Literature Cited (1) Leighton, P. A., “Photochemistry of Air Pollution,” p 2, Academic Press, New York, N.Y., 1961. (2) Altshuller, A. P., Bufalini, J . J., Photochem. Photobiol., 4, 97 (1965). (3) Wiebe, H. A,, Villa, A,, Hellman, T . M., Heicklen, J., J . A m . Chem. Soc., 95,7 (1973). (4) Tuesday, C. S., in “Chemical Reactions in Lower and Upper Atmospheres,” R. D. Cadle, Ed., p 15, Interscience, New York, N.Y., 1961. (5) Stedman, D. H., Niki, H., Enuiron. Sci. Technol., 7, 735 (1973). (6) Gray, J. A., Style, D. W. G., Trans. Faraday Soc., 48, 1137 (1952). ( 7 ) Hanst, P. L., Calvert, J. G., J. Phys. Chern., 63,2071 (1959). (8) Gay, B. W., Jr., Bufalini, J . J., Enuiron. Sci. Technol., 5, 422 (1971). (9) Gray, D., Lissi, E., Heicklen, J., J . Phys. Chem., 76, 1919 (1972).
(10) McGraw, G. E., Johnston, H. S., Int. J . Chem. Kinet., 1, 89 (1969). (11) Heicklen, J., Ado. Chem. Ser., No. 76, “Oxidation of Organic Compounds-11,” 23 (1968). (12) Arden, E. A., Phillips, L., Shaw, R., J . Chem. Soc., 1964, p 5126. (13) Wiebe, H. A., Heicklen, J., J . A m . Chem. SOC.,95, l(1973). (14) Morris, E. D., Jr., Niki, H., J . Chem. Phys., 55, 1991 (1971). (15) Westenberg, A. A., deHass, N., ibid., 57,5375 (1972). (16) Sato, S., Cvetanovic, R. J., Can. J . Chem., 37,953 (1959). (17) Glasson, W. A,, Tuesday, C. S., presented a t the Division of Water, Air, and Waste Chem., 149th Meeting, ACS, Detroit, Mich., 1965. (18) Morris, E. D., Jr., Niki, H., J . Phys. Chern., 75,3640 (1971). (19) Lundgren, D. A , , J . Air Pollut. Control Assoc., 20,603 (1970). Received for review April 19, 1974. Accepted April 14, 1975. Presented at the American Chemical Society Los Angeles Meeting, California, April I , 1974.
Gas Chromatographic Method for Concentration and Analysis of Traces of Industrial Organic Pollutants in Environmental Air and Stacks James S. Parsons,* and Stanley Mitzner Chemical Research Division, American Cyanamid Co., Bound Brook, N.J. 08805
A simplified quantitative method is described for collection of air pollutants on a porous polymer (Tenax GC) trap, for heat desorption onto a column and for analysis by gas chromatography. The method has been applied to a number of volatile industrial substances from stacks and ambient air such as aromatics, alcohols, ketones, acids, nitro, chloro, amino, and sulfur compounds. Low-molecularweight compounds were not included. ~
Methods for organic volatiles in air have been reported (1-4). However, faster and simpler methods are needed for
both sampling and analysis of industrial organic pollutants. Scrubbing in a series of liquid absorbers like the EPA method for particulates ( 5 ) involves bulky equipment, long sample lines, high flow rates, and finally analysis of a number of liquids containing the pollutants. Smaller sample size scrubbers (30-ml size) require slower flow rates and longer sampling times, and the absorbing solvent may present problems if the analysis is done by gas chromatography. Recently Bertsh et al. ( I ) described an excellent trapping technique that involves adsorbing pollutants in a tube containing a porous polymer, heat desorbing the pollutants onto a low-volume subambient cold trap, and volatilizing the sample onto a capillary column for gas chromatographic analysis. Mieure and Dietrich (2) also reported on the use of porous polymers for collection of trace organics in air and water for subsequent gas chromatographic analysis. Dravnieks et al. ( 4 ) described a porous polymer trap for high-speed collection of organic vapors from the atmosphere. In all these methods the technique for transferring the sample to the column needed to be simplified as well as establish rigorous calibration procedures for quantitative analysis.
