Anal, Chem. 1981, 53, 1209-1213
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Determination of Copper as a Dithiocarbamate Complex by Reversed-Phase Liquid Chromatography with Electrochemical Detection A. M. Bond” and G. G. Wallace Division of Chemical and Physical Sciences, Deakin University, Waurn Ponds 32 17, Victoria, Australia
A method for the specific determination of copper based on reversed-phase liquid chromatography with electrochemical detectlon has been developed. Acetonltrlle-water mixtures are used as the solvent. A dithiocarbamate (dtc) salt may be included in the running solvent and aqueous solutions lnjected onto the column to form the copper dlthiocarbamate complex Cu(dtc), In sltu. Alternatively, external formation of Cu(dtc), and Injection of the complex onto the column may be used. Cu(dtc), undergoes reversible one-electron reduction and oxidation steps at platinum, gold, and glassy carbon electrodes in the acetonitrile-water medlum enabling copper to be determined at levels down to 1 ng, using electrochemical detection. Interference effects were examined for 20 species, and at a 10-fold excess (welght) no Interference was found. Interference studles Indicate that multielement analysis should be posslble as marly other elements are also electroactive.
The determination of many metals via polarographic, voltammetric, and other electrochemical techniques is extremely sensitive (1-3). However, many determinations are subject to interference via overlapping waves (1-5) and not surprisingly high-performance liquid chromatography to achieve separation of compounds coupled with electrochemical detection (LCEC) is a rapidly developing field of analytical chemistry (6-10). To date the majority of work using LCEC has concerned the trace determination of organic compounds in complex mixtures. However, trace metal analysis is an extremely important area of research which equally well can be expected to substantially benefit from the application of LCEC. Dithiocarbamate compounds have been known since the last century and form an extensive field of analytical chemistry (11-13). The fact that metal dithiocarbamate complexes can be extracted so readily from aqueous systems into organic solvents (13) has made these complexes extremely useful in solvent extraction coupled with detection by atomic absorption spectrometry (14). This characteristic also makes these complexes attractive for separation via high-performance liquid chromatography (15-18). Literature reports indicate that many metal dithiocarbamate complexes are electroactive at various working electrodes (1S25). Significantly, data indicate a widespread ability of the ligand to form complexes in a wide range of oxidation states including Mn(IV), Mn(III), Mn(II), Fe(IV), Fe(III), Fe(II), Cu(III), Cu(II), Cu(I), etc. Thus, both oxidation and reduction processes would appear to be available for direct electrochemical detection in a nonaqueous solvent. Several workers have extracted dithiocarbamate complexes and detected the element electrochemically (26,27) after destruction of the complexes via back-extraction into an aqueous phase or other means, but little direct use of the electrode processes in a nonaqueous solvent has occurred. Information available
on copper determination indicates that excellent results are likely to be obtained (28). In the present work, reversed-phase liquid chromatography was considered for investigation using acetonitrile-water mixtures. Acetonitrile is a commonly used solvent in both reversed-phase LC and electrochemistry. The determination of copper was chosen to develop all the required methodology because it was known to give very well-behaved electrochemical responses in nonaqueous solvents at platinum electrodes and both reduction and oxiation processes could be examined (25). It is also a very important element, whose electrochemical detection is prone to interference (1,2,4,5,29,30). We have examined the use of platinum, gold, and glassy carbon electrodes, formation of the complexes externally and in situ with respect to the column, the use of oxidation and reduction processes, variable solvent composition, and the use of sodium diethyldithiocarbamate and ammonium pyrrolidinedithiocarbamate. This paper provides a report of all these and related investigations with respect to the determination of copper. Possibilities for multielement analysis are only briefly touched upon as part of the investigation of interferences. This aspect will be examined in detail in future work.
