Gas Chromatographic Analysis of Polynuclear Aromatic Hydrocarbons with Packed Columns Application to Air Pollution Studies
EXPERIMENTAL
when the carrier gas flow rate of column A was changed, the flow through column B was also affected slightly. With the exception of this modification the instrument was used as received from stock. Filtered helium was the carrier gas and oxygen and hydrogen were supplied to the flame ionization detectors. Two pairs of columns were used. Set A was composed of two stainless steel columns, 6 feet long, '/s-inch. o.d., packed with 2% ilpiezon L coated on 60-80 mesh Diatoport S (F and h1 Scientific Co., Avondale, Penna.). Set B was composed of two copper columns, 20 feet long, '/*-inch o.d., packed with 2% SE-30 coated on 60-80 mesh Gas Chrom Z. (Applied Science Laboratories, Inc., State College, Pa.) Set B was prepared and filled in 10-foot sections using a technique described by Wells, Sweeley, and Bentley (11). Freshly-prepared columns were conditioned for 2 hours a t 250' C. without gas flow, and then for 6 hours a t 300' C. with a very slow stream of helium passing through the columns. Reagents. Polynuclear aromatic hydrocarbons for preparing calibration standards were purchased from K and K Laboratories, Inc., 121 Express Street, Plainview, S . Y. Only t h e major peak was utilized, both qualitatively and quantitatively in each standard . Procedure. Standards of pyrene, benz (a)anthracene, chrysene, benzo(k)fluoranthene, benzo(a)pyrene, benzo (e)pyrene, and coronene were prepared by dissolving known amounts of each compound in 25.0 ml. of benzene. Relative retention times were calculated from data obtained by analyzing the standards on the two column systems a t different carrier gas flow rates (Tables I and 11). Optimum flow rates for helium, hydrogen, and oxygen were obtained by holding the flow of two gases constant while varying the other, and plotting the number of theoretical plates us. the flow rate of the gas being varied. The number of theoretical plates was calculated from the formula (5)
Apparatus. An F and iLI Model 810 dual column research gas chromatograph, equipped with dual flame ionization detectors was used for analysis. The instrument is equipped with separate heaters for the injection block, column oven, and detector assemblies. It is capable of isothermal or programmed temperature operation, the latter a t rates between '1 and 40' C. per minute. However, in practice when the instrument was programmed over a wide temperature range (150350' C.) the base line drift became excessive. Drift was compensated by installing a second carrier gas flow system so that the gas flow through each column and detector was independently controlled. Prior to the modification,
where N = the number of theoretical plates, TR = the distance to peak height, and W112 = the width of the peak a t half-height. TR and Wl/2 are in the same units. Calibration curves were prepared by analyzing different quantities of each compound a t the optimum conditions and plotting peak area us. concentration. The injection port was maintained a t a temperature which caused instant vaporization of the sample upon injection, but which was not high enough to cause decomposition of the injected materials. The optimum temperature was found to be 310' C. The two detectors were
SIR: There is great interest in the polynuclear aromatic hydrocarbon content of community air because of the carcinogenicity of these compounds (3). Air samples have been analyzed routinely by the Lnited States Public Health Service for polynuclear aromatic hydrocarbons for several years. The usual collection and analytical procedure utilizes a glass fiber filter, which is extracted with benzene. The compounds are then separated by column chromatography and identified by ultraviolet-visible spectroscopy. This technique usually requires two to three days for completion, with the bulk of the time being used for separation (7, 8). Recent advances have been made in the fields of fluorescent spectroscopy and thin-layer chromatography (9, 10). However, these refinements are aimed a t more complete separation of components and, therefore, more accurate measurement, but analysis time is not significantly reduced, Sawicki, in his review article on the analysis of polynuclear aromatic hydrocarbons gives several references for analysis of polycyclics by gas Chromatography (6). Since that time a few other workers have reported on this subject (4). However, this paper offers a new aspect: the parallel use of a second carrier gas flow system t o allow for the bleeding of the liquid phases, which can be significant when working a t these high temperatures. I n the work reported here conventional packed columns were used after a, single benzene extraction of suspended atmospheric particulate matter collected on a glass fiber filter paper. By using gas chromatographic methods, time for completion of an analysis after benzene extraction was reduced to approximately two hours.
