2222
Anal. Chem. 1983, 55,2222-2226
(8) Rubinson, Kenneth L.; Mark, Harry B., Jr. Anal. Chem. 1082, 54,
1204-1206. (9) Anderson, James L. Anal. Chem. 1970, 51,2312-2315. (10) Brewster, Jeffery D.; Anderson, James L. Anal. Chem. 1082, 54, 2560-2566. Slmone, Michael J.; Heineman, William R.; Kreishman, George P. Anal. Chem. 1982, 54,2382-2384. Porter, Marc D.;Kuwana, Theodore, submitted for publication in Anal. Chem . Sorlaga, Manuel P.; Hubbard, Arthur T. J. Am. Chem. SOC. 1082, 104,2735-2742. Soriaga, Manuel P.; Hubbard, Arthur T. J. Am. Chem. SOC. 1982, IO4 I 2742-2747. Soriaga, Manuel P.; Hubbard, Arthur T. J. Am. Chem. SOC. 1082. 104,3937-3945. Sorlaga, Manuel P.; Wilson, Peggy H.; Hubbard Arthur T.; Benton, Cllfford S. J. Electroanal. Chem. 1982, 142,317-336. Miller, Charles W.; Karwelk, Dale H.; Kuwana, Theodore Anal. Chem. 1081, 53, 2319-2323. Zak, Jerzy; Kuwana, Theodore J . Am. Chem. SOC. 1082, 104, 55 14-55 15. Hawkridge, Fred W.; Kuwana, Theodore Anal. Chem. 1073, 45, 1021-1027,
(20) Hubbard, Arthur T.; Anson, Fred C. I n "Electroanalytlcal Chemistry"; Bard, Allen J., Ed.; Marcel Dekker: New York, 1970; Voi. 4. (21) Hubbard Arthur T. CRC Crit. Rev. Anal. Chem. 1073, 3 ,201-242. (22) Bard, Allen J.; Faulkner, Larry R. "Electrochemical Methods: Fundumentals and Applications"; Wlley: New York, 1980; Chapter IO. (23) DeAngells, Thomas P.; Helneman, Wllllam R. J. Chem. €doc. 1076, 53,594-597. (24) Anderson, James L.; Kuwana, Theodore; Hartzell, Charles R. Biochemistry 1076, 15,3847-3855. (25) Rohrback, D. F.; Deutsch, E.; Helneman, W. R.; Pasternack, R. F. Inorg. Chem. 1077, 16,2650-2652. (26) Kolthoff, I. M.; Tomslek, W. J. J. Phys. Chem. 1035, 39,945-954.
RECEIVED for review July 22, 1983. Accepted September 12, 1983. The support of the National Science Foundation (Grant No. 8110013),The Air Force Office of Scientific Research, and The Ohio State University Materials Research Laboratory is appreciated* M*D.P.gratefully acknowledges the support of an OSU Presidential Fellowship.
Square-Wave HydrodynamicalIy Modulated Voltammetry for Study of Anodic Electrocatalysis Deborah S. Austin and Dennis C. Johnson* Ames Laboratory-U.S.D.O.E.
and Department of Chemistry, Iowa State University, Ames, Iowa 50011
Theodore G . Hines and Edward T. Berti Pine Instrument Company, Grove City, Pennsylvania 16127
A response, dependent solely upon the mass transport coupled component of the total current, Is obtained by alternating the rotational velocity of a rotating disk electrode about a nonzero mean value and cuinputlng the difference of the total currents obtained for the two velocities. Hence, relatively small transport-controlled currents can be observed wlthout interference from large, simultaneous, surface-controlled reactions, e.g., the formation of surface oxides and the evoiutlon of 0,. As a r e a , the useful anodic potentlal lhlt Is extended ca. 350 mV beyond the practical ilmlt for conventional voltammetry. An important application of the title technique Is for the study of the eiectrocataiysis of anodlc reactlons by surface oxldes at noble-metal electrodes. Results are shown for the oxidation of I- at a Pt electrode In 0.5 M H2S0,. I n addition to the transport-ilmlted production of I, In 0.5 mM I(E,,, N 0.48 V vs. SCE), the oxidatlon to IOs-Is observed to occur at a transport-limlted rate (E,,, N 1.45 V vs. SCE) simultaneously with 0, evolution.
