Anel. Chem. 1991, 63, 1228-1232
1228
Collection of Nonpolar Organic Compounds from Ambient Air Using Polyurethane Foam-Granular Adsorbent Sandwich Cartridges Mark T. Zaranski,'$ Gregory W. Patton,'L Laura L. McConnell,' and Terry F. Bidleman*J~' Department of Chemistry, Marine Science Program, and Belle W . Baruch Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, South Carolina 29208 James D. Mulik Environmental Monitoring Systems Laboratory, U S . Environmental Protection Agency, Research Triangle Park, North Carolina 27711
Glass cartrldges contalnlng 8-10 g of Tenax-GC or 15 g of XAD-2 resin packed between two skes of polyurethane foam (PUF) were used In a General Metal Works PS1 highvolune sampler to collect chlorobenzenes (CeS) contalnlng three to SIX chlorlne atoms, hexachlorocyclohexanes (HCHs), and two-ring aromatic hydrocarbons from 35-385 ma of alr. Laboratory experlments were run by vaporizing known quantltles of analytes Into a clean alrstream for sampllng by the PS1 system at 20 O C . collectkn enlcknder, detetmlned from mass balance of the quantltles Introduced and recovered, ranged from 70 to 120% for lndlvldual compounds and averaged 93% overall. Penetratbn d analytes to backup adsorbent traps showed an Inverse correlation to vapor pressure. The method was used to collect the above compounds from urban and rural alr.
INTRODUCTION Polyurethane foam (PUF)is often used as a vapor-trapping medium for semivolatile organic compounds in high-volume air samplers operated at several hundred cubic meters per day. Some compounds for which PUF has found wide application are pesticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins and dibenzofurans, and phthalate esters. PUF has a low specific surface area (0.007-0.035 m2 g-l) compared to other adsorbents (e.g., 6.4-25 m2g-l for Tenax-GC and 300-360 m2 g-l for XAD-2) (I, 2), and its usefulness is limited to compounds having liquid-phase saturation vapor pressures ( p L o ) below about 0.1 Pa. More volatile species may show breakthrough losses during sampling. For example, retention volumes (Vd of hexachlorobenzene (HCB) and fluorene (pL0 = 0.08-0.3 Pa) an 8-g PUF plug (7.8 cm diameter X 7.5 cm thick) a t 20 "C are only 120-125 m3 (2, 3). Lewis and Jackson ( 4 ) found that collection of lower molecular weight PCBs was improved by using a "sandwich" cartridge in which a granular adsorbent such as Tenax-GC, XAD-2, or Florisil was contained between two P U F slices. These and traps filled with granular adsorbents alone have been used for sampling organochlorine (OC) pesticides and PCBs (5-8) and PAHs (9-11). This laboratory study was done to evaluate sandwich cartridges for some nonpolar compounds ]Department of Chemistry. *Present address: Dow Chemical U.S.A.,Michigan Division, Environmental Analysis Research Laborator Midland, MI 48667. Present address: Battelle Pacific Nortgkest Laboratories, P.O. Box 999, Rich!and, WA 99352. 'Marine Science Program. 0003-2700/91/0363-1228$02.50/0
that show poor-to-borderline collection with PUF alone: two-ring aromatic hydrocarbons (AHs) and several OC compounds (chlorobenzenes (CBs) containing three to six chlorine atoms, and hexachlorocyclohexanes (HCHs)). V , values of dichlorobenzene (DCB) vapors for PUF-Tenax cartridges under high-volume airflow were reported earlier (12).
