Anal. Chem. 1987,5 9 , 1494-1498
1494
(16) Spencer, C. F.; Adler. S. 8. J . Chem. Eng. Data 1978, 23,82-89. (17) Hayden, J. 0.;OConnell, J. P. Ind. Eng. Chem. Process Des. Dev. 1975, 74, 209-216. (18) ROth, M.; NOVHk, J. MaCfOmOleCUleS 1986, 79, 364-369.
RECEIVED for review June 23, 1986. Resubmitted March 5,
1987. Accepted March 5, 1987. This study was supported by the grants from the ~ ~ t ihience ~ ~ Foundation a l ( N ~cm . 82-00034) and the Office of Naval Research. Presented, in part, at the 191st National Meeting of the American Chemical Society, New York, April 13-18, 1986.
Continuous Aerodispersive Enrichment Unit for Trace Determination of Pollutants in Air Zbynek Ve5ei.a a n d Jaroslav J a n i k * Institute of Analytical Chemistry, Czechoslovak Academy of Sciences, Leninova 82, 611 42 Bmo, Czechoslovakia
A method and a device operatlng on the prhclpk of balanced accumulation of pollutants from a gas by means of a polydispersive aerosol of a liquid are descrlbed. The devke enables preconcentratlon of analytes of different chemlcal propertleshom Wfer quantities d the gas to microliter volumes of the Ilquld. Its dlmendons are such as to enable up to a 5 X I O 4 Increase of anatyte concentratlon In the llquld In comparlson wlth Its orlglnal concentratlon In the gas phase without lash8 affec4ed by the relathre hmkllty of the air. The device Is appllcah for conthwowr monitoring. The reoponse tlme Is dependent on the means of detection of the analyte In the conoentrate; Le. lt usually Is tens of seconds maximally, but the lower thne lknlt for response can be comparable to the rate of supplying the analyte to the enrlchment unlt. Repoduclbillty and rellablllty of the results were vermed for concentrations of phenol and o-cresol of I O a to I O d g, 2naphthol of IO-' g, and toluene of IO-' g In a llter of the alr In alr-water and alr-n-decane models. The results correspond wlth the theory very well.
Growing civilization and human interferences in the environment result in increasing pollution of the atmosphere by means of various pollutants of both organic and inorganic origin (1,2). As some of them are directly or i n p c t l y biologically active even in their trace concentrations, when their direct detection and quantification are often difficult, enrichment techniques have become an integral part of trace analysis of pollutants (3). Enrichment of traces of different substances from a gas medium is usually carried out either statically (extraction) or dynamically (chromatography) by means of sorption on solid materials, in suitable liquids, or by condensation of an analyte (4,5). A number of recent surveys (6) and approaches to this problem (7-12) prove that this is still the case. From the point of view of enrichment, the methods based on adsorption by solid materials are generally more efficient than those based on absorption in liquids, especially with respect to a higher value of the distribution constant of the analyte at a given temperature, a more favorable dimension of the interphase boundary, and a higher rate of adsorption than that of dissolution. However, the higher value of the distribution constant of the analyte a t adsorption allows the analyte to be released from the sorbent only with the use of thermal desorption or extraction by means of a suitable liquid. Then the enrichment process is discontinuous by nature and 0003-2700/87/0359-1494$01.50/0
the enrichment efficiency cannot easily be estimated. The general problem of preconcentration of analytes from the atmosphere seems to be a permanent and variable content of water vapor in air, which nearly always exceeds the amount of trace components by orders of magnitude and complicates the enrichment process. Therefore it is necessary to use special solid sorbents (6, 7,IO),adjustment of liquid absorbers (II), or special instrumentation (8, 12). An interesting method for enrichment of trace components from air in water was described by Dawson and Farmer (13, 14). The essence of this approach is the absorption of soluble gases in water vapor condensed from air on a cooled cuprous plate. The method is suitable for enrichment of highly soluble gases, the sorption being controlled by their rate of dissolution. The advantages of the adsorption process have been made use of together with the advantages of the use of a liquid medium in such a way that the analyte is accumulated by means of polydispersive aerosol of a liquid (15). This has been done with respect to the work of Freed (16) and Kat0 et al. (17). Freed determined organic substances liable to thermal decomposition in the air by means of their cocondensation with saturated vapors of n-pentane with an aim to reach their quick and quantitative absorption in an organic solvent. Kato et al. used the method of spraying a water solution of flavine mononucleotide and direct chemiluminescence to trace sulfur dioxide in the atmosphere. This work presents theoretical analysis and practical solution of the problem of preconcentration: a liquid is dispersed in a gas in such a way as to provide sufficient amounts of aerosol aggregateswith a surface enabling analyte adsorption to become the controlling process of distribution of the analyte between gas and liquid phases. Adsorption shows a substantially faster rate of reaching equilibrium than is enabled by dissolution. Under such circumstances it is also possible to use a water mist for considerable preconcentration of analytes of various chemical properties from the atmosphere (generally from gas media) with different and variable water vapor content. The enrichment unit can be miniaturized and is applicable for continuous monitoring of gaseous environments.
