ave., Milwaukee, Wis. 53218
Two methods of atomic absorption spectroscopic analysis of lake water were used in this study, flameless atomization, using a Massmann-type graphite furnace, and flame atomization preceded by a chelation/solvent extraction concentration procedure. Analyses were performed for seven metals, Cu, Cr, Cd, Mn, Pb, Ni, and Zn. The sensitivities and detection limits for many metals using a graphite furnace are known to be better than those using any flame methods. Results from this study indicate that, by using proper procedures, accuracy and precision of flameless atomization methods are equal to those for chelation/solvent extraction flame methods.
In recent years, a considerable amount of water analysis has been performed by atomic absorption spectroscopy. A recent review article by Ediger ( 1 ) discussed recent trace metal analyses of water samples by atomic absorption spectroscopy. Walsh ( 2 ) has recently discussed the present state-of-the-art of atomic absorption spectroscopy with an emphasis on the continually increasing potential on new techniques, such as flameless atomic absorption spectroscopy. The flameless methods have a number of advantages over the conventional flame techniques. These include: lower detection limits than can normally be obtained by conventional flame methods; less sample pretreatment; much smaller sample size is necessary; more rapid method
of analysis; a greater variety of samples is possible, such as solvents not normally used in flames and, in some cases, solids applied directly into the sample chamber. There can be interferences with both methods of analysis, although corrections for lake water matrix interferences are relatively simple in flameless atomic absorption spectroscopy. The primary interference encountered in the flameless technique is nonatomic background absorption, attributab!e to molecular absorption and/or light scattering. These interferences and corrective procedures have been discussed in a previous publication ( 3 ) . Despite the advantages of the flameless method over the flame technique, there is still controversy regarding the precision and accuracy of the flameless technique ( 4 ) . Many still prefer the chelation/solvent extraction method. The chelation/solvent extraction technique has received mixed reviews. Although excellent results are achievable on any given water system, some problem areas should be recogn iz ed : a. No one chelation/solvent extraction system produces optimum results for all metals or water systems. By varying the pH and the nonaqueous solvent, the.detection limit for some metals will be enhanced, while, simultaneously, for other metals, it will become poorer. b. Only select groups of metals can be simultaneously extracted. c. An increased probability for sample contamination arises from increased sample handling. d. Stability varies among the various chelates. Volume 9, Number 12, November 1975
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Kjellstrom et al. have done comparative work for cadmium analysis in grain by a variety of procedures, including chelation/solvent extraction and flameless atomic absorption spectroscopy ( 5 ) . However, further studies, particularly in water analysis, are lacking. The purpose of this study, therefore, is to illustrate that results obtained by flameless atomic absorption spectroscopy are as precise and accurate as those obtained by standard flame methods and, further, illustrate that the flameless technique has wider applicability due to lower detection limits and simpler sample handling techniques. In particular, the flameless technique will be compared to the chelation/solvent extraction methods outlined by the Environmental Protection Agency (6).
Experimental Methods Apparatus. A Perkin-Elmer Model 306 atomic absorption spectrophotometer was employed in this study and was equipped with a Deuterium Background Corrector. Deuterium background correction was used to compensate for nonspecific absorption. Its use was dependent upon the sample matrix and the element being determined. A Perkin-Elmer HGA-2000 heated graphite atomizer was used in the flameless atomic absorption part of the study. The data were recorded on a Perkin-Elmer Model 056 recorder. The operating conditions used for the HGA-2000 Graphite Furnace and spectrophotometer were those recommended in the instrumentation manual (7). Reagents. The standard solutions were prepared with commercially available standard solutions, and distilled, deionized water was used for their preparation. Double distilled reagent grade nitric acid was employed as final cleaning agent and was used for digestion and preservation purposes. All standards (minimum volume = 250 ml) were made from stock solutions prior to use to prevent erroneous results due to surface adsorption phenomena. Procedure. Composite water samples