EXPERIMENTAL SECTION Sampling Train and Test Procedures. The high-volume sampler was a PS-1 from General Metal Works (division of Andersen, Inc., Village of Cleves, OH). Descriptions of the unit, including diagrams of the airflow path and the filter-adsorbent cartridge module, have been given by Lewis and Jackson (4) and Fairless et al. (13). The apparatus in Figure 1 was built to introduce gaseous test compounds into a clean airstream for sampling by PUF-adsorbent cartridges in the PS-1 unit. Laboratory air was passed through a 20 X 25 cm glass fiber filter (Gelman A/E, binderless) to remove particles and then through a 77 mm diameter X 65 mm thick bed of activated carbon (6-14 mesh, Fisher ScientificCo.) to remove organic vapors. Test compounds in methanol or hexane (25-150 pL) were injected in a single pulse through a silicone rubber septum into a heated glass port, vaporized, and carried into a 12 X 15 X 100 cm stainless steel mixing chamber by passing precleaned air through the inlet. Air wm pulled through the apparatus at 0.1-0.3ms mi& with the PS-1 sampler, sweeping the vapors from the mixing chamber into the adsorbent trap. Flow rates were determined from readings of the Magnehelic gauge on the PS-1unit; the relationship between flow rate and gauge reading was established by using an orifice calibrator supplied with the sampler. Experiments were carried out in a room thermostated at 18-24 "C (mean = 20.7 f 1.1 "C). Adsorbent Traps. PUF was obtained from Olympic Producta Corp., Greensboro, NC (Product 3014, density 0.022 g cm4). Plugs were cut from 7.5 cm thick sheet stock with a 2.75 in. (70-mm) hole saw, cut into 3-cm slices with a band saw, and cleaned and dried as previously described (14). Tenax-GC (AlltechAssociates, 35/60 mesh) was extracted for 24 h in a Soxhlet apparatus with 15% diethyl ether-&% petroleum ether (EE-PE). XAD-2 (Mallinckrodt,20/50 mesh) was washed with tap water and then extracted in a Soxhlet apparatus with the following solvents in the order listed: distilled water, acetone, dichloromethane, EEPE. Solvents were chromatographic quality. Cleaned Tenax and XAD-2 were dried in a vacuum desiccator under water aspiration at 40 "C. Most collection experiments were carried out by using 5.8cm i.d. glass sleeves packed with one layer of Tenas or x A D 2 between two PUF slices (FTX and PXD cartridges, Figure 1). Two of these cartridges were placed in the aluminum canister of the PS-1 sampler, which had been fitted with a 10 X 6.8 cm i.d. screw-on extender section to accommodate the extra length. Seals between the two traps and between the glass and the aluminum canister were made with red silicone rubber gaskets. After sampling, the two intact traps were separately extracted with EE-PE in a large Soxhlet apparatus built by the USC Chemistry glass shop. Traps were dried in a vacuum desiccator under water aspiration at 40 @ 1991 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 63, NO. 13, JULY 1, 1991
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Table I. Test Compounds Used in Collection Experiments vapoP pressure, level 1 level 2 Pa mt, clg mt, clg
aromatic hydrocarbons naphthalene (NAP) 2-methylnaphthalene (2-MN) 2,6-dimethylnaphthalene (2,6-DMN) biphenyl (BIPH) chlorobenzenes and hexachlorocyclohexanes 1,2,4-trichlorobenzene (1,2,4-TCB) 1,2,4,5-tetrachlorobenzene
L
Fi~urr1. Samplng train for laboratory collection experiments. Lower part of mixing chamber connects to the expanded PS-1 cartridge chamber (circled) holding PTX or PXD cartridges.