The method described in the present paper has been used for several years and involves adsorption on a porous polymer (Tenax) trap and heat desorption (by way of a gas sampling valve) directly onto a conventional packed column for analysis by program temperature gas chromatography. The method is simple, fast, convenient in the procedural aspects and involves relatively inexpensive accessory equipment for adapting to any chromatograph. The method is particularly suited for surveying concentration profiles on stacks.
Experimental Preparation of Traps. Traps were prepared from lk-in. Pyrex glass tubing (medium wall 3/s4 in.) cut into 4I/4-in. lengths and fire polished a t both ends. A glass wool plug is inserted into the tube approximately 6 cm from the inlet end and about 0.1 g of Tenax (available from Applied Science Laboratories, Inc., PO Box 440, State College, Pa. 16801), 35iS~ mesh is added such that it occupies about 1% in. of space in the ‘/4-in. glass tubing. The tubing is tapped gently to compact the Tenax and then a glass wool plug is inserted a t the other end to hold the Tenax in place. It is useful to reinforce the traps by placing approximately 0.5in. lengths of melting point capillary tubing on the inlet side of the trap with an additional glass wool plug. A slightly modified versi.m of this trap is used for liquid samples; the 1.5-in. section of the Tenax is placed in the center of the tube so that the needle of a 1O-bl. syringe can reach the surface of the Tenax. After being assembled, the traps are conditioned by heating at 230’C for 15 min while purging with nitrogen. To condition more than one trap a t a time, a manifold can be assembled so that six or more traps can be conditioned simultaneously. After cooling with nitrogen flow, the traps are capped with polyethylene end caps (1/4 in., Regis Chemical Co.). Volume 9, Number 12, November 1975
1053
For ambient air work and for certain substances, such as methanol and ethanol, large size traps are necessary. These are prepared by cutting the ends off a 5-ml Pyrex pipet, leaving about 1.5 cm of tubing on each end of the bulb or total length of 4l/4 in. After fire polishing, a glass wool plug is inserted, and the bulb filled with approximately 6 g of Tenax, and then another glass wool plug is inserted to seal both ends. This trap is conditioned in the same manner as the traps described previously. Sampling Procedure. Samples are collected in the traps by use of either a portable pump or a syringe. The portable pump has been that from Mine Safety Appliance Co., Pittsburgh, Pa., part No. 92813. The equipment is set up such that a rotameter (Gilmont) is placed between the trap and the pump. The flow rate is approximated without the trap in place (the flow will change after the trap is in place because of a change in resistance). Teflon tubing is used for all connections when possible. If some degree of flexibility is required, silicone tubing can be used; however, the Teflon is preferred. The stack is sampled by inserting the trap into the stack, and starting the pump. The time of sampling is noted so that knowing the flow rate and the time, the volume of sample taken can be calculated. When small samples (10 ml or less) are to be taken, a syringe is used. The size of the syringe used will depend on the size of the sample to be taken so that a 1.0-ml syringe may be required. When a syringe is used, the trap is connected to the syringe with Teflon and/or silicon rubber tubing. During sampling, the trap is inserted into the stack, the syringe pulled back until the desired volume is taken, and then the trap is removed from the stack to outside air and the syringe continued to be pulled out so that the sample in the open space of the trap, but not adsorbed on the Tenax, is then drawn through the Tenax. If a 1-ml syringe is needed, a larger syringe is very quickly substituted for this after the sample is taken; it is used to pull a few ml of outside air through the syringe to adsorb any of the sample that is trapped in the dead space of the trap. Inlet. A simple inlet was used for introducing samples collected on Tenax glass tubes (lh in. 0.d. by 4% in. and 5-ml pipet bulb) into the chromatograph column. The Varian-Aerograph-heated six-port gas sampling valve (57000036-00) was satisfactory for most work. The sample tube was connected in place of the “U” shaped sample loop as shown in Figure 1. A Teflon &l/s-in. reducing union (Swagelok) was used on the outlet side next to the column and a brass %-l/~in. reducing union (Swagelok) on the inlet flow direction. Brass nuts (l/4 in.) with a back ferrule (backward) and three red “0”rings ( H - P 5080-4982) are used to seal the glass sample tubes. With the 5-ml pipet trap, the diameter of the brass nut should