ANALYTICAL CHEMISTRY, VOL. 50, NO. 1, JANUARY 1978
This technique may also be used to measure other quantities t h a t reflect the aqueous solubility behavior of PAHs. By varying the temperature and salinity of the water that is passed through the generator column, enthalpies of solutions, AHs, and salting out effects (Setschenow Constants) (32) can be calculated. This system is also being used to investigate the partitioning of some PAHs between aqueous solutions and some sediment samples.
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(17) A. Hill, J . Am. Cbem. Soc., 44, 1163 (1922). (18) M. Hayashi and T. Sasaki, Bull. Cbem. SOC.Jpn., 29, 857 (1956). (19) H. Booth and H. Everson, Ind. Eng. Cbem., 40, 1491 (1948). (20) P. Leionen, D. MacKay, and C. Phillips, Can. J . Cbem. Eng., 49, 288 (1971). (21) W. Davis, M. Krohl, and G. Clower, J . A m . Cbem. Soc., 64, 108 (1942). (22) H. Kelvens, J . Pbys. Colloid Cbem., 54, 283 (1950). (23) D. MacKay and W. Shiu, J . Chem. Eng. Data, accepted for publication. (24) C. Tsonopoulos and J. Prausnitz, Ind. Eng. Cbem. Fundam., I O . 593 (1971). (25) C. Pierotti, C. Deal, and E. Derr, Ind. Eng. Chem. Fundam., 51, 95 (1959). (26) R. Wauchope and F. Getzen, J . Chem. Eng. Data, 17, 38 (1972). (27) R. Weimer and J. Pausnitz, J . Cbem. Pbys., 42, 3643 (1965). (28) F. Schwartz, J . Cbem. Eng. Data, 22, 273 (1977). (29) L. Andrews and R. Keefer. J . Am. Cbem. Soc., 71, 3644 (1949). (30) W. May, S. Chesler, S. Cram, B. Gump, H. Hertz, D. Enagonio, and S. Dyszel, J . Chromatogr. Sci., 13, 535 (1975). (31) E. Peake and G. Hodgson, J . Am. 01 Chem. Soc., 44, 696 (1967). (32) J. Setschenow, Z.Pbys. Cbem., 4, 117 (1889).
LITERATURE CITED C. Tsonopoulos and J. Prausnitz, Ind. f n g . Cbem. Fundam., 10, 503 (1971). A. LeFewre, "Water and Water Pollution Handbook", Vol. 1, L. L. Ciaccio, Ed., Marcel Dekker, New York, N.Y.. 1971, p 263. E. Peak and G. Hodgson. J . Am. Oil Chem. Soc., 215 (1966). A. Ben-Naim. J . Cbem. Pbys., 57, 5257 (1972). A. Ben-Naim, "Water and Aqueous Solutions", R. A. Horne, Ed., Wiley, New York, N.Y., 1972, p 425. R. Hites, hoceedings of the "Source, Effects and Sinks of Hydrocarbons in the Aquatic Envkonment" Symposium, American University, Washington, D.C., August 1976. D. MacKay and W. Shiu, Can. J . Chem. Eng., 53, 239 (1975). C. McAuliffe, J . Pbys. Chem., 70, 1274 (1966). C. Sutton and J. Clader. J . Chem. Ena. Data. 20. 320 (1975). D, Arnold, C. Phnk, and E. Erickson, Chem. Eng. Data Ser., 3, 253 (1958). R. Bohon and W. Claussen, J . Am. Cbem. Soc., 73, 1571 (1951). F. Franks, M. Gent, and H. Johnson, J . Cbem. Soc., 2716 (1973). L. Andres and R. Keefer, J . Am. Cbem. Soc., 72, 5034 (1950). T. Morrison and F. Billet, J . Cbem. SOC.,3819 (1952). H. Vermillion, PhD. Thesis, Duke University, Durham, N.C., 1939. R. Stearns, H. Oppenheimer, E. Simon, and W. Harkins, J . Cbem. Phys., 14, 496 (1974).
