Determination of Polycyclic Aromatic Hydrocarbons in White Petroleum Products Milan Popl, Michal Stejskal, and Jiti Mostecky Institute of Chemical Technology, 166 28 Prague 6, Suchbstarova 5, Czechoslovakia
Polycyclic aromatlc hydrocarbons (PAH) occur In white petroleum products in the ppb range accompanied by some sulfur and polar compounds. PAH were concentrated by frontal elution on silica gel and separated from polar compounds by adsorption chromatography on basic alumina. Final Separation was achieved by gradlent elution adsorption chromatography on alumina or by gel permeation chromatography and PAH were identified using fluorescence and phosphorescence spectrometry.
Because of their carcinogenic activity ( I ), polycyclic aromatic hydrocarbons belong to the most intensely studied mixtures of industrial products which come into contact with the human organism (2). The content of polycyclic aromatic hydrocarbons becomes an important factor when considering the use of white oils and n-alkanes (3-5). Oils for medical purposes not only affect the skin (in the form of cosmetic and medical preparations) but also are taken internally because of their application in the food industry. In the case of n-alkanes, which are one of the raw materials for producing fodder yeast, there is an indirect action on the human organism through the accumulation of the aromatic hydrocarbons in the meat of animals intended for human consumption. This indicates the need of a reliable method for determining polycyclic aromatic hydrocarbons in white oils and n-alkanes that would enable determination of individual aromatic skeletons in concentrations of about 1 ppb. Determination of this level of concentration corresponds to the maximum possibilities of the present analytical methods (6, 7). The most important step of the analytical procedure is a preliminary concentration of the polycyclic aromatic hydrocarbons with subsequent separation of the concentrate for the final identification (8, 9). Fluorescence and phosphorescence spectrophotometry (10-14) represents an optimum method for identifying these compounds. In the present paper, we employed frontal chromatography on silica gel for separating the polyaromatic portion, adsorption elution chromatography on alumina for separation of the aromatic hydrocarbons and polar components, and gradient adsorption or gel chromatography for the final separation of aromatic hydrocarbons (Figure 1).The fractions were then submitted to fluorescence and phosphorescence analysis.
EXPERIMENTAL Apparatus. Frontal elution chromatography was carried out on a column 1-cm i.d. by 90 cm packed with 34 g of silica gel (Woelm Eschwege, activity grade I). Sample flow rate 100 ml/hr was maintained using pump MC '706 (Mikrotechna, Prague). Elution adsorption chromatography was carried out on a column 0.4-cm i.d. by 90 cm packed with 9.3 g of alumina (Woelm Eschwege Basic) deactivated by 6% w t of water and the n-pentane flow rate was 60 ml/hr. Eluted compounds were detected by means of a differential UV detector (Waters Associates Inc.) working a t 254 nm, and a Line Recorder TZ 21 S (Laboratorn; Pibtroje, Prague).
Gradient elution adsorption chromatography (GEAC) was carried out on a column 0.3-cm i.d. by 100 cm packed with 5.7 g of alumina (Woelm Eschwege Acid) deactivated by 2% w t of water. As an eluent, we used a mixture of n-pentane-diethyl ether in a 2-hr gradient program with increasing concentration of ether in n-pentane (0:4:5.5:9:20:35:45:50:50:50:50%vol of ether) using a Dialagrad Programmed Gradient Pump, Model 190 (ISCO). Eluent flow rate was 28 ml/hr; detection is the same as mentioned previously. Gel permeation chromatography (GPC) was carried out on two columns in series, each 1.3-cm i.d. by 150 cm, packed with styrene8%wt divinylbenzene. Benzene flow rate was 60 ml/hr. Fluorescence a n d Phosphorescence Spectrometry. An Aminco-Bowman Spectrofluorophotometer was used for recording all fluorescence and phosphorescence spectra. Cells having a 1-cm path, photomultiplier tube 1P 2 1 and Xenon lamp Hanovia 90 1C-11, 150 W were used. Slit arrangements: cell excitation 1 mm, emission 0.5 mm, P M tube 0.5 mm. Phosphorescence spectra were measured a t the temperature of liquid nitrogen in a mixture of methylcyclohexane and n-pentane (4:l vol), and mean lifetimes were evaluated using a Recorder SP 22 (Pye Unicam Ltd). Reagents. Model Compounds. The model compounds were obtained commercially and their purity was controlled UV-spectrophotometrically. Soluents. Distilled n-pentane, diethyl ether, and methylcyclohexane were used after percolation through a column of silica gel. Fluorescence analysis did not show aromatic hydrocarbons or other fluorescing impurities. Benzene was dried and redistilled before use. Samples. Sample A. Medicinal oil for pharmaceutical use, 1000 ml; density, 0.854 g/ml. Sample B. Dearomatized n-alkanes CIO-CI~,765 ml; density, 0.755 g/ml. Procedure. The samples were separately processed by frontal chromatography on silica gel. In the course of frontal elution, the silica gel column retained anthracene in a concentration of 10-6 g/ml in 1300 ml of sample A. The penetration of anthracene into the eluate was monitored by measuring the