with the analytical columns. The pH 4.15 and 5.00 buffers were introduced earlier, and as a result, arginine emerged completely before fraction 4.15. Experience has shown that a sharp symmetrical peak may contain more than one component, especially when unhydrolyzed tissue fluids have been chromatographed. A study of all the amino acids listed in Table I, by paper chromatography and paper electrophoresis, has indicated that a n y two components which might emerge together from the column can always be separated by one or other of these procedures. Conversely, a n amino acid which appears in the column effluent as a simple peak is probably pure if it is not resolved further, by paper chromatography and paper electrophoresis.
ACKNOWLEDGMENT
The authors gratefully acknowledge samples of amino acid test solution (IS) supplied by Darrel H. Spackman, Rockefeller Institute for Medical Research, New York, N. Y., which were of assistance in cbecking the method. Thanks are also due t o the Beckman Instrument Co., Los $ngeles, Calif., for gifts of amino acid solution, which is now commercially available for test purposes, a t nominal cost. LITERATURE CITED
(1) Hamilton, P. B., ~ A L CHEM. . 30, 914 (1958). . ( 2 ) Ibid., p. 1887. (3) Hamilton, P. B., “Ion Exchangers in
Organic and Biochemistry,” Calman and Kressman, Chap. 14, Interscience, Kern-York, 1957.
(4) Hamilton, P. B Anderson, R. A., J. Biol. Chem. 211, (1954). (5) Kent’s Mechanical Engineers Handbook, Carmichael, ed., 12th ed., pp. 5-27, Wiley, Xew York, 1956. ( G ) “Machinery’s Handbook,” 15th ed., p. 1770, Industrial Press, Kew York, 1956. (7) Moore, S., Spackman, D. H., Stein, W. H., ANAL.CHEM.30, 1185 (1958). (8) Moore, S., Stein, W. H., J . Biol. Chem. 176, 367 (1948). (9) Zbzd., 192, 663 (1951). (10) Ibid., 211, 893 (1954). ( 1 1 ) Muers, &‘I. M., House, M, il., Analyst 74,85 (1949). (121 Aimmonds, D. H., ANAL. CHEM. ‘ 30,1043 (1958). (13) Spackman, D. H., Moore, S., Stein, IT. H., Ibid., 30. 1190 (1958). (11) Spackman, D. H., Moore, S., Stein, W. H., Federation Proe. 15, 358 (1956).
Qk
RECEIVED for review December 22, 1958. Accepted May 4, 1959.
Detection of Trace Constituents by Gas Chromatography Analysis of Polluted Atmosphere P. S. FARRINGTON, R. L. PECSOK, R. L. MEEKER, and T. J. OLSON Department of Chemistry, University of California, los Angeles, Calif.
b Apparatus and techniques are described which are applicable to the detailed analysis of polluted atmospheres, including the detection and determination of components present in the range of a few parts per hundred million. Important features are the sample handling technique and the ion gage detector. Large amounts of water have been removed under conditions shown to b e inert toward oxygenated organic compounds. The method is generally applicable to trace constituents.
I
of trace constituents in the atmosphere has become increasingly important, particularly in urban areas where pollution (smog) is a problem. Gas chromatography is a n obvious approach to this type of analysis and several papers have described methods for the detection of lowboiling hydrocarbons by this technique. However, with the exception of a recent paper b y K e s t et al. (W), little work has been done on the detection of organic compounds other than hydrocarbons. Samples have been obtained by two general methods: adsorption on a suitable adsorbent, or freeze-out of the material in a cold trap. West et al. (I) applied the adsorption technique using DENTIFICATION
15 12 *
ANALYTICAL CHEMISTRY
20-liter air samples t o detect components in the range of 1 to 50 p.p.m. This paper describes techniques suitable for the detection of components present in amounts as small as a few parts per hundred million in the presence of large amounts of water. The methods are applicable t o a large variety of organic compounds, including saturated and unsaturated hydrocarbons, aromatics, and most oxygenated materials occurring in the atmosphere. With a few exceptions, water has been removed without the concomitant loss of oxygenated materials. A 16.4-liter sample of polluted air is drawn through a drying agent and then through a trap containing column material immersed in liquid oxygen. In this manner, the components of interest are concentrated and separated from the water vapor. The column is all glass of conventional design utilizing a n ion gage detector which is extremely sensitive and requires only a small fraction of the effluent gas stream. The separated constituents are thus available for further study if desired. Identification is made by comparison of elution time ratios of unknowns to standards, using one or more kinds of column material. Quantitative estimation is made by measuring the area
under the chromatographic peak.