RECEIVED for review May 9, 1977. Accepted October 26, 1977. T h e authors are grateful to the Office of Air and Water Measurement, National Bureau of Standards, for partial support of this work. This work is from a dissertation to be submitted to the Graduate School, University of Maryland, by Willie E. May, in partial fulfillment of the requirements for a Ph.D. degree in Chemistry. Identification of any commercial product does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material or equipment identified is necessarily the best available for the purpose.
Nondestructive High Temperature Gas Radiochromatography 6. E. Gordon,* W.
R. Erwin, M. Press,
and
R. M.
Lemmon
Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94 720
GRC detectors have been described in the literature by many authors ( I ) . These have included Geiger counters, proportional flow counters, ion chambers, and liquid scintillation counters (2-5). In general, they may be divided into two groups; the nondestructive group which analyzes the effluent without chemical change (e.g., heated ion chambers ( 5 ) or flow liquid scintillation counters (4,and destructive systems which burn the GC effluent to '*C02 and 3H20, convert the water to 3H2,and pass these through a n appropriate detector for analyses (6-8). In recent years the combustion systems have gained acceptance because room temperature flow counters are less subject to erratic behavior and require less maintenance than heated counters. Proportional counters have considerable advantages (see below), but they are particularly sensitive to high temperature malfunction because weak signals (1 mV) must be amplified several hundred times before processing by analyzers, scalers, or ratemeters. Thus, any spurious thermal electrons or low leakage currents cause erratic, unacceptable backgrounds and short, steep high-voltage/counting plateaus. Nonetheless, there exist high temperature applications of GRC that require nondestructive on. line analysis of the gas chromatographic effluents because the fractions separated must be trapped for further study. The work in our laboratory on the reactions of accelerated carbon ions impinging on carious targets, primarily benzene (9, 10) has required just such a technique. The fate of these reactive species (e.g., C', CH', CH2+, CH3+) striking solid benzene requires the
A proportional flow counter for continuous operation at 300 O C has been developed. It serves as the radioactivity detector in a gas radiochromatographic system. With associated electronics It is capable of both qualitative and quantitative analyses of the emerging peaks. The counter is decontaminated in situ by treatment with oxygen at 325-350 O C . Backgrounds are low (-75 cpm) and at the flow rates used, 5 dpm generate 2 counts. Possible quenchers are readily detected by their effect on the count rate produced by an external cobalt-60 source. Frequency of disassembly is low, averaging about once a year over the past three years.
Gas radiochromatography (GRC) has been an important analytical tool for many years. T h e ability to measure, quantitatively as well as qualitatively, the mass and radioactivity of peaks emerging from t h e gas chromatograph permits one t o identify the labeled fractions and determine their specific activities in a single pass through the instrument. This approach has considerable attraction over that of dividing t h e effluent of a n entire chromatogram into a large number of trapped fractions for subsequent liquid scintillation counting to locate and integrate the peaks of interest. Even when the chromatographic radioactivity detector is only qualitative, it permits one to locate for trapping the peaks of interest, thus sharply reducing the time and effort for such separations and analyses. 0003-2700/78/0350-0179$01 O O / O
C
1977 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 1, JANUARY 1978
HV and SIGNAL CONTA TEFLON INSULATOR
\ ANODE "IRE
He-4j PROPANE
Figure 1. Schematic drawing of proportional flow counter
identification and isolation of the many products formed. Since only nanograms of product are produced in a normal experiment, t h e impinging ions are carbon-14 labeled to provide the requisite sensitivity for chromatographic analysis. I n addition, it is frequently necessary to isolate and degrade an identified product to determine the distribution of the label in t h e compound. Thus, nondestructive GRC is essential.
