Anal. Chem. 1982, 5 4 , 2433-2437
constituents such as sulfates, chlorides, phosphates, etc. but is time-consuming sinos it is a two-step determination: the combustion in the oxygen bomb and analysis by ion chromatography. The two steps take approximately 1 h to carry out. Also, nitrates interfere with the determination of sulfate due to the proximity of‘the two peaks in the ion chromatogram. This problem was addressed by Mizisin et al. ( 4 ) and Butler et al. (5). Nitrates are formed by the oxidation of nitrogen in the sample, in the trapped air in the bomb, or nitrogen present as impurity in the oxygen used to pressurize the bomb. The problem is significantly reduced by using high-purity oxygen, by purging the bomb several times, and by the removing of niitrates prior to ion chromatographic analysis. When a rapid determination of a single constituent is desired, the Parr bomb ion chromatographic method may not be the best choice. A single sulfur determination by the LECO titrimetric method takes approximately 5-10 min. Also, the LECO titrimetric metlhod requires sample sizes as small as 100 mg. Results by the Parr bomb ion chromatographic method are influenced bly the sample size, as shown in Tables I1 and 111. Analysis of 1621a with approximately 0.8-g samples gave sulfur content values significantly less than the expected 0.94. Reduction in the sample size to 0.4 g improved the results substantially, indicating incomplete conversion to sulfate in the oxidation process. The same trend was observed in the analysis of the residual fuel oil no. 6. This observation is in variance to that made by Mizisin et d,(4),where smaller samples indicated evidence of incomplete combustion (soot). The degree of combustion depends not only on sample size but on several factors such as the nature of the sample, voltage,
2433
and current parameters for promoting ignition, nature of the wick (2) used, oxygen pressure in the bomb, etc. Thus, it would appear that optimum conditions for complete combustion must be arrived at for any given experimental setup. Any effects due to nonlinearity in the response can be minimized by running standards that contain similar sulfur content to those of the unknown samples. Thus, the two methods are comparable and, where a rapid determination of sulfur in a number of samples is required, the preferred method appears to be the titrimetric method.
ACKNOWLEDGMENT The authors acknowledge the assistance of Michael G. McNutt in this project. LITERATURE CITED (1) Siegfrledt, R. K.; Wlberly, J. S.; Moore, R. W. Anal. Chem. 1951, 23, 1008. (2) “Book of ASTM Standards”; American Soclety for Testing Materials: Philadelphia, PA, 1978; Part 23, Method D1552-64, p 812. (3) Furman, N. H.; Scott, W. W. “Standard Methods of Chemical Analysis”, 6th ed.; D Van Nostrand: New York, 1962 pp 1007-1011. (4) Mizisin, C. S.; Kuivinen, D. E,; Otterson, D. A. “Ion Chromatographic Analysis of Envlronmental Pollutants”; Mulick, J. D., Sawicki, E., Eds.; Ann Arbor Science: Ann Arbor, MI, 1979; Vol. 2, pp 129-139. (5) Butler, F. E.; Toth, F. J.: Driscoli, D. J.; Hein, J. N.: Jungers, R. H. “Ion Chromatographic Anelysis of Environmental Pollutants”; Mulllck, J. D., Sawicki, E., Eds.; Ann Arbor Science: Ann Arbor, MI, 1979: Voi. 2, pp 185-192. (8) “Instructlon Manual for DB-64”; Model 765-100, Dlgital Titrator; LECO Corp.: St Joseph, MI, 1974. (7) Small, H.: Stevens, T. S.; Bauman, W. C. Anal. Chem. 1975, 4 7 , 1801.
(8) Muiik; J. D.: Sawicki, E. Environ. Scl. Techno/. 1979, 13, 804.
RECEIVED for review April 8,1982. Accepted August 30,1982.
