Anal. Chem. 1983, (19) Eskins, K.; Scholfield, C. R.; Dutton, H. J. J. Chromatogr. 1977, 135, 217-220. (20) Abaychi, J. K.; Riley, J. P. Anal. Chlm. Acta 1979, 707, 1-11, (21) Stransky, H. 2.Naturforsch., C 1978, 33C,836-840. (22) Iriyama, K.; Yoshiura, IM.; Shirakl, M. J . Chromatogr. 1978, 754, 302-305. (23) Braumann, T.; Grirnme, L. H. J. Chromatogr. 1979, 770, 264-268. (24) Braumann, T.; Mahro, B.; Grimrne, L. H. Ber. Dtsch. Bot. Ges. 1978, 97, S. 583-587. (25) Eskins. K.; Harris, L. Photochem. Photoblol. 1981, 33, 131-133. (26) Esklns, K.; Dutton, H. J. Anal. Chem. 1979, 57, 1885-1888. (27) Davies, D.; Holdsworth, 13. S. J . Llq. Chromatogr. 1980, 3, 123-132. (28) Flksdahl, A.; Mortensen, J. T.; LiaaenJensen, S. J . Chromatogr. 1978, 757, 111-117. (29) Hajlbrahim. S. K.; Tlbbens, P. J. C.; Watts, C. D.;Maxwell, J. R.; Eglinton, G.; Colin, H.; Gulochon, G. Anal. Chem. 1978, 50, 549-553. (30) Pfander, H.; Schurtenberger, H.; Meyer, V. R. Chhla 1980, 34, 179-180. (31) Matus, Z.; Baranyal, M.; ‘T6th, 0.; Szabolcs, J. Chromatographla 1981, 74, 337-340.
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RECEIVED for review August 23, 1982. Accepted October 25, 1982. This work was supported by the National Fund for Scientific Research (NFWO) through a grant to H.J.C.F.N.
Dynamic Coupled-Column Liquid Chromatographic Determination of Ambient Temperature Vapor Pressures of Polynuclear Aromatic Hydrocarbons W. J. Sonnefeld and W. H. Zoller Department of Chemistry, b’nlversl@ of Maryland, College Park, Maryland 20742
W. E. May” Organic Analytical Research Division, National Bureau of Standards, Building 222, A 1 13, Washington, D.C. 20234
A method Is descrlbed far the direct coupllng of a gas saturatlon system to a hlgh-performance llquld chromatograph for the detennlnatlon of the vapor pressure of organic compounds In the range of 102-10-6 Pa. The method has been used to determine the vapor pressures of selected polynuclear aromatlc hydrocarbons In the ambient temperature range between 10 and 50 OC. The vapor pressures (In pascals f standard deviation) at 25 O C as determined by this method are as follows: naphthalene, 10.4 f 0.2; naphthalene-d,, 10.4 f 0.1; acenaphthylene, (8.9 f 0.2) X IO-’; acenaphthene, (2.9 f 0.9) X IO-’; fluorene, (8.0 f 0.2) X lo-’; phenanthrene, (1.61 f 0.04) X phenanthrene-d,,, (1.92 f. 0.05) X IO-’; anthracene, (8.0 f 0.2) X lo4; fluoranthene, pyrene, (6.0 f 0.2) X benz[a].. (1.23 f 0.07) X anthracene, (2.8 f 0.1) >C These values are generally In good agreement with values extrapolated from determlnatlons made at hlgher temperatures reported In the literature.