The analytical utility of hydrodynamically modulated voltammetry based on application of sine-wave and squarewave modulations about a nonzero, average rotational velocity for rotating disk electrodes was examined by Miller, Bellavance, and Bruckenstein (1). Subsequently, Miller, Bruckenstein, and co-workers have focused their efforts on the sinusoidal version of hydrodynamically modulated voltammetry (SHMV) (2-7). Major emphasis by these workers has been placed upon the theoretical basis of the technique, the determination of heterogeneous kinetic parameters for quasi-reversible and irreversible systems, the determination of diffusion coefficients, and applications to trace analysis.
Blaedel and co-workers (8, 9) investigated the square-wave modulated technique which they referred to as "pulsed rotation voltammetry". They also emphasized the application to trace analysis, and the determination of reaction rate constants and transfer coefficients. In addition, they recognized the advantages of automating the square-wave technique through use of small computers (9). The theory and application of hydrodynamically modulated techniques have been reviewed extensively by Wang (10). Our interest in modulated voltammetry has been primarily in the application of computer-controlled, square-wave, hydrodynamically modulated voltammetry (QHMV) for the characterization of surfacecatalyzed anodic reactions at noble-metal electrodes. Numerous anodic reactions of proven or potential electrosynthetic importance in aqueous solutions occur at oxidecovered "inert" electrodes with simultaneous evolution of 02, and the electrocatalytic involvement of surface oxygen has been implicated. Yet, the voltammetric study of such processes is not convenient by conventional electroanalytical techniques, particularly when the faradaic current resulting from the reaction of interest is only a small component of the total current. Both SHMV and QHMV have been demonstrated to successfully extract the transport-limited faradaic signal from a total current dominated by the surface-controlled processes of double-layer charging and formation of surface oxides. The large extension of the positive potential limit for modulated voltammetry beyond the useful limit for conventional voltammetry has become an important advantage of the modulated techniques. Our choice of QHMV for the study of anodic electrocatalysis was based on the commercial availability and ease of operation of the computerized square-wave technique. Conway et al. have studied extensively the formation of surface oxides on Pt in acidic solutions (11-13). They con-
0 1983 American Chemical Soclety 0003-2700/83/0355-2222$01.50/0
ANALYTICAL CHEMISTRY, VOL. 55,
cluded that the initial step involves the production of adsorbed OH radicals by the reaction H20 OH + H+ + e- to form a “lower oxide” designated as “PtOH”. The initial PtOH produced with low surface coverage can be reduced by a nearly reversible cathodic process. This “reversible” PtOH has only a transient existence, however, and with time, as a result of local potential fields, adsorbed OH radicals and Pt atoms at the electrode surface undergo place-exchange to produce a more stable form of the lower oxide designated as “OHPt”. For E > 1.0 V vs. SCE in acidic media, a monolayer of adsorbed OH is formed rapidly with subsequent conversion by oxidation to the “higher oxide“, designated as “PtO”. It is speculated frequently that the adsorbed hydroxyl radical a t some noble-metal electrodes can participate catalytically in many anodic reactions, whereas the higher surface oxide inhibits those same reactions. For example, enhanced activity for the oxidation of methanol at Pt electrodes alloyed with Ru has been explained as the result of increased OH adsorption by the Ru (14). We interpret the electrocatalytic effect as resulting partly from the decrease in the energy barrier associated with the activation of the HZO molecules consumed in the anodic reactions. Furthermore, the electrode surface provides a reaction zone whereby the reactants, including H20, in their activated states can exist in close proximity for a significant period of time, thereby maximizing the probability of reaction. Hence, if the adsorption of the activated state of either reactant is blocked, electrocatalysis is no longer expected to occur. The electrochemical evolution of O2 at Pt anodes has been investigated by Damjanovic and Jovanovic (15)who proposed that the process involves the direct participation of oxygen atoms in the oxide film. The participation of the surface oxygen is supported by the work of Rosenthal and Veselovski (16),and Churchill and Hibbert ( I n , using a tracer technique. The Pt surface oxide was formed by anodic polarization in an Is0-enriched aqueous solution followed by the evolution of molecular