Anal. Chem. 1987, 59,2066-2069
2066
Table IV. Determination of Total Selenium, Trimethylselonium Ion, and Selenite Ion in Urine of Normal Subjects (concentrations in ng of Se/mL; limit of detection 10 ng of Se/mL)
sample
TMSe"
1 male 2 male
23
56 22 63 21 ND 20 ND 33 ND 13 ND
3 male 9 male 10 male 11 male 1 3 male 4 female
5 female 6 female 7 female 8 female 12 female
11
Se032-
ND' 13 ND ND 41 ND ND 62 ND ND 38 ND ND
total Seb 97 f 12 70 f 10 50 10
*
160 f 10 89 f 13 14 f 3 51 f 6 65 f 7 37 f 5 32 f 8 56 f 7 54 f 9 50 f 20
"Determined by the method of additive spikes. bDeterminedby INAA. Nondetectable. ng of Se/mL. While there appears to be no correlation in the concentration of the ions and total selenium between male and female subjects, the data suggest that urine samples with increasing total selenium have an increasing amount of TMSe. Our data support the results of Nahapetian et al. (16),which found no detectable free selenite in urine samples of rats ingesting 75Selabeled selenoamino acids or selenite. It appears that the MoNAA approach is sensitive enough to detect four selenite concentration values in a sample pool of 13 subjects.
LITERATURE CITED (1) McConnell, K. P.; Broghamer, W. L., Jr.; Blotcky, A. J.; Hart, 0. J. J . Nutr. 1975, 705,206. (2) Broghamer, W. L., Jr.; McConnell, K. P.; Blotcky. A. J. Cancer (Philadelphia) 1978, 4 7 , 1462.
(3) Broghamer, W. L., Jr.; McConnell, K. P.; Blotcky, A. J. Cancer(Philadelphia) 1976, 37, 1384. (4) Shamberger, R. J.; Rukovena, E.; Longfeld, S. A,; Tylko, S.; Deodhar, C. E.; Willis, C. E. J . Natl. Cancer I n s t ( U . S . ) 1973, 50, 863. (5) Willett, W. C.; Polk, B. F.; Morris, J. E.; et al. Lancet 1983, July 16, 130. (6) Iyengar, G. V.; Kollmer, W. E.; Bowen, H. J. M. The Hemental Composition of Human Tissues and Body Fluids; Verlag Chemie: New York, 1978. (7) Cornelis, R.; Speecke, A.; Hoste, J. Anal. Chim. Acta 1975, 78, 317. (8) Valentine, J. L.; Kang, H. K.; Spiney, G. H. Environ. Res. 1978, 77, 347. (9) Ishizaki, M. Talanta 1978, 25, 167. (IO) Versieck, J.; Cornelis, R. Anal. Chim. Acta 1980, 776, 217. (11) Sunde, R. A.; Hoekstra, W. G. Biochem. Biophys. Res. Commun. 1980, 93, 1181. (12) Burk, R. F. J . N u h . 1988, 776, 1564. (13) Foster, S. J.; Ganther, H. E. Anal. Biochem. 1984, 737,205. (14) Palmer, L. s.; Gunsalus, R. P.; Halverson, A. W.; Olson, 0. E. Biochim. Biophys. Acta 1970, 208, 260. (15) Palmer, L. S.; Fischer, D.D.; Halverson. A. W.; Olson, 0. E. Biochim. Biophys. Acta 1989, 777,336. (16) Nahapetian, A. T.; Janghorbani, M.; Young, V. R. J . Nutr. 1983, 773, 401. (17) Nahapetian, A. T.; Young, V. R.; Janghorbani, M. Anal. Biochem. 1984, 740, 56. (18) Oyamada, N.; Ishizaki, M. Jpn. J . Ind. Health 1983, 25. 319. (19) Blotcky, A. J.; Hansen, G. T.; Opelanio-Buencamino, L. R.; Rack, E. P. Anal. Chem. 1985, 57, 137. (20) Blotcky, A. J.; Rack, E. P. J . Res. Natl. Bur. Stand. (U.S.) 1986, 9 7 , 93. (21) Kessler, G.; Pileggi, V. J. Clin. Chem. (Winston-Salem, N . C . ) 1968, 14, 811. (22) Bancroft, H. Introduction to Biostatistics; Hoeber 8, Harper: New York, 1959; p 161. (23) Schwarz, K.; Sweeney, E. Fed. Proc. Fed. Am. SOC. Exp. Bioi. 1964, 23, 421. (24) Cummins. L. M.; Martin, J. L. Biochemistry 1967, 6, 3162.