Gas Chromatographic Determination of Lower Fatty Acids in Air at Part-per-Trillion Levels Yasuyukl Hoshlka’ Aichi Envlronmental Reseigrch Center, 7-6, Nagare, Tsuji-machl, Kita-ku, Nagoya-shi, Alchl, 462, Japan
Samples were collecttrd by using 1% Sr(OH), coated on glass beads (15128 mesh), 500 mg. The lower fatty aclds (C,-C,) trapped on the adsorbent were regenerated wlth formic acld-aqueous soiutlon In the gas phase under nltrogen carrier gas flow and were detected with a flame Ionization detector. The method has been applled successfully to the determinatlon of lower fatty aclds in amblent air samples from an urban area and In the alr near a poultry manure pen. I n the case of a 50-L sample gas volume, the mlnlmum detectable concentratlon was about 0.5 part-per-trillion (pptr) (10-l2) for n- and lsobutyrlc aclds and n- and isovaleric acids. The tlme requlred for the entlre procedure lnciudlng the sampling and analysis tlmes for one sample was about 25 mln. The preclslon (as relative standard devlatlon) was less than about 15 min.
Organic acids and their derivatives are known to be present in the environment and are the major constituents of all living ‘Present address: Depa:rtment of Hygiene, Shinshu University, School of Medicine, 3-1-1, Asahi, Matsumoto-shi, Nagano, 390, Japan. 0003-2700/82/0354-2433$01.25/0
organisms. Several of these compounds are primary irritants (I). These acids also have unpleasant odors with low odor threshold concentrations (below 1part per billion, in air (2, 3). Gas chromatography (GC) has been found to be a highly sensitive and specific technique for the determination of the lower fatty acids present in air in low concentrations. However, direct GC determination of the acid present at low concentrations has been limited by adsorption on conventional column packing and column walls in analytical column materials. A review on recent developments in methodology and application of the GC to the analysis of free fatty acids in the underivatized form has been reported ( 4 ) . DiCorcia and coworkers developed gas-liquid-solid chromatography (GLSC) for complete separation of C2-C5 lower fatty acids at low nanogram levels without adsorption and tailing, and the peaks obtained were sharp and symmetrical (5-9). The quantitative and selective sample preparation methods of the lower fatty acids present in air at low concentration (parts per trillion, levels are very important problems. Two approaches have been used to try to overcome these problems, Le.: (i) Chemical reaction methods using alkaline aqueous solutions (10-15)or alkaline on filter paper, followed by desorption with some proper organic solvents without acids 0 1982 American Chemical Society
2434
ANALYTICAL CHEMISTRY, VOL. 54, NO. 14, DECEMBER 1982
or with acids (16-19). (However, these methods also have disadvantages, such as having low sensitivity necessitating long sampling times and being time-consuming, and the sensitivity is limited by a dilution of the sample with the solvent of at least 100- to 1000-fold.) (ii) Adsorption methods with proper adsorbents, Le., Porapak N (20, 21), Tenax-GC (22, 23), strotium hydroxide on glass beads (24-26), silica gel 0, and (FFAP + H3P04)on Carbopack C (28), at room temperature, and then followed by thermal desorption techniques in gas phase under the carrier gas of gas chromatograph. There are few reports on the highly sensitive determination of partsper-trillion levels of the lower fatty acids in air under conditions of the low ghosting peaks and small sample gas volumes. In this study, a sampling and analysis procedure for measuring these lower fatty acids in air was developed. Strontium hydroxide coated on glass beads used as the adsorbent was preconditioned by heating at 280 "C and then followed by the regeneration of the lower fatty acids trapped on the adsorbent with 1.5 pL of 5% formic acid-aqueous solution a t 200 "C in the gas phase under nitrogen carrier gas flow (50 mL/min). The optimum conditions, such as temperature and reagent concentration, break-through volume for the adsorbent, and sampling velocity, were also described. The method has been applied to determination of the lower fatty acids (C,-C,) present in practical specimens.
