Anal. Chem. 1082, 5 4 , 146-148
148
venient for direct connection of a liquid chromatograph and a mass spectrometer (24).
(7) Mltchum, R. K.; Moier, G. F.; Korfmacher, W. A. Anal. Chem. 1960, 52, 2278. (8) Carroll, D. 1.; Dzldic, 1.; Stlllwell, R. N.;Haegeie, K. D.;Horning, E. C. Anal. Cbem. 1975, 4 7 , 2369. (9) Arpino, P.; Baidwin, M. A.; McLafferty, F. W. Biomed. Mass Specfrom. 1974, 1 , 80. (IO)Tsuge, S.;Hirata, Y.; Takeuchi, T. Anal. Chem. 1979, 51, 167. (11) Henion, J. D. Anal. Chem. 1978, 5 0 , 1687. (12) Kambara, H.; Mitsui, Y.; Kanomata, I. Anal. Cbem. 1979, 51. 1447. (13) Kambara, H.; Mitsui, Y.; Hirose, H., to be submitted for publication in Sbitsuryo Bunseki (14) Arpino, P. J.; Gulochon, G. Anal. Cbem. 1979, 5 1 , 682 A.
LITERATURE CITED (1) Horning, E. C.; Carroll, D. I.; Dzidic, I.; Haegele, K. D.; Lin, S. N.;
Oertii, C. U.; Stillwell, R. N. Clin. Chem. (Winston-Salem N . C . ) 1977, 23, 13. (2) Gray, A. L. Anal. Cbem. 1976, 4 7 , 600. (3) Reid, N. M.; French, J. B.; Buckiey, J. A.; Lane, D. A.; Lane, A. M. Sclex Inc. Appllcatlon Note, 1977, No. 677. (4) Lovett. A. M.; Reld, N. M.; Buckiey, J. A.; French, J. B.; Cameron, D. M. Blomed. Mass Soectrom. 1979. 6 . 91. (5) Kambara. H.; KanGata, I. Anal. Chern. 1977, 4 9 , 270. (6) Kambara, H.; Ogawa, Y.; Mitsui, Y.; Kanomata, I. Anal. Cbem. 1980, 52, 1500.
.
for review August 4, l981- Accepted October 1, 1981.
Solvent Extraction of Low-Molecular-Weight Polycyclic Aromatic Hydrocarbons from Reversed-Phase Liquid Chromatographic Effluents I. Ogawa and C. D. Chrlswell" Ames Laboratory-USDOE,
Iowa State Universl~,Ames, Iowa 5001 1
High-performance liquid chromatography provides an effective means of separating constituents of samples of environmental origin, When suck samples contain large numbers of constituents a t low concentrations, retention times and detector responses provide insufficient data for component characterization. Coupling of HPLC fractionation with GC/MS characterization has proven t o be a powerful technique for determining compounds of interest. Reversed-phase HPLC procedures are the most effective for separation of samples containing low-molecular-weight polycyclic aromatic hydrocarbons. However, the aqueous methanol or acetonitrile solvents used with reversed-phase HPLC are incompatible with high-resolution, high-sensitivity gas chromatography. Reversed-phase solvents can be removed from a sample by distillation or by evaporation with an inert gas. Both of these techniques also lead to significant losses of volatile analytes such as low-molecular-weight polycyclic aromatic hydrocarbons. Solvent extraction with large volumes of pentane has been used to isolate polycyclic aromatic hydrocarbons from HPLC effluents containing methanol (1) and from lowpressure liquid chromatographic effluents containing 2propanol (2). In the present work it has been demonstrated that low-molecular-weight polycyclic aromatic hydrocarbons can be isolated from reversed-phase HPLC solvents by a one-step solvent extraction using a small volume of solvent. The procedure is rapid and convenient and the use of a small volume of solvent eliminates the need for reducing the volume of extraction solvent by distillation or other techniques. The utility of the method has been demonstrated by the determination of biphenyl on fly ash.