RECEIVED for review March 12,1987. Accepted May 12,1987. This research was supported by the US. Department of Energy, Division of Chemical Sciences, Fundamental Interaction Branch, under Contract DE-FG02-84ER13231 and a University of Nebraska Research Council NIH Biomedical Research Support Grant No. RR-07055.
Extraction of Low Molecular Weight Polynuclear Aromatic Hydrocarbons from Ashes of Coal-Operated Power Plants Filippo Mangani, Achille Cappiello, Giancarlo Crescentini, and Fabrizio Bruner* Istituto di Scienze Chimiche, Universitd di Urbino, Piazza Rinascimento, 6, 61029 Urbino, Italy
Loretta Bonfanti
ENEL-CRTN,Via Cesare Battisti, 69, 56100 Pisa, Italy
A new procedure based on llquld-solld chromatography for the extraction of polynuclear aromatic hydrocarbons has been implemented. This ylelds results analogous to those of Soxhlet extractlon for low molecular weight compounds up to the four-membered ring compounds. A very Important reductlon In the time required for sample preparatlon prlor to gas chromatography/mass spectrometry analyds Is obtalned.
The large amount of ashes produced by coal-operated power plants and the necessity for their disposal make it necessary to frequently carry out careful measurements of the polynuclear aromatic hydrocarbon (PAH) content of these materials. This implies extraction from the matrix and separation by chromatographic procedures. The most widely used methods for recovering PAHs from solid matrices involve Soxhlet ex-
traction with methylene chloride (1-3). The use of ultrasonic extraction and of a rotary shaker has also been recently evaluated (4). Vacuum sublimination has also been used (5). The effectiveness of the extraction methods, expressed as recovery of PAH from spiked ashes, decreases with decreasing concentration of these compounds. It is well-known (6) that toluene shows a higher extraction efficiency with respect to methylene chloride because its structure is similar to that of the compounds of interest. Moreover, methylene chloride tends to extract more unwanted polar compounds, being a more polar solvent than toluene. However, concentration of large volumes of solvent is needed in the traditional Soxhlet extraction procedures so that methylene chloride is usually the solvent of choice because of the lower boiling point. By the use of alternative methods of extraction that require small volumes of solvent, the superior extraction efficiency of toluene could be more conveniently exploited.
0003-2700/87/0359-2066$01.50/0 0 1987 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 59, NO. 17, SEPTEMBER 1, 1987
2067
Table I. PAHs Concentration in the Standard Solution and in the Ash for Two Different Spiked Samples
compound acenaphthylene acenaphthene fluorene anthracene fluoranthrene pyrene benz[a]anthracene chrysene
spiked sample 1 std solution ash concn, concn, ng/mL ng/g 97.1 83.0 89.6 100.1 171.6 95.4 93.4 118.7
32.3 27.7 30.0 33.7 57.3 31.7 31.0 39.7
spiked sample 2 std solution ash concn, concn, ng/mL ng/g 7.4 7.4 7.7 10.3 11.4 12.9 9.0 10.9
t-7
i!*I f:I -
2.6 2.6 2.6
:I :I
a
2.1
3.8 4.3 3.0 3.6
In this paper we describe an extraction method that uses hot toluene (at 100 " C ) as a solvent and a direct extraction from the matrix. The main advantage of the method described here over Soxhlet extraction is that the overall time needed for sample extraction and preparation prior the gas chromatography/mass spectrometry (CG/MS) analysis is greatly reduced and involves a simpler apparatus. EXPERIMENTAL S E C T I O N Ash Samples and Solvents. Ash samples have been obtained from several 320-MW coal-operated power plants in Italy and used as received except for the spiking procedure where preextraction was carried out. Particles size was smaller than 105 pm. All batches have been taken from the electrostatic precipitator that works a t a temperature of 140 "C. The furnace was fed by coal powder (75% with dimension smaller than 75 km) transported by a moving belt in all the plants where ash samples have been taken. The average percent composition of the coal used can be summarized as follows: moisture, 6-10%; volatiles, 18-35%; ashes, 7-16%; fixed carbon, 40-67%; sulfur, 0.2-1.0%; calorific value, 6000-7200 kcal/kg. Both methylene chloride and toulene have been obtained from Carlo Erba Analyticals RS grade (99.8%) for