EXPERIMENTAL A proportional flow counter (PFC) was selected as detector for a number of reasons. I t is capable of high count rates without coincidence loss; it can discriminate, if necessary, between radioisotopes (e.g., 3H,14C); it is an internal counting system with 4 7 geometry, and it is basically simple in design so that it is readily coupled into a flowing gas system. To prevent condensation of fractions, nondestructive GRC requires a heated PFC. Our first approach was to purchase from Nuclear/Chicago (now Searle/Analytic) their Model 000461 PFC, which was used directly. It functioned rather well up to 250 "C but showed a distressing tendency to rapidly build up contamination (high radioactivity background) after every analysis. Since some of the products in these studies required a gas chromatograph (GC) temperature of 250 O C , it was obvious that the PFC operating temperature should be higher than this to prevent condensation. We decided that we needed to operate our GC at 300 "C, at which temperature the commercial PFC was inoperable due to high backgrounds and the virtual absence of a good counting plateau. The barrel of the commercial PFC is of chromium plated brass and this was replaced by seamless 304 stainless steel that had been honed to a mirror finish. This PFC also showed poor performance at 300 "C, Le., little or no counting plateau (H.V. vs cpm tested with a small 6oCoexternal source). Reasoning that the poor performance might be due to micro asperites in the barrel or on the center wire that acted as discharge points, 2-mil tungsten wire was examined under a low power microscope to choose a length free of sharp edges. In addition, the barrel was electropolished in a bath, as shown below, for several minutes to remove any sharp points. This latter step dramatically improved the performance of the PFC, and acceptable counting plateaus were obtained at temperatures well above 300 "C, the limit (370-400 "C), apparently being hot flow of the Teflon insulators, which resulted in severe leaks. A rough schematic of the PFC is shown in Figure 1. It is almost identical to the commercial unit with small design changes. An engineering drawing may be obtained from Searle/Analytic as Drawing Number 839468. Assembly of the PFC is done after all parts are sonicated in detergent and rinsed in anhydrous methanol. Based on the PFC, a system was assembled for quantitative gas radiochromatography from the following equipment.
Equipment. (1) Gas Chromatograph-Varian 3700 with thermal conductivity detector only. Modified by supplier to include a four-port heated (300 "C) switching valve, Part No. 57-000132-00. (2) Proportional Flow Counter-as described. (3) Preamplifier-constructed at LBL-schematics available on request. (4) Scaler/conditioner-constructed at LBL-schematics available on request. (5) Nimbin-Power Designs Inc. Model AEC-520-5A. (6) Ratemeter-Tennelec Inc. Model TC-596. (7) H.V. Power Supply-Power Designs, Model AEC-50008. (8) Multichannel Analyzer (MCA)-Tracor/Northern Model TN-1705. Modified by the supplier to increase channel dwell time lox. Used only in the multiscaling mode. (9) Two-pen recorder-Hewlett-Packard Model 7100 B with two model 7505-A preamplifiers.
1
-
GbS " a C I O C H R c F ~ ~ T O s ~ A ~ HSl C YSlELI L
~~
~~
2
Figure 2. Block diagram of t h e gas radiochromatographic system
(10) Temperature Control for PFC-Eagle Systems TCD 312A504, 0-399 "C, Type J. (11)Temperature Readout-John Fluke Digital Thermometer Model 2160 A, and multipoint selector 2160A. Used to read temperatures of the PFC, switching valve, and exit port. Note: Items 3 and 4 can probably be replaced by a commercially available preamplifier, scaler with discriminator, and pulse shaper for interfacing with the MCA. The heated switching valve in the chromatograph was installed by the manufacturer. It occupies the chamber normally reserved for a flame ionization detector which was not purchased. Since this chamber is heated, good temperature control from the GC panel board was possible. Another factory modification to the GC was the installation of flow meters for both columns. Quantitative gas radiochromatography requires a constant gas flow since the counts collected are inversely proportional to the flow rate (11). For the same reason the temperature of the PFC must also be reasonably constant (-i2"). A block diagram of the system is shown in Figure 2. The radioactivity pen of the two-pen recorder has, for convenience, been bent to correct for the transit time between the thermal conductivity mass detector and the radioactivity detector so that when labeled compounds emerge, the mass and radioactivity peaks will coincide. Because we employ 1/4-inchcolumns, the helium flow rate is 50 mL/min and the propane counting gas is 100 mL/min. A simple Swagelok T introduced the propane immediately before the PFC and mixing is adequate to provide very good counting plateaus (