EXPERIMENTAL SECTION Reagents and Materials. The six standard lower fatty acids (CZC,) and other reagenh used in this study were obtained from PolyScience (Niles, IL), Wako Pure Chemical Industries (Osaka, Japan), Katayama Chemical Industries (Osaka,Japan),and Tokyo Kasei Kogyo (Tokyo, Japan). All reagents were of guaranteed or reagent grade. The standard solutions of the lower fatty acids were prepared by dissolving each acid in 10 mL of distilled water to give the concentrations of 0.001, 0.01, and 0.1 mmol/lO mL of solvent. The column packings were purchased from Wako. Apparatus. The gas chromatograph used was Shimadzu Model GC5AP6F (on-column and on-detector system) equipped with a flame ionization detector (FID) and a digital integrator (Shimadzu Model ITG-BA),for the determination of retention times and quantitative analysis. The detector signal via an electrometer (Shimadzu Model EM-5s) was recorded at 10 mV fullscale on a Shimadzu Model R-201 recorder. The nitrogen carrier gas used was purified by using molecular sieve 5A 60/80 mesh (40 cm X 6 mm i.d., stainless steel column) and was further purified by using 40% sodium hydroxide on Chromosorb W(AW) 60/80 mesh (7 cm X 5 mm i.d., glass column, which was preconditioned at 250 "C for 4 h with nitrogen carrier gas flow 0.25 L/min). Operating Conditions for Gas Chromatography. The main analytical column was glass (1.5 m X 3 mm i.d.), packed with 0.3% FFAP + 0.3% H3P04on Carbopack B 60/80 mesh. This column was preconditioned at 250 "C for 10 h with a constant flow of nitrogen carrier gas (50 mL/min) before being connected t o the FID. The chromatographic conditions for the FID were as follows: main analytical column temperature, 220 "C; injection port and detector temperature, 250 "C; carrier gas (nitrogen) flow rate, 50 mL/min; hydrogen and air flow rates for the FID, 50 mL/min and 1.0 L/min, respectively. Procedure for Preconditioning of the Adsorbent. The procedure for preconditioning of the adsorbent, 1% strontium hydroxide (Sr(OH),) coated on glass beads (15/28 mesh), was as follows. The adsorbent was packed into a glass tube of 10 cm X 5 mm i.d. and was heated at 280 "C for 2 h with a constant flow (0.25 L/min) of nitrogen carrier gas, and then the glass tube was cooled to room temperature (about 21 "C). The heat-treated adsorbent, 500 mg, was packed into a precolumn (2 cm in length), which consisted of a 16 cm X 5 mm i.d., glass tube. The design of the precolumn used has been described previously (23). The precolumn was heated from room temperature to 200 "C and maintained at this temperature and 1.5 pL of 5% formic acidaqueous solution was injected through a silicone-rubber septum
of the precolumn with a 10-pL microsyringe (Hamilton 701-N) in the gas phase under nitrogen carrier gas flow (50 mL/min). This preconditioning procedure was repeated at least three times to decrease the peaks produced from the regeneration of the acidic compounds trapped on the adsorbent. A 5% formic acid-aqueous solution was prepared by mixing 0.5 mL of formic acid and 0.5 mL of distilled water and 0.1 mL of the resultant mixture was diluted to 1.0 mL with distilled water. The preconditioned adsorbent was transferred into a glass sampling tube (10 cm X 5 mm i.d.) packed with a silica wool plug in 2 cm toward vacuum pump port only and was sealed with a silicone-rubberseptum coated with "Parafii-M (laboratory film, American Can Company Dixie/Marathon, Greenwich, CT) until the gas sampling. Procedures for Collection and Regeneration Technique of Lower Fatty Acids. ( i )Ambient Air Samples in an Urban Environment (in the Nagoya Area): Fifty liters of the sample air was