fluorescence spectra of collected fractions. After allowing 1000 ml of sample A to pass through the column, the elution was carried out with 150 ml of n pentane and 100 ml of ether. By evaporating the ether eluate in a dry nitrogen stream a t 30 OC, 1.052 g of the sample A aromatic concentrate was obtained; 0.0257 g of the aromatic concentrate was obtained in the same way from 756 ml of sample B. The concentrate of sample A was a faint yellow, viscous, oil-like liquid. The concentrate of sample B was a white powder, sparingly soluble in n-pentane. Finally, in the two cases, the elution was performed with 100 ml of methanol and, after evaporation, fractions were obtained and marked as polar compounds I. Separation of aromatic concentrates of the two samples into aromatic hydrocarbons and polar components, which were marked as polar compounds 11, was carried out on basic alumina. The aromatic concentrate of sample A was injected into a prewetted column and washed out with n-pentane under an adsorbent loading of 0.0294 g/g. From the moment when the UV detector revealed an absorption of UV light, the eluate (100 ml) was collected. After evaporation of pentane, it yielded the portion containing aromatic hydrocarbons. Polar compounds I1 were then obtained by means of elution with ether and evaporation of the eluate. The aromatic hydrocarbons to polar compounds I1 ratio in sample A was 5.51 by weight. With respect to the character of sample B aromatic concentrate, only a portion soluble in n-pentane was separated on basic alumina. Aromatic hydrocarbons and polar compounds I1 occurred in the n-pentane extract in a ratio of 1:1.5; in the whole sample B, the ratio was 1:11.8 by weight. The quantitative elution of polynuclear hydrocarbons in 100 ml
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
1947
WHITE OIL
c m ~ w n rs
ON SILICAGEL
HYaPOCARKNS
I AROMATIC C3NCEN TRATE
SATURATED
SEPARATION CoMpoUN3S I I
ON ALUMINA AROMATIC
0
20
10
40 ELUTION OLUME
30
Flgure 4. GEAC separation of aromatic hydrocarbons (1) and polar compounds II (2) from sample B
-2
-1 FRACTIONS
-3
FRACTIONS
Figure 1. Separation scheme
Figure 5. Ultraviolet (l), phosphorescence (2) and infrared (3) spectra of unknown compound isolated from polar compounds II of sample B
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a
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40
1 ELUTION VOLUME [d]
Flgure 2. GEAC separation of model mixture
. .
25C
C
10
20
3C
40 ELUTION WLUM€.
Figure 3. GEAC separation of aromatic hydrocarbons (1) and polar compounds II (2) from sample A
of the eluate was checked by specific elution volumes of triphenylene (1.06 ml/g) and benzo[a]pyrene (2.14 ml/g) measured under identical conditions. The aromatic hydrocarbons and polar compounds I1 from the two samples were further separated with the help of GEAC; the aromatic hydrocarbons from sample A also were separated with the help of GPC. A gradient program (15) suitable for separating model mixtures of 3- to 6-nuclear aromatic hydrocarbons (see Figure 2) and the separation of samples, was performed under the same conditions (Figures 3 and 4) collecting 25 fractions (3 ml each) for the following analysis. NOTE: During GEAC, the most distinct peak of the sample B polar portion I1 (Figure 4) corresponds, according to its elution 1946
* ANALYTICAL CHEMISTRY, VOL. 47,
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Figure 6. Fluorescence excitation (left) and emission (right) spectra alkylfluoranthenes fraction from GEAC of fluoranthene standard (l), of aromatic hydrocarbons from sample A (2). and fluoranthene fraction from GEAC of aromatic hydrocarbons from sample B (3) (excitation 360-370 nm, emission 460 nm)
volume and UV spectrum, to a residue after the extraction of the aromatic concentrate of sample B with n-pentane. (For its spectral characteristic see Figure 5 . ) The ultraviolet and phosphorescence spectra indicate presence of an aromatic ring and the infrared spectrum with absorption bands a t 1390 cm-’ and 1180 cm-l is characteristic for disulfones. According to MS analysis, the unknown compound contains two 4 0 2 - groups and alkyls Cz and C4 and its molecular weight is 290. The suggested formula of this compound is C Z H ~ C ~ H ~ S O ~ S O Z C ~ H ~ . With the aid of GPC, aromatic hydrocarbons of sample A were separated. After the elution of 150 ml, 40 fractions ( 5 ml each) were collected. Analysis of Fractions from GEAC. Fluorescence excitation and emission spectra were obtained for all fractions-in original volume, diluted ten times, and diluted one hundred times with n pentane. The analysis of one fraction, Le., of the three solutions a t excitation (200 to 450 nm) and emission (300 to 500 nm) wave-
NO. 12, OCTOBER 1975
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Flgure 7. Fluorescence excitation (left) and emission (right) spectra of benzo[ k]fluoranthene standard (1). benzo[k]fluoranthene from GEAC of aromatic hydrocarbons from sample B (2) and b(k)f fraction from GEAC of aromatic hydrocarbons from sample A (3) (excitation 308 nm, emission 426 nm)
WEIW'
300
3%
40C
450
5CC
550
A
17-3
