Determination of Benzo[a]pyrene in Tars and Petroleum Milan Popl, Michal Stejskal, and Ji"d Mostecki Institute of Chemical Technology, 166 28 Prague 6 , Suchbatarova 1905, Czechoslovakia
Fluorescence analysis as a method for identification of polynuclear aromatic hydrocarbons is widely used (1-10). The successful application of the method depends on good separation of the hydrocarbon mixture. McKay and Latham ( 1 2 ) suggested a combination of several methods for isolation of polynuclear aromatics from high boiling petroleum fraction (400-500"). Analysis involved the use of ion exchange chromatography, GPC, and TLC. Using this procedure, carbazoles and some aromatic hydrocarbons with 4-6 rings were identified. Schamp and Wassenhove (12) described a fluorometric determination of benzo[alpyrene in bitumen and plants. Separation was accomplished by means of TLC on different adsorbents. Fred and Giufrida (13) separated polycyclic aromatic hydrocarbons with Durapak OPN on cellulose powder (40% acetylated) with isooctane or methanol, respectively, as the eluent. It is obvious that the best separation will be achieved if different methods based on different principles (molecular weight, adsorption energy, chemisorption) are combined. We used GPC, AEC on alumina, and LLC on Durapak OPN. All the procedures were performed with regard to the quantitative evaluation of the results obtained.
EXPERIMENTAL Apparatus. For GPC we used Liquid Chromatograph ALCi GPC 501 (Waters Associates) a n d two columns 1.3-cm i.d. by 150 cm, each packed with styrene-8 wt 70divinylbenzene were a p plied with benzene as the eluent; flow rate, 60 ml/hour; Detector RI-Differential Refractometer R 400 (Waters Associates); Recorder SP 22 (Unicam). Elution Chromatograph,. A column 0.4-cm i.d. by 90 cm. packed with 7.31 grams of Durapak O P X on Porasil C (80-100 mesh, Waters Associates), isooctane a s eluent a n d a column 0.2cm i.d. by 100 cm packed with 6.08 grams of alumina 4.5 wt 7 c H20 (N'oelm Eschwege Neutral), 20 vol 70 chloroform in n-heptane a s eluent were used. An eluent flow rate of 72 nil/hour was maintained using a Dialagrad p u m p (Isco): detector. Spectrofluorophotometer (Aminco-Bowman) with flow through-cell (0.3-cm i.d.1; and Recorder SP 22 (Unicam). T h e excitation wavelength of rJ i i nm and emission wavelength of 403 n m were chosen for detection of henzo[a]pyrene. Fluorcwence Spwtromctry (SPF). An Xminco-Bowman Spect,rofluorophotometer with Xenon lamp Hanovia 901 C-11, 15O-N', Photomultiplier tube 1 P 21; slits arrangement: excitation, 1 m m : I
( 1 ) M K Charkviani and 0 A Usharauli Tr lnst Khim Akad Nauk G r u z SSR 1 7 , 8 5 (1964) ( 2 ) V F Fedonin N F Tolikina and 0 N Belyatskaya Zh Anal Khim 20, 1022 ( 1 9 6 5 ) ( 3 ) R I Personov and T A Teplitskaya Zh Ana/ Khim 20, 1125 (1965) (4) P P D i k u n H D Krasnitskaya N D Gorelova and I A Kalinina Zh P r i k l Speklrosk 8. 406 (1968) (5) H P Burchfield R J Wheeler and J B Bernos A n a / Chem 40, 535 (1968) (6) J Jaeger Atmos Envfron 2 , 2 9 3 (1968) (7) J Eisenbrand and G Z Becker Fresenfus 2 Anal Chem 242, 145 (1968) ( 8 ) H P Burchfield R J Wheeler and J B Bernos Anal Chem 43, 1976 (1971) (9) D J Freed and L R Faulkner A n a / Chem 44, 1194 (1972) ( 1 0 ) E D Pellizzari and C M Sparacino Anal Chem 45, 378 (1973) (11) J F McKayand D R Latham Anal Chem 44, 2132 (1972) (12) N Schamp and F Van Wassenhove J Chromalogr 69, 421 11972) ( 1 3 ) lves N Fred and L Giufrida J Ass Oftic A n a / Chem 55 757 (1972)
I
L
