An Analytical Method for Polynuclear Aromatic Compounds in Coke Oven Effluents by Combined Use of Gas Chromatography and Ultraviolet Absorption Spectrometry T. D. Searl, F. J. Cassidy, W. H. King, and R. A. Brown &so Research and Engineering Company, Analytical & Information Division, Linden, N . J .
A routine method was developed to measure polynuclear aromatic compounds in coke oven effluents. Although other techni ues are involved, the method is designated as a G%/UV procedure. In practice, samples are collected on a filter and the filter is extracted with cyclohexane. An internal standard is added and a portion of the extract is injected into a gas chromatograph for separation intofractionsthatare trapped. UV absorption spectra of selected fractions provide a quantitative measurement of fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[a]pyrene, and benzo[~]pyrene. Benr[c]acridine and benz[a]anthrone are also included in the method but were not observed to be present. It is difficult to establish the absolute accuracy for sam les of this nature since only a small pro ortion o the material present is reported upon. faking this into consideration, each step in the method was accepted as satisfactory only after being proved to be quantitative. Good cross checks were obtained by mass spectrometer and fluorescence analysis.
P
AIR QUALITY is a concern to government and industry alike, and substantial technical effort is directed to this area. One need is a routine method to analyze coke oven effluents. As a result, the American Iron and Steel Institute provided support for development of the method described in this manuscript. The objective was to demonstrate the ability to routinely measure benz[a]anthracene, benzo[a]pyrene, benz[c]acridine, and benz[a]anthrone, and other compounds which could be conveniently handled. The starting point was a silver membrane filter containing material collected at a coke oven site using the technique of Richards, Donovan, and Hall ( I ) . Many techniques have been described to analyze particulates in auto exhaust, tobacco smoke, and coke oven effluents. Most of this work deals with composition of materials and the methods employed were usually too lengthy to serve as routine procedures. Possible routes being considered at this time did indicate that any potential method would require separation and then measurement by a suitable technique such as ultraviolet absorption, fluorescence, electron capture, or flame ionization detectors. Gas chromatography was selected for the separation because its application to polynuclear aromatics had been demonstrated. In addition, it is a rapid and highly efficient technique. In the early stages of this work it was decided to utilize UV absorption as the quantitative measurement of G C fractions. This choice evolved from learning that it had the required sensitivity and specificity for this application. The method finally developed provides a rapid measurement that is suitable for routine use in a plant laboratory. EXPERIMENTAL
Chemicals. Reference compounds were purchased from different supply houses. Each compound was checked by
(1) R. T. Richards, D. T. Donovan, and J. R. Hall, Amer. Ind. Hyg.Ass. J.,28,590 (1967). 954
gas chromatography and mass spectrometry. No peaks were observed to indicate impurities. The only impurity to be missed by the two tests would be an isomer whose G C retention time and molecular weight coincide with those of the compound being tested. Compounds and their source were as follows: 1,3,5-triphenyl benzene, benz[c]acridine, Aldrich Chemical; pyrene, benz[a]anthracene, benz[a]anthrone, benzo[a]pyrene, Eastman Organics. The most critical chemical from a purity standpoint is cyclohexane. To check purity, evaporate 180 ml to 5 ml, then obtain a spectrum of this residue in a 1-cm cell. To be satisfactory, the absorbance should be no more than 0.01 in the region, 280-400 mp. Cyclohexane can be purified by percolation through activated silica gel, if necessary. Extraction, The initial hope was that cyclohexane would prove to be a satisfactory solvent for the PNA hydrocarbons and nonhydrocarbons. If suitable, cyclohexane would be advantageous as compared with the unusual solvent, benzene, because benzene would tend to dissolve undesirable polar compounds and might interfere with subsequent measurements by gas chromatography and UV. All of the PNA’s listed previously were soluble in cyclohexane