THEORY When a gas contaminated by the analyte i gets into contact with a liquid phase able to sorbe the analyte, the sorption reaches equilibrium at a certain definite rate. Its instantaneous value can, at usual ways of accumulation of pollutants from a gas into a liquid, be described (Dic/DiL= 104-105) by means of the following diffusively convective equation (18) 0 1987 Amerlcan Chemical Soclety
ANALYTICAL CHEMISTRY, VOL. 59, NO. 11, JUNE 1, 1987
1495
.
dCiL/dt = DiL div CiL - u grad C ~ L
(1) where CL is concentrationof the analyte in the liquid, t is time, u is a linear rate of the liquid medium close to the interphase boundary, and DiG and DiL are diffusion coefficients of the analyte in the gas phase and in the liquid. The amount of the analyte entering the absorption matrix (QjL) from the gas is expressed by the relationship
in which Sa is the area of the liquid3as interphase boundary. At currently used ways of accumulation of pollutants into the liquid, the area of the interphase boundary is small. As a consequence of that, the time necessary to reach the equilibrium gets longer. This is compensated by increasing the liquid volume and intensifying its contact with the gas containing the pollutants. The accompanying effect of the increased liquid-phase volume is a decrease of the enrichment degree and a consequent decrease of sensitivity of the analytical method. An essentially different situation occurs when the analyte is accumulated from the gas phase into a liquid phase that is dispersed in the gas phase in the form of an aerosol. It is presumed that the analyte of molecular weight Mi is sorbed from the volume of the gas phase VG into the volume of the liquid phase VL, which is dispersed uniformly in the gas phase in the form of microscopic droplets. In this case, the limiting factor for the rate of transfer of the analyte mass from the gas phase into the liquid phase through the interphase boundary is the diffusion of the analyte in the gas phase (19). As follows from the kinetic theory of gases, e.g. ref 20, this transfer of the mass can be described by the relationship ~i
=
TT(T~L%,,~*N~G*NL
(3)
in which qL= j Z (QL + ui) and u,,l = (uL2+ ut)1/2where uL and ui are mean moving rates of droplets of the liquid and molecules of the analyte, ui and uL are gasokinetic cross sections of the analyte and of aggregates of the sorption medium, and zi is the number of collisions between the molecules of the analyte in the gas (NiG)and the aggregates of the liquid (NL) per time unit. For the system in which a heavy particle (liquid aggregates) interacts with a light particle (molecules of the analyte), i.e. for ML >> Mi, ureI= ui, relationship (3) changes into zi = TuL~*u~*N~G'NL (4) In such a form it describes with a sufficient accuracy the limiting rate of mass transfer to the interphase boundary. The absorption of the analyte in the droplets of the aerosol, taking place at the same time, is characterized by the relationship given in eq 2. The distribution of the analyte mass in the gas-aerosol system can be characterized by the relationship
(5) QiGO = QiL + QiAL + QiG In this relationship, QiGO is the amount of the analyte in the volume VG of the gas phase prior to its contact with the aercsol of the sorbing medium, QiAL is the amount of the analyte adsorbed on the surface of aerosol aggregates, and QiG is the amount of the analyte in the gas phase after contact with the aerosol. It has been proved, in many cases (21-26),for milliliter and smaller amounts of the sorbing liquid matrix distributed in the gas phase in the form of aerosol with the aggregates in the order of magnitude of lo4 to m, that the amount of the analyte adsorbed on the surface of aerosol aggregates is comparable or higher than the amount of the analyte dissolved in them. As after quick contraction of the aerosol surface by coagulation the adsorbate is included into the volume of the
Flgure 1. Basic configuration of the enrichment unit.