collected directly onto the preconditioned adsorbent (1% &(OH), coated on glass beads 15/28 mesh) packed in the glass sampling tube (4 cm X 5 mm i.d., lo00 mg) using a vacuum pump (Mini-Vac, Model PS-05, Yamato, Japan, maximum rate 5 L/min) and a gas meter (T-3 Dry test gas meter, Chubushinagawa Seisakusho, Japan, 1L/revolution). The sampling velocity was about 4.5 L/min. Each 2 cm (500 mg) of the adsorbent was individually preconditioned, and each 500 mg was packed in the sampling tube in series. (ii) Air Near a Poultry Manure Pen. The sample air was trapped directly in the sampling tube packed with the preconditioned adsorbent (1% Sr(OH), coated on glass beads 15/28 mesh, 2 cm X 5 mm id., 500 mg). The volume concentrated was 15 L under a sampling velocity of about 3 L/min. The adsorbent which trapped the lower fatty acids in the sample air was transferred into the precolumn and was analyzed by the regeneration technique. (iii) Standard Ester Gases. The standard ester gases were prepared by evaporating the liquid esters (1pL) using the 10-pL Hamilton microsyringe in an 1-L Pyrex sampling glass bottle filled with a laboratory room air and left for 1h at room temperature. One milliliter (about 1000 ng as esters) of the gas was taken with a 5-mL PS gastight syringe (Series A-2 Pressure-Lok gas syringe, Baton, Rouge, LA) and was injected through the silicone-rubber septum into the precolumn. For preparation of the calibration graphs, the volume of the standard solutions and diluted solution of the lower fatty acids (Cz-C,) injected into the precolumn was usually 1-5 pL with a 10-pL microsyringe. The identification of the lower fatty acids was carried out by comparison of the relative retention times of the sample gases with those of the known standard acids. The retention time of propionic acid was defined as unity. The amounts of the lower fatty acids of unknown samples were obtained from calibration graphs for the known standard acids.
RESULTS AND DISCUSSION Blank ChromatogramsProduced from the Adsorbent in the Preconditioning Procedure with Formic AcidAqueous Solution. Figure 1 shows the typical gas chromatograms produced from the precolumn packed with the adsorbent (1% coated on glass beads 15/28 mesh, 2 cm X 5 mm i.d., 500 mg). The adsorbent used was preconditioned by thermal pretreatment a t 280 "C for 2 h with a constant nitrogen carrier gas flow. The concentration of the formic acid-aqueous solution was 5 % , and the volume injected was 1.5 pL. The precolumn was maintained a t 200 "C for 8 min. The blank peaks which are responsible for the acidic compounds trapped on the adsorbent were reduced effectively by using the preconditioning procedure three times. Typical Gas Chromatogram of Standard Six Lower Fatty Acids. Figure 2A shows a typical gas chromatogram of the six standard lower fatty acids injected into the precolumn which is packed with the preconditioned adsorbent (1% Sr(OH), coated on glass beads 15/28 mesh, 2 cm X 5 mm id., 500 mg) at 200 "C. The six lower fatty acids were completely trapped on the preconditioned adsorbent. Figure 2B shows
ANALYTICAL CHEMISTRY, VOL. 54, NO. 14, DECEMBER 1982
2435
-2
M
>,
L 100
I/
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,
_.._.---
=g ? I
4
50
I
G
140
I
I
160
180
I
I
200
I
240
220
pre-column temp. 'C A
L
0
I
-
- 1
0
5
Flgure 3. Effect of temperatures of the precoiumn in regeneration procedure with formic acid-aqueous soiutlon on recovery percentages of the six lower fatty aclds: (0)acetic acid (90 ng); (0)propionic acid (1 11 ng); (X) isobutyric acid (132 ng); (A)n-butyric acid (132 ng); (0) Isovaleric acid (153 ng); (*) n-valeric acid (153 ng).