“C. Between uses, clean traps were wrapped in solvent-rinsed aluminum foil and stored at room temperature in Mason jars with aluminum foil between the jar and lid. Traps used for laboratory experiments and field sampling were frozen until analyzed. Some tests were made by using a single glass sleeve packed as a double sandwich Two layers of granular adsorbent were separated by a PUF slice and contained between top and bottom PUF slices. These traps were disassembled after sampling. Granular adsorbents were transferred to precleaned cellulose thimbles; these and the PUF plugs were extracted with EE-PE in conventional Soxhlets. Test Compounds. Laboratory collection experiments were done with the following compounds (Table I): naphthalene (NAP), 2-methylnaphthalene (2-MN), 2,6-dimethylnaphthalene (2,6DMN), biphenyl (BIPH), 1,2,4-trichlorobenzene (1,2,4-TCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), pentachlorobenzene (PeCB), hexachlorobenzene (HCB), a- and y-hexachlorocyclohexanes (a-HCH, y-HCH). HCB and HCHs were supplied by the Environmental Protection Agency Pesticides and Industrial Chemicals Repository; other compounds were reagent grade and were purchased from chemical supply companies. Analytical Methods. Adsorbent trap extracts were concentrated by flash evaporation to 10-20 mL at room temperature, transferred to graduated centrifuge tubes, and blown down to 3-5 mL in the presence of hexane or isooctane with a stream of nitrogen that had been filtered through clean Tenax or activated carbon. Extracts of ambient-air samples were shaken with 0.1 M Na2COSto separate base-neutral and acidic compounds. The baseneutrals from the 1985 Columbia samples were fractionated on a column of alumina-silicic acid (15) to separate PCBs and n-alkanes from OC pesticides and PAHs; this step was omitted for the remaining samples. Extracts to be analyzed for CBs and HCHs were fmt shaken with 18 M sulfuric acid for cleanup. Traps from laboratory collection experiments yielded cleaner extracts because the air used was prefiltered through activated carbon.
(1,2,4,5-TeCB) pentachlorobenzene(PeCB) hexachlorobenzene (HCB) a-hexachlorocyclohexane (a-HCH) y-hexachlorocyclohexane (y-HCH) at 20 “C.
6.3
103-752 86-440 90-593
30 17 23
3.2
97-508
20
27
vapoP pressure, Pa level 1, ng 43
level 2, ng
1000-15000
6.9
900-1500
20-400
0.57 0.077 0.14
100-160 60-600
60-160
21-43 13-26 13-35
0.039
60-160
13-35
The Na2C03step was omitted and AHs were determined without cleanup. Analysis for CBs and HCHs was carried out after sulfuric acid treatment. CBs and HCHs were determined by capillary gas chromatography with @Nielectron capture detection (GC/ECD). AHs were determined by capillary GC with flame ionization detection (GC/FID) for the September, 1985, air sample and by mass for spectrometry (GC/MS) using selected-ion monitoring (SIM) the remaining air samples. Ions ( m / z )employed for the latter were as follows: NAP 127, 128; 2-MN 141, 142; 2,6-DMN 141, 156; BiPH 153,154; dibenzofuran (DBF) 139,168. AHs in laboratory experiments were determined by either GC/FID or GC/MS. Analyses were carried out on the following 25-30-m bonded-phase capillary columns,0.25-0.33-pm f i i thickness, 0.25 mm id.: methyl silicone (BP-1, SGE Corp.) or methyl silicone with 5% phenyl (HP-5, Hewlett-Packard Corp.). Instruments: Carlo Erba 4160 (FID and ECD), Varian 3700 (ECD), HewlettPackard 5890 with a 5970 mass-selective detector (GC/MS). Samples were injected splitless (Grob technique, 1-2.5rL volume, 30-s split time). Temperature program: injection at 70-90 OC, hold 1 min, 5-8 OC m i d ramp to 250 “C. Other GC conditions: carrier gas, He or H2at 20-40cm k ; injector, 220-240 OC; detector, 320 OC. Chromatographic data were processed with a HewlettPackard 3390 or Shimadzu CR3A integrator or, in the case of GC/MS, the HP-9133 data system. R E S U L T S AND DISCUSSION Analytical Recovery of Test Compounds and Cartridge Blank Values. Tenax in paper thimbles or intact PTX cartridges were spiked with the compounds of interest and immediately extracted to evaluate recoveries in the analytical procedure. Average yields were 100 f 23% for OCs (n = 6) and 89 f 5% for AHs (n = 3). Analytes found in collection experiments were corrected for “procedural” trap blank values, obtained by running the sampling train for 24 h with the cartridges in place, but with no injection of test compounds. These were higher than blanks for cartridges that had been cleaned, dried, and stored in sealed containers (“analytical” blanks) but for most target compounds were low relative to quantities that would be collected from urban air in 24 h (Table II). Higher procedural blanks may have been due to incomplete removal of organic contaminants from laboratory air by the prefilter or drying and cracking of the resins during sampling, which exposed uncleaned surfaces. High analytical and procedural blanks for 1,2,4-TCB (or an artifact with the same GC retention time) were obtained for both Tenax and XAD-2, which suggests that
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ANALYTICAL CHEMISTRY, VOL. 63, NO. 13, JULY 1, 1991
Table 11. Analytical and Procedural Blank Values for PUF-Adsorbent Cartridges PTX anal.