EXPERIMENTAL SECTION Reagents and Standard Solutions. All chemicals used were of analytical grade purity unless otherwise stated. Copper dithiocarbamate complexes, Cu(dt&, were prepared by the method described by Martin et al. (25). Acetate buffer was prepared by using the method described by Vogel (31). Copper dithiocarbamate stock solutions for use in acetonitrile were initially prepared by dissolving Cu(dtc)z (dtc = dithiocarbamate) in the solvent. Subsequently, they were prepared by mixing copper nitrate and dithiocarbamate in acetonitrile. Liquid chromatography (LC) grade acetonitrile from Waters Associates was employed for most of the work reported in this paper. Acetonitrile purified by the method of O’Donnell and co-workers (32)was as suitable as the LC grade for determination of copper. Instrumentation. A Princeton Applied Research (Princeton, NJ) Model 174 polarographic analyzer was used for measurements in both the stationary and flow through electrochemical cells. Gold, platinum, and glassy carbon “minielectrodes”obtained from Metrohm Ltd. (Herisau, Switzerland) were employed as the working electrodes. These electrodes were cleaned at least once a day using the polishing powder (a-Al2O3,fineness = 0.3 pm) also obtained from Metrohm. The auxiliary electrodes were either platinum or glassy carbon and the reference electrode was Ag/AgCl (3 M KCLwater). Metrohm EA 1096 detector cell was used in all LCEC work. All high-performance liquid chromatography equipment was obtained from Waters Associates (Milford, MA). A Model 6000A solvent delivery system with a Model U6K universal injector and a C-18 pBondapak column (internal diameter 3.9 mm, length 30 cm) protected by a preceding guard column were employed. The guard column was repacked with C-18 packing material once a week. A Waters Model 450 variable-wavelength detector was used for determination of retention times. After each working period, the pump and column were initially flushed with acetonitrile and then water-methanol. The column was stored in methanol.
0003-2700/81/0353-1209$01.25/00 1981 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
Atomic absorption measurements were performed with an air-acetylene flame and copper hollow cathode lamp (A = 324.7 nm) on a Varian Techtron (Springvale,Victoria, Australia) Model AA6 atomic absorption spectrometer.
RESULTS AND DISCUSSION Electrochemistry of Copper Complexes in Conventional Electrochemical (Stationary) Cells. As an essential step to understanding the electrode processes for the copper dithiocarbamate system, a detailed investigation of electrochemical responses in various media was undertaken in a conventional electrochemical cell. In pure acetonitrile (0.1 M Et4NC104),cyclic voltammograms of C ~ ( d e d t c(dedtc )~ = diethyldithiocarbamate) and C ~ ( p y d t c (pydtc )~ = pyrrolidinedithiocarbamate) were essentially the same at the platinum electrode as those reported by Martin et al. (25) in acetone. That is, a chemically reversible oxidation
Table I. Detection Limits for Determination of Cu(dedtc), in 70% Acetonitrile-30% Water (0.2 M NaNO,) by Differential Pulse VoltammetryQ electrode
compound form
detection limit, M
copper nitrate + M 1X Na( dedtc) M 1 x lo-' gold copper nitrate + Na(dedtc) platinum copper nitrate + M 1 x 10'' Na( dedtc) platinum Cu(dedtc), 2 x 1o-'c a Pulse amplitude = 50 mV. Duration between pulse = 1s; temperature = (20 1)"C. For signal to noise ratio of 2 : l and for reduction process. Oxidation detection limit, same as for reduction, glassy carbon
current per unit concentration leading to a marginally improved detection limit. Limits of detection for C ~ ( p y d t care )~ essentially the same as for Cu(dedtc),. and a chemically reversible reduction step In practical analysis using reversed-phase LC, a buffer is usually required. The buffer should itself be electroinactive Cu(dtc), + e- ==[Cu(dtc),](2) and not interfere with the determination of copper. Instead of using 30% water (0.2 M NaN03) a suitable aqueous comwere found. ponent was 30% water (0.2 M NaN03, 0.02 M acetate buffer). At platinum electrodes and a scan rate of 200 mV s-l (20 The low concentration of buffer ensured no interference from OC) peak potentials in cyclic voltammetry were -0.53 and -0.46 reduction of hydrogen ion and the pH of the buffer is comV for the reduction step and +0.47 and +0.40 V for the oxpatible with the pH restrictions applicable to the reversedidation process for the Cu(dedtd2 complex. Results for Cu)~ (pydt& at platinum were essentially identical with C ~ ( d e d t c ) ~ phase column employed in this work. The C ~ ( d e d t ccomplex was unstable below pH 6 whereas the C ~ ( p y d t ccomplex )~ was except that peak positons are shifted to slightly more positive stable in the pH range 5-7 as ascertained by monitoring of potentials (25). The electrochemical responses a t gold and differential pulse voltammograms as a function of time. In glassy carbon electrodes in a conventional cell