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,
I
3w
2m ELUTION
I/OLdME
90
lml
0
1
Figure 1. G P C separation of Wilmington oil Arrows indicate the area of the benzo[a]pyrene fraction emission, 0.5 m m ; slide, 0.5 m m , meter multiplier, 0.3. 1, 3 were used. Cltrac-ioiet Spectroscopy (Lib'). A Unicam Ltd. Ultraviolet Spectrophotometer SP 800 B was used to obtain C V spectra using a microcell ( I x 0.25 c m ) . Reagents M o d e l Compound. Benzo[a]pyrene (K and K Laboratories); isooctane solutions of model compound concn. 3.2 X gram/ml (Standard I ) and concn 3.2 X gram/ml (Standard 2) were used. Solvents. Distilled n-heptane, chloroform. and isooctane were used after percolation through a column of silica gel. Fluorescence analysis of these solvents did not show aromatic hydrocarbons or other fluorescing impurities. Benzene was dried and rectified before use. Preparation of Samples. For separation on a GPC column following solutions of samples in benzene were prepared: Sample I, coal tar pitch. 2 wt 70solution: Sample 11. pyrolysis resin ( I d ) , 10 wt % solution; Sample 111, oil distillate 370-535 "C (Wilmington, Calif.) (15). non-diluted. Solutions I a n d I1 were filtered before injection. Pyrolysis resin is a hard aromatic resin obtained by treatment of heavy oil from cracking of virgin naphtha. Separation Procedure. By means of a loop, 1.23 ml of benzo[alpyrene (Standard I) solution were charged into the GPC column, 10-ml fractions were collected, and their UV spectra recorded. A maximum of benzo[a]pyrene was eluted after 5.7 hours a t 337.5 ml (fraction 34); traces were determined in fraction 32 and fraction 36. T h e CY-spectrum of combined fractions 32, 33, 34, 35. and 36 was measured and the quantity of benzo[a]pyrene was determined. At identical conditions, separations of samples I, 11. and I11 were performed. In all the cases, 1.23 ml of sample were charged and fractions 32-36 were combined, evaporated a t 60 "C in a flow of nitrogen, dissolved in a mixture of 50 vol. ?k chloroform and n-heptane and the final volume was adjusted a s follows: Sample 1', 10 ml: Sample 11', 5 ml, Sample 111'. 2 ml. GPC separation of Wilmington oil is showed in Figure l . Samples I, 11. and I11 after separation on GPC are marked 1', 11', 111'. Separation on Durapai: 0PLhr.Into the column. we alternatively injected solutions of standard (Standard 2 ) and 1'. 11', and 111'. During the separations of samples 1'. 11', and 111', the part of eluate corresponding to the elution volume of standard (Standard 2 ) was collected. After each injection of a sample. the column was eluted for 2 hours to remove the high molecular weight compounds. Charges: 20 p1 Standard 2, 20 p l 1'. 20 p l Standard 2 , 20 p1 11', 10 p l Standard 2, 40 ~1111'. Separation on A l u m i n a . Onlr one charge of standard and one of sample were injected into the column and the column was refilled (14) M . Popl, M KuraS, and J . Mostecky, ErdolKohle. 23. 492 ( 1 9 7 0 ) . (15) API 60. Report No. 12. 11 (1972)
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 11, S E P T E M B E R 1974
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250
300
350
+GC
250
?W
350
--
400
#.JE~ENGTLI
Fluorescence excitation spectra of benzo[a]pyrene fractions (Samples l’, II’, I l l ’ ) Figure 2.
Left from alumina. right from Durapak OPN
7
YL
L
hGrh
nm
Fluorescence spectra of benzo[a]pyrene and benzo[k]fluoranthene isolated from coal tar pitch Excitation spectrum left emission spectrum right ( 1 ) benzo[a]pyrene ( 2 ) benzo[k]fluoranthene Figure 4.