Flgure 9. Phosphorescence excitation (left) and emission (right) spectra of dibenzothiophene standard (1) and dibenzothiophene fraction (2) from GPC of aromatic concentrate from sample A (excitation 326 nm, emission 424 nm 7 = mean lifetime)
DISTRlEUJ7ON
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I
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Figure 8. GPC separation of aromatic hydrocarbons from sample A, distribution of identified aromatic types
lengths (by 5-nm steps) took a t least one hour. Mixed fluorescence spectra, typical for mono- (excitation 225, 270-280 nm, emission 300-315 nm) and diaromatic (excitation 225,280-290 nm, emission 325-345 nm) hydrocarbons also occurred in fractions exceeding the assumed regions of the elution of these hydrocarbons. The above fluorescence leads to interference difficulties over the whole gradient separation interval in spite of the fact that its intensity drops with the increasing number of the fractions. Tri- and polynuclear aromatic hydrocarbons that can be excited in the region of 290 to 450 nm, which are characterized by fluorescence a t 350 to 500 nm, can be identified in the presence of mono- and diaromatic hydrocarbons under the assumption that no deactivation of their excited state will occur. The comparison of the fluorescence spectra of fractions with standards and with respect to elution volumes identified the following components in sample A: alkylfluoranthenes (Figure 6), a mixture of benzofluorenes (exc. 260, 300 nm, emis. 335-355 nm), chrysene (exc. 266 nm, emis. 360, 380, 400 nm), benzo[k]fluoranthene (Figure 7); the components identified in sample B were as follows: anthracene, fluoranthene (Figure 6), chrysene (exc. 270 nm, emis. 360, 380 nm), and benzo[k]fluoranthene (Figure 7). For phosphorescence analysis, the solvent was removed from the fractions a t 30 OC in a nitrogen stream. Then, the fractions were dissolved in 0.25 ml of a mixture methylcyc1ohexane:n-pentane (4:l by volume). The analysis of one fraction with simultaneous measurement of the mean lifetime of the phosphorescence took about one hour. In the fractions of sample A, predominantly mixed spectra were found with an emission maximum between 380 and 480 nm with no remarkable vibrational structure over the whole gradient range, roughly corresponding to the type of spectra of monoaromatic hydrocarbons. Phenanthrene was found in sample B in the fraction of trinuclear aromatic hydrocarbons. The charac-
.
300
.
4m
I
450
,
500
xI..[
Figure 10. Phosphorescence excitation (left) and emission (right)
spectra of triphenylene standard (1) and triphenylene fraction ( 2 ) from GPC of aromatic concentrate from sample A (excitation 280 nm, emission 461 nm, 7 = mean lifetime)
teristics of spectra of the other fractions were the same as in the case of sample A. Analysis of Fractions from GPC. The fractions obtained by separating aromatic hydrocarbons from sample A were evaporated a t 60 O C in a nitrogen stream and weighed (Figure 8). Odd fractions were dissolved in the same volume of n-pentane (5 ml) and, after diluting them for analysis, their fluorescence spectra were measured. The spectra were much more complex and identification of individual types was much more difficult. Starting from the fraction with log V = 2.4472 the vibrational spectra appear in a region of 325 to 370 nm (bands 325,338,352, 355,370 nm). In the region of the elution of polynuclear hydrocarbons, an indistinct maximum of benzo[k]fluoranthene was observed. The unique position of fluoranthene, which is characterized by its long wave fluorescence in the region of about 460 nm, enabled us to determine its relative concentrations in individual fractions by evaluating fluorescence excitation spectra scanned a t an emission wavelength of 460 nm. It is suggested that red shift in fluorescence excitation spectrum (Figure 6) in comparison with fluoranthene is due to alkylation of parent aromatic hydrocarbon. The distribution of alkyldibenzothiophenes and dibenzothiophene were established by phosphorescence spectra (Figure 8). With the separation methods used, dibenzothiophene accompanied trinuclear hydrocarbons and further fluoranthene and triphenylene. Phosphorescence spectra of dibenzothiophene and triphenylene from GPC separation are given in Figures 9 and 10. The spectra of fractions were simpler than the corresponding fluorescence spectra starting from those with log V = 2.4472. Up to this value of the elution volume, they have a character of mixed spectra of mono- and diaromatic hydrocarbons with no marked vibrational structure.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
1949
Quantitative Determination of Identified Compounds. The fractions, in which a certain compound was identified, were combined and correlated with spectra of standard compounds, maintaining quantitative ratios. From concentration data by volume and weight, their probable concentration in the original sample was calculated. In a case where the sample spectrum was not disturbed by interference, direct correlation of spectrum intensities with standards was carried out, maintaining measurement conditions. In the other cases, the correlation was based on differences between relative intensities of distinct neighboring minimum and maximum values of the excitation or emission spectra of the identified compound.