be drilled slightly larger and a Teflon back ferrule used. Copper tubing is employed from the valve to the glass tube bottom brass fitting. A Teflon lk-in. line is used to the column which may be heated with a heating tape (100°C) or passed through the injection port (maintained a t 100°C) with a Teflon tube inside the Ih-in. copper tubing to keep the tubing warm. For low levels of pollutants where stainless steel contact in the valve may cause adsorption losses for certain sulfur compounds, a Chromatronix rotary gas sampling valve (R6031SV) was used that has Teflon or Kel-F contact parts. Chromatographs. The sampling valve trap inlet has been used on the H - P 810, Perkin-Elmer 900, Beckman GC-4, and Tracor MT-150 chromatographs. The Tracor MT-150 was used exclusively for air pollution studies. The Tracor has dual flame ionization, electron capture, and flame photometric detectors. The other chromatographs are used with flame ionization detectors. A nitrogen detector was constructed on one flame jet of the Tracor chroma1054
Environmental Science & Technology
tograph using the homemade rubidium sulfate potassium bromide pellet according to the method of Craven (6).The Perkin-Elmer 900 was connected a t the exit of the column by the splitter valve to the Hatachi RMU-6-E mass spectrometer using a Watson-Biemann all-glass helium separator. Carrier gas flows were 80-100 ml/min. Inlet heaters were 100°C; flame ionization detector was 220OC; electron capture was 190OC; flame photometric detector was 12OOC. Hydrogen and air fuel was according to the manufacturer’s operating manual’s recommendations. Columns. Several columns useful in the present work are described: A. Polyphenylether (five-ring) with phosphoric acid on Chromosorb T was prepared by Supelco, Inc., using a solution coating technique. A 6-ft length of 0.085-in. i.d. FEP Teflon tubing was filled with 40/60 mesh dry Chromosorb T and coated by pressure’s forcing 100 ml of solution containing 12 g of five-ring polyphenylether (OS-124) and 0.85 g of phosphoric acid dissolved in acetone through the column, and finally passing nitrogen until the acetone is removed. The column was finally conditioned overnight a t 150°C with carrier gas flow. B. Polyphenylether (five-ring) with Amine 220 on Chromosorb T was prepared similar to Column A except 0.5 g of Amine 220 was used in place of the phosphoric acid. C. Chromosorb 101 50/60 mesh was packed into 2 ft of ys-in. F E P Teflon tubing. The Chromosorb 101 packing had been conditioned in a separate stainless steel column for several days a t 225°C with helium carrier gas. The Teflon packed column was conditioned overnight at 150” with carrier gas. D. A 10% high-vacuum silicone grease on Fluoropak 80 support was packed into a 3-ft length of %-in. 0.d. F E P Teflon tubing and conditioned overnight a t 150°C. E. 3% OV-225 on 100/120 mesh Gas Chrom Q was packed in a 2-ft length of 2 mm i.d. Pyrex glass column and conditioned a t 150°C overnight with carrier gas. This column was installed for on-column injection of liquid samples. The Teflon columns although lacking in theoretical plates were used to reduce adsorptive losses; also, their flexibility was a convenience for having several columns available in the oven with carrier gas flow for making quick hand-tightened connections to the various detectors as needed. Since no more than several components were present in a given stack, high-resolution columns were not required. Heated Air Bath. A heated air bath for volatilizing pollutants from a “U” trap was constructed as follows: a metal beverage can (6 X 10 cm) was first wrapped with asbestos tape for insulation and then with 4 ft of glass-coated heating tape (Briskeat, B l/2 in. X 4 ft, 115 V, 192 W). The can was placed in a 10 X 10 X 14 cm high box made of 1 in. thick aluminized fiber glass insulation. An opening (6 X 3 cm) in the top was provided for accommodating the “U” trap. A laboratory Variac set a t 50 V furnished the heat, giving a temperature of approximately 200-250°C to the heated air bath. Chromatographic Procedure. The trap sample tube is connected to the inlet valve as shown in Figure 1 with the direction of carrier gas flow to the column opposite the sample flow direction (back flush). With the column a t room temperature, the sample is injected and the heated air bath is immediately raised to immerse the trap. A large strip of glass wool is wrapped around the Teflon fittings and opening of the heated air bath. After 4 min from injection, the oven lid is closed, the temperature raised to 50°C and after another minute (5 min from the start) the oven temperature is programmed a t 10°/min to 150°C. The heated air bath is removed after 6-8 min. Calibration. Calibration has been accomplished by use
CARRIER
.