5
5
0
mln
Flgure 1. Typlcal gas chromatograms produced from precolumn packed with adsorbent preconditioned three times with formic acldaqueous solution. B 2
A
1I 1 3
0
5
.021
m I ri
Flgure 2. Typical gas chromatograms of the SIX lower fatty aclds injected into the precolumn packed with adsorbent preconditioned and regenerated from the precolumn with formic acid-aqueous solutlon.
a typical gas Chromatogram of the six lower fatty acids regenerated from the precolumn with 5% formic acid-aqueous solution at 200 O C in the gas phase under nitrogen carrier gas flow (50 mL/min), and maintained at this temperature for about 6 min. Position a irepresents the precolumn heating to 200 O C in the carrier gats line and position b represents the injecting point of the formic acid-aqueous solution. The adsorbent used in the Figure 2 was preconditioned by thermal pretreatment at 280 "C for 2 h with a constant nitrogen carrier gas flow and further preconditioned with three portions of a 5% formic acid-aqueouis solution at 200 "C with a constant nitrogen carrier gas flow. The amounts tested were about 30-50 ng of the six lower fatty acids. The recovery percentages (94.3-101%) of the six lower fatty acids produced from the precolumn in the trapping and regeneration procedures were calculated from the comparison of the peak area with those by the direct injection method of equal amounts of the acids into the gas chromatograph. Effects of Concentration of Formic Acid-Aqueous Solution and Temperature of the Precolumn Packed with Preconditioned Adsorbent on Recovery Percentages of Six Lower Fatty Acids. The optimum concentration of formic acid-aqueous solution for regeneration of the lower fatty acids trapped on the adsorbent in the precolumn was 5%. The volume of the formic acid-aqueous solution injected was 1.5 pL. Figure 3 shows the effect of the temperature of the precolumn in the regenerating procedure on the recovery percentages of the six loweir fatty acids regenerated from the precolumn. The precolumn was packed with the precondi-
1
",
, , ,
,
,,,I
10
,
,
, , ,,,.I
100
,
,
, ,
,
,,
,, 1
om
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Flgure 4. Calibration graphs.
tioned adsorbent (1%Sr(OH)2coated on glass beads 15/28 mesh, 2 cm X 5 mm i.d., 500 mg), and the six lower fatty acids were trapped into the precolumn at 200 "C for 8 min. The amounts of the lower fatty acids tested were 90-153 ng. As shown in Figure 3, the quantitative data in recovery percentages of the six lower fatty acids were obtained a t a precolumn temperature other than 180 "C. The effects of the maintained times at 200 "C on the recovery percentages of the six lower fatty acids regenerated from the precolumn were also tested. The acids trapped in the precolumn did not break through the precolumn until 30 min at 200 "C in the gas phase under nitrogen carrier gas flow condition (50 mL/min). Calibration Graphs for Six Lower Fatty Acids Obtained from the Precolumn Trapping and Regeneration Procedures. The FID response produced a straight line in the approximate range 2-1500 ng of the six lower fatty acids obtained from the precolumn trapping at 200 "C for 6 min and the regeneration with 1.5 pL of 5% formic acid-aqueous solution at 200 "C in the gas phase under nitrogen carrier gas flow (50 mL/min) (Figure 4). The detection limit at twice the noise level was about 0.2 ng. Therefore, when the concentration volume is 50 L, the minimum detectable concentration is about 0.5 pptr. The sensitivity is adequate for use in air or odor pollution analysis. Repeatability of Peaks of the Six Lower Fatty Acids Obtained from the Precolumn Trapping and Regeneration Procedures. The repeatability and uniformity of the relative retention times and peak area (as counts of the digital integrator) of the lower fatty acids were evaluated by the precolumn trapping and regeneration procedures. They showed good uniformity and repeatability. The amounts of
2438
ANALYTICAL CHEMISTRY, VOL. 54, NO. 14, DECEMBER 1982
Table I. Relationship between Recovery Percentages of the S i x Lower Fatty Acids from the Strontium Hydroxide Coated on Glass Beads Precolumn and Volume of Nitrogen Carrier Gas Passed through the Precolumn % ~
15
50
60
acid
amt, ng
vol/L
vol/L
vol/L
acetic propionic isobutyric n-butyric isovaleric a-valeric
1200 148 176 176 204 204
101 100 100 100 100 100
104 100 101 101 100 100
108 100 100 100 98.7 99.1
a Nitrogen carrier gas flow rate; 0.25 L/min at 22 "C. Regeneration conditions of the six lower fatty acids trapped on the adsorbent; 200 "C for 5 min: 1.5 pL of 5% formic acid-aqueous solution.