oxygen from the enriched oxide surface in an unlabeled aqueous solution. The initial gas evolved was rich in the dimer ls0l6Oresulting in the progressive depletion of ls0from the surface oxide. The first step in the mechanism postulated by Damjanovic and Jovanovic for the evolution of O2 involves the generation of OH radicals on the PtO surface. When the O2 molecule leaves the surface of the electrode, the oxide must be re-formed which involves, presumably, hydroxyl radicals as an intermediate product. The apparent abundance of hydroxyl radicals present on the electrode surface during O2 evolution and the fact that catalysis is observed in the presence of the lower oxide (i.e,, PtOH) caused us to suspect that O2 evolution may exhibit an electrocatalytic effect on many anodic reactions. Confirming evidence for this conclusion is presented here for oxidation of I- to IO3- a t a Pt electrode in 0.5 M HzSO4. The last factor to be considered is the effect of adsorbed ions on the initial stage of oxide formation (18). As a result of competition between the ions and the hydroxyl radicals for sites on the electrode surface, the potential a t which oxide formation commences is shifted to more positive values. Adsorbed ions also facilitate place-exchange between Pt atoms and the hydroxyl radicals, thereby decreasing the number of OH species available on the surface for reaction. As mentioned previously, place exchange is also promoted at higher potential values. Therefore, the combination of these effects can contribute to the shortening of the potential range over which PtOH can exist for a significant time period. +
EXPERIMENTAL SECTION Materials. All solutions were prepared from reagent grade chemicals and triply distilled water. The supporting electrolyte was 0.5 M H2S04. Dissolved O2 was removed from all solutions
NO. 14, DECEMBER 1983
2223
by saturation with N2. The electrode surface was polished prior to each use with 0.05-km Buehler Alumina on microcloth and then thoroughly rinsed with triply distilled water. Instrumentation. Current-potential curves were obtained by cyclic voltammetry (I-E) and square-wave hydrodynamically modulated voltammetry (AGE) at a Pt rotating disk electrode (Model AFMD19,0.166 cm2;Pine Instrument Co., Grove City, PA). The rotator (Model MSR, Pine Instrument Co.) was a solid-state, servo-controlled system capable of rapid acceleration and deceleration. An external analog signal applied to the input jack on the speed control box made possible the application of the square-wave modulation as well as other wave forms. Potentiostatic control for application of cyclic and staircase potential wave forms was achieved by use of the K-1 circuit of Model RDE-3 (Pine Instrument Co). The faster potentiostatic response necessary for application of the triple-step wave form was achieved with a PAR-174A (EG&G Princeton Applied Research). A miniature saturated calomel electrode (SCE) filled with a saturated solution of KC1 served as the reference electrode. All potentials were measured and are reported in V vs. SCE. External signals for control of rotational velocity and potential were generated, and data were acquired, under computer control. The computer (Model 6800, Southwest Technical Products Corp.) was equipped with 32K-bytes of memory, four 12-bit digital/ analog (D/A) converters, and eight multiplexed 12-bit analog/ digital (A/D) converters. Peripheral devices included a Beehive International B-150 computer terminal, a Centronics microprinter P-1, and floppy-disk storage. Programming was done in BASIC. All raw data taken during experimentation were processed and plotted following completion of the experiment. All I-E and AI-E curves were recorded on a X-Y recorder (Model 7035B, Hewlett-Packard). The QHMV experiment, utilizing a staircase potential wave form, was performed according to the following sequence: (1) Experimental parameters were specified, including the cathodic (EJ and anodic (EJ limits for the potential scan, the potential-step the lower (W,)and upper (W,) rotation speeds, increment (AE), the time delay ( t d ) required after application of a change in rotation speed ( A w ) to allow current stabilization prior to the measurement of current, and the number of data points (N) t o be collected for each rotation speed. (2) The experiment was performed, the average of the N values of the current measured at W, and W, was calculated for each value of potential, and the was difference between the two average current values computed. (3) Finally, the data were plotted. The optimum values of rotation speed and delay time were determined from preliminary experiments by observing the time response of the rotating electrode and the electrode current with the aid of an oscilloscope. The acquisition time for each of the N values of current was 10 ms.