Table I. Retention Times of Selected Polycyclics Relative to Pyrene (Column: dual 6-ft., inch, 2y0 Apiezon L on 60-80 mesh Diatoport S)
OPERATING CONDITIOKS No. 1 No. 2
Detector temperature ( O C.) Injection port temperature ("
c.1
Starting oven temperature ( " C.) Final oven temperature ( " C.) Program rate ( O C./min.) Post injection interval (mini) Upper limit interval (min.) Carrier cas flow rate
318 320 310 330 220 240 268 280 6 6
(cc./&n.)
4 10
4 60
85
25
RELATIVE RETENTION TIMES Pyrene Chrysene Benz(a)anthracene Benzo(k)fluoranthene Benzo(e)pyrene Benzo(a)pyrene Benzo(g,h,i)perylene
No. 1 1.00 1.74 2.04 2.56 2.81 2.89 5.45
No. 2 1.00 1.71 2.19 3.28 3.80 3.86 9.87
Table II. Retention Times of Selected Polycyclics Relative to Pyrene (Column: Dual 20-ft., l/a-inch, 2% SE-30 on 60-80 mesh Gas Chrom Z )
OPERATINGCONDITIONS No. 1No. 2 Detector temperature ( O C.) 320 322 Injection port temperature ( " C.) 305 308 Starting oven temperature ( " C.) 180 250 Final oven temperature (' C.) 250 250 Program rate iO C. /min.) 4 ... ost tu injection 'interval (min.) 10 . . . Upper limit interval (min.) 20 . . . Carrier gas flow rate (cc./min.) 55 50
RELATIVE RETENTION TIMES No. 1 No. 2 1 . 0 0 1.00 Pyrene 1.59 1.75 Chrysene Benz(a)anthracene 1.32 1 . 7 1 Benzo(k)fluoranthene 2.08 3.28 Benzo(e)pyrene 2.46 3.79 2.51 4.00 Benzo(a)pyrene Benzo(g,h,i)perylene ... 11.8
heated to a slightly higher temperature so that the polycyclic compounds would not condense after elution from the columns. Because of the wide range of boiling points of the polycyclics under investigation, a programmed temperature operation was necessary. The VOL. 38, NO. 1, JANUARY 1966
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Figure 1. Chromatogram on Apiezon L of standard hydrocarbons in benzene
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lower temperature limit was set sufficiently high to detect pyrene (b.p. 394' C.) in a reasonable length of time, but low enough to prevent the retention times of the other tetracyclic compounds -i.e., chrysene b.p. 448' C.-from blending to the point of indistinguishability. The upper limit was sufficiently high to permit detection of pentacyclics [benzo(a)pyrene b.p. 493' C. and benzo(a)pyrene b.p. 496' C.)] but did not cause excessive bleedoff of the liquid phase. The optimum programming rate was found to be 4' or 6' C. per minute, which permitted a moderately rapid rise in temperature and minimized base line drift. Even with the modification of the instrument previously mentioned it was still extremely difficult to obtain a balanced bleed rate for the two columns while programming the temperature over an extended range and operating the instrument a t near maximum sensitivity. This ideal condition was never achieved in practice so that all runs show a slightly shifted base line. Samples were analyzed on each set of columns a t two different sets of conditions to verify peak identification. However, it is conceivable that in the complex mixture of compounds found in urban air there will be compounds not yet identified, which could have retention times similar to those reported here. After identification was confirmed all samples were analyzed a t the optimum
conditions and peaks were measured by the height times width a t half-height method, with the proper adjustment being made for the sloping base line (2). The concentrations of each compound were read from the calibration curves prepared from standards. RESULTS AND DISCUSSION
The data obtained with the silicone rubber columns were the basis for quantitative evaluation of unknowns, while the Apiezon L column data were utilized primarily to identify compounds. Figure 1 is a chromatogram showing a mixture containing six polynuclear aromatic hydrocarbons analyzed on the ilpiezon L columns. The slope in the base line resulted from the unbalanced bleed rate. A chromatogram obtained by analyzing the standards on the SE-30 columns is shown in Figure 2. With each column the temperature was programmed only after an initial 10minute isothermal period. Figure 3 is a chromatogram of an air sample analyzed on the SE-30 columns. The same pair of columns was used for the analysis of all
Airborne Concentrations of Selected Polycyclic Hydrocarbons for Several Cities
Table 111.