Table 11. Determination of the Trace Concentrations of S i x Lower Fatty Acids in the 175-L Tedlar Bag
acid
ref method, a ppb
present method, ppb av * % re1 std dev std dev
acetic 36.2 32.7 % 4.8 14.7 propionic 3.6 3 . 2 I 0.3 9.4 3.6 isobutyric 2.9 t 0.4 13.8 n-butyric 3.6 2.9 * 0.2 6.9 isovaleric 3.6 2.9 i 0.4 13.8 n-valeric 3.6 2.9 f 0.2 6.9 a Reference 28: sampling velocity, 5 L/min, 22 "C; sample volume collected, 1 0 L. Relative standard deviation based on four replicas.
Table 111. Interference Effects of 39 Esters on the Trapping and Regeneration Procedures by Using Strontium Hydroxide Coated on Glass Beads Precolumn of the Six Lower Fatty Acids (Amounts of the Esters Tested, 1000 ng) ester acetate methyl ethyl vinyl allyl n-propyl isopropyl n-butyl isobutyl see-butyl tert-butyl n-amyl isoamyl sec-amyl tert-amyl n-hexyl propionate methyl ethyl vinyl n-propyl isopropyl n-butyl isobutyl isoamyl
found
ester
as acetic acid 1 0 ng as acetic acid 10 ng
as acetic acid 1 0 ng
as acetic acid 10 ng
as propionic acid 5 ng
found
n- butyrate methyl ethyl vinyl n-propyl isopropyl n - bu t y1 isobutyl isobutyrate methyl ethyl n-propyl isopropyl n-valerate methyl ethyl n-propyl isovalerate methyl ethyl
*
the acids tested were 84 to 143 ng. The precision (as relative standard deviation) was less than about 4%. Relationship between Recovery Percentages of the Six Lower Fatty Acids on the Preconditioned Adsorbent and Nitrogen Carrier Gas Volumes Passed through the Preconditioned Adsorbent. This test was carried out at 22 "C under a constant flow of nitrogen of 0.25 L/min. The amounts of each acid used were 148-1200 ng. Quantitative recovery was obtained up to a sampling gas volume of 60 L (Table I). The recovery percentages were determined from the calibration graphs (Figure 4). Relationship between Recovery Percentages of the Six Lower Fatty Acids from the Preconditioned Adsorbent and Sampling Velocity. Relationship between the recovery percentages of the six lower fatty acids on the preconditioned adsorbent in the sampling tube and the sampling velocity (5 L/min) was tested by using a 175-L Tedlar bag with known concentrations of the six lower fatty acids in the laboratory room air in the bag of 3.6-36.2 ppb. Table I1 lists the data of the determination of the trace known concentrations (3.6-36.2 ppb) of the six lower fatty acids in the bag by the proposed method. The results show a good repeatability and are quantitative. The precision (asrelative standard deviation) was less than about 15%. Interference Studies. It is well-known that alkaline hydroxide such as sodium hydroxide has a high reactivity to many esters, due to the formation of corresponding alcohols and acids, which can lead to problems in the analysis of the six lower fatty acids by the proposed method. Therefore, 39 representative esters (15 acetates, 8 propionates, 4 isobutyrates, 7 n-butyrates, 2 isovalerates, 3 n-valerates) were tested. The results obtained are listed in Table 111. Methyl acetate, vinyl acetate, n-amyl acetate, and tert-amyl acetate gave trace acetic acid findings, and vinyl propionate gave also
0
5
min