(en
RESULTS AND DISCUSSION Cyclic Voltammetry. Fundamental investigations of the electrochemical response of I- in acidic media at a Pt RDE have been described previously (19,20). The results of these studies will be briefly summarized to establish the basis for reporting the results of our work. To facilitate this discussion, an I-E curve obtained for 0.5 mM I- in 0.5 M H2S04is shown in Figure 1. During the positive scan of potential, I- is oxidized to 12 (Ell2 = 0.48 V) to yield an anodic wave (A) with a limiting current plateau in the region +0.55 V to +0.90 V. Peak B observed at E > 0.90 V is produced by the oxidation of I- to IO;. A significant part of the 103-produced has been concluded to originate from adsorbed I- with oxidation to IO, occurring simultaneously with the anodic formation of oxide on the electrode surface (19,20). A limiting current plateau is not attained for the oxidation of I- to IO3- in the region of peak B by cyclic voltammetry. Apparently, the production of IO; is inhibited by the rapid conversion of the lower oxide to the higher oxide in the potential region of peak B. At E > 1.3 V, the anodic decomposition of the solvent to produce 02 serves as a practical limit for the positive scan of potential. Two cathodic peaks are observed during the subsequent negative scan of potential. Peak C a t 0.45 V is the result of
I
I
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-
0
-;L
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,
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,
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I V vs S C E I
Figure 3. A I - € curve for 0.5 mM I- at the Pt RDE: AW = 4000-1000 rev min-I, A€ = 5.0 mV, t , = 150 ms, N = 10.
I
-0.2
E i V vs S C E )
Figure 1. I-€ curves for 0.5 mM I- at the Pt RDE in 0.5 M H,SO,: W = 1000 rev min-I; 4 = 6.0 V min-’. W
r-1
i
I 1
E
I
I il.4
* I .0
10.6
10.2
-0.2
E ( V v s SCE)
Flgure 2. Residual I-€ and AI-€ curves for the Pt RDE in 0.5 M H,S04: (---) ( I - € ) W = 1000 rev min-’, 4 = 6.0 V min-l; (-) ( A I - € ) AW = 4000-1000 rev min-I, A€ = 5.0 mV, t , = 150 ms, N = 10.
the reduction of the surface oxide formed during the positive scan for E > 1.0 V. The electrochemical reduction of Iz irreversibly adsorbed at the surface produces peak D at 0.0 V (19).
Current-potential curves were recorded as a function of the potential scan rate (4) for a constant value of rotation speed (W). The height of peak B varied in a nearly linear fashion with changes in 4, as expected for a surface-controlled process, whereas the faradaic signal corresponding to the oxidation of I- to Iz (A) was independent of 4, as expected for a transport-controlled process. The I-E curves obtained at a single value of 4, while varying W, demonstrated that the electrode current for both anodic reactions (A and B) increased as W was increased. Whereas the oxidation of I- to I2 (A) is mass transport limited (i.e., linear plot of Ilim vs. W12),peak B consists of currents resulting from the formation of surface oxide and the anodic production of IO, from adsorbed I- (i.e., surface controlled reactions), in addition to any transportcontrolled oxidation of I- from the bulk solution. To investigate further the transport-controlled process of 10,- formation, it is essential to observe only the convective component of the total current, as can be achieved by application of QHMV. The behavior of the current in the absence of an electroactive species was examined to establish the practical positive limit for potential scan (E,). The residual I-E and AI-E curves in 0.5 M H2S04are shown in Figure 2. For cyclic voltammetry, E, for Pt in 0.5 M H2S04is considered to be ca. 1.3 V for the current sensitivity shown for Figure 2. For QHMV, E, can be extended to ca. 1.65 V which is ca. 350 mV beyond the limit for cyclic voltammetry. For E > 1.65 V, the electrode current for O2evolution exceeds several milliamperes and the uncertainty in the computed difference ( A I ) of the two large signals renders the modulated technique unreliable. The electrochemical response of I- at the Pt electrode was characterized by QHMV with the result shown in Figure 3.
time Figure 4. Triple-step potential wave form. Arrows indicate point at which measurement of current commences, Le., 200 ms after application of E,.