sorbing liquid matrix, it is possible to neglect the effect of the effective rate of reaching the thermodynamic equilibrium on distribution of the analyte between the gas phase and the liquid phase existing in the form of aerosol. For the analyte in coagulate, it is possible to determine the mass balance of the enrichment process for the known distribution constant Ki = CiL/CiG and the known volumes of the liquid and gas phases (VL, VG). Then QiGO
=
QiL
(6)
QiG
+
(7) pi = P i L PiG where Pi is the s u m of probabilities that the analyte is in the system of gas phase-liquid matrix, Picis the probability that it is in the gas phase, and PiLis the probability that it is in the liquid phase. As Qz = f(Mi)PiLand QiG = f '(Mi)PiGand for the same analyte /(Mi) = f '(Mi), it is possible to rewrite eq 6 in the form QiL/QiGo
+ QiG/QiGo
=1
(8)
With respect to the fact that
Ki = c i L / c i G = QiL'VG/QiG'VL
(9)
it is possible, by combination of the relationships 8 and 9, to get probability mass distribution of the analyte between the liquid and gas phases as follows:
Recovery of the analyte equals the product of PiLX 100. The degree of concentration (D), defined as CiLjCiGO, where CiGo is the original concentration of the analyte in the gas phase, is expressed by the relationship
CiL = D-CiG"
(12a)
and the original amount of the analyte in the gas phase (QiG") can be expressed by the relationship QiGO = QiL/PiL (13) EXPERIMENTAL SECTION The enrichment unit (Figure 1) has been designed with the aims of minimizing the memory effect to get, as quickly as possible, the analytical response to the analyte and of making the enrichment process continuous (12). The unit is designed to be able to enrich the trace substance 50000 times in the liquid. It consists of a nebulizer (A) and a condensation part (B). The nebulizer consists of a stainless tube (1) screwed on in the front face (11)
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ANALYTICAL CHEMISTRY, VOL. 59, NO. 11, JUNE 1, 1987
Table 1. Evaluation of the Number of Interactions per Time between 10" Heavy Particles (Aggregates of Water Aerosol) and NiGMolecules of Phenol"
'p resistance
1
Deristaitic
t o iiquid
sampling valve
*vie
analyte concn, 10" gL-' of air
interactions/s
1017
1 1 x 10-3 1 x 104
1023
1014 10"
1020 10'7
nInterphase boundary area of 1.2 mZ;temperature of 293.15 K. Flgure 2. Schematic presentation of apparatus with the enrichment unit.
of the condensation part. In the tube, a special jet (2), (1-mm i.d.) is screwed on, into which a coaxially placed stainless capillary (3) leads, (0.8-mmo.d., 0.45-mm, i.d.). The capillary is connected to a reservoir of the absorption medium. The stainless tube (1) is provided with a suction inlet for the gas (5). The front face is inserted in a glass cylinder (4) whose inside surface was made hydrophobic by silanization. In the cylinder, a slanting barrier (6) is placed enabling continuous transport of the concentrate for analysis ( 7 ) . The excess condensate flows down to the bottom of the glass cylinder and is collected in its lowest part (8), from which it can be sucked out to the collector of excess concentrate (9). The glass cylinder is closed with a back face (10) with an opening (12) by which it is connected to a vacuum. Operation. The contaminated air is sucked into the enrichment unit at a volume rate of ca. 125m L d by the underpressure in the system of 32.8 kPa (250 mmHg) compared to the surrounding atmosphere. If the stainless capillary inside the jet is positioned well, the gas flows through it at linear rate of ca. 150 m.5-l. By means of an ejection effect of the streaming air, the sorption liquid is sucked into the gas and dispersed. A polydispersive liquid aerosol is formed and the gas-contaminating substancesare adsorbed on the surface of aggregates. The aerosol comes out of the jet in the form of a narrow beam into the condensation part of the enrichment unit and there, as a consequence of quasi-adiabatic expansion and collision with the slanting barrier, it coagulates on an area of ca. 1 cm2. Apparatus. A schematic diagram of the apparatus determined to verify the operation of the enrichment unit, is given in Figure 2. Phenol, o-cresol,and 2-naphthol,transferred from air to water, and toluene, transferred from air to n-decane, were used as model substances. Suitable concentrations of model substances were prepared by driving nitrogen through a thermostated glass saturator. The saturator was filled with solid phenol, o-cresol, and 2-naphthol, respectively. Toluene was applied on Chromosorb W. The nitrogen flow rate through the saturator was measured by a differential flowmeter and the temperature of the aerosol was measured by a resistance thermometer inserted at the