Be-
cause the detector response is also a function of the ionization cross section, highest accuracy requires a separate calibration for each compound. I n this study, several components -were found at a concentration of a few parts per hundred million, corresponding to a liquid volume of about p1. The estimated accuracy a t this level is about 50%, in part due t o the difficulty of measuring small amounts of standards. EXPERIMENTAL
Collection and Handling of Samples. T h e sampling unit, shown in Figures 1 a n d 2, consists of a series of three U-traps and a 16.4-liter metal tank. Two of t h e traps are made of glass tubing, 7 mm. in outside diameter, 15 em. high, with 10/30 standard taper joints for connection t o t h e sample handling system. T h e third t r a p is made of 5-mm. outside diameter glass tubing, 6 cm. high, attached directly t o two three-way stopcocks. Traps 1 and 2 are partly filled with about 5 em. of column material. The remaining space in trap 1 and in one side of trap 2 is filled with drying agent. Trap 3 is completely filled with column material. The column material used in the traps consists of 20-mesh Sil-0-Cel C-22 insulating brick coated with di-nbutyl phthalate. Probably other ma-
-HELIUM
*+?
DRYING AGENT
-'
DRYING AGENT
COLUMN MATERIAL TRAP TqA?
2
Figure 1 .
TRAP
I
COLUMN MATERIAL
Figure 2.
I
Sample collection system
Sample handling system
terials mould serve as nell, as the components are presumably trapped mechanically by condensation. For the collection of the sample, trap 1 is attached to the evacuated 16.4-liter tank (Figure 21. The intake side of the trap is attached to a 20-em. drying tube. With the trap immersed in liquid oxygen, the needle valve on the tank is opened, allowing air to pass through slowly at a rate of 0.5 liter per minute. After collection, the stopcocks are closed and the trap, still immersed in liquid oxygen. can be transported to the laboratory. The efficiency of the trapping system was tested with pentane and diethyl ether; all other compounds of interest to this study have boiling points in this region or higher. With the procedure described above, 100% of the pentane and 95 to 1 0 0 ~ oof the ether were trapped. Presumably, the trapping efficiency of higher boiling compounds \$ill be essentially 100%. Trap 1, containing the sample, is then connected as s h o m in Figure 1. While still at liquid oxygen temperature, it is flushed briefly with helium t o remove e w e s air, and then the stopcocks are closed. The trap is then allowed t o remain a t room temperature for 1.5 hours to permit equilibration with the drying agent. T o remove remaining water, the sample is transferred to trap 2 , which is immersed in liquid oxygen. Helium is passed through to effect the transfer which requires about 0.5 hour. Trap 2 is then closed and brought t o room temperature for 1 hour. I n a similar manner, the sample is transferred from trap 2 t o trap 3, which is actuallv a n extension of the column itself. Because the sample can be cooled easily. it is possible t o restrict it initially to a small part of the column, thus sharpening the peaks and increasing the sensitivity. Retention times are measured relative t o the air peak. The efficiency of the transfer steps described above was tested with oxygenated organic compounds boiling as high as 140" C. and with saturated and aromatic hvdrocarbons boiling u p to 120" C. With transfer times of 0.5 hour, the efficiency n a s 100% in all cases. Samples of standards were measured and injected b r means of capillary micropipets, calibrated by weighing the amount of mercury delivered. The accuracy was about 1% for 1-p1. pipets and 15y0for 0.05-pl. pipets. Standard
Table 1.
Per Cent Recovery of Sample through Various Drying Agents a t 25" C. CaSO, Mg( C101'? Ba( ClO4)r K,CO, -r 100 100 13 loo 40 5 10 !j0 100 50 I 3 25 c10 0 50 rn
Mol. Sieve Compound 25 Isopropyl ether 0 Acetone 10 Isobutyraldehyde n Isopropyl alcohol 0 n-Butyraldehyde 5 Methyl ethyl ketone 5 Isopropyl acetate 0 All 1 ether 0 ~sogutylformate 0 n-Propyl acetate
--
50 20 0 50