were simifar view of the above, a pH buffer of 6.0 was chosen as being to those obtained at platinum. However, at glassy carbon the suitable for either complex. peak-to-peak separation was considerably greater than at Pt High-Performance Liquid Chromatography with or Au under conditions of cyclic voltammetry indicating a Electrochemical Detection (LCEC). On the basis of slower electron transfer rate. Presumably, this accounts for findings from the preliminary investigation in a conventional the less favorable detection limit at glassy carbon electrodes electrochemical cell, the medium chosen for the running as noted in a subsequent discussion. solvent with LC was 70% acetonitrile-30% water (0.02 M Examination of cyclic voltammograms in acetonitrile-water acetate buffer) with 0.2 M NaN03 as supporting electrolyte. mixtures demonstrated that excellent electrochemical reElectrodes to be investigated with LCEC were glassy carbon, sponses for Cu(dt& could still be obtained in the presence gold, and platinum and both oxidation and reduction processes of 30% water. However, solubility of the complex decreases for C ~ ( d t cwere ) ~ to be compared. It was also believed to be as the water concentration increases and higher water content essential to examine the possibility of in situ formation of the than 30% results in precipitation of the complex. With 30% C ~ ( d t cas ) ~an alternative to formation of the complex exwater, up to 4 X lo4 M concentrations of Cu(dedtc), could ternally to the column. be used, but with Cu(pydtc)z solubility was limited to apStudies with a variable-wavelength UV detector set at 254 proximately 4 X M. nm were initially undertaken to determine the retention As an alternative to using the preprepared Cu(dtc)z comvolume of the copper complexes. Values of 14.4 and 10.4 mL plex, mixtures of copper nitrate and ligand produced elecwere obtained for Cu(dedtc), and C ~ ( p y d t c )respectively. ~, trochemical curves essentially the same as that obtained with This smaller retention volume of C ~ ( p y d t chas ) ~ been atthe prepared complex. In the presence of a considerable excess tributed to the more polar nature of the complexes (35). of the ligand, C ~ ( d t cformation )~ was rapid. However, under Method A. Formation of Cu(dtc),Prior to Injection onto these conditions waves due to the oxidation of ligand (33,341 Column, The initial LCEC tests undertaken used Cu(dtc)z masked the Cu(dt& [Cu(dtc),]+ + e- electrode process. complexes formed externally to the column in the presence Thus, with a large ligand excess only the reduction wave could of an excess of dtc. Results are described below. be used analytically. Reduction at Glassy Carbon, Gold, and Platinum ElecIn a conventional electrochemical cell, differential pulse trodes, Figure 1 shows the response for reduction of Cu(dtc)z voltammetry provided considerably superior analytical reat a glassy carbon electrode using the DC detection method. sponse compared with DC curves. Table I provides data for A well-defined wave for oxygen is also seen. Despite extensive limits of detection for C ~ ( d e d t cdetermination )~ using difendeavors to eliminate oxygen from the injected sample, a ferential pulse voltammetry at various electrodes in 70% small residual peak due to oxygen was always observed. acetonitrile-30% water. A solution of 0.2 M NaN03 could Minimization of oxygen from the running solvent via nitrogen be conveniently substituted for the far more expensive gassing was essential to decrease the noise level associated with Et4NC104as the supporting electrolyte in this medium, and the glassy carbon response to an acceptable level. A detection data in Table I refer to this electrolyte. Lower concentrations limit of 15 ng was obtained by using the reduction process at of NaN03 down to 0.005 M have also been used successuflly a glassy carbon electrode direct current (DC) detection and with LCEC. Clearly, platinum and gold electrodes are superior with a 2 0 - ~ Linjection. A reverse pulse waveform (36) instead to glassy carbon with respect to detection limits. The presence of the DC potential successfully eliminates the oxygen process of a large excess of ligand slightly enhances the observed Cu(dtc),
F=
[Cu(dtc),]+
+ e-
(1)
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
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Table 11. Analytical Data Obtained When Detecting Either Cu(dedtc), or Cu(pydtc), via Method A or Method B Using LCEC' concn range for linear response detection limitb (ng of Cu) (ng of Cu) electrode electrode pro cess a method A method B method A method B 15-400 15-400 15 15 reduction glassy carbon 10-700 10-200 10 10 oxidation glassy carbon 1-250 1-200 1 1 oxidation platinum 1-450 1-600 1 1 oxidation gold a DC current measured at +0.6 V vs. Ag/AgCl for oxidation process and -0.6 V vs. Ag/AgCl for reduction process. Flow rate = 2 mL/min. Injection volume = 20 pL. Temperature = 20 * 1 "C. For signal to noise ratio of 2 : l .