place of aerosol condensation. The solution enriched by the analyte was transported to analysis by means of a peristaltic pump. Phenol was analyzed by the method of peak compression (27). The concentrate was sampled in the liquid chromatograph of a kit design (L-Chrom, Laboratory Equipment, Prague, Czechoslovakia) with a packed microcolumn (0.7-mmi.d. and 156 mm long) filled with Separon SI C 18 (particle size of 10 pm, the mobile phase of 1:l acetone-water, electrochemicaldetector EMD 10). In the case of enrichmentof toluene in n-decane,the concentrate amount of 1 pL was injected into a gas chromatograph (Chrom 5, Laboratory Equipment, Prague, Czechoslovakia) containing a 1-m-long and 0.8-cm4.d. column f i e d with Porapak PS (grain size of W100 mesh, temperature of 350 K, FID). RESULTS AND DISCUSSION The evaluation of the situation in the enrichment unit using relationship 4 for the analyte with a relative molecular weight of 94.1 (phenol), which is in the air in concentrations lo4 to g-L-', for V , = 7.5 L and VL = 4.18 X L of water dispersed into aerosol with aggregates of 2 X lo4 m, is given in Table I. For the diameter of water aggregates of 2 X m, the interphase boundary area equals 12 m2; the number of interactions for NIG= loll is lo1*;for N,G= it is on the order
Other values can be easily found by of magnitude of interpolation within the framework of the order of magnitude. From the practical point of view, distribution of water aggregates into particles of less than lo-' m has not been considered because no simple device is known that is able to produce a sufficient amount of a monodispersive aerosol with a smaller particle dimension or a polydispersive aerosol with a dispersive function showing a maximum in the area lower than lo-' m. From the dependence of the number of interactions between the analyte and water aggregates on time, it follows that for pollutants of both organic and inorganic origin with the relative molecular weight of up to ca. 500, the rate of mass transfer to the interphase boundary is sufficient to form, in the interval of 104-10-6 s, thermodynamic equilibrium between the amount of the analyte in the gas phase and the surface of the aerosol aggregates. This statement is also justifiable, in the case where the magnitude of the striking probability coefficient is considered to be 0.01; i.e., every hundredth molecule is adsorbed on the interphase boundary. With respect to the dimension of aerosol aggregates, their total surface area, and the diffusive coefficient of analyte in the liquid phase of ca. cm2+r1, the equilibrium between the analyte in gas and liquid phases is formed within the given interval of time. Under the circumstances, it is proper to describe the accumulation even in a nonstationary system, in which the contact of the liquid phase in the form of aerosol with the gas-containing pollutants is limited to 10-4-10-5 s, by means of eq 5-13 in which V G and VL are substituted for volume rates of the gas ( u ~and ) the liquid (uL). A graphic presentation of these conditions is given in Figures 3 and 4. Figure 3 illustrates recovery of the analyte from the gas to the liquid and Figure 4 the concentration degree of the analyte in the liquid phase a t a variable volume flow rate of the liquid through the enrichment unit for different values of the distribution constant. Figure 3 can be explained by the following example: An analyte with a distribution constant of lo6 is presumed. It is evident that recovery of the analyte by the liquid in the range uL = 1.66 /ILK' to uL = m, i.e. for the ratio of u G / u ~ = 5 X lo4to 0, increases in a linear way from the value of 0.952 to 1. With increasing value of the distribution constant, the form of the dependence changes. The dependences for K, less than lo4 are already clearly hyperbolic. Recovery of the analyte to the absorption matrix changes in the following ways: K , = 105,0.666; 104,0.166; 103,1.96 x 10-2; 102,i.gg x 10-3. Figure 4 shows the theoretical curves of the dependence of the degree of concentration of the analyte in the condensate on the amount of the sorbing matrix from UL = 1.66 p L d up to the moment when the volume rate of the liquid phase through the concentration unit is indefinitely high, i.e., for the ratio of uG/uL = 5 X lo4 up to 0. From the course of the dependence, it is evident that the degree of concentration (expressed on a logarithmic scale of axis of ordinates) is, in this method of enrichment, clearly dependent on the magnitude of the distribution constant. It means that the distribution constant is its limiting factor, especially at enrichment by substances with the distribution constants less than
ANALYTICAL CHEMISTRY, VOL. 59, NO. 11, JUNE 1, 1987
[164g/r1 1.7
. .