were collected from six different areas along the western Lake Michigan shoreline near Point Beach. Samples were collected in 1-gal polyethylene containers. Sample preservation was carried out in accordance with procedures listed by the EPA (6). Concentrations of seven metals, Cd, Zn, Cu, Cr, Mn, Pb, and Ni, were determined by the chelation/solvent extraction procedure outlined by the EPA (6). For the flameless method, all samples and standards were introduced into the graphite furnace by Eppendorf micropipets with disposable plastic tips. Standard curves were obtained by analyzing standard solutions prepared by serial dilution of 1000 Wglrnl stock solution. The direct method analysis was used for all work and was checked by means of standard additions. The results were in good agreement. Results. Wide ranges of element concentrations can be analyzed without prior concentration or dilution when using flameless atomic absorption spectroscopy by proper selection of scale expansion and gas interrupt modes, as illustrated by the calibration slopes obtained for the seven metals in the 0-0.5-ppb range and 0-10-ppb range shown in Table I. Given the detection limitations of the chelation/ solvent extraction technique, the possibility for obtaining an expanded calibration curve for low levels of these metals can only be realized by tedious preconcentration of the sample. Increasing the volume ratios of sample vs. extracting solvent is limited by the solubility of any solvent in water. For example, the solubility of methyl isobutyl ketone (MIBK), a commonly used extracting solvent, is 2.15 ml in 100 ml of deionized water (8). Thus, at increasingly larger ratios of water to MIBK, increasingly greater 1074
Environmental Science 8. Technology
Table I. Calibration Slopes for Standard Solutions of Trace Metals Metal
Range, ppb
Cd
Slope
0-0.5 0-5.0 0-1.0 0-1.0 0-5.0 0-1.0 0-10 0-2.0 0-10 0-5.0 0-10 0-2.0
Cr cu Mn Ni Pb Zn
11.0 10.0 5.5 7.0 5.4 6.6 5.6 7.0 1.7 9.8 5.3 9.0
Table II. Concentrations of Trace Metals in Lake Water Obtained by Flameless and Chelation/Solvent Extraction Methods Amount, ppba Metal
Flarneless
S/Nb
Cd Cr Cu Mn Ni Pb Zn
0.3 1.6 1.5 3.8 3.0 1.5 7.0
35 40 110 140 56 50 600
Flame/ extraction S/Nb
NDe ND 1.6 3.2 2.8 ND 6.7
50 12 5 525
Av concnc
Detec. limitd
0.1-1.1 1-3 2-4 1-13 1-5 1-6 1-15
0.01 0.05 0.1 0.02 0.4 0.01 0.1
a Mean o f five replicate determinations. bsignal-to-noise ratios based on root mean square noise equal t o 0.2 of peak-to-peak noise ( 9 ) .CRange of trace metal concentration i n lake water over a fivem o n t h period. dlOO pi sample (10).eBelOw detection limit.
Table Ill. Recovery Data for Spiked Lake Water Samples Found, ng
Added, ng
Total found, ng
Metal
HGAa
FIExb
HGA
F/Ex
HGA
F/Ex
Cd Cr Cu Mn Ni Pb Zn
0.3 1.6 1.5 3.8 3.0 1.5 7.0
NDC NDC 1.6 3.2 2.8 NDC 6.7
1.o 5.0 2.0 5.0 1.o 10.0 2.0
1.o 5.0 2.0 5.0 1.0 10.0 2.0
1.3 6.5 3.5 8.6 4.0 11.0 9.0
1.1 5.3 3.6 6.3 3.9 10.0 8.6
a Flameless A A procedure. b Flame/extraction procedure. detection limit.
Below
amounts of nonaqueous solvent will dissolve in the aqueous layer, leading to erroneous results. Table I1 lists data for concentrations of the seven trace metals in the lake water. Note that for a number of metals, the concentrations are too low to be easily determined by the standard chelation/solvent extraction technique. Data are also presented in Table I1 illustrating the lower detection limits achievable using the flameless method. Table I11 contains recovery data from this study. A known amount of metal was added to all lake water samples. In this manner, there were sufficient amounts of all metals present for analysis by both techniques. Thus, the effect of the sample matrix could be studied by both methods. The data presented in Table I11 comparing methods of analysis are in good agreement. One problem arising in the chelation/solvent extraction method is the probable loss of metal in the chemical procedure of the extraction technique. This type of study has been performed recently where the two techniques used in this study were compared
with analyses of radioactive cadmium ( 5 ) .Results showed that the flameless technique was in better agreement with the radioactive analyses of cadmium than the chelation/ solvent extraction technique, whose results were consistently lower. Thus, the accuracy of the results was better with the flameless method. Summary
Flameless atomic absorption spectroscopy has been shown to be a precise, rapid, and accurate method for analysis of low concentrations of trace metals. When confronted with analyses for this range of concentrations, the’ flameless method proves to be advantageous over the chelation/solvent extraction method. No major interferences are noted and the decrease in sample handling reduces the possibility of sample contamination, while the detection limit is reduced to a lower value.