T
I
I
8
I
l
6
l
I
4
I
l
2
l
J
0
I
TIME (rnlnl
Figure 1. Determination of copper as Cu(dedtc), by the reduction electrode process at a glassy carbon electrode and method A: (1) current response for reduction of oxygen: (2)current response for reduction of Cu(dedtc),. DC current measured at a potential of -0.6 V vs. Ag/AgCI. Flow rate = 2 mL/min. Injection volume = 20 pL (200 ng copper). Temperature = 20 f 1 O C . from the readout, e.g., initial potential -0.45 V, final potential -0.20 V. In the acetonitrile-aqueous medium, the oxygen reduction process is irreversible and can be discriminated against in favor of the reversible Cu(dtc), reaction. The pulse technique enables a detection limit of 1ng to be obtained and provides a significant advantage with respect to both sensitivity and the oxygen problem. At platinum and gold electrodes the limited potential range available for reduction at pH 6 causes difficulties. Additionally, the oxygen reduction process overlaps with reduction of the copper complex and significantly alters the electrochemical response. Glassy carbon is therefore the preferred electrode for use with the reduction process. Oxidation a t Glassy Carbon, Gold, and Platinum Electrodes. Figure 2 shows the excellent response obtained at a gold electrode when using the oxidation process and the DC detection techniques. A similar response was obtained a t platinum. With glassy carbon electrodes, peaks appear in the same positions, but a smaller current response per unit concentration is observed. The first peak observed corresponds to oxidation of the ligand and occurs near the solvent front. Thus, interference observed in conventional electrochemical methods is eliminated. Table I1 provides detection limits and the concentration range over which the peak height is a linear function of concentration.. Figure 3 shows calibration curves for different electrodes. The wider linear range of the Calibration curve for copper at gold electrodes coupled with the lower detection limit made the oxidation process with this electrode the recommended method for determination of
I
l
8
l
6
I
1
4
I
1
2
l
i
0
TIME lmlnl
Figure 2. Determination of copper as Cu(dedtc), using the oxidation process at a gold electrode and method A: (1) current response due to oxidation of ligand. (2)current response for oxidation of Cu(dedtck. DC current measured at +0.6 V vs. Ag/AgCI. Other conditions as in Figure 1.
4 J
..
Cu In] P Q
Figure 3. Peak current (I,,) vs. amount of copper injected (as Cu(dedtc),) with a gold electrode using method A: (+) copper amount copper amount varied varied at flxed volume (20 pL) of injection: (0) by altering volume of injection. Other conditions as in Figure 2. copper. Results compared very closely to those observed in a conventional electrochemical cell. That is, glassy carbon electrodes exhibit the least sensitive response while the responses at gold and platinum electrodes are very similar. Results are almost the same when using either Cu(dedt& or Cu(pydt& complexes. Little or no advantage in using either the differential or normal pulse techniques was found when using the oxidation process.
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
i A
[
B
i
0
. 1.0
12
0 1.4
1 1.6
1.8
2.0
2.2
2.6
2.4
FLCI, RArE (mL/mln)
Figure 4. Variation of Dc peak current (I,) with flow rate using method A: (1) gold or platinum electrodes; (2) glassy carbon electrodes. A total of 200 ng of copper was injected as Cu(dedtc),. Other conditions as in Figure 2.