-
The reaction I- 0.512 + e- occurs with the thermodynamically predicted value of Ellz = 0.48 V and the transportlimited current is observed in the region E = 0.55-0.90 V (A). The value of A I in Figure 3 (67 PA) corresponds closely to the theoretical value (69 PA) predicted from the linear Levich plot (I-W/2) constructed for this anodic process from data obtained by cyclic voltammetry. Peak B at ca. 1.05 V in Figure 3 corresponds to the oxidation of I- transported from the bulk solution to IO3-; the oxidation of adsorbed I- to IO3- does not contribute to A I in QHMV. The height of peak B is significantly less than that predicted for the transport-limited value for this reaction (i.e., 6 X 69 PA). The appearance of a peak signal for oxidation of I- to IO, can be explained on the basis of the catalytic properties of the surface oxide. Oxidation of I- to IO3- is thermodynamically allowed in this solution for E > 0.84 V. However, the reaction is not observed to occur until E > 1.0 V corresponding to the onset of the formation of surface oxide. It is concluded that oxidation of I- from the bulk, as well as adsorbed I-, to IO3- is initiated by the production of PtOH as the first step in the forhation of the surface oxide. Unfortunately the adsorbed I- suppresses onset of oxide formation (19), and the potential range is quite narrow over which the oxidation of I- to IO3- is thermodynamically allowed and in which PtOH exists in an appreciable quantity a t the electrode surface. Rearrangement of PtOH to the inactive OHPt and further oxidation to PtO occur rapidly for E > 1.2 V and production of 10,- is suppressed sharply. As the potential is increased beyond 1.3 V, A I increases to a limiting current plateau for E > 1.5 V (C). The ratio of A I values for the two limiting values of current for waves C and A (AIc/AIA)is 6.0, as expected on the basis of the assigned reactions. Upon reversal of the potential scan, the transport-limited production of IO3-proceeds as long as O2 is evolved. A t E C 1.3 V, only the oxidation of I- to I2 occurs
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
-
2225
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‘d 200
4
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- -300 100
200
300
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t2 (msec) -
++it++++
,--420
Flgure 6. Plots of AI vs. t , as a function of E, for 0.5 rnM I-at the Pt RDE: El= 0.00 V (250 ms), E , = variable, E, = 1.05 V (20 rns), AW = 4000-1000 rev min-’, N = 10.
1.20 V, the catalytic activity of the electrode surface, as measured by Al,decreases with increasing t,, approaching the limiting value for oxidation of I- to I2for t , > ca. 400 ms. For E2 2 1.30 V, hl corresponds approximately to the transport limited value for the oxidation of I- to I2 at all values of t,. In similar experiments, t3 was increased for E3 = 1.05 with Ez > 1.3 V for t z = 100 ms. The A I signal decreased for increasing t3, finally reaching the value for the transportlimited oxidation of I- to I* Furthermore, the rate of decrease of Al increased as the bulk concentration of I- was increased. We conclude that adsorbed hydroxyl radicals generated in the first step of the anodic generation of PtO are consumed in the reaction IIO3-. It is significant that whereas the production of IO; under these circumstances is an example of anodic electrocatalysis by the surface oxide, the reactive hydroxyl radical cannot be called a “catalyst” since it is consumed by the anodic reaction. Clearly, hydrodynamically modulated voltammetry has been demonstrated to be useful for study of anodic, electrocatalytic phenomena at solid electrodes because of the ability to extract the transport-coupled component of total electrode current exhibiting mixed surface/transport control. We anticipate highly significant applicability for the study of anodic electrosynthetic reactions which occur with simultaneous evolution of O2 from aqueous media.