procedural
anal.
procedural
Amounta of Aromatic Hydrocarbons, pgb NAP 2-MN 2,6-DMN BIPH 1,2,4-TCB 1,2,4,5-TeCB PeCB HCB CY-HCH Y-HCH
1.6 f 1.6 (2) 0.55 & 0.50 (2) 0.20 f 0.22 (2) 0.27 f 0.27 (2)
0.40 f 0.55 (3) 0.13 f 0.18 (5) 0.02 f 0.009 (5) 0.02 f 0.008 (5) 71 f 132 (7) 5.8 f 5.9 (6) 0.5 f 0.3 (7) 0.4 f 0.2 (7) 0.4 f 0.2 (7) 0.7 f 0.6 (7)
quantity collcd" from 300 ma of urban air
PXD
Amounte of Organochlorines, n g 175 f 22 (2) 59 f 51 (4) 19 f 15 (2) 7.3 f 7.7 (4) 2.1 f 0.5 (2) 1.1 f 1.0 (4) 1.8 f 0.5 (2) 0.7 f 0.5 (4) 4.5 f 0.0 (2) 0.6 f 0.5 (4) 1.9 f 0.8 (2) 0.9 f 0.7 (4)
50-1300 30-200 6-40 3-8
129 f 89 (5) 9.1 f 6.4 (5) 1.7 f 2.0 (5) 1.7 f 0.9 (5) 2.9 f 1.9 (5) 1.3 f 1.1 (5)
600-1800 30-600 30-400 30-180 60-130 50-480
"Based on average Columbia air samples (Table VI) and refs 11, 15, and 16. bGC/MS analysis. 'GC/ECD analysis. Table 111. Collection of Nonpolar Organic Compounds on PTX Cartridges, Percent Recovery4 32-165 ma of airb level 1 level 2 NAP 2-MN 2,6-DMN BIPH
Table IV. Collection of Nonpolar Organic Compounds on PXD Cartridges, Percent Recovery4 232-372 ma of air level 2 level 1
285-385 m3 of aif level 1 level 2
Aromatic Hydrocarbons 121 f 38 (4) 107 f 23 (4) 87 f 14 (4) 88 f 14 (4) Organochlorines 1,2,4-TCB 119 f 21 (4) 1,2,4,5-TeCB 95 f 5 (4) PeCB 92 f 7 (4) HCB 92 f 9 (4) 90 f 14 (4) a-HCH Y-HCH 93 f I1 (4)
Aromatic Hydrocarbons 86 f 9 (4) 79 f 8 (3) 109 f 33 (5) 89 f 7 ( 5 ) 81 f 4 (3) 100 f 17 (5) 91 f 8 (5) 83 f 5 (3) 80 f 15 (5) 91 f 8 (5) 81 f 4 (3) 74 f 15 (5)
Organochlorines 1,2,4-TCB 106 f 8 (4) 112 f 17 (4) 108 f 20 (3) 1,2,4,592 f 9 (4) 90 f 12 (5) TeCB PeCB 110 f 32 (4) 95 f 20 (5) HCB 100 f 20 (4) 93 f 13 (3) 98 f 9 (4) 88 f 24 (5) a-HCH 117 f 38 (4) 73 f 21 (5) Y-HCH 95 f 13 (4) 85 f 27 (5) OAverage percent recovery of quantity injected f sd (n),based on sum of front and back traps. See Table I for abbreviations and levels. b10 g of Tenax in front trap, 3 g in back trap. (5-6 g of Tenax in front traD, 5-6 Iin back traD. in this case the problem was not related to the adsorbent. In the course of running procedural blank experiments, we noticed that back traps occasionally yielded blank values higher than front traps. This suggested that vapors were migrating against the airflow and contaminating the back trap. Two experimenta were run in which a spike of the OC pesticide heptachlor was placed down in the inlet tube to the air pump, behind the back cartridge, to serve