.1
Figure 6. Peaks due to (A) cadmium(II), (B) lead(II), (C) cobalt(III), and (D) iron(II1) observed using method B with a gold electrode and forming Cu(pydtc), in situ for detection of 20 pL of a 5 X lo4 M copper nitrate solution. Peak 2 corresponds to copper and peak 1 to other element. Flow rate = 2 mL/min for A, B, and C and 1 mL/min for (D). Other conditions as in Figure 2.
c
~
1.0
1.2
1.4
1.6 FLC, 'PTE
1.8
2.0
2.2
2.4
iL/nlr
Figure 5. Variation of DC peak current (I,) with flow rate using method B and forming Cu(pydtc), in situ: (1) gold or platinum electrodes; (2) glassy carbon electrodes. A total of 60 ng of Cu was injected as copper nitrate. Other conditions as in Figure 2.
Injection Volumes. Injection volumes greater than 40 pL produced a decrease in the current per unit concentration as shown in Figure 3. Consequently volumes in the range 20-40 pL were employed on all subsequent occasions. Flow Rates. Figure 4 shows the variation of DC peak current with flow rate at glassy carbon, platinum, and gold electrodes. An increase in flow rate leads to an increase in current because of increased convection. Above about 2 mL/min the enhanced current is marginal and the decrease in effective plate count occurring as the flow rate increases means that flow rates in the range of 1-2 mL/min are optimum for determining copper. Problems with Method A. Method A has the disadvantage of requiring sample preparation which also dilutes the concentration of copper. As an alternative to generating the complex prior to injection onto the column, in situ formation of the complex on the column was employed by including M ammonium pyrrolidinedithiocarbamate in the running solvent. Method B. In Situ Formation of C ~ ( d t con) ~Column. Results with this technique are summarized in Table 11. Generally, similar detection limits were obtained with method B as for method A. However, characteristics are not always identical. Figure 5 shows the DC peak height as a function of flow rate with method B. The dependence of peak height on flow rate is seen to be different to that for method A depicted in Figure 4. Results from injection volume studies were similar to those obtained with the previous system, and it is again recommended that injection volumes be kept below 40 fiL.
Method B has several distinct advantages over method A which should be emphasized: a real sample can be collected, filtered, and injected onto the column without further preparation; sensitivity is increased inherently because the dilution factor in external complex preparation is eliminated; there is less chance of decomposition on the column since excess ligand is always present. Disadvantages of method B include raising of the background current due to oxidation of the ligand if the oxidation process is being used. In view of the inherently greater sensitivity of method B and ease of use, it was decided to use this method on real samples and also to study interferences using gold electrodes, the oxidation process for Cu(pydtc),, and the DC detection method at +0.60 V vs. Ag/AgCl. All subsequent data refer to these conditions at (20 f 1) "C. Tests for Interference. Anions. Anions NO3-, C1-, Br-, I-, SO-,: F-, and Pod3were separately added to a standard M copper solution. Each anion was added in the form of the sodium or potassium salt in a 10-fold weight excess. The only anion to record a current response at a gold electrode was I- which came through with the solvent front. I- is readily oxidized at gold electrodes. Tailing of the iodide (suggesting adsorption on gold) resulted in a sloping base line but the Cu(pydtc)2complex current was unaltered. Cations. K+, Ca2+,Mg2+,Pb2+,Cd2+,Fez+,Coz+,2n2+,C$+, AP+, Mn2+,and Hg2+were added as their chloride or nitrate salts. None of these metals altered the current response of the copper complex; however, the presence of additional peaks was noted with some metals. These peaks are presumably due to dithiocarbamate complexes of cadmium(II), lead(II), cobalt(III), and iron (111) with retention volumes of 3.6, 7.5, 9.4, and 11.4 mL, respectively (Figure 6). The iron(II1) complex overlapped the tail of the copper peak, but the peak height was unaffected. With a decrease of the flow rate from 2 to 1 mL/min the two peaks could be satisfactorily resolved. In the presence of large excesses of iron(II1) flow rates need to be carefully adjusted to obtain separation.