1.4
.
1497
0.8
0.6
1.1 .
08.
0.4
I
0
. 100
,
.
.
. , 500
.
.
.
.
.
ow
1
uL[p/mlnl
0.2
Figure 5. Effect of the lqubphase flow rate through the concentration unit on the concentration of phenol in the concentrate ( C E O = 2 X 10-7 g.L-1). 1
2
3
4
5
G ' /'
L' 10'
detection of pollutants in gaseous environment and also to choose the most suitable detection method. The experimental data (0) concerning the enrichment of phenol from the air (for concentration of lo4 gL-') to the water matrix, when changing volume rates through the concentration unit are within the range of 100-1100 NL-rnin-', are given in Figure 5. It is evident that within the range of 100-800 NLmmin-' of water the experimentally determined values of concentration of phenol correspond very well with the graphic diagram of relationship 12a. The increase of the flow rate of the liquid above 800 pL.min-' leads to an obvious decrease in the enrichment process efficiency. This is, most probably, due to imperfect distribution of aggregates of polydispersive aerosol in the extraction beam or to shifting of the maximum aerosol particles distribution to a value higher than lo4 m. The difference between theoretical and experimental concentrations of the analyte increases within the range of U L = 100-1100 NL-min-' nearly linearly with the increasing volume of the liquid, and for 1100 KLsmin-' of the sorption matrix, it is 10% of the theoretical value. The value of 800 NL-min-' is the upper limit for the volume flow rate of water through the enrichment unit at which it is still possible to describe quantitatively the enrichment of the concentrate of the analyte by relationships 10-13. The minimal volume flow rate of the absorption liquid through the enrichment unit is given by water volatility. The dependence of enrichment efficiency, for analytes with different physical and chemical properties, on their distribution constant for three different values of the ratio u G / u L (5 X lo3, lo4, and 5 X lo4) is illustrated in Figure 6. The experimentally determined values of enrichment efficiency for accumulation of organic substances are indicated. The magnitude of the distribution constants in the air-water system was calculated from the table of dissolubility (28),the tension of saturated vapors (29)for 293.15 K, supposing that neither in the gas nor in the liquid phases do any interactions appear among the molecules of the analyte. In the case of o-cresol, the distribution constant is 1.06 X lo4;for 2-naphthol it is 7 X lo5. The distribution constant of toluene in the system of air-n-decane was determined experimentally and its value is 3.7 X lo3 at 293.15 K. A very good correspondence of the experiment with the course of the function QiL/QiGo= f(K,) confirms that the enrichment unit has a wider application area, both from the point of view of analytes with different distribution constants and of sorption media with different surface tensions (water 72 dyn-cm-', n-decane 29 dymcm-l) and physical and chemical properties. The long-term stability of the enrichment unit has been tested by enriching water by 2-naphthol from the air in parts
D104E= 6
1o3
o
l1o1
3
1
4
2
ut/.
*
lo4
Figure 4. (jraphic presentationof the concentration w e e ( D )defined by relationship 12 OR the ratlo U ~ / U* (1)K ,= 10'; (2)K , = lo2; (3) K , = lo3;(4)K, = lo4;(5)K , = 10L;; (6) K , = 10'.