Pittsburgh" Birmingham* Detroitb a
Figure 2. Chromatogram on SE-30 of standard hydrocarbons in benzene
Arithmetic mean
Pyrene
4 . 5 3~ 3 . 3 9.5 13.9
Benzo(k)fluoranthene
Benzo(a)
9.4 f7.7
1 1 . 0 f 11.1
8.8 12.4
7.9 14.1
15.7 18.5
+ S.D. (12 samples, June 1964-Feb.
1965)
* Analyzed by ultraviolet spectrophotometric procedures (8).
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ANALYTICAL CHEMISTRY
Benzo(e)pyrene
pyrene 6.6 & 6.1
standards and samples, a period of a t least 200 hours, without the separation of benzo(a) pyrene and benzo(e)pyrene diminishing. Relative retention times for seven polycyclic hydrocarbons are given in Tables I and 11. The relative retention time of perylene was extremely close to that of benzen(e)pyrene u s b g thr Apiezon L columns. However, with the SE-30 columns it had a value between that of benzo(k)fluoranthene and that of benzo(e)pyrene. It is not reported here although it is recognized that the amount of perylene present will be reported as benzo(e)pyrene; however, perylene is generally found to be present in concentrations of less than 20% of the amount of benzo(e)pyrene so that the data reported here will not be altered significantly. The results given in Table I11 can only be significant when considered as maximum values. However, the concentrations obtained by this method are comparable to those obtained with the usual ultraviolet procedures as evidenced by the data in Table 111, which shows the arithmetic mean air concentrations of four polycyclics analyzed by gas chromatography in Pittsburgh. Also shown are the arithmetic mean air concentrations of the same four polycyclics in other cities where analysis was by ultraviolet spectrophotometric procedures. A better comparison could have been made had a sample been analyzed by both the gas chromatographic method and the ultraviolet method. However, data relative to this are not available. The complete findings of the study of polycyclic hydrocarbons in Pittsburgh air, including details of sampling methodology were reported recently ( I ) .
LITERATURE CITED
(1) DeMaio, L., Corn, M., “Polynuclear
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Figure 3. Chromatogram of a typical sample on SE-30 V
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CONCLUSIONS
h method utilizing gas chromatography for the analysis of polynuclear aromatic hydrocarbons has been suggested for general use. The method was developed for use in analyzing polycyclic hydrocarbons associated with particulate matter in the air: however, it can be used wherever it is required t o
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analyze for polynuclear aromatic hydrocarbons. The primary advantages of this method when compared to the methods now used are the ease of performance and time differential. One man can easily complete the analysis in two hours after the sample is extracted from the filter. Previously, several analysts required two days t o complete the procedures.