Figure 5. Typical gas chromatograms of the six lower fatty acids in the ambient air sample in the city (in the Nagoya area). Sample taken on Sept. 22th, 1981, 5 0 7 pm-5:18 pm, 25 O C . Sample volume collected was 50 L. Peak 1 was recorded on the FID sensitivity of 16 X 10' and peaks 2-6 were recorded on the sensitivity of 2 X 10'. propionic acid. Therefore, the four acetates were decomposed on the adsorbent and trapped as strontium acetate, whereas vinyl propionate was decomposed on the adsorbent and trapped as strontium propionate. Thus, in the trapping and regenerating procedures in this study, when these acetates and propionate are copresent in air sample gas, the results gave positive error onto acetic acid and propionic acid. Each 1000 ng of the four acetates and vinyl propionate gave corresponding trace acetic acid (10 ng) and propionic acid ( 5 ng), respectively. However, no evidence was found for interfering effects of the other 34 esters. Application. Ambient Air Samples in the City (in the Nagoya Area). Figure 5 shows typical gas chromatograms of the six lower fatty acids in ambient air samples taken in the city (in the Nagoya area). The procedures for the collection of the sample gas and for the analysis of the acids concentrated were as described under the Experimental Section. Figure 5A shows the typical gas chromatogram of the acids in the air sample collected on the preconditioned adsorbent of the front port of the sampling tube. Acetic acid (main component, peak 1, detected concentration 2433 pptr), propionic acid (peak 2, detected concentration 263 pptr), iso-
ANALYTICAL CHEMISTRY, VOL. 54, NO. 14, DECEMBER 1982
Table IV. Determination of Trace Concentrations (in pptn) of the Six Lower Fatty Acids in Urban Air (in the Nagoya Area)a acid acetic propionic isobutyric n-butyric isovaleric n-valeric a
range, pptr
av, Pptr
837-2930 39.3-263 2.6-24.3 9.5-56.0 0.6-4.1 3.8-29.9
1690 102 8.9 25.3 2.5 13.9
Date: Sept 5th-Oct 26th, 1981; sample 32.
butyric acid (peak 3, detected concentration 22.1 pptr), nbutyric acid (peak 4, detected concentration 52.5 pptr), isovaleric acid (peak 5, detected concentration 3.6 pptr), and n-valeric acid (peak 6, detected concentration 14.3 pptr) were detected. Figure 5B shows the typical gas chromatogram of the acids in the air saniple collected on the preconditioned adsorbent of the vacuum pump port but passed through the preconditioned adsorbent of the front port of the sampling tube. As shown in Figure 5, the collection efficiency on the six lower fatty acids in the urban air sample of the preconditioned adsorbent (2 cni x 5 mm i.d., 500 mg) in the sampling tube was quantitative. The ranges and averqqge concentrations of the six lower fatty acids detected in 32 urban air samples were listed in Table
IV. The gas Chromatography of 50 L of urban air was also studied, using cooled (dry ice-acetone temperature) Tenax-GC precolumn methods (29,30). Gas chromatography was carried out with a glass capillary column (PEG-BOM, 30 m X 0.25 mm i.d., 60 "C, carrier gas helium flow rate, 0.'7mL/min; detector, FID). Some acetates and propionate, which give large interference effects in the determination of acetic acid and propionic acid by the piresent method, were not detected in the gas chromatogramei (50 ng/50 L urban air sample). No evidence was found for the odor perception responsible for lower fatty acids, i.e., rancid, putrid, faecal, pungent, and sour in the sampling site. 'These results of the acetic acid and propionic acid were in reasonable agreeeinent with literature values (acetic acid, 0.5-1.4 ppb; propionic acid, 0.08-0.13 ppb) (25). Air Sample Near Poultry Manure Pen. In the air sample near a poultry manure pen, acetic acid (detected concentration 6630 pptr), propionic acid (detected concentration 2570 pptr), isobutyric acid (detected concentration 415 pptr), n-butyric acid (detected concent ration 830 pptr), isovaleric acid (de-
2437
tected concentration 407 pptr) and n-valeric acid (detected concentration 48.8 pptr) were detected.