Table I. Separation on Silica Gel Sample B
Sample A Weiaht aft& eva o ratpmmgll.
Ammatics
ASTM; mgll.
Original oil Oil after percolation on silica gel n-Pentane eluate, 150 ml Diethyl ether eluate, 100 ml, i . e . , aromatic concentrate Methanol eluate, 100 ml, i . e . , polar compounds I
mgll.
... , .. ...
547 387 508
839
. .. .. . ...
5.03
0.00 0.00
1052
. ..
Weight after evaporation mgll.
Aro-
17.3
34.0
...
17.4
RESULTS A N D DISCUSSION
0.00
Table 11. Separation of Aromatic Concentrates on Basic Alumina Sample A , g
Sample B, g
0.273 0.194 0.03 53
0.0257 0.0020 0.0227
5.5:l
1:11.8
Charge Aromatic hydrocarbons Polar compounds I1 Ratio of aromatic hydrocarbons to polar compounds I1
Table 111. Combination of Methods and Quantity of Determined Aromates Sample A
Sample B Quant-
Aromatic type
Anthracene Phenanthrene Alkylfluoranthenes Benzo[k]fluoranthene Triphenylene Alkyldibenzothio: phenes Alkylaryl disulf one
1950
Methods
...
$ ;
. ..
~
Methods
GEAC + Fluor.
GPC + Phosph. 140 GEAC + Phosph. GEAC + Fluor. GPC + Fluor. 10 GEAC + Fluor. GEAC + Fluor,
GPC + Phosph. 180
...
e . .
... IR, UV sp.
,
1 30 1
1 GEAC + Fluor.
GPC + Phosph. 1.5
...
Quantity PPb
1
... ... 39,000
The two samples differed in their total contents of aromatic compounds as determined according to ASTM D 2008-65. Based on this standard and by means of weight analysis, the distribution of aromatic compounds was determined in the course of the first separation step (Table I). About 85% of the mono- and diaromatic hydrocarbons from sample A passed through the silica gel column in original oil and in n-pentane eluate. The rest of these compounds were eluted by means of ether together with triand polyaromatic and polar compounds. Sample B contained only compounds that can be eluted by means of ether. The separation on basic alumina (Table 11) yielded results which were of interest with respect to very different contents of polar compounds I1 in the two samples. The UV absorption of sample B could be attributed t o the portion of the polar compounds 11, where its main component is represented by alkylaryldisulfone. The results of the analysis according to ASTM D 2008-65 do not correspond to the content of aromatic hydrocarbons in the case of sample B. Table I11 lists the identified aromatic types, methods of their quantitative determination in the analyzed samples, and amounts found. The separation method used enabled us to determine certain polyaromatic hydrocarbons present in oil for medicinal use and in n-alkanes in amounts of about 1 ppb when using GEAC as well as GPC. LITERATURE CITED (1) V . KovBi, Ochr. Ovzduli 3(10), 153 (1971). (2) W. M. Catchpole, E. Macmillan. and H. Powell, J. lnst. Petrol., 57, 247 (1971). (3) L. G. Khmiiyar, Z. V. Kocheva. and G. T. Pasichnik, Neftepererab. Neftekhim. (Kiev), 7, 42 (1972). (4) J. C. Suatoni. Anal. Chem., 39, 1505 (1967). (5) i. Muntean and N . Mosescu, Chim. Anal., 1, 237 (1971). (6) M. A. H. RiJk and D. Van Battum, Dtsch. Lebensm-Rundsch., 69(2), 75 (1973). (7) W . Strubert. Chromatographia, 8(4), 205 (1973). (8) H. Matsushita and Y . Esumi, BunsekiKagaku, 21, 1594 (1972). (9) J. F. McKay and D. R. Latham, Anal. Chem., 44, 2132 (1972). (10) L. Dubois, A. Zdrojewski, and J. L. Monkrnann. Staub-Reinhalf. Luft, 32(12), 487 (1972). (1 1) J. F. McKay and D. R. Latham, Anal. Chem., 45, 1050 (1973). (12) H. V. Drushei and A. L. Sommers, Anal. Chem., 38, 10 (1966). (13) M. Zander, Agnew. Chem., lnt. Ed. Engl., 4, 930 (1965). (14) M. Zander, ErdolKohle, 19(4), 278 (1966). (15) M. Popi, J. Mostecky, and Z. Havei, J. Chromatogr.,53, 233 (1970).
RECEIVEDfor review January 21, 1975. Accepted June 13, 1975.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
Polycyclic aromatlc hydrocarbons (PAH) occur In white petroleum products in the ppb range accompanied by some sulfur and polar compounds. PAH were concentrated by frontal elution on silica gel and separated from polar compounds by adsorption chromatography on basic alumina. Final Separation was achieved by gradlent elution adsorption chromatography on alumina or by gel permeation chromatography and PAH were identified using fluorescence and phosphorescence spectrometry.
Because of their carcinogenic activity ( I ), polycyclic aromatic hydrocarbons belong to the most intensely studied mixtures of industrial products which come into contact with the human organism (2). The content of polycyclic aromatic hydrocarbons becomes an important factor when considering the use of white oils and n-alkanes (3-5). Oils for medical purposes not only affect the skin (in the form of cosmetic and medical preparations) but also are taken internally because of their application in the food industry. In the case of n-alkanes, which are one of the raw materials for producing fodder yeast, there is an indirect action on the human organism through the accumulation of the aromatic hydrocarbons in the meat of animals intended for human consumption. This indicates the need of a reliable method for determining polycyclic aromatic hydrocarbons in white oils and n-alkanes that would enable determination of individual aromatic skeletons in concentrations of about 1 ppb. Determination of this level of concentration corresponds to the maximum possibilities of the present analytical methods (6, 7). The most important step of the analytical procedure is a preliminary concentration of the polycyclic aromatic hydrocarbons with subsequent separation of the concentrate for the final identification (8, 9). Fluorescence and phosphorescence spectrophotometry (10-14) represents an optimum method for identifying these compounds. In the present paper, we employed frontal chromatography on silica gel for separating the polyaromatic portion, adsorption elution chromatography on alumina for separation of the aromatic hydrocarbons and polar components, and gradient adsorption or gel chromatography for the final separation of aromatic hydrocarbons (Figure 1).The fractions were then submitted to fluorescence and phosphorescence analysis.
EXPERIMENTAL Apparatus. Frontal elution chromatography was carried out on a column 1-cm i.d. by 90 cm packed with 34 g of silica gel (Woelm Eschwege, activity grade I). Sample flow rate 100 ml/hr was maintained using pump MC '706 (Mikrotechna, Prague). Elution adsorption chromatography was carried out on a column 0.4-cm i.d. by 90 cm packed with 9.3 g of alumina (Woelm Eschwege Basic) deactivated by 6% w t of water and the n-pentane flow rate was 60 ml/hr. Eluted compounds were detected by means of a differential UV detector (Waters Associates Inc.) working a t 254 nm, and a Line Recorder TZ 21 S (Laboratorn; Pibtroje, Prague).
Gradient elution adsorption chromatography (GEAC) was carried out on a column 0.3-cm i.d. by 100 cm packed with 5.7 g of alumina (Woelm Eschwege Acid) deactivated by 2% w t of water. As an eluent, we used a mixture of n-pentane-diethyl ether in a 2-hr gradient program with increasing concentration of ether in n-pentane (0:4:5.5:9:20:35:45:50:50:50:50%vol of ether) using a Dialagrad Programmed Gradient Pump, Model 190 (ISCO). Eluent flow rate was 28 ml/hr; detection is the same as mentioned previously. Gel permeation chromatography (GPC) was carried out on two columns in series, each 1.3-cm i.d. by 150 cm, packed with styrene8%wt divinylbenzene. Benzene flow rate was 60 ml/hr. Fluorescence a n d Phosphorescence Spectrometry. An Aminco-Bowman Spectrofluorophotometer was used for recording all fluorescence and phosphorescence spectra. Cells having a 1-cm path, photomultiplier tube 1P 2 1 and Xenon lamp Hanovia 90 1C-11, 150 W were used. Slit arrangements: cell excitation 1 mm, emission 0.5 mm, P M tube 0.5 mm. Phosphorescence spectra were measured a t the temperature of liquid nitrogen in a mixture of methylcyclohexane and n-pentane (4:l vol), and mean lifetimes were evaluated using a Recorder SP 22 (Pye Unicam Ltd). Reagents. Model Compounds. The model compounds were obtained commercially and their purity was controlled UV-spectrophotometrically. Soluents. Distilled n-pentane, diethyl ether, and methylcyclohexane were used after percolation through a column of silica gel. Fluorescence analysis did not show aromatic hydrocarbons or other fluorescing impurities. Benzene was dried and redistilled before use. Samples. Sample A. Medicinal oil for pharmaceutical use, 1000 ml; density, 0.854 g/ml. Sample B. Dearomatized n-alkanes CIO-CI~,765 ml; density, 0.755 g/ml. Procedure. The samples were separately processed by frontal chromatography on silica gel. In the course of frontal elution, the silica gel column retained anthracene in a concentration of 10-6 g/ml in 1300 ml of sample A. The penetration of anthracene into the eluate was monitored by measuring the fluorescence spectra of collected fractions. After allowing 1000 ml of sample A to pass through the column, the elution was carried out with 150 ml of n pentane and 100 ml of ether. By evaporating the ether eluate in a dry nitrogen stream a t 30 OC, 1.052 g of the sample A aromatic concentrate was obtained; 0.0257 g of the aromatic concentrate was obtained in the same way from 756 ml of sample B. The concentrate of sample A was a faint yellow, viscous, oil-like liquid. The concentrate of sample B was a white powder, sparingly soluble in n-pentane. Finally, in the two cases, the elution was performed with 100 ml of methanol and, after evaporation, fractions were obtained and marked as polar compounds I. Separation of aromatic concentrates of the two samples into aromatic hydrocarbons and polar components, which were marked as polar compounds 11, was carried out on basic alumina. The aromatic concentrate of sample A was injected into a prewetted column and washed out with n-pentane under an adsorbent loading of 0.0294 g/g. From the moment when the UV detector revealed an absorption of UV light, the eluate (100 ml) was collected. After evaporation of pentane, it yielded the portion containing aromatic hydrocarbons. Polar compounds I1 were then obtained by means of elution with ether and evaporation of the eluate. The aromatic hydrocarbons to polar compounds I1 ratio in sample A was 5.51 by weight. With respect to the character of sample B aromatic concentrate, only a portion soluble in n-pentane was separated on basic alumina. Aromatic hydrocarbons and polar compounds I1 occurred in the n-pentane extract in a ratio of 1:1.5; in the whole sample B, the ratio was 1:11.8 by weight. The quantitative elution of polynuclear hydrocarbons in 100 ml
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
1947
WHITE OIL
c m ~ w n rs
ON SILICAGEL
HYaPOCARKNS
I AROMATIC C3NCEN TRATE
SATURATED
SEPARATION CoMpoUN3S I I
ON ALUMINA AROMATIC
0
20
10
40 ELUTION OLUME
30
Flgure 4. GEAC separation of aromatic hydrocarbons (1) and polar compounds II (2) from sample B
-2
-1 FRACTIONS
-3
FRACTIONS
Figure 1. Separation scheme
Figure 5. Ultraviolet (l), phosphorescence (2) and infrared (3) spectra of unknown compound isolated from polar compounds II of sample B
I
: x1
0
a
20
40
1 ELUTION VOLUME [d]
Flgure 2. GEAC separation of model mixture
. .
25C
C
10
20
3C
40 ELUTION WLUM€.
Figure 3. GEAC separation of aromatic hydrocarbons (1) and polar compounds II (2) from sample A
of the eluate was checked by specific elution volumes of triphenylene (1.06 ml/g) and benzo[a]pyrene (2.14 ml/g) measured under identical conditions. The aromatic hydrocarbons and polar compounds I1 from the two samples were further separated with the help of GEAC; the aromatic hydrocarbons from sample A also were separated with the help of GPC. A gradient program (15) suitable for separating model mixtures of 3- to 6-nuclear aromatic hydrocarbons (see Figure 2) and the separation of samples, was performed under the same conditions (Figures 3 and 4) collecting 25 fractions (3 ml each) for the following analysis. NOTE: During GEAC, the most distinct peak of the sample B polar portion I1 (Figure 4) corresponds, according to its elution 1946
* ANALYTICAL CHEMISTRY, VOL. 47,
?CC
35C
L30
LOO
45C
503
’ -“-.