HPLC. Phenanthrene was found to be present in toulene at a level of 2-5 ppb (w/v). Spiking Procedure. Three grams of ashes was washed with 20-30 mL of toluene at 100 "C as described in the Apparatus and Experimental Procedure section. No compounds were detected when the cleaned ashes were extracted and analyzed. After being dried under a flow of nitrogen, the ashes were placed in Petri dish and a solution of known concentration of the compounds of interest in methylene chloride was added. The slurry obtained was gently stirred while evaporation occurred at room temperature. The volume of the solvent initially used is about double that of the loose volume of the ash sample. The procedure is similar to the one used to coat the support of a GC stationary phase, and after the first evaporation fresh solvent is added. After the solvent is completely evaporated for the second time, the ash sample is placed in the stainless steel tube. Two types of samples have been prepared that differ in concentration of PAHs by a factor of 10. The actual concentrations of the single compounds in the two samples are reported in Table I. A standard solution is prepared, which is then diluted to the desired concentrations shown also in Table I. Apparatus and Experimental Procedures. The ash sample was dry packed in a stainless steel tube (4 mm i.d., 20 cm long) that contains about 3 g of ashes. A heating mantle allows the temperature of the tube to be regulated between 25 and 100 "C. Toluene at the same temperature is flowed through the tube from a stainless steel reservoir placed over the column and also heated (Figure 1). With these conditions a flow rate of about 0.5 mL/min is obtained through the column with a nitrogen pressure of 2.5 kg/cm2. The effluent from the column is collected at the bottom of the apparatus. The analysis of the extract is carried out by capillary gas chromatography/mass spectrometry by using a 0.25-pm SPB-5 bonded fused silica capillary column (30 m X 0.25 mm i.d.) from
toluene
'
U'
a s h sample
.
mantle
~-
Flgure 1. Extraction apparatus.
Supelco (Bellefonte, PA) and a Dani 3800 gas chromatograph (Dani, Monza, Italy)) equipped with a program temperature vaporizer (PTV). The column temperature was kept initially at 100 "C for 2 min, and then it was programmed to increase by 10 "C/min up to 300 "C. Helium was used as carrier gas and 0.7 mL/min was the initial flowrate. The column was directly coupled with a VG 70-70H double focusing mass spectrometer (VG Micromass, Altrincham, England), which was kept at resolving power of lo00 (10% valley) and employed in the selected ion monitoring (SIM) mode. Mass spectrometer conditions were as follows: source temperature, 200 "C; electron energy, 70 eV; accelerating potential (reference mass), 4 kV. Table I1 shows the SIM programs used for the analysis of PAHs. Implementation of the SIM programs was based on two reference peaks coming from n-octylbenzene (m/e 133.1017 and 190.1720, respectively), which was continuously bled into the ion source. The two most intense and structurally significant ions in the mass spectra of the single compounds were monitored. In program 1 the magnet current was adjusted to a value such that the reference peak at m/e 133.1066 is focused when the entire accelerating potential Eo (4 kV) is operating. The other values of m/e are focused when the accelerating potential is set at the corresponding E / E ovalue. The same is true for the other programs. The dwell time indicates the time of residence of the ion beam due to a certain value of m/e on the outlet slit and is chosen as the best compromise between sensitivity and reproducibility. The overall sensitivity of the CG/MS system is such that for the conditions described 0.25 pg of injected chrysene yields a peak relative to m/e 228 with a signal to noise ration of 5:l. For benzo[e]pyrene, a much more retained peak, the same signal to noise ratio is obtained. The analysis of the spiked ashes is performed in fractions of 1 mL each in order to build the elution curves of the single PAH. Such a methodology has been proven to be very useful for obtaining reliable information about the extraction process (7, 8). When the actual samples are analyzed, the extract is collected in one fraction of 6-10 mL and directly analyzed via HRGC/MS. Analysis time is about 22 min.