ACKNOWLEDGMENT The author thanks K. Yoshimoto, Aichi Environmental Research Center, for useful suggestions. LITERATURE CITED Fasset, D. W. I n "Industrial Hygiene and Toxicology, Volume 11, Toxicology", 2nd ed.;Patty, F. A,, Ed.; Interscience: New York, 1962; Chapter XL, pp 1771-1795. Summer, W. "Methods of Alr Deodorization"; Elsevier: Amsterdam, 1963; Chapter 1, pp 45-46. Leonardos, G.; Kendall, D.; Barnard, N. J . Air Pollut. Controi Assoc. 1989, 19, 91-95. Preston, S.; Ackman, R. G.; Metcalfe, L. "Analysis of Fatty Aclds and Their Esters by ChromatograDhlc Methods"; Preston Publications: _ . Niles, IL, 19771 p 547. DiCorcia, A.; Fritz, D.; Bruner, F. Anal. Chem. 1970, 42, 1500-1504. DiCorcla, A.; Bruner, F. Anal. Chem. 1971, 4 3 , 1634-1639. DICorcla, A. Anal. Chem. 1973, 45, 492-496. DiCorcla, A.; Samperl, R. Anal. Chem. 1974, 4 6 , 140-143. DICorcla, A.; Samperi, R. ; Sebastiani, E.; Severinl, C. Anal. Chem. 1980, 52, 1345-1350. Okabayashi, M.; Ishiguro, T.; Hasegawa, T.; Shigeta, Y. Bunseki Kagaku 1978, 25, 436-440. Smallwood, A. W. Am. Ind. Hyg. Assoc. J . 1978, No. 39, 151-153. Willlams, K. W.; Mazur, J. F. Am. Ind. Hyg. Assoc. J . 1980, No. 41, 1-4. Colenutt, 8. A.; Davies, D. N. Int. J . Environ. Anal. Chem. 1980, 7 , 223-229. Colenutt, B. A. Int. J . Environ. Anal. Chem. 1979, 7 , 71-77. Williams, K.; Esposito, G. G.; Rinehart, D. S. Am. Ind. Hyg Assoc J . 1981, 42, 476-478. Tsuji, M.; Yamasaki, T.; Okuno, T.; Shintani, Y. Hyogoken Kogai Kenkyu Hokoku 1977, No. 9, 71-73. TsuJl, M.; Okuno, T.; Yamasakl, T.; Shintani, Y. Hyogoken Kogai KenkYU HOkOkU 1978 NO. 10, 51-54. Horiba, H.; Yamanaka, S.; Hattori, T. Akusyu no Kenkyu 1978, 7 (31), 35-39. Saito, T.; Takashlna, T.; Yanagisawa, S.; Shirai, T. Bunseki Kagaku 1981. 30. 790-795. Russell, J. W. Environ. Sci. Technol. 1975, 9 , 1175-1178. Dletrich, M. W.; Chapman, L. M.; Mieure, J. P. Am. Ind. Hyg. Assoc. J . 1978, 39, 385-392. Parsons, J. S.; Mitzner, S . Envlron. Sci. Technol. 1975, 9 , 1053-1058. Hoshika, Y. J. Chromatogr. 1977, 144, 181-189. Nakayama, S.; Ishiguro, T.; Shlgeta, Y. Buil. Jpn. Environmental Sanitation Center 1978, No. 3, 79-83. Nakayama, S.; Ishiguro, T.; Shlgeta, Y. Bull. Jpn. Environmental Sanitation Center 1978, No. 5, 90-93. Kato, T. "Taikiosen no Gasukuromato Gijutsu"; Sankyo: Shuppan, Japan, 1975; pp 312-322. Glliand, J. C., Jr.; John, G. T.; McGee, W. A. Am. Ind. Hyg. Assoc. J . 1981, No. 42, 630-632. Hoshika, Y. Ana/yst (London) 1981, 106, 166-171. Pellizzari, E. D.; Bunch, J. E.; Carpenter, B. H.; Sawickl, E. Environ. Sci. Technoi. 1975, 9 , 552-555. Pellizzari, E. D.; Bunch, J. E.; Berkley, R. E.; McRae, J. Anal. Chem. 1978, 4 8 , 803-807.
.
.
RECEIVED for review March 24, 1982. Accepted September 8, 1982.