1O00, when the magnitude of the concentration degree within the range of u G / u L = (5-0.5) X lo4 comes close to the magnitude of the distribution constant. For u G / u L = 0.5 X lo4, if Ki = 1,D equals 0.999; for Ki = 10, D = 9.98; for Ki = 100, D is 98.0. When the distribution constant is 1000, the concentration of the analyte in the condensate increases 909 times in comparison to its original concentration in the gas phase. In the case of u G / u L = 5 X lo4 the degree of concentration at the above-mentioned distribution constants is expressed by the values of 0.999, 9.99, 99.8, and 980. With the increasing distribution constant the effect of the ratio u G / u L on the magnitude of the degree of concentration also increases, then D for uG/uL= 0.5 X lo4 is 3333, for the distribution constant lo4, 4761 for Ki = lo5. In the case of an analyte with a distribution constant of 1@,its concentration is increased in the liquid phase 9900 times. The increase of the ratio u G / u L to 5 X lo4 is accompanied by an increase in the degree of concentration to 8333,33 333, and 47 619. For the degree of concentration of the analyte, the ratio u G / u L becomes the limiting factor. From the mentioned data, it is now possible to evaluate the area of effective application of the aerodispersive unit for
1498
ANALYTICAL CHEMISTRY, VOL. 59,NO. 11, JUNE 1, 1987
t
O8
/samples
3
o,2 102 ~
1o3
1rJL
1o5
Ki
I
(il
0.25cA
lo6
Figure 6. Graphic presentation of the dependence of recovery ((Q,/Q,") on the distribution constant (K,): (1)u d u L= 5 X lo4;(2) uG/uL = 1 0'; ( 3 ) uG/uL = 5 X lo3. Enrichment efficiency for accumulation of organic substances: A, o-cresol (1 X g-L-'); 0, toluene (1 X 10" g-L-I); 0,2-naphthol (1 X g-L-').
per trillion by volume [ppt(v)] concentration. At the air temperature of 293.15-295.8 K, relative humidity of 42-45%, and at volume flow rates of the air and water through the enrichment unit of 7.5 L-min-l and 400 PL-min-', respectively, the enrichment efficiency was 91.5% of the theoretical value with a standard deviation of 9.3%. The linearity of the enrichment process has been traced at sorption of phenol vapors to the water matrix within the range of (1-40) X lo4 gL-'of air on September 24,26, and 28,1985. At the changes in relative humidity of the air within the range of 32-6170 and in the temperature of 290-295 K (uG = 7.5 L-min-l and uL = 500 PLernin-') the data seemed consistent; the correlation coefficient of the examined dependence was within 0.943-0.973. The enrichment unit has been used for determining SOz from air in parts per billion by volume concentration. Being evolved from the concentrate, the analyte is determined pneumatoamperically on a golden porous Teflon electrode (30). The detection limit is 0.3 ppb(v) of sulfur dioxide, and the linear range covers several orders of magnitude. Figure 7 illustrate a typical record on sulfur dioxide at 15,22,38,45, and 60 ppb(v), and a sample of air at a concentration of about 42 ppb(v) of SOZ. CONCLUSION The presented method works on the principle of adsorptive extraction of trace substances from a gaseous medium (air) by a suitable liquid medium in the form of a polydispersive aerosol having a sufficiently large contact surface. The method offers the following advantages: (1) It is suitable for enrichment of substances having great differences in vapor pressures and/or solubilities (e.g. SOzand 2-naphthol). (2) It is possible to predict exactly the efficiency of the enrichment process and to select suitable matrices for any given analyte. (3) The device is suitable for a further miniaturization, nearly down to a dimension limited only by the active condensation space, which needs to be only few cubic centimeters. The reaponse time of the analyte content can be reduced to few seconds starting from the entrance of the analyte into the enrichment unit. The device is fairly robust for field applications. (4) Since the enrichment process is continual, the device is very suitable for combination with different FIA techniques to reach further analytical goals.
-
I
-I
200 5
Flgure 7. Determinationof SO2 from the air: 1 = 15 ppb(v); 2 = 22 ppb(v); 3 = 38 ppb(v); 4 = 45 ppb(v); 5 = 60 ppb(v).