Literature Cited (1) Ediger, R. D., A t . Absorpt. Newsl.,12,151 (1973). (2) Walsh, A., Anal. Chern., 46,698A (1974). (3) Culver, B. R., Surles, T., ibid., 47,920 (1975). (4) Barnard, W. M., Fishman, M. J., A t . Absorpt. Newsl., 12, 118 (1973). (5) Kjellstrom, T., Lind, B., Linnman, L., Nordberg, G., Enuiron. Res., 8,92 (1974). (6) Environmental Protection Agency, Cincinnati, Ohio, “Methods for Chemical Analysis of Water and Wastes,” 1971. (7) Perkin-Elmer Corp., Norwalk, Conn., “Analytical Methods for Atomic Absorption Spectroscopy Using the HGA Graphite Furnace,” 1973. (8) Everson, R. J., Parker, H. E., Anal. Chern., 46,2040 (1974). (9) Varian Associates, Palo Alto, Calif., “Optimum Parameters for Spectrophotometry,” 1973. (10) Guillaumin, J. C., A t . Absorpt. Newsl., 13,135 (1974).
Received for review February 3, 1975. Accepted July 10, 1975.
Determination of Nitrate in Water Samples Using a Portable Polarographic Instrument Richard L. Young, J. Everett Spell, Henry M. Slu, and Robert H. Philp’.’ Department of Chemistry, University of South Carolina, Columbia, S.C. 29208
Edwin R. Jones Department of Physics, University of South Carolina, Columbia, S.C. 29208
w A simple portable polarographic analyzer is described. Use of this system for the determination of nitrate in natural water samples employing the polarographic waves developed in the presence of Zr(1V) and U(V1) is reported. The use of these catalytic systems allows direct compensation of background currents due to interferences. Results for both methods are in good agreement with those from spectrophotometric analyses, provided analyses are done a t the same time. While polarographic methods for the determination of a large number of substances of interest in the environment have been reported, they are seldom used routinely. The relative complexity of polarographic instrumentation and the inconvenience of cumbersome dropping mercury electrode (DME) assemblies no doubt account for the lack of popularity of polarography vis-a-vis spectrophotometric methods. With the increased availability of low cost, reliable and small solid state operational amplifiers (OA’s), it would seem that these objections could be largely overcome and that the ease of sample preparation, accuracy, and reliability of polarographic methods would warrant their reexamination. During the course of this work, a portable polarographic analyzer has been described ( I ) that takes advantage of these advances in technology. The possibility of routine polarographic determination of nitrate is particularly attractive. Because nitrate reduction is observed at the DME only in the presence of metal ion catalysts such as La(II1) (2, 3), Zr(IV) ( 4 ) , and U(V1) ( 5 ) ,the possibility exists to compensate directly for interferences that are reduced a t the same potential by a simple differential measurement. On sabbatical a t the University of Georgia, Athens, Ga.
While the Zr02+ and U02*+ methods’have appeared as tentative methods in a standard reference (6), they do not appear to be widely employed. Although numerous studies have been made, the course of the electrode reaction is not completely understood in the case of any of the catalysts. In the La3+ and U0p2+ systems, the reactions appear to be reduction of nitrate to ammonia and/or hydroxylamine, catalyzed by intermediate oxidation states of the metal. The wave observed in the presence of ZrOCl2 has been reported to be due to distinct Zr-NO3 complexes (7). In general nitrite, if present, gives a similar wave under conditions where the nitrate wave is observed and methods have been reported (8) for differentiating between nitrate and nitrite in the polarographic analysis. The presence of nitrite in samples studied was not indicated and no differentiating techniques were employed. Experimental
The Circuit. The circuit employed is shown in Figure 1. The potential is applied through the follower (OAl), and
50 K
50K
IK
Figure 1. Circuit of
polarographic instrument Volume 9, Number
12, November 1975
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