RESULTS A N D D I S C U S S I O N In Figure 2 the elution curves for some PAHs obtained from spiked ashes are reported as an example. The experiments have been made operating with toluene at 25 (b) and 100 "C (a and c), and at two different ranges of concentration. The elution curves for the low molecular weight PAHs have not been reported, since these compounds show at least a 95% recovery. More interesting is the behavior shown by the
2068
ANALYTICAL CHEMISTRY, VOL. 59, NO. 17, SEPTEMBER 1, 1987 [
Table 11. SIM Program Used for Spiked and Actual Samples (EIE,)
channel ions, m / e
X
10
dwell time, s
compound
program 1 1
133.1017
9.99999
2
152.0627 153.0704 154.0782 165.0704 166.0782
8.75307 8.69545 8.63857 8.06332 8.014 38
3 4 5
6
n-octylbenzene-lock mass acenaphthylene acenaphthene acenapthene fluorene fluorene
0.1 0.1
0.1 0.1 0.1
0.1
0 FLUORAWlHtUt
program 2
rn PIREHE
1
133.1017
9.99999
0.1
2
176.0626
7.55990
0.1
3
178.0782
7.474 33
0.1
n-octylbenzene-lock mass phenanthrene-anthracene phenanthrene-anthracene
b
program 3 1
190.1720
9.99999
0.1
2
200.0662 202.0782 228.0939
9.505 44 9.41080 8.33743
0.1
3 4 5
252.0939
7.543 69
0.1
n-octylbenzene-lock mass fluoranthene-pyrene fluoranthene-pyrene benzo[a]anthracene, chrysene benzo[b]- and benzo[k] fluoranthene and benzo[c]- and benzo-[alpyrene
0.1 0.1
C I
tA
four-membered-ring compounds, the elution curves of which are reported in Figure 2, obtained under different conditions. The two ranges of concentration differ by a factor of about 10, the lower concentrations being more consistent with the actual content of ash samples. The recovery obtained when the ashes are spiked with a large amount of PAHs is similar when operating either a t lower or higher temperature. However, the curves of Figure 2, part b, look broader than those of Figure 2, part a, (toulene a t 100 "C), indicating that the extraction of the four-membered-ring compounds is more difficult. Very low recoveries (-10%) are obtained for the five-membered rings in both cases and the elution curves have not been reported. In Figure 2c the elution curves for the four-membered rings at low concentrations show pronounced tailing and a satisfactory recovery is only obtained by using 10-12 mL of solvent. The obvious explanation for the difference slope of the elution curves lies in the structural difference of the four compounds. Of more interest is the fact that spiking the ash with very low amounts of PAHs, which are strongly absorbed on the active sites of the inorganic matrix, causes the ex-
ni
I
2
3
4
5
6
7
8
9
tu
Figure 2. Examples of elution curves of some PAHs spiked with
different concentrations: (a) high concentration, elution temperature 100 'C; (b) high concentration, elution temperature 25 "C; (c) low concentration, elution temperature 100 "C; for single compounds concentration, see Table I.