Figure 6. Fluorescence excitation (left) and emission (right) spectra alkylfluoranthenes fraction from GEAC of fluoranthene standard (l), of aromatic hydrocarbons from sample A (2). and fluoranthene fraction from GEAC of aromatic hydrocarbons from sample B (3) (excitation 360-370 nm, emission 460 nm)
volume and UV spectrum, to a residue after the extraction of the aromatic concentrate of sample B with n-pentane. (For its spectral characteristic see Figure 5 . ) The ultraviolet and phosphorescence spectra indicate presence of an aromatic ring and the infrared spectrum with absorption bands a t 1390 cm-’ and 1180 cm-l is characteristic for disulfones. According to MS analysis, the unknown compound contains two 4 0 2 - groups and alkyls Cz and C4 and its molecular weight is 290. The suggested formula of this compound is C Z H ~ C ~ H ~ S O ~ S O Z C ~ H ~ . With the aid of GPC, aromatic hydrocarbons of sample A were separated. After the elution of 150 ml, 40 fractions ( 5 ml each) were collected. Analysis of Fractions from GEAC. Fluorescence excitation and emission spectra were obtained for all fractions-in original volume, diluted ten times, and diluted one hundred times with n pentane. The analysis of one fraction, Le., of the three solutions a t excitation (200 to 450 nm) and emission (300 to 500 nm) wave-
NO. 12, OCTOBER 1975
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Flgure 7. Fluorescence excitation (left) and emission (right) spectra of benzo[ k]fluoranthene standard (1). benzo[k]fluoranthene from GEAC of aromatic hydrocarbons from sample B (2) and b(k)f fraction from GEAC of aromatic hydrocarbons from sample A (3) (excitation 308 nm, emission 426 nm)
WEIW'
300
3%
40C
450
5CC
550
A
17-3
Flgure 9. Phosphorescence excitation (left) and emission (right) spectra of dibenzothiophene standard (1) and dibenzothiophene fraction (2) from GPC of aromatic concentrate from sample A (excitation 326 nm, emission 424 nm 7 = mean lifetime)
DISTRlEUJ7ON
--T
I
250
Figure 8. GPC separation of aromatic hydrocarbons from sample A, distribution of identified aromatic types
lengths (by 5-nm steps) took a t least one hour. Mixed fluorescence spectra, typical for mono- (excitation 225, 270-280 nm, emission 300-315 nm) and diaromatic (excitation 225,280-290 nm, emission 325-345 nm) hydrocarbons also occurred in fractions exceeding the assumed regions of the elution of these hydrocarbons. The above fluorescence leads to interference difficulties over the whole gradient separation interval in spite of the fact that its intensity drops with the increasing number of the fractions. Tri- and polynuclear aromatic hydrocarbons that can be excited in the region of 290 to 450 nm, which are characterized by fluorescence a t 350 to 500 nm, can be identified in the presence of mono- and diaromatic hydrocarbons under the assumption that no deactivation of their excited state will occur. The comparison of the fluorescence spectra of fractions with standards and with respect to elution volumes identified the following components in sample A: alkylfluoranthenes (Figure 6), a mixture of benzofluorenes (exc. 260, 300 nm, emis. 335-355 nm), chrysene (exc. 266 nm, emis. 360, 380, 400 nm), benzo[k]fluoranthene (Figure 7); the components identified in sample B were as follows: anthracene, fluoranthene (Figure 6), chrysene (exc. 270 nm, emis. 360, 380 nm), and benzo[k]fluoranthene (Figure 7). For phosphorescence analysis, the solvent was removed from the fractions a t 30 OC in a nitrogen stream. Then, the fractions were dissolved in 0.25 ml of a mixture methylcyc1ohexane:n-pentane (4:l by volume). The analysis of one fraction with simultaneous measurement of the mean lifetime of the phosphorescence took about one hour. In the fractions of sample A, predominantly mixed spectra were found with an emission maximum between 380 and 480 nm with no remarkable vibrational structure over the whole gradient range, roughly corresponding to the type of spectra of monoaromatic hydrocarbons. Phenanthrene was found in sample B in the fraction of trinuclear aromatic hydrocarbons. The charac-
.
300
.
4m
I
450
,
500
xI..[
Figure 10. Phosphorescence excitation (left) and emission (right)
spectra of triphenylene standard (1) and triphenylene fraction ( 2 ) from GPC of aromatic concentrate from sample A (excitation 280 nm, emission 461 nm, 7 = mean lifetime)
teristics of spectra of the other fractions were the same as in the case of sample A. Analysis of Fractions from GPC. The fractions obtained by separating aromatic hydrocarbons from sample A were evaporated a t 60 O C in a nitrogen stream and weighed (Figure 8). Odd fractions were dissolved in the same volume of n-pentane (5 ml) and, after diluting them for analysis, their fluorescence spectra were measured. The spectra were much more complex and identification of individual types was much more difficult. Starting from the fraction with log V = 2.4472 the vibrational spectra appear in a region of 325 to 370 nm (bands 325,338,352, 355,370 nm). In the region of the elution of polynuclear hydrocarbons, an indistinct maximum of benzo[k]fluoranthene was observed. The unique position of fluoranthene, which is characterized by its long wave fluorescence in the region of about 460 nm, enabled us to determine its relative concentrations in individual fractions by evaluating fluorescence excitation spectra scanned a t an emission wavelength of 460 nm. It is suggested that red shift in fluorescence excitation spectrum (Figure 6) in comparison with fluoranthene is due to alkylation of parent aromatic hydrocarbon. The distribution of alkyldibenzothiophenes and dibenzothiophene were established by phosphorescence spectra (Figure 8). With the separation methods used, dibenzothiophene accompanied trinuclear hydrocarbons and further fluoranthene and triphenylene. Phosphorescence spectra of dibenzothiophene and triphenylene from GPC separation are given in Figures 9 and 10. The spectra of fractions were simpler than the corresponding fluorescence spectra starting from those with log V = 2.4472. Up to this value of the elution volume, they have a character of mixed spectra of mono- and diaromatic hydrocarbons with no marked vibrational structure.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
1949
Quantitative Determination of Identified Compounds. The fractions, in which a certain compound was identified, were combined and correlated with spectra of standard compounds, maintaining quantitative ratios. From concentration data by volume and weight, their probable concentration in the original sample was calculated. In a case where the sample spectrum was not disturbed by interference, direct correlation of spectrum intensities with standards was carried out, maintaining measurement conditions. In the other cases, the correlation was based on differences between relative intensities of distinct neighboring minimum and maximum values of the excitation or emission spectra of the identified compound.