h,
G-
HEAT JACKETED
-TEFLON LINE TO COLUMN
F E -
t D -
- 6
c -
Figure 1. Sample
inlet
A, heated valve block. 6, copper tube, ‘I8in. 0.d. C, brass reducing union, in. F, Teflon nut, ’18 1/8-’h in. D, sample trap. E, Teflon reducing union, in., and tube, ‘1, in. G, valve plunger (in inject). H, plugs
of diffusion tubes, permeation tubes or by placing a solution of the component directly on a trap. When commercially available the permeation tube is used for calibration. However, there are a number of substances for which permeation tubes are not available and, in such cases, a diffusion tube is used. A diffusion tube can be prepared from an ordinary soft glass melting point tube (15 cm X 1.2 mm i.d.). The liquid for which the calibration is being studied is placed into the melting point tube by means of a syringe fitted with a 15-cm, 24-ga needle. The height of the liquid in the capillary is such that a diffusion path of a t least 10 cm is used. The wall of the capillary is dried by rotating a long thin sliver of filter paper in the capillary tube. The tube is then placed in the calibration apparatus for a t least 4 or 5 hr to ensure that all traces of liquid are removed from the walls of the tube. I t is then removed from the calibration apparatus, weighed, and then replaced. Several hours should be allowed for equilibration. The rate of diffusion may be established by weighing the diffusion tube periodically. The calibration apparatus used has been the Analytical Instrument Development (AID) Model 303 gas mixing system that has a temperature range of 30-80’C and the AID Model 309 calibration system that also has a temperature range of 30-80’C. A calibration apparatus similar to that described in the Metronics Technical Bulletin 7-70 has been used which involves the use of a water bath kept a t 30’C. In most of the applications, a nitrogen flow of from 10-100 ml/min has been used. With the AID equipment, which has a special “0” ring Teflon seal fitting, the melting point diffusion tube may be inserted through the lh-in. Teflon bulkhead fitting a t the exit of the oven. This is conveniently done by attaching a thin-wall Teflon tube over the open end of the melting point diffusion tube such that the Teflon tube has a 1-cm long opening above the top of the melting point tube. The other end of the Teflon tube is joined to another melting point tube so that the diffusion tube can be inserted into the oven and removed conveniently.
During the calibration procedure, a trap is attached to the end of the calibration apparatus by means of Teflon tubing. The trap is kept in place for different known lengths of time and knowing the rate of diffusion in microgramdminute and the number of minutes the collection is made, the number of micrograms of component on the trap can be calculated. After the required amount of component is collected on the trap, it is removed from the calibration apparatus and placed into the inlet system of the gas chromatograph. During the calibration procedure, the possibility of breakthrough can be checked by using two traps in series. If it is found that some of the component is appearing in the second trap, indicating breakthrough, the flow rate of the nitrogen can be decreased. If this does not work and breakthrough is still occurring, then one can use the total response of both traps. However, a third trap may be necessary to ensure that the component is not coming through the second trap. In the case of high-boiling liquids where the vapor pressure is such that a diffusion tube may not be practical, a very useful technique is the placement of a solution of the sample directly on the Tenax trap. Solutions of the component to be studied are prepared in methanol. The concentrations are such that 2.0 pl contain anywhere from 2-50 pg of the component. A 2-pl sample is placed on the surface of the Tenax by means of a 10-111 syringe. The methanol is then removed by placing the trap in a stream of nitrogen (60 ml/min) for 2 min. The stream of nitrogen through the trap is in the direction such that it enters the trap on the end where the sample was placed on the Tenax. W h e i placed in the inlet system of the gas chromatograph, the end of the trap that contains the sample is in a position such that it is closest to the column. Other solvents can be used besides methanol but one must make sure that they do not dissolve the polymer. Calibration graphs (peak height response vs. micrograms of component) covering the range of 0.05-100 pg were suitable for most of the collected samples.