Table I. D e t e r m i n a t i o n of Benzo [alpyrene (in w t 7 0 ) f r o m Fluorescence E x c i t a t i o n Spectra Durapak
L ELLTION
80
50
I 4‘1
20
0
VOLUME 1-11
Separation of benzo[a]pyrene fraction (Sample 1 ’ ) on Durapak O P N (left)and on alumina (right)
Coal t a r p i t c h P y r o l y s i s resin
Oil fraction
Alumina
2.44 1.41 1.29 0.054 0.060 0.052 0.00033 0.00077 0.00040
1.30 0.062 0.00028
Figure 3.
with fresh adsorbent. T h e procedure was similar to the separation on Durapak. Separation time was about 45 minutes. Charges: 20 p1 Standard 2, 20 p1 1’, 10 p1 Standard 2, 20 ~1 II’, 2 p l Standard 2,50 pl111’. Fluorescence excitation spectra of fractions from the separation on Durapak a n d alumina were measured under the same conditions (sample-standard) a t a n emission wavelength of 403 n m and the quantity of benzo[a]pyrene in the original sample was calculated. Spectra of fractions from separation on Durapak and alumina are shown in Figure 2. Observation of Interference. Records from the separations of Sample I’ on alumina and Durapak are quite different (Figure 3 ) . This shows t h a t the compound corresponding to peak 3’ was not separated on Durapak from peak 2’. It was found t h a t peak 2 on Durapak was a mixture of two components: one was benzo[a]pyrene and the other was a compound with a fluorescence spectrum very similar to benzo[a]pyrene. This compoiund was very well separated from benzo[a]pyrene on alumina, where it w’as eluted in peak 3’ together with a n thanthrene. T o identify this compound, 100 p1 of I’ were separated on Durapak, and the fraction corresponding to benzo[a]pyrene was evaporated and dissolved in a minimum quantity of 20% CHCls-n-heptane. This solution was separated on alumina. The eluate corresponding to peak 3’ was evaporated to a volume of about 0.5 ml. The UV-spectrum of this solution showed the presence of benzo[k]fluoranthene (Figure 4).
RESULTS AND DISCUSSION The spectrofluorometer with the flow-through cell, which was used as a detector for elution chromatography enabled a very selective recording of a n individual compound in a complicated mixture. Nevertheless, this technique was also not free of interference. Quantitative evaluation by the measurement of peak area is not applicable because the results are always higher. From all the possible combinations of well defined peaks in excitation and emission spectra of benzo[a]pyrene (excitation: 292, 360, 377 nm; emission: 403, 427 nm), it seems best to utilize the couple (ex. 377, em. 403 n m ) . For direct comparison of
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sample and standard, this couple offers the lowest result at highest sensitivity for determination (both bands belong to the most intensive in the spectrum). Excitation spectra of samples separated on Durapak and alumina were quantitatively evaluated by means of differences in relative intensities of 1360-1315 and 13771367, respectively. These differences of samples were compared with the same differences in relative intensities of standards. The results are given in Table I. Quantitative evaluation using values of A I helps for estimation of interference. If there is no interference, both results are the same. In the case of coal t a r pitch separated on alumina, the observed interference was very low and the obtained spectrum is practically identical with spectrum of pure benzo[alpyrene. The strong interference of benzo[h]fluoranthene was observed when coal tar pitch was separated on Durapak. The high interference can be also seen in case of separation of pyrolysis resin on the both adsorbents, and this interference increased in the case of oil fraction. Reproducibility was checked by analysis of the pyrolysis resin with 0.05 wt % addition of benzo[a]pyrene. Using alumina as adsorbent, the total content 0.107 wt % (for 11367377) and 0.116 wt 70 (for 11315360) of benzo[a]pyrene was determined. A limit of detection is about gram benzo[a]pyrene per ml, which means that 0.1 ppm of benzo[a]pyrene in raw material can be determined. ACKNOWLEDGMENT The authors thank Charles J. Thompson, Bartlesville Energy Research Center, for providing the sample of Wilmington oil distillate.
RECEIVED for review November 12, 1973. Accepted March 5 , 1974.
A N A L Y T I C A L CHEMISTRY, VOL. 46, NO. 11, S E P T E M B E R 1974