Aromatic Hydrocarbons Associated with Particulates in Pittsburgh Air,” 58th Annual Meeting, Air Pollution Control Association, June 22, 1965, Toronto, Canada. (2) Hawkes, S. J. and Russell, C. P., J. Gas Chromatog. 3,72 (1965.) (3) Hoffman, D., Wynder, E. L., NCI RIonograph No. 9, E. Sawicki, K. Cassel, Jr., eds., pp. 91-116, U. S. Govt. Printing Office, Washington, 1962. (4)Liberti, A., Cartoni, G., Cantuti, V., J. Chromatog. 15, 141 (1964). (5) Purnell, H., “Gas Chromatography,” p. 105, Wiley, New York, 1962. (6) Sawicki, E., Chemist-Analyst 53, 56 (1964). (7) Sawicki, E., Elbert, W. C., Stanley, T. W., Hauser, T. R., Fox, F. T., ANAL. CHEM.32, 810 (1960). (8) Sawicki, E., Hauser, T. R., Elbert, W. C., Fox, F. T., Meeker, J. E., Am. Ing. Hyg. Assoc. J. 23, 137 (1962). (9) Sawicki, E., Hauser, T. R., Stanley, T. W., Intern. J. Air Pollution 2, 253 (1960). (10) Thomas, J. F., Tebbens, B. D., Sanborn, E. N., Cripps, J. AI., Ibid., p. 210. (11) Wells, W. C., Sweeley, C. C.! Bentley, R., “Biomedical Applications of Gas Chromatography,” p. 200, Plenum Press, New York, 1964. LAWRENCE DEMAIO MORTON CORN Graduate School of Public Health University of Pittsburgh Pittsburgh, Pa. 15213 WORKsupported by funds contributed to the Graduate School of Public Health, University of Pittsburgh, by the Allegheny County Health Department.
Responses of Electron-Capture Detector to Halogenated Substances SIR: Halogenated substances of certain types produce responses of great sensitivity in the electron-capture detector. I n his early work, Lovelock reported responses for selected halogenated substances ( 3 ) . Subsequently, much work has been done applying electron-capture techniques to the analysis of chlorinated types of pesticides; however, relatively few data are available on the experimental responses of lower molecular weight halogenated substances. Here responses have been measured for a considerable number of halogenated organic substances containing one to six carbon atoms and for several inorganic halogencontaining compounds. The substances contained fluorine, chlorine, bromine, and iodine atoms; a number contained two or three different halogen atoms. The responses varied over a t least seven orders of magnitude. The responses of certain of these substances to the electron-capture detector will be compared to those obtained with the flameionization detector.
EXPERIMENTAL
Apparatus. A Model 2500 MicroTek dual-column gas chromatograph was equipped with a n electron-capture detector mounted in parallel with a flame detector by use of a column effluent splitter. T h e electron-capture detector was a Micro-Tek detector with a 300-mc. tritium source substituted for a conventional 130-mc. source. The detector was equipped with a heater and with various controls for maintaining sample and scavenger flows; this arrangement allowed maximum versatility in studying the effects of various parameters. ii Micro-Tek polarizing voltage supply modified to provide 0 to 50 volts d.c. calibrated in 0.05-volt increments was used to apply a potential across the detector; a Gyra Model E-302 electrometer completed the assembly. The system was mounted to provide easy access to each component and was connected to allow measurement of either the standing current or a specific response, as required. The outputs from the two detectors were recorded on separate 0- to 1-mv. potentiometric records hav-
ing 1-second responses. All responses were brought to a common electrometer ampere and the base scale of 1 X widths for all areas were computed at a chart speed of 2 inches/minute. The prepurified nitrogen that served as the carrier gas, the prepurified hydrogen, and the air supply for the flame ionization detector were passed through a molecular sieve to remove water and other impurities. The flow rate to the electron-capture detector was 90 cc./minute, and the detector was maintained a t 100’ C. Polarization voltage of 11 to 14 volts was based on the optimization of response from the measurements on sulfur hexafluoride and bromotrifluoromethane. Sampling volume was 0.3 cc. Chemicals. M a n y of the halogenated substances were obtained from the usual sources of Freons and other common halogenated substances. Samules of CBrF9CBrF2 and IFzCCFzf were provihed 6y Du Pont. Samples of CF2Br2 and CFaCF2CFJ were obtained from K & K Chemicals. Imperial Chemicals provided the three SF5(CF2),C1 telomers. Halocarbons Products Corp. supplied unsaturated VOL. 38, NO. 1, JANUARY 1966
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