Discussion Porous Polymer Adsorbents. A number of papers deal with the determination of low-molecular-weight hydrocarbon pollutants and automobile emissions. These include cryogenic trapping, gas chromatography column packings as a trap, and charcoal adsorption technique which were reviewed ( I ) . Williams and Umstead ( 3 ) determined trace air contaminants by concentrating on a porous polymer column (Porapak Q and S) a t room temperature from a largesample loop and used program temperature gas chromatography analysis. The porous polymer Chromosorb 102 which was reported by Dravnieks ( 4 ) for collection of air pollutants is a styrene divinyl-benzene polymer which has high capacity for collection of air pollutants. Its chief disadvantage is the limited thermal stability, particularly in the presence of small amounts of air that produce artifact peaks from the packing itself. Dravnieks stressed the advantage of a porous polymer collector in that water vapor normally present in air is not retained on the packing. In our early work, Chromosorb 101, a low-surface area styrene divinylbenzene polymer, was used for trapping air pollutants but this material was also subject to artifact peaks. Tenax GC is the more desirable trapping material. Van Wijk ( 7 ) in 1970 described Tenax GC (poly-p-2,6-diphenylphenylene oxide) as a porous linear polymer packing for gas chromatography, pointing out that the material is stable to temperatures in excess of 400’C and is resistant to oxygen in the carrier gas. Zlatkis pointed out in 1972 (New York City ACS Meeting) the advantages of Tenax for Volume 9, Number 12, November 1975
1055
collection of air pollutants based on its excellent thermal stability and little affinity for water. We have been using Tenax for collecting organic air pollutants since Zlatkis suggested this application. The first publication using Tenax for air samples was reported (8). Two recent publications (9, 1 0 ) deal with porous polymers for collection and analysis of trace organic vapor pollutants in ambient air. Efficiency of Trapping. The capacity of Tenax for retaining pollutants depends in principle on the retention volume of each substance on Tenax a t the given temperature of the packing. Instead of retention volume, the breakthrough volume was determined by having two traps connected in series and determining what volume was required for the substance to break through into the second trap when passing a calibration gas stream through the traps. Data in column 2 of Table I for maximum sample volume for the small size trap were approximately determined by measuring the breakthrough volume. Table I also lists some typical organic substances determined with the column and detector. For a mixture of pollutants of varying affinities for the adsorbant, some displacement effects may take place. Hence, the amount of Tenax present in the trap should be in excess. The small size trap which has low-flow resistance is adequate for most stack work. Methanol and ethanol required the larger size trap. The latter size is recommended for most ambient collections. The small traps are not reused but the larger traps may be reused for economic reasons. In the latter case, a 30-min heat treatment with nitrogen in the backflow direction (opposite sampling direction) is recommended to remove any high-boiling compounds. The sampling rate for the small size trap should be under 300 ml/min to maintain complete collection efficiency. The effect of flow on sampling rate was studied with low concentrations of aniline established in a nitrogen stream using the large size trap as shown in Table 11. GC Considerations. For stacks with one to several pollutants present, the silicone column or Chromosorb 101 column was satisfactory. Column A was suitable for acidic and neutral compounds whereas B was for basic compounds. The latter two columns were used primarily for ambient air samples taken in the vicinity of sources. The capability of splitting a t the end of the column and simultaneous recording of the two detectors are advantages in identification and quantitative analysis depending on the concentration level as indicated in Figure 2 for both flame ionization and electron capture detectors. The electron capture detector is better for low levels of nitrobenzene, whereas a t high levels flame ionization is the choice detection for quantitative analysis since the electron capture detector response becomes quite nonlinear. Figure 3 illustrates separations on column B showing the specific response of the flame photometric detector for sulfur compounds. The flame ionization output on this detector, although less sensitive than conventional flame ionization is useful for nonsulfur compounds. A nitrogen-alkali flame detector (rubidium sulfate potassium bromide bead), which was constructed on the unused flame jet of the dual flame detector, was valuable in distinguishing nitrogen compounds in the presence of hydrocarbons, for example, pyridine in the presence of large amounts of toluene. For unknowns or for additional confirmation of a peak, the column using the same chromatographic conditions was installed on the Perkin-Elmer 900 GC-MS instrument and the peaks in a similar sample were identified by mass spectrometry. Calibration Techniques. The use of permeation tubes for preparation of dynamic gas mixtures is well documented ( 1 1 ) . Altshuller and Cohen (12) studied diffusion tubes and describe an equation for calculation of the emis1056
Environmental Science & Technology
Table I. Organic Substances Compound
Acetone Chloroform Acetic acid 2,4-Pentanedione Hexane Pyridine Methanol Ethanol
Sample vol, ml ( m a x ) small t r a p Columns
125 300
>1,000
> 1,000 >200 > 900 100
(large trap)
325 (large trap) 1,2-Dichloroethane > 1,000 Isopropanol 250 n-Butanol 500 Ani1 ine >20liters (large trap) Ethyl acrylate 1,000 Benzene 1,000 Dimethyldisulfide >2,000 Nitrobenzene Large Benzothiazole Large m-Xylene > 1,800 Toluene > 1,000 Chlorobenzene > 1,800 Trichlorobenzenes Large Naphthalene Large b Phenol b p-Cresol 2-t-Butyl-4b methylphenol P- N a p h t ho I b Acrylonitrile 125
Detectora
C C C, A C C D, B C
FI D FID, EC FID
C
FI D
C C C D
FI D FI D
A, A, A, A,
FI D
FI D FID, N FI D
FI D
FID, N D
FID FID FPD
D B D B, D A, D A, D A, D D, B, A A, D E, A, C E, A E
FI D
E C
FI D FI D
FID, EC FPD, FID
FID FID FID FID, EC FID
FID FID
a FID, flame ionization detector: E C , electron capture detector: N, nitrogen detector: and FPD, flame photometric detector. bsolvent collection and liquid injection used.