at >3 pg/pl of solution. In another check on solubility, a portion of a dust sample (20 mg) was extracted with 250 ml of cyclohexane. The cyclohexane insoluble was then extracted with hot benzene. UV spectra of the two fractions, Figure 1, show that the principal UV absorbers were extracted by cyclohexane. In addition, the absence of peaks in the absorption curve of the benzene fraction indicates the absence of PNA’s of interest in this method. Experience with the method has also indicated that cyclohexane is a satisfactory solvent. Gas Chromatography. Numerous published papers deal with the measurement of PNA’s by gas chromatography (2-10). The state of the art represented by these papers did not precisely satisfy the need for the coke oven effluent analysis. The previous investigators reported success with capillary and l/s-inch 0.d. packed columns. A study indicated that l/s-inch packed columns provided resolution as good as that achieved by capillary columns. This was fortunate because only packed columns provide sample sizes compatible for UV measurement. Columns were evaluated with blends of pure compounds and the cyclohexane extract of a typical sample. The most consistently good results were achieved with the column packing, 2x SE30 (GC grade) on Chromosorb G (2) H. Arti, R. Sodan, and H. Matsushita, Znd. Health, 5 , No. 3-4, 243 (1967). (3) N. Carugno and S.Rossi, J . Gas Chromatogr., 5 , 103 (1967). (4) B. B. Chakraborty and R. Long, Enuiron. Sei. Technol., 1, 828 (1967). ( 5 ) 0. T. Chertyk, W. S. Schlatzhauer, and R. L. Stedman, J . Gas Chromatogr., 3, 394 (1965). (6) H. J. Davis, ANAL.CHEM.,40, 1583 (1968). (7) H. J. Dawson, ibid., 36, 1852 (1964). (8) L. DeMaio and M. Carn, J. Air Pollut. Control Ass., 16, 67 (1966). (9) L. S. Ettre, R. D. Condon, F. J. Kabor, and E. W. Creplinski, J. Chromatogr. 13,305 (1964). (10) J. R. Wilrnshurst, J . Chromatogr., 17, 50 (1965).
ANALYTICAL CHEMISTRY, VOL. 42, NO. 9, AUGUST 1970
80/100 mesh (acid washed and dimethyl silyl ether treated). Of the compounds studied, the two most difficult separations were benz[a]anthracene from chrysene and benzo[a]pyrene from benzo[e]pyrene. Fortunately, UV spectral data will readily do this. The SE 30 column was also felt to be satisfactory from the standpoint of thermal stability. The nature of a chromatogram is illustrated by the examples in Figures 2 and 3. The operating conditions are also shown. A known blend of seven components is shown in Figure 2. Well resolved peaks are obtained for a stable, flat base line. This capability has been demonstrated repeatedly. Retention times are also shown in Figure 2. The last eluted component is triphenylbenzene, the internal standard. Benzanthracenedione was included in this portion of the study but there was no interest in measuring this compound and it was not worked with to any further extent. The chromatogram of an actual sample is shown in Figure 3. In contrast to the blend of pure compounds, this chromatogram is very complex. The base line is an envelope which does not return to zero during the entire run. Peaks themselves vary from single entities to partially resolved shapes of several components. Fortunately, it is unnecessary to use peak area measurements except for that of the internal standard, triphenylbenzene, and this compound elutes separately at the end of the sample. The chromatogram was valuable in verifying the UV measurement which indicated that benz[c]acridine and benz[a]anthrone were not present at the microgram level. It was necessary to introduce a representative sample to the chromatograph and to collect representative fractions for UV analysis. Since high boiling compounds are involved, fairly high temperatures must be used to completely vaporize a sample and to allow effluent to be trapped with no prior condensation occurring. This presented a possible decomposition problem, particularly for the oxygenated compound, benz[a]anthrone. A study of some sample injection systems indicated that older model chromatographs may be unsatisfactory in this
I
1
1
I
1
C, 250
400 MILLIMICRONS
Figure 1. Ultraviolet absorption spectra of cyclohexaneand benzene extracts