During the past decade increased concern has developed concerning the environmental impact of anthropogenic trace organic compounds. One factor which governs the transport of organic compounds, both in the workplace and in the general environment, is the volatility of these compounds. The vapor pressure of a compound will determine, in part, the rate of evaporation from indust,rial processes or waste sites, as well as the tendency for the compound to adsorb on particulate matter present in the environment. Vapor pressure data can be combined with aqueous solubility data to calculate Henry’s law constants, which can be used to predict the equilibrium of dissolved organics in water with their atmospheric concentrations (I). The determination of the vapor pressures of
organic compounds in the ambient temperature range (0-50 “C) is therefore important for the development of environmental transport models as well as for the assessment of possible health hazards present in the atmosphere. While many methods have been described in the literature for the measurement of vapor pressure (2),no single method is applicable for the entire vapor pressure range of environmentally significant compounds [ lo5 to lo4 Pa (-760 to mmHg)]. Literature methods usually involved a measurement of the mass loss or gain at temperatures well above the ambient range. The gas saturation method has been shown to be applicable for compounds having vapor pressures lower than lo2Pa (1 mmHg) and is generally used in the ambient temperature range. This method was first proposed in 1845 (3) but was not used extensively until the advent of modern chromatographic analytical techniques. The gas saturation method involves the production of a saturated vapor phase by passing an inert gas through a column packed with either the pure compound of interest or with an analyte-coated inert support. The analyte is collected from a known volume of the saturated vapor using impingers, sorbents, or cryogenic traps and the amount of analyte determined by some suitable method. In the late 1960s and early 1970s, Spencer and Cliath ( 4 , 5 ) used sand and/or soil with hexane impingers for the coated support materials and subsequent collection of several pesticides. They utilized gas chromatography (GC) for the quantification of the collected analyte. Pella (6) utilized Chromosorb G (60/80 mesh) coated columns to generate saturated vapors of several explosives, charcoal adsorption traps for collection, and GC to measure the collected analyte. More recently, Westcott et al. (7) developed a “micro-scale”procedure by coating polychlorinated biphenyls (PCB’s) on 3-mm spherical glass beads
Thls article not subJectto U S . Copyright. Publlshed 1983 by the American Chernlcal Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
I
BOETECTOR
MOLECULAR SIEVE & MAGNESIUM PERCHLORATE TRAPS
k"N%lOL VALVE
1
WASTE
GAS VOLUME METER
el ~
1
Figure 1. Schematic diagram of coupled column HPLC/vapor gen-
erator column assembly.
and collecting the vapor of the PCB's on Florisil traps. The collected material was desorbed and the amount present determined by GC. The U.S. Environmental Protection Agency (EPA) has recently proposed a standard method (8) for determining the vapor pressure of organic compounds by a gas saturation method. The method was developed at the Stanford Research Institute and involves passing an inert gas through a column packed with the pure analyte fitted between glass wool retainer plugs. The analyte vapors are trapped on activated sorbent (e.g., charcoal, Tenax) traps and desorbed with an appropriate solvent and the amount was determined by GC. During the past few years, we have developed a gas-saturation method utilizing high-performance liquid chromatography (HPLC) for analyte measurement. The HPLC is directly coupled to the vapor saturator (generator) column, thus avoiding the associated problems of subsampling and sorption/desorption efficiencies found in some of the earlier methods. Furthermore, the time for the determination is decreased, since smaller volumes are collected and the entire amount of analyte, not an aliquot, is ultimately measured. In this paper we describe the system and demonstrate its applicability to the determination of vapor pressures of polynuclear aromatic hydrocarbons (PAH).
EXPERIMENTAL SECTION The experimental system was composed of three sections: a generator column for the production of an analyte saturated vapor; an extraction trap for the collection and concentration of the analyte vapor; and a reversed-phase HPLC system for the measurement of the collected material. The generator column consisted of a tube filled either with the pure analyte or with an inert support material on which the analyte had been coated. The inert support materials used in this work were glass beads (60/80 mesh) or quintus quartz (60/80 mesh) which had been cleaned with a series of HPLC-grade solvents (CHzClz/CH3CN/Hz0/1% HF(aqueous)/HzO/ CH2CN/CH2ClZ)before coating with the analyte. The analyte (-80 mg) was then dissolved in dichloromethane, the mixture was added to the support material (-20 g), and the solvent was evaporated off with continual stirring to produce the coated support. The dry coated material was poured with constant tapping into a coiled stainless steel column (600 X 6 mm) fitted with 2- or 5-pm end frits. The column was purged with 500 cm3 of water at 50 "C followed by an inert gas (nitrogen) purge for 48 h. The tubing connecting the generator column to the valve assembly (Figure 1) was connected during these purging steps so that it became coated with the analyte and thus became an extension of the generator column. Two coating procedures are commonly employed to manufacture the generator columns. One technique involves packing the uncoated support material into the column, fiiing the column with a concentrated solution of the analyte in a volatile solvent, and evaporating the solvent (6, 7). The column is then conditioned for several hours or days by purging with an inert gas at elevated
temperature. The other technique, which was used in this work, is to coat the support material and then pack the column with the dry, coated material. This can result in the mechanical abrasion of the coated support. We recommend that the packed column be purged with water at an elevated temperature. This conditioning has two purposes: it allows for the repair of any damaged surfaces;and it permits the selective fractionation and removal of many trace impurities present in the starting materials. An example of this is observed in the determination of the vapor pressure of anthracene. Most commercial sources of anthracene (>98% purity) contain a trace amount of ita isomer, phenanthrene. Both the partial pressure and aqueous solubility are 20 times higher for phenanthrene than for anthracene (9). Although phenanthrene is present in only minor amounts (