sion rate from known vapor pressure and other measurements. The equation is as follows: Emission rate (g/sec) = 2.3 DMPA
P x logRTL p-P D = diffusion coefficient, cm2/sec M = molecular weight of component P = total pressure, atm = 1 A = cross-sectional area of diffusion tube, cm2 R = gas constant 82 cm3 atm/deg mol T = temperature of diffusion tube, O K L = distance from component liquid level to top of capillary, cm p = vapor pressure of component diffusing, atmos If the vapor pressure is known at the temperature or it can be calculated from temperature dependence, and the diffusion coefficient is known for the component in nitrogen, the emission rate can be calculated. Fuller et al. (13) list diffusion coefficients for various substances in nitrogen and air and describe an equation for calculating diffusion coefficients based on atomic and diffusion volume increments. The agreement between emission rate calculated by the above equation and rate based on weight loss was reasonably good as shown by the data in Table I11 for a melting point capillary (1.2 mm i.d.). Lower output rates at reduced temperatures where weight loss determination was not practical were calculated. In the case of nitrobenzene at 4OoC an output rate of 0.03 pg/min was calculated. Flame ionization response data obtained with 0.03 pg/min and the higher rate of 0.22 pgl min were in close agreement. With aniline at 5OoC,a calcu-
Table I I . Effect of Flow (Large Trap)
3 '
Flow rate, ml/min
Aniline concn, ppm
Collection time, min
Eff iciencya
1025 1025 1000 1000 1000 1000 2000 2000
0.02 0.02 0.02 0.02 0.02 0.007 0.004 0.004
12 12 20 20 45 12 12 12
94 85 91 90 81 91 73 74
-ANILINE
BENZENE'
4Y
'1 \
TOLUENE
PYRIDINE
CHLOROBENZENE
P
f
it Y
a Based o n nitrogen detector response f o r 1 2 - m i n c o l l e c t i o n at 6 0 m i / m i n . These data suggest t h a t f l o w of 1 0 0 0 rnl/rnin can be used w i t h losses o f a p p r o x i m a t e l y 10% b u t at 2 0 0 0 rnl/rnin, the losses are
t
more significant.
O
,
10
I
I
20
30
RETENTION TIME (MIN.)