-
Registry No. Iodide, 20461-54-5; iodine, 7553-56-2; IO;, 15454-31-6; PtOH, 32588-43-5; PtO, 12035-82-4;Pt, 7440-06-4; HzS04, 7664-93-9.
LITERATURE CITED Miller. B.; Beliavance, M. I.; Bruckensteln, S. Anal. Chem. 1972, 4 4 , 1983. Bruckenstein, S.; Beliavance, M. I.: Miller, B. J . Nectrochem. SOC. 1973, 120, 1351. Miller, 8.; Bruckensteln, S. J . Nectrochem. SOC. 1974, 727, 1558. Miller, E.; Bruckenstein, S. Anal. Chem. 1974, 46, 2026. Tokuda, K.; Bruckenstein, S.; Miller, B. J . Nectrochem. SOC. 1975, 122. 1316. Tokudai K.; Bruckensteln, S. J . Electrochem. SOC.1979, 126, 431. Kanzaki, Y.; Bruckenstein, S. J . Nectrochem. SOC.1979, 726. 437. Blaedel, W. J.; Engstrom, R. C. Anal. Chem. 1976, 50, 476. Engstrom, R. C.; Blaedel, W. J. J . Chem. Elomed. Environ. Instrum. 1979, 9. 61. Wang, J. Talanta 1981, 28, 369. Angerstein-Kozlowska, H.; Conway, B. E.; Sharp, W. B. A. J . Nectroanal. Chem. 1973, 4 3 , 9, Conway, B. E., Gottesfeld, S. J . Chem. Soc., Faraday Trans. I 1973, 69, 1090. Tilak, E. V.; Conway, E. E.; Angerstein-Kozlowska, H. J . Electroanal. Chem. 1973, 48, 1. Watanabe, M.; Motoo, S. J . Electroanal. Chem. 1975, 60, 267. Damjanovlc, A.; Jovanovic, B. J . Nectrochem. SOC. 1976, 123, 374. Rosenthal, N. I.; Veselovsky, V. I. Dokl. Akad. Nauk SSSR 1956, 1 1 7 , 637. Churchill, C. R.; Hibbert, D. 8. J . Chem. Soc., Faraday Trans. I 1982, 78, 2937. Angerstein-Kozlowska, H.; Conway, 6. E.; Barnett, B.; Mozota, J. J . Nectroanal. Chem. 1979, 100, 417.
2226
Anal. Chem. 1983, 55. 2226-2228
(19) Johnson, D.C.J . Electrochem. SOC. 1972, 119, 331. (20) Hubbard, A. T.; Osteryoung, R. A.; Anson, F. C. Anal. Chem. 1966, 38,692.
RECEIVED for review July 1, 1983. Accepted September 12,
1983. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. This work was supported by the Office of .. Basic Energy Sciences.
Membrane Filters as Adsorbents for Polynuclear Aromatic Hydrocarbons during High-Volume Sampling of Air Particulate Matter Torsten Spitzer*' Environmental, Industrial and Food Analysis, Leipziger Strasse 68, 3330 Helmstedt, German Federal Republic
Walter Dannecker Institut fur Anorganische Chemie, Martin-Luther-King-Platz6,2000 Hamburg 13, German Federal Republic
Urban air particulate matter is sampled by the high-volume method wlth glass fiber filters and membrane filters. Polynuclear aromatic hydrocarbons are then determined by cleanup on XAD-2 and glass caplllary gas chromatography. It Is found that membrane fllters retain polynuclear aromatlc hydrocarbons wlth three and four fused benzene rings more efficiently than glass fiber filters. The rapid blow-off of phenanthrene and pyrene from glass flber fllters is demonstrated. Membrane filters can also adsorb vaporized PNA.