as a tracer of air back-flow. After sampling, heptachlor amounting to a few tenths of a percent of the spike was found on the back trap. No heptachlor was detected on the front trap. These observations point to the possibility of cartridge contamination from pump air. To avoid this, we now place a small PUF plug in the recessed rear end of the sampling cartridge (Figure 1). The PUF plug is discarded before analysis. Laboratory-Determined Collection Efficiencies. The ability of PTX and PXD cartridges to collect organic vapors was evaluated from the mass balance of quantities injected into the mixing chamber and found on front and back traps. Quantities of OCs and AHs (Table I) were chosen to fall within the ranges that would be collected from urban air in 24 h (approximately 300 m3 of air, Table 11). For PTX, collection efficiencies were obtained at two air-volume ranges, 32-165 and 285-385 m3. The former experiments, using front and back traps containing 10 and 3 g of Tenax, respectively, also included 1,2- and 1,4-DCBs (12). The average recovery of these was 90 f 12% (n = 7). Average recoveries of other OCs and AHs (Table I) ranged from 79 to 112% (Table 111).
NAP 2-MN 2,6-DMN BIPH
107 f 22 (4) 102 f 46 (4) 86 f 34 (4) 70 f 27 (4) 70 f 28 (4)
a Average percent recovery of quantity injected f sd (n),based on sum of front and back traps. 15 g of XAD-2 in front trap, 15 g in back trap. See Table I for abbreviations and levels.
Table V. Summary of Collection Experiments at 232386 ma of Air
a
I.
adsorbent
adsorbate'
levelb
mean f sd
n
PTX PTX PTX PXD PXD PXD
ocs OCS AHs ocs
1
2
AHs
1
86 f 21 103 f 23 91 f 21 97 f 12 87 f 32 101 f 24
25 23 20 24 20 16
ocs
1 1
2
OCs = organochlorines,AHs = aromatic hydrocarbons. Table
Since VR values of the DCBs on the 10-g PTX cartridge were about 100-200 m3 (12), collection experiments in the higher air volume range were done with only the less volatile OCs and AHs in Table I. In these runs front and back traps each contained 5-6 g of Tenax or 15 g of XAD-2. Recoveries of individual compounds ranged from 70 to 121% (Tables I11 and IV), and pooled data for different compound classes and levels gave means of 86-103% (Table V). The overall mean recovery for all compounds was 93%. Differences in mean recoveries were significant 0,I 0.05) for PTX level 1OCs vs PTX level 2 OCs, PTX level 2 OCs vs PXD level 2 OCs, and PTX level 1 OCs vs PXD level 1 AHs (see Table I for levels).