Flgure 3. Chromatogram showing flame photometric detector response for sulfur compounds and flame ionization response (hydrogen rich) for other organic compounds
u 2
/v
TOLUENE
Table I l l . Diffusion Tube Output Rates
v
NITROBENZENE
./
z
P
Nitro benzene Benzothiazole Aniline p-Cresol Naphthalene
0-DICHLOROBENZENE
/
0
I 5
10
15
Substance
T:mp, C
70 70 70 70 70
Diffusion distance, cm, av
Output rate, pg/min Calcd
W t loss
9.3 8.8 10.2 7.7 13.0
0.22 0.091 0.337 0.162 0.107
0.23 0.1 1 0.34 0.157 0.1 1
1 20
RETENTION TIME (MIN )
Table IV. Solution vs Diffusion Tube Calibration
Figure 2. Chromatogram showing simultaneous flame ionization and electron capture detector responses (1:1 split)
Amount added, pg Amount found, pga
Trichlorobenzene lated rate of 0.085 pglmin compared with 0.092 pglmin in which the latter was based on injecting a methanol solution on the trap. However, the calculated value for aniline a t 33.7OC of 0.027 pglmin was low (0.036 pglmin) based on a methanol solution of aniline. The calculated values are based on extrapolation of vapor pressure data to the lower temperatures. The calculation technique is useful for establishing low dynamic concentrations of pollutants. The methanol solution technique can be used to check the accuracy of the values of given pollutants. Table IV shows in column 2 the amounts of trichlorobenzene and aniline added to a small size Tenax trap in methanol solution and the amount found in column 3 based on a diffusion tube calibration curve. Stack Analysis. The Tenax traps can be inserted in the stack or exhaust opening so as to eliminate any sample line which is an important advantage. However, if the stack is hot (in which breakthrough of a component could be sooner than under ambient conditions), the use of two traps in series is recommended to assure complete collection since the second trap can be kept outside a t close to ambient temperatures. Since the rotameter is placed between the trap and the pump, the accuracy of flow should be checked with a rotameter on the inlet since pressure drop across the two traps may cause an inaccuracy in the flow measurement. This is best done with a similar trap or before inserting the trap in the stack using ambient air. Steam in the stack gas will show entrainment in the trap but the presence of water often does not interfere with the chromatography. Particulate matter is best removed using a Teflon filter (Millipore
Aniline
20.0 40.0 10.0 20.0
20.3 39.5 9.6 19.5
a Based o n calibration o f d i f f u s i o n t u b e
type) before the trap. Certain inorganic gases, for example chlorine, may cause reactive effects on the trap and artifacts in the chromatography. Chlorine has been removed with a pretrap containing potassium iodide crystals without loss of the organic pollutant. These effects or possible interferences should be checked using a known dynamic gas stream of the pollutant. Another strong advantage of the trap technique is that several samples can be taken for short sample times of 10-20 sec so as to establish a concentration profile of the stack. Chromatographic analysis time is usually less than 30 min for running a trap. Defining the peak emission is important in calculations involving prediction of downwind concentrations to determine if an odor problem may exist a t plant boundaries. In dealing with phenolic compounds, adsorption in aqueous caustic or chloroform (30-ml fritted glass scrubber) was preferred since neutral and basic compounds could be removed by extraction. Chromatography was done by injecting 2 pl of a chloroform solution onto the OV-225 column. This procedure was suitable when emission of phenolics was relatively constant but was not suitable for defining concentration profiles. Phenol was determined in a stack using the Tenax trapping technique with gas chromatography on the Chromosorb 101 column. Volume 9, Number 12, November 1975
1057
In the case of acetic acid collected on Tenax traps, our calibration data with added amounts of acetic acid from a diffusion tube vapor stream showed nonlinearity of peak response vs. amount of acetic acid a t low microgram levels, suggesting adsorption. Hence, it is recommended that calibration data be obtained on the same day that samples are run. Acknowledgments The authors wish to thank W. B. Prescott and F. N. Santacana for their helpful suggestions. Literature Cited W., Chang, R. C., Zlatkis, A., J. Chromatogr. Sei., 12, 175 (1974). (2) Mieure, J. P., Dietrich, M. W., ibid., 11,559 (1973). (3) Williams, F. W., Umstead, M. E., Anal. Chem., 40, 2232 (1968).
( 1 ) Bertsh,
(4) Dravnieks, A., Krotoszynski, B. K., Whitfield, J. O’Donnell, A., Burgwald, T., Enuiron. Sci. Technol., 5,1220 (1971). (5) Environmental Protection Agency, Standards of Performance for Stationary Sources, Fed. Regist., 36, No. 247, Thursday, December 23, 1971. (6) Craven, D. A., Anal. Chem.. 42.1679 (1970). (7) Van Wijk, R., “Advances in Chromatography,” A. Zlatkis, Ed., p 122, U. Houston, 1970. (8) Zlatkis, A., Lichtenstein, H. A., Tishbee, A., Chromatographia, 6.67 . 11973). ~~(9) Pellizzari, E. D., Bunch, J. E., Carpenter, B. H., Enuiron. Sci. Technol., 9,552 (1975). (10) Pellizzari, E. D., Carpenter, B. H., Bunch, J. E., ibid., 9, 556 (1975). (11) O’Keeffe, A. E., Ortman, G. C., Anal. Chem., 38,760 (1966). (12) Altshuller, A. P., Cohen, I. R., ibid., 32,802 (1960). (13) Fuller, E. N., Schettler, P. D., Giddings, J. C., Ind. Eng. Chem., 58, (5),19 (1966). ~
- I
Received f o r review February 14, 1975. Accepted July 17,1975.