Anal. Chem. 1981, 53, 1213-1217
The fact that other metals give separate peaks suggests that the general method proposed in this work will ultimately lead to a very attractive method of multielement analysis. In the present work only the determination of copper has been optimized and equivalent studies, on the other elements, will be required before a highly efficient method for multielement determinations becomes possible. Determination of Capper in Water Samples by LCEC and Atomic Absorption Spectrometry. All of the above data suggest that a relatively interference free method for the determination of copper should be possible with LCEC. Determination of real samples over the concentration range lo* to 5 x 10" M was undertaken with tap water in contact with copper pipes and results compared with those obtained by atomic absorption spectrometry (AAS). Excellent agreement, for example, (2.20 f 0.05) X lo* M and (14.2 f 0.3) X lo4 M (LCEC) vs. (2.20 f 0.05) X lo4 M and (14.3 f 0.3) X lo4 M (AAS), suggests total copper is being determined. Certainly this should be true with AAS, and in view of the very strong complex formation of Cu(dtc)2,this is also probably not surprising with the LCEC method. Applications to a wide range of industrial effluents and other samples were equally successful, so the method is believed to be relatively specific. For determination of copper, AAS would generally be the preferred technique except when only small volumes of samples are available. The detection limits of the two techniques are similar (flameless AAS methods would be considerably more sensitive) and can be used with small volumes but potential for extensive multielement determination on very small volumes of sample could provide a distinct use for LCEC in trace metal determinations. ACKNOWLEDGMENT Extensive discussions with Ian Russell in the early stages of this work are gratefully acknowledged. LITERATURE CITED (1) Kotthoff, I.M.; Lingane, J. J. In "Polarography", 2nd ed.; Interscience: New York, 1952. (2) Bond, A. M. I n "Modern Polarographic Methods In Analytical Chemistry"; Marcel Dekker: New York, 1980. (3) Flato, J. B. Anal. Chem. 1972, 44 ( l l ) , 75A-87A. (4) Barendrecht, E. In "Electroanalytical Chemistry"; Bard, A. J., Ed., Marcel Dekker: New York, 1967, Vol. 2, pp 53-103.
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(5) Copeland, T. R.; Osteryoung, R. A.; Skogerboe, R. K. Anal. Chem. 1974, 46, 2093-2097. (6) Kissinger, P. T. Anal. Chem. 1977, 49, 447A-456A. (7) Felice, L. J.; Kissinger, P. T. Anal. Chem. 1976, 48, 794-796. (8) Swartzfager, D. G. Anal. Chem. 1976, 48, 2189-2192. (9) Fleet, B.; Little, C. J. J. Chromatogr. Sci. 1974, 12, 747-752. (10) Kissinger, P. T.; Refshauge, C.; Dreiling, R.; Adams, R. N. Anal. Lett. 1973, 6, 465-477. (11) Magee, R. J. Rev. Anal. Chem. 1973, 1, 335-377. (12) Delepine, M. Bull. SOC. Chim. h. 1908, 3 , 652-654. (13) Hulanicki, A. Talanta 1967, 14, 1371-1392. (14) Koirtyohann, S. R.; Wen, J. W. Anal. Chem. 1973, 45, 1986-1989
and references cited therein.