Breakthrough of Test Compounds from Front to Back Traps. The PS-1 sampler is designed to hold a single glass sleeve, which makes breakthrough experiments with multiple traps difficult. In these experiments we attached an extender
ANALYTICAL CHEMISTRY, VOL. 63, NO. 13, JULY 1, l B B l
BREAKTHROUGH OF VAPORS FROM FRONT TO BACK CARTRIDGES
Table VI. Retention Behavior of Nonpolar Organic Compounds on Tenax-GC and Polyurethane Foam
1
Parameters for Ekq 1 Tenax-CC (17)' compd type m mixed nonpolar mixednonpolar mixed nonpolar
-1.44 -1.24 -1.14
b
PUF (2) compdtype m
4.36 3.55 3.81
PAHs OCs
VR,ms (6 g of Tenax-GCb) 1,2,4-TCB NAP 1,2,4,5-TeCB 2-MN BIPH PeCB HCB a-HCH Y-HCH
200-610 360-1190 1940-8500 2170-9700 5030-25700 4.2 X 1Oc3.1 X 1.9 X 106-1.8 X 4.6 X 106-4.9 X 1.6 x 1oe-2.0 x
106 l@ l@
107
1291
PTX
b
-1.195 -1.059
0.694 0.485
VR,ma (2.5 g of PUF) 0.14 0.24 1.0 1.4 3.1 14 50 105 300
NAP
MN
BIPH
DMN
TCB
TeCB
Flgure 2. Breakthrough (% B = 1000b/O,)of naphthalene (NAP), Pmethylnaphthalene (MN), biphenyl (BIPH), 2,gdhnethylnaphthalene (DMN), 1,2,4trichlorobenzene(TCB), and 1,2,4,5tetrachlorobenzme (TeCB) in laboratory trials with PTX and PXD cartridges.
OFrom three studies referenced in ref 17. bRange of V R estimated from above parameters. piece to lengthen the cartridge holder and allow tandem cartridges to be used. Percent breakthrough (% B) of two-ring AHs, 1,2,4TCB, and 1,2,4,5-TeCB beyond the front trap was calculated as 100(Qb/Qr),where Q, and Qfare quantities found on the back and front traps. Results for 230-385 m3 of air (Figure 2) showed greater breakthrough for the more volatile compounds. Specific retention volumes (V,, m3 g-*) for organic vapors on Tenax-GC and PUF have been reviewed and correlated to PL' by (2,17) log V, = m log pLo b (1)
+
Parameters of eq 1 at 20 O C are given in Table VI, where b has been adjusted to reflect the unit changes in V, from liters per gram (17)to cubic meters per gram and pLofrom Torr (2,17) to pascal. Table VI also gives the calculated VR for 6 g of Tenax-GC and 2.5 g of PUF, the latter being the mass of the top PUF plug in a P T X cartridge. The results show that, for all compounds in Table I except 7-HCH, the upper PUF plug contributes little to their retention. This is because V R on 2.5 g of PUF is greatly exceeded and nearly all the vapor-trapping ability is in the Tenax layer. The upper plug
participates to a greater extent in the collection of higher molecular weight compounds such as PCBs and three- to four-ring PAHs. The advantage of the k n d w i c h - (PUFsorbent-PUF) configuration is the ease of handling the granular sorbents in a cartridge suitable for high-volume sampling. The lower PUF plug keeps the particles from clogging the screen at the bottom of the glass sleeve and thus aids in maintaining flow rate. The use of front and back cartridges gave insights to recovery that would not have been obtained through mass balance runs with a single trap. Even though mass balances for NAP and 1,2,4-TCB were quantitative (Tables 111and rV), the % B was about 40% for P T X and 15-45% for PXD (Figure 2). Thus if only a single trap is used,it should contain at least 12 g of Tenax and 30 g of XAD-2 to quantitatively collect 1,2,4-TCB and NAP within this air-volume range at 20 o c . Ambient-Air Sampling. OCs and AHs were determined in Columbia, SC, and a t North Inlet Estuary, a rural site approximately 5 km from Georgetown, SC. Levels are compared to those reported from Hamburg, FRG (151, and Portland, OR (16, 17), in Table VII. In two of the Columbia experiments P T X cartridges containing 10 and 3 g of Tenax in the front and back traps were
Table VU. Semivolatile Organic Compounds in Ambient Air (ne md) 9/19 1985
Columbia, SC 9/29 12/12 1988 1985
11/22 1986
North Inlet Estuary, SC 11/23 10/22 1/27 1986 1988 1989
Hamburg,FRG 1986-87 (15)
adsorbent PTX PTX PXD PTX PTX PTX PTX V , m3 148 108 375 360 330 330 360 11 16 17 5 av temp, OC 24 19 24 1,P-DCB 10 24