Sources and Elemental Composition of Aerosol in Pasadena, Calif., by Energy-Dispersive X-ray Fluorescence Robert H. Hammerle” and William R. Piersbn Ford Motor Co., Research Staff, P.O. Box 2053, Dearborn, Mich. 48121
In the fall of 1972 we performed a 29-day study to identify sources of atmospheric particulate matter and assess their contributions to the aerosol in Pasadena, Calif. Sizefractionated and unfractionated filter samples were collected automatically and were analyzed by an automatic X-ray fluorescence spectrometer. Nine elements proved consistently measurable with reasonable accuracy: Ca, Ti, V, Mn, Fe, Ni, Zn, Br, and Pb. All show orders-of-magnitude fluctuations, with a tendency to follow diurnal patterns related to meteorological factors. Most of the elements can be classified as small-particle elements (Ni, Zn, Br, Pb) or largeparticle elements (Ca, Ti, Mn, Fe), with V falling in an intermediate size range. Statistical analysis of interelement correlations and size distributions indicates that gasoline engine exhaust is the source of the Br and Pb; soil from the basin is the main source of the Ti, Mn, and Fe; much of the Ca probably is from cement dust contamination of the soil, and the rest of the Ca is indigenous to the soil. Proportionality and high correlation coefficients (No. 8) characterize elements from the same sources and correlation coefficients No. 4 characterize unrelated elements. Using appropriate gravimetric factors, we estimate that the soil contributed 8 pg/m3 and the primary exhaust particulate from gasoline engines contributed 5 pg/m3, on the average, to the aerosol mass at the Pasadena site during the 29-day period.
There is considerable interest in identifying the origins of the atmospheric aerosol. With this as a major objective, a coordinated effort by many investigators was initiated in 1969 in the Los Angeles basin. The results of that study [reported in a series of papers in J . Colloid Interface Sei., 39, 136-304 (1972)] stimulated planning in 1970 for the large-scale California Aerosol Characterization Experiment (ACHEX) ( I , 2 ) , the observational phase of which was conducted in Pasadena and other sites in August through late October 1972. 1058
Environmental Science & Technology
During planning of ACHEX, a major difficulty was recognized to be the lack of a means of obtaining chemical information on the aerosol with good time resolution. We believed that X-ray fluorescence on-line with a Si(Li) semiconductor detector could yield elemental analyses for a number of elements concurrently in the aerosol on a reasonably fast time scale. An apparatus embodying this idea was designed and built at the University of California Lawrence Berkeley Laboratory by Jaklevic et al. (3, 4 ) under the auspicies of the U.S. Environmental Protection Agency, with the intent that its first utilization would be in the Pasadena ACHEX, prior to final modifications by LBL and subsequent transfer to EPA. The present paper reports the results obtained in Pasadena with this system. It represents the first extensive series of measurements, with prompt analysis and readout in the field, of the elemental composition of particulate matter with an automatic X-ray fluorescence spectrometer. It demonstrates not only the value of the superior time resolution but also the advantage offered by the rapid response in permitting decisions to be made during the course of the experiment. Technical difficulties delayed commencement of measurements until the end of October 1972. By this time, the main part of the program involving most of the other ACHEX participants had been truncated owing to unseasonably smog-free weather, and therefore we are able to relate our results to other properties of the basin atmosphere to a less extent than had been anticipated. Whitby et al. ( 5 ) report that the size distribution of aerosols often has two modes separated by a particle-deficient region at approximately 1-2 pm. This bimodality may be the result of different formation processes for the two size modes. Any attempt to identify aerosol sources by means of elemental composition should therefore include measurements of composition as a function of particle size. This was done in the present study by measuring the composition of the undifferentiated aerosol and the portion below 1.5 pm concurrently.