(15) Ai-Mahdi, A. K.; Wilson, C. Mlkorchem Ver. Mikrochim. Acta 1951, 36/37, 218-223. (16) Smith, E.; Hayes, J. R. Anal. Chem. 1959, 31, 898-902. (17) O'Laughiin, J. W.; O'Brien, T. P. Anal. Lett. 1978, 1 1 , 829-844. (18) Liska, 0.; Lehotay, J.; Brandsteterova, E.; Guichon, G.; Colin, H. J. Chromatogr. 1979, 172, 384-387. (19) Toropova, V. F.; Budnikov, R. G. K.; Ulakovich, N. A. Talanta 1977, 25, 263-267. (20) Chant, R.; Hendrickson, A. R. Martin, R. C.; Rohde, N. J. Aust. J . Chem. 1973, 26, 2533-2536. (21) Wheeler, S. H.; Mattson, B. M.; Mlessler, G. L.; Pignolet, L. H. Inorg. Chem. 1978. 17, 340-350. (22) Dix, A. H.; Diesveid, J. W.; Van der Linden, J. G. M. Inorg. Chim. Acta 1977, 24, L51-L52. (23) Hendrickson, A. R.; Martin, R. L.; Rohde, N. M. Inorg. Chem. 1975, 14, 2980-2985. (24) Hendrickson, A. R.; Martin, R. L.; Rohde, N. M. Inorg. Chem. 1974, 13, 1933-1939. (25) Hendrickson, A. R.; Martin, R. L.; Rohde, N. M. Inorg. Chem. 1976, 15, 2115-2119. (26) Budnlkov, G. K.; Toropova, V. F.; Ulakhovich, N. A,; Viter, I.P. Zh. Anal. Khim. 1975, 30, 2120-2124. (27) Kitamura, H.; Ichimura A.; Kitigawa, T. Nippon Kagaku Kaishi 1979, 354-358 and references cited therein. (28) Uiakovich, N. A.; Budnikov, G. K.; Fomina, L. G. Zh. Anal. Khlm. 1979, 34, 241-244. (29) Tindall, G. W.; Bruckensteln, S. J . Nectroanal. Chem. 1969, 22, 367-373. (30) Cathro, K. J.; Walkley, A. J. J. Polarogr. SOC. 1958, 2 , 36-40. (31) . . Voael. A. "A Textbook of Quantitativelnoraanic Analvsis"; Lonamans: Loridon, 1968; p 869. (32) O'Donnell, J. F.; Ayres, J. T.; Mann, C. K. Anal. Chem. 1965, 37, 1161-1164. . , - . . . - .. (33) Cauquis, G.; Lachenal, D. J . Electroanal. Chem. 1973, 43, 205-213. (34) Scrimage, C.; Dehayes, L. J. Inorg. Nucl. Chem. Lett. 1978, 14, 125-1 33. (35) Bigley, I.E. Ph.D. Thesis, University of Massachusetts, Amherst, MA, 1978. (36) Maitoza, P.;Johnson, D. C. Anal. Chim. Acta 1980, 118, 233-241.
RECEIVED for review August 15, 1980. Accepted March 17, 1981.
Liquid Chromatographic Determination of Benzo[ a Ipyrene in Natural, Synthetic, and Refined Crudes Bruce A. Tomkins," Roberta R. Reagan, John E. Caton, and Wayne H. Griest Analytical Chemistry Divislon, Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, Tennessee 37830
Benzo[a]pyrene (BaP) is isolated and quantitated by using a sequential high-pressure llquid chromatographlc (HPLC) procedure. The sample is first injected onto a semipreparative HPLC column containing a bonded polar aminocyano (PAC) packlng material, from which a BaP-enriched fraction is obtained. This Isolate is then reinjected onto a Zorbaw ODS reversed-phase analytical-scale column, and fluorescence detection is used to quantitate BaP. This procedure Is applicable to samples with BsP concentrations ranging from 0.02 to 500 pg/g. The precision is nominally f6% (relative standard deviation), and the accuracy compares favorably with that dlsplayed by more tedious methods. Recoveries, as determined by counting a radioactive BaP tracer, usually exceed 95 %. Two samples may be processed per personday.
The current interest in synthetic fuels, derived from either shale oil or coal, has been matched only by the desire that these materials present a minimal hazard to health and to the environment. For this reason, there is a substantial interest in identifying and quantitating any biologically harmful component present in these new fuels, Benzo[a]pyrene (BaP) is a case in point. BaP is a wellknown carcinogen ( I ) which is usually present in fossil fuels and has been used for years as an indicator of the polycyclic aromatic hydrocarbon content of fuels. As a result, there has been an extensive effort to develop rapid, convenient, accurate, and precise methods for determining BaP in natural, synthetic, and refined crudes. BaP has been determined by using direct-injection gas
0003-2700/81/0353-1213$01.25/0 0 1981 American Chemical Society