ACKNOWLEDGMENT We thank J. Vejrosta for his help in measuring the distribution constant of toluene. Registry No. C&OH, 108-95-2; C&,CH,, 108-88-3; 2HsCC~H~OH, 95-48-7; SOz, 7446-09-5; HzO, 7732-18-5; H3C(CH2)&H3, 124-18-5; 2-naphthol, 135-19-3. LITERATURE CITED (1) Rowland, F. S.J. Chromatogr. Libr. 1985, 32,461. (2) Walkee, J. C. G. Evolution of Atmosphere; MacMillan: New York, 1977. (3) Trace Organic Analysis: A New Frontier in Analytical Chemistty; Hertz, H. S., Chesler,
S. N.,
Eds.; National Bureau Standards: Wash-
ington, DC, 1979;Publlcatlon No. 519. (4) Janik, J. J. Chromtogr. Libr. 1983; 228,504. (5) Zlatkis, A.; Weisner, S.;Ghaoui, L.; Shanfield, H. J. Chromatogr.Libr. 1985, 32, 449. (6) NuHz, A. J.; GonzBles, L. B.; Janik, J. J. Chromatogr. 1984, 300,
127. (7) Ligocki, M. P.; Pankow, J. F. Anal. Chem. 1985, 57, 1138. (8)Bandy, A. R.; Tucker, B. J.; Maroulis, P. J. Anal. Chem. 1985, 57,
1310. (9) Goo,R. K. S.;Kansako, S.;Kanai, H.; Inouye, V. J. Chromatogr. Sci. 1985. 23,328. (10) Termonia, M.; Alaerts, 0. J. Chromatogr. 1985, 328,367. (11) Lucero, D. P. J. Chromatogr . Sci. 1985, 23, 293. (12) Sevcik, J. Am. Lab. (FairfleM, Conn.) 1985, 16(7),48. (13) Farmer, J. C.; Dawson, G. A. J. Geophys. Res., C : Oceans Atmos. 1982, 87(Cll),8931. (14) Dawson. G. A.; Farmer, J. C. J. Geophys. Res. D : Atmos. 1984, 89(D3), 4779. (15) VeEeFa, 2 . ; Janik, J.; VanEdiovi. J. Czechoslovak patent pending. (16) Freed, D. J. I n Trace Organic Analysis: A New Frontier in Anawical
Chemistty; Hertz, H. S., Chesler, S. N., Eds.; National Bureau of Standards: Washington, DC, 1979: Publication No. 519,p 95. (17) Kato, M.;Yamada, M.; Suzuki, S. Anal. Chem. 1984, 56, 2529. (18) Mka, V. Fundamentals of Chemical Engineering (in Czech); SNTL: Prague, Czechoslovakia, 1981. (19) Walcek, C. J.; Pruppacher, H. R. J. A t m s . Chem. 1984, 269. (20) Kauzman, Kinetic Theory of Gases; W. A. Benjamin: New York and Amsterdam, 1966. (21) Martin, R. L. Anal. Chem. 1981, 3 3 , 347. (22) Martin, R. L. Anal. C b m . 1963, 35, 116. (23) Martire, D. Anal. Chem. 1966, 38,244. (24) Pecsok, R. L.; Gump, B. H. J. fhys. Chem. 1987, 7 1 , 2202. (25) Pecsok, R. L.; De Yllana, A.; Aziz Abdul-Karim Anal. Chem. 1984.
36,452. (26) l&o, HsueMiaug; Martire, D. Anal. Chem. 1972, 4 4 , 498. (27) Skis, K.; Kouiilov6, D.; Krej8, M. J. Chromatogr. 1983, 282, 363. (28) The Coal Tar Data Book. 2nd ed.; The Coal Tar Research Assoc.: Leeds, England, 1965. (29) Dykyj, J.; Repig, M. Vapour Pressure of Organic Compounds (in Czech); Slov. Acad. Sci.: Bratislava, Czechoslovakia, 1979. (30) Opekar, F.; Vehia, Z.; JanBk. J. Inf. J. Environ. Anal. Chem. 1988, 27, 123.
RECE~VED for review July 22,1986. Accepted January 27,1987.