The monitoring of polynuclear aromatic hydrocarbons in air is of considerable importance due to the carcinogenic properties of this class of compounds. In the past, glass fiber filters have been the material of choice for both high-volume and low-volume sampling (I, 2). High-volume sampling with glass fiber filters cannot avoid losses of polynuclear aromatic hydrocarbons with three or four fused rings, which can be quite substantial (3). This deficiency of glass fiber filters was recognized some time ago, and the decomposition of benzo[alpyrene on the filter was also observed (4-6). Membrane filters are thought to be less suitable for sampling of polynuclear aromatic hydrocarbons due to their higher content of soluble organic material, which is coextracted with polynuclear aromatic hydrocarbons during analysis. If polynuclear aromatic hydrocarbons are isolated by cleanup on XAD-2 (7) after sampling and analyzed by glass capillary gas chromatography, no interference from the m,embrane fiiter can be observed. In this work both membrane filters and glass fiber filters are employed in the sampling of polynuclear aromatic hydrocarbons from the air, and their collection efficiencies are compared.
EXPERIMENTAL SECTION Cellulose acetate membrane filters with 260 mm diameter and a pore size of 1.2 pm were used (type ST 69, Schleicher + Schull, Dassel, GFR). These were dried at 120 "C immediately before use, which reduced their diameter to 257 mm. Glass fiber filters (257 mm diameter, type 6, Schleicher + Schull) quantitatively retained all airborne dust, since no particulate matter could be Present address: Nagoya Daigaku Ryugakusei Kaikan, 2-23 Tosei-cho, Showa-ku, Nagoya 466, Japan.
detected on a back-up membrane filter (type ST 69,l.z ,.tmpore size). Another type of glass fiber fiiter (type 8, Schleicher + Schull, Dassel, GFR) retained 97-98% of the airborne dust under the selected sampling conditions,while 2-3% of the total particulate matter was found on a backup membrane filter (type ST 69,1.2 bm pore size). Glass fiber filters used in this work had collection efficiencies of 99% (type 8) or 99.97% (type 6) for oil aerosol with a particle size of less than 1.0 pm (8). Air flow rates were adjusted to 50 m3/h with high-volume samplers (HVS-1, Stroehlein instruments, Dusseldorf, GFR). Two filter heads were mounted on frames 1.5 m above the ground and placed 80 cm apart. Particulate matter was collected simultaneously by using a membrane filter on one sampling head and a glass fiber filter on the other. Mean sampling temperatures were 8-15 "C. The sampling site was situated in an urban area. Main roads carrying heavy traffic, residential areas, and a coal-fired power station were located within a radius of 1km from the sampling site. Loaded filters were dried over silica gel (5 h) and extracted with toluene (Soxhlet, 4 h) after weighing. Polynuclear aromatic hydrocarbons were isolated by cleanup on XAD-2 (7) and determined by gas chromatography with capillary columns and splitless injection. The columns employed were drawn from Duran 50 borosilicate glass. They were leached at 180 "C with 20% HC1 for 8 h and rinsed successivelywith one column volume of water and methanol immediately afterward. They were dried under a stream of nitrogen at 250 "C and deactivated by high-temperature silylation with diphenyltetramethyldisilazane (9). They were then coated statically (IO)with Dexsil3OO,OV-l, and SE-54 stationary phases. The instruments used were Carlo Erba 2400 and 2150 capillary gas chromatographs. Hydrogen was employed as the carrier gas. The detector system was an FID.
RESULTS AND DISCUSSION Simultaneous air sampling with a glass fiber filter followed by a membrane filter and with just a membrane filter was carried out for 30 h and 72 h in a series of experiments. Total particulate matter on the glass fiber filters and membrane filters differed by only 5% at maximum. Polynuclear aromatic hydrocarbons with three or four fused rings were found in much larger amounts on the membrane filters than on the glass fiber fiiters. Table I lists results typical of those obtained by high-volume air sampling for 72 h. The smaller amount of benzo[a]pyrene found on the glass fiber filter is not due to its volatility but may be a result of decomposition during sampling. Membrane filters succeeding glass fiber fiiters contained substantial amounts of polynuclear aromatic hydrocarbons from phenanthrene to chrysene,
0003-2700/83/0355-2226$01.50/00 1983 American Chemical Society