EXPERIMENTAL SECTION Solvent Extraction. Separate solutions were prepared in 60-mL separatory funnels containing 50 mL of high-purity water (Millipore,Bedford, MA), 3 mL of either methanol or acetonitrile (Burdick and Jackson, Muskegon, MI), and 2,100, or 1000 pg of naphthalene, anthracene (Chem. Services, West Chester, PA), or acenaphthylene (Aldrich, Milwaukee, WI). Between 0.2 and 0.5 mL of a candidate extraction solvent was added to each separatory funnel, and the mixture was shaken vigorously for 2 min. After the phases separated, the aqueous layer was discarded and the organic layer drained into a collection vessel. The separatory funnel was rinsed with 0.1-0.2 mL of the same solvent which was then combined with the extraction solvent. The combined ex0003-2700/82/0354-0146$01.25/0
traction and rinse solvents were dried over anhydrous sodium sulfate (Fisher, Fair Lawn, NJ) which had been heated previously to 450 "C for 2 h. When dichloromethane was used as an extraction solvent, its solubility in water required the use of 1.3 mL for extraction in order to recover 0.5 mL. In addition, a second extraction was required with 0.2 mL of dichloromethane in order to obtain reproducible results. Recovery of Analytes from HPLC Effluents. Mixtures containing either 2 or 100 pg each of the dicyclic and tricyclic aromatic hydrocarbons naphthalene, acenaphthylene, and anthracene per 25 pL of solution were prepared in methanol and in acetonitrile. These solutions were separated with an SP8000 liquid chromatograph (SpectraPhysics, Santa Clara, CA) equipped with a 25-pL injection loop, a 254-nm UV absorbance detector, and a 4.6 mm X 25 cm, 10 pm Lichrosorb RP-8 column (Jones Chromatography, Columbus, OH). Both linear gradient and isocratic separation modes were used with acetonitrile-water and methanol-water elution solvents. In all cases separations were performed at a flow rate of 1 mL/min at ambient temperature. Three-milliliter fractions containing the individual components of interest were collected manually. These fractions were diluted with 50 mL of water, extracted, and dried by using procedures described above. Determination of Analytes. Recovery of model compounds from standard mixtures and from HPLC effluents was determined by gas chromatography using a Tracor Model 560 gas chromatograph (Tracor, Austin, TX) equipped with a flame ionization detector and 6 ft X 2 mm i.d. glass column packed with 3% OV-17 on Chromosorb W-AW-DMCS. Quantitation was by comparison with an internal standard of 2-methylnaphthalene. Determination of Low-Molecular-Weight Polyaromatic Hydrocarbons on Fly Ash. A 50-g sample of electrostatic precipitator hopper ash from a local power plant coburning refuse and coal was subjected to ultrasonic extraction with 100 mL of 1:l dichloromethane-benzene. The volume of the extraction solvent was reduced to approximately 1mL by distillation, acetonitrile added, and the remaining dichloromethane-benzene removed by distillation. Constituents of the sample were separated by liquid chromatography using an SP8OOO instrument. Duplicate separations were performed by using a 250-pL injection loop, a 4.6 mm X 10 cm, 10-pm medium-performance RP-8 column (Brownlee Labs, Santa Clara, CA) at a flow rate of 1mL/min and ambient temperature. For these separations a linear gradient from an initial 20:80 acetonitrilewater t o 50:50 acetonitrile-water in 10 min was used. The final composition was held for 15 min and the composition was then raised to 100% acetonitrile to flush the column. In addition, duplicate separations were performed by 0 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 1, JANUARY 1982 ~~
Table I. Average Recovery of Naphthalene, Acenaphthylene, and Amthracene from Aqueous Methanol and Acetonitrile Solutionsa extraction solvent toluene benzene cyclohexane pentane hexane heptane isooctane dichlorome t hane
recovery, RSD, determi'To nations % 95 97 94 88 92 93 96 94
6 4 5 5 8
5 6 5
36 36 36 34 36 24 6 24
a Average of replicate determinations of all three compounds.
using a 25-wL injection loop, a 4.6 mm X 25 cm, 10-wm RP-8 column (Jones Chromatography, Columbus, OH) at a flow rate of 1 mL/min and ambient temperature. For these separations a linear gradient from an initial 2080 acetonitrile-water to 100% acetonitrile in 30 min was used. In both cases, 3-mL fractions were collected in the regions of the chrornatogram where acenaphthylene, naphthalene, and anthracene would elute and Rn additional fraction was Ioollected encompassing the major component of the sample. These fractions were extracted and constituents determined by use of the procedures described above. In addition, the major component was characterized by gas chromatography/mass fipectrometry. RESULTS E x t r a c t i o n of Standard Solution#. Extractions were performed with eight different solvents-toluene, benzene, cyclohexane, pentane, hexane, heptane, isooctane, and dichloromethane. Only minor differences were noted in extraction efficiencies (Table I). The range of recoveries was from approximately 80% to 110%. When dichloromethaine was used, a second extraction was required to obtain extraction recoveries comparable with other solvents. Virtually identical average recoveries of acenaphthylene (94% f 5%, 78 detorminations), naphthalene (93% f 6%, 78