Table I. Separation on Silica Gel Sample B
Sample A Weiaht aft& eva o ratpmmgll.
Ammatics
ASTM; mgll.
Original oil Oil after percolation on silica gel n-Pentane eluate, 150 ml Diethyl ether eluate, 100 ml, i . e . , aromatic concentrate Methanol eluate, 100 ml, i . e . , polar compounds I
mgll.
... , .. ...
547 387 508
839
. .. .. . ...
5.03
0.00 0.00
1052
. ..
Weight after evaporation mgll.
Aro-
17.3
34.0
...
17.4
RESULTS A N D DISCUSSION
0.00
Table 11. Separation of Aromatic Concentrates on Basic Alumina Sample A , g
Sample B, g
0.273 0.194 0.03 53
0.0257 0.0020 0.0227
5.5:l
1:11.8
Charge Aromatic hydrocarbons Polar compounds I1 Ratio of aromatic hydrocarbons to polar compounds I1
Table 111. Combination of Methods and Quantity of Determined Aromates Sample A
Sample B Quant-
Aromatic type
Anthracene Phenanthrene Alkylfluoranthenes Benzo[k]fluoranthene Triphenylene Alkyldibenzothio: phenes Alkylaryl disulf one
1950
Methods
...
$ ;
. ..
~
Methods
GEAC + Fluor.
GPC + Phosph. 140 GEAC + Phosph. GEAC + Fluor. GPC + Fluor. 10 GEAC + Fluor. GEAC + Fluor,
GPC + Phosph. 180
...
e . .
... IR, UV sp.
,
1 30 1
1 GEAC + Fluor.
GPC + Phosph. 1.5
...
Quantity PPb
1
... ... 39,000
The two samples differed in their total contents of aromatic compounds as determined according to ASTM D 2008-65. Based on this standard and by means of weight analysis, the distribution of aromatic compounds was determined in the course of the first separation step (Table I). About 85% of the mono- and diaromatic hydrocarbons from sample A passed through the silica gel column in original oil and in n-pentane eluate. The rest of these compounds were eluted by means of ether together with triand polyaromatic and polar compounds. Sample B contained only compounds that can be eluted by means of ether. The separation on basic alumina (Table 11) yielded results which were of interest with respect to very different contents of polar compounds I1 in the two samples. The UV absorption of sample B could be attributed t o the portion of the polar compounds 11, where its main component is represented by alkylaryldisulfone. The results of the analysis according to ASTM D 2008-65 do not correspond to the content of aromatic hydrocarbons in the case of sample B. Table I11 lists the identified aromatic types, methods of their quantitative determination in the analyzed samples, and amounts found. The separation method used enabled us to determine certain polyaromatic hydrocarbons present in oil for medicinal use and in n-alkanes in amounts of about 1 ppb when using GEAC as well as GPC. LITERATURE CITED (1) V . KovBi, Ochr. Ovzduli 3(10), 153 (1971). (2) W. M. Catchpole, E. Macmillan. and H. Powell, J. lnst. Petrol., 57, 247 (1971). (3) L. G. Khmiiyar, Z. V. Kocheva. and G. T. Pasichnik, Neftepererab. Neftekhim. (Kiev), 7, 42 (1972). (4) J. C. Suatoni. Anal. Chem., 39, 1505 (1967). (5) i. Muntean and N . Mosescu, Chim. Anal., 1, 237 (1971). (6) M. A. H. RiJk and D. Van Battum, Dtsch. Lebensm-Rundsch., 69(2), 75 (1973). (7) W . Strubert. Chromatographia, 8(4), 205 (1973). (8) H. Matsushita and Y . Esumi, BunsekiKagaku, 21, 1594 (1972). (9) J. F. McKay and D. R. Latham, Anal. Chem., 44, 2132 (1972). (10) L. Dubois, A. Zdrojewski, and J. L. Monkrnann. Staub-Reinhalf. Luft, 32(12), 487 (1972). (1 1) J. F. McKay and D. R. Latham, Anal. Chem., 45, 1050 (1973). (12) H. V. Drushei and A. L. Sommers, Anal. Chem., 38, 10 (1966). (13) M. Zander, Agnew. Chem., lnt. Ed. Engl., 4, 930 (1965). (14) M. Zander, ErdolKohle, 19(4), 278 (1966). (15) M. Popi, J. Mostecky, and Z. Havei, J. Chromatogr.,53, 233 (1970).
RECEIVEDfor review January 21, 1975. Accepted June 13, 1975.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