respect. Their satisfactory use would necessitate that a modified injection unit be installed. However, sampling with a Perkin-Elmer Model 900 chromatograph was satisfactory. This unit has a replaceable glass sleeve which minimizes contact with hot metal and possible decomposition. These sleeves must be frequently replaced as an oil and column coating will collect at this point. Operation at 310 "C. was established as good practice. Trapping. In order to satisfactorily split the effluent for measurement by flame detector and to obtain a sample for UV, it was necessary to modify the chromatograph as shown in Figure 4. By means of this arrangement, 15% of the effluent passes to the detector with the major portion (85%) being available for trapping. To trap a fraction, the stainless steel tube can be easily slid into position when a fraction is to be taken. To stop trapping, the tube is simply taken out. The design and subsequent performance of the trap system is a key point to obtaining quantitative results. The trap has a volume of 0.37 ml and can be washed out quantitatively with a small volume of solvent. The pressure drop across the trap is near zero and tests showed the flow to the flame
I
PE-MODEL 9 0 0 CHROMATOGRAPH 10 F T . x 1/8" O.D. COLUMN 2% SE-30 ON G INJECTION 315'C. DETECTOR 290'C. START 175'C. PROGRAM 4 T . / M I N U T E FINAL 275'C. HOLD 1 5 MINUTES SAMPLE SIZE 0.5 MICROLITER
28
26
24
22
20
18
16 14 TIME IN MINUTES
i 10
8
Figure 2. Blend of six polynuclear aromatics ANALYTICAL CHEMISTRY, VOL. 42, NO. 9, AUGUST 1970
955
u 32
34
30
28
T I M E IN MINUTES
Figure 3. Chromatogram of coke oven effluent. Conditions same as Figure 2
Table I. Vaporization and Collection of Benzo[u]pyrene Micrograms of Benzo(a)pyrene Without column With column Injected Recovered Injected Recovered 2.5 5.2 5.4
,LOCKNUT
2.5 5.7 5.2
1.8 3.0 4.5 10.0
1.6 3.3
4.1 8.6
-c
number of times. It was found that benzo[a]pyrene was particularly difficult to handle. Only by optimizing conditions could satisfactory results be attained. A key consideration is that B[a]P decomposed in the system at temperatures above 315 "C. Injection and recovery of B[a]P is shown in Table I for 2 to 10 micrograms with and without the GC column. After this capability was demonstrated, all components of the blend shown in Figure 2 could be handled satisfactorily. In fact, this blend was run as a routine test along with unknown samples. UV Absorption Spectra. To obtain the UV spectrum of a fraction, the trap containing the material was rinsed with cyclohexane. The cyclohexane solution was made up to a volume of 3.8 ml, which was used to fill a 1-cm cell for measurement on a Cary Model 11 spectrophotometer. Figure 4. Gas chromatograph trapping assembly PROCEDURE
and trap are unaffected by the presence or absence of the trap. The traps are inexpensive and can be changed rapidly; thus any or all peaks can be trapped. There is a temperature gradient across the trap which causes the sample to condense at its first opportunity. Separate tests showed that PNA's never appear at the room temperature end of the trap. The traps are effective as described next. The ability to completely vaporize and to quantitatively collect samples for UV measurement was demonstrated a 956
0
The method is shown schematically in Figure 5. First, the sample filter is extracted for six hours by refluxing with 250 ml of cyclohexane in a Soxhlet extractor. During extraction the Soxhlet is covered with aluminum foil to protect from light. After the addition of 0.02 ml of toluene containing 20 pg of the internal standard, triphenyl benzene, the extract is evaporated to a small volume. In evaporating the sample care is taken to prevent losses. The sample is first handled in a 150-ml beaker and finally in a 1-dram vial. A
ANALYTICAL CHEMISTRY, VOL. 42, NO. 9, AUGUST 1970
Table 11. Wave Lengths Used to Measure UV Absorbances Wavelength mM Peak Background corr. Compound 288 295 Fluoranthene 335 350 Pyrene 383 400 Benz[c]acridine 288 295 Benz[a]anthracene 269 Base line from Chrysene 240 to 295 Benz[a]anthrone 315 340 383 395 Benzo[a]pyrene 332 345 Benzo[e]pyrene 1,3,5-Triphenylbenzene 253 Base line from 235 to 290
WITH CYCLOHEXANE EVAPORATE TO SMALL VOLUME, ADD TOLUENE AND INTERNAL STANDARD
---T---
j-[
I
I
PEAK TRAPPING FRACTION FRACTION FRACTION FRACTION FRACTION FRACTION
1 FLUORANTHENE (UV)
PYRENE (UV) BENZ (c) ACRIDINE (UV, GC) BENZ (c) ANTHRACENE (UV) CHRYSENE (UV) BENZ (a) ANTHRONE (UV, GC) BENZ (a) PYRENE (UV. FLUORESCENCE) BENZ (e) PYRENE cuvj FRACTION 7 TRIPHENYLBENZENE (GC, UV, INTERNAL STANDARD)
Table 111. Range in Composition of Coke Oven Effluent Samples Polynuclear aromatic compounds Range, pg 1-45 Fluoranthene 1-34 Pyrene Benz[c]acridine