traction to be difficult (9). When higher amounts of PAHs are deposited on the ash surface, the first molecules absorbed act as a deactivating agent and the extraction of the remaining molecules becomes easier. In Table I11 a comparison of the recovery obtained by using Soxhlet extraction with two solvents, methylene chloride and toluene, and the one obtained with the method desribed in this paper, is reported. Toulene yields higher recoveries than methylene chloride, especially for the four-membered ring compounds. This effect is enhanced when a lower concentration is used. Anthracene is very poorly recovered with both solvents in the Soxhlet method. This should be attributed to a decomposition of this compound that takes place in the
Table 111. Comparison of the Recovery (%) of Some PAH from Spiked Ashes Obtained with Different Techniques
compound
concn (ng/g) in the ash
acenaphthylene acenaphthene fluorene anthracene fluoranthene pyrene benz[a]anthracene chrvsene
32.3 27.7 30.0 33.7 57.3 31.7 31.0 39.7
spiked sample 1 % recovery soxhlet soxhlet this method CH,Cl, toluene toluene 100 O C 95 98 100 31 84 98 6
8
100 100 100
57 85 98 85 60
95 99 97 96 98 96 86 90
concn (ng/g) in the ash
spiked sample 2 % recovery soxhlet soxhlet this method CH2Cl2 toluene toluene 100 "C
2.6 2.6 2.6
100
2.1
11
3.8 4.3
45 49
3.0
3.6
100 100
100 100
100 46 82 87 49 43
98 99 98 98 99 95 74 71
Anal. Chem. 1987, 59, 2069-2073
Table IV. Examples of Low Molecular Weight PAHs Content of Ashes Sampled in Two Different Coal-Operated Power Plants (ppb)a
compound acenaphthylene acenaphthene fluorene anthracene fluoranthene PYene
benz [ a ]anthracene
concn sample A, ppb concn sample B, ppb soxhlet soxhlet this method toluene this method toluene 1.4 2.0 2.7 3.2 1.3 1.0
ndb
0.9 1.7 2.2 1.4 0.8 0.3
nd
1.3 1.6 3.0 0.9 0.8 0.5
nd
0.9 1.2 2.3 0.5 0.6 0.4
nd
a Results obtained by using the direct elution extraction method (toluene at 100 “C)and the toluene Soxhlet extraction. *nd = not determined.
lengthy operation of this method, rather than to an actual poor recovery (IO). Of course the results of Soxhlet extraction related to anthracene could be improved with some precautions to avoid the exposure of the sample to light. Table I11 shows that the method described allows for recoveries of the four-ring PAHs of higher than 70% in all cases and 90% in all cases except three, a t concentrations ranging between 2 and 60 ng of PAH/g of ash, while only 6-12 mL of solvent are used. A very important problem arises with five-membered-ring compounds, which show absolutely unsatisfactory recoveries both with Soxhlet and with our method. At low concentrations of benzo[e]pyrene the recovery with Soxhlet by using toluene is 9%, while it is practically absent with the present method. These results are compatible with those obtained in previous work ( 4 ) , so that the question of whether the heavier compounds are present or not in coal fly ashes remains open. In Table IV the results obtained with the present method for two actual samples of fly ash are reported as an example. The same sample has been analyzed by using Soxhlet with toluene and the resulta are consistent with those obtained with
2069
the spiked samples. The two power plants where sampling was made have analogous characteristics as described. However, it should be noted that an average standard deviation of about 8% (measured on 10 samples) is found for the overall analytical method in the range of concentration between the detection limit (0.1 ppb) and 10 ppb, so that some numerical differences may not be significant. The advantages of the method described lie essentially in the ease of operation and in the enormous time saving during sample preparation prior to GC/MS analysis. With the present method the sample is ready for analysis within half an hour, while using Soxhlet followed by solvent concentration, a t least 24 h is necessary. ACKNOWLEDGMENT The authors thank E. Sisti for technical assistance. Registry No. Acenaphthylene, 208-96-8; acenaphthene, 8332-9; fluorene, 86-73-7; anthracene, 120-12-7; fluoranthene, 20644-0; pyrene, 129-00-0; benz[a]anthracene, 56-55-3; chrysene, 218-01-9; toluene, 108-88-3. LITERATURE CITED (1) Lee, M. L.; Hltes, R. A. Anal. Chem. 1976, 4 8 , 1890-1893. (2) Peaden, P. A.; Lee, M. L.; Hlrata, Y.; Novotny, M. Anal. Chern. 1980, 52, 2266-2271. (3) Cretney, J. R.; Lee, H. K.; Wright, G. J.; Swallow, W. H.; Taylor, M. C. Environ. Sci. Technol. 1985, 19, 397-404. (4) Harrison, F. L.; Bishop, D. J.; Mallon, B. J. Environ. Sci. Technol. 1985, 19, 186-193. (5) Constable, D. J. C.; Smith, S. R.; Tonaka, J. Environ. Sci. Techno/. 1984. 18, 975-978. (6) Tomkins et ai. In Polynuclear Aromatic Hydrocarbons : Formuktion, Metabolism and Measurement; Cooke, M.,Dennls,A. J., Eds.; Battelie Press: Columbus, Ohio 1983; pp 1173-1 187. (7) Manganl, F.; Crescentlnl, G.; Bruner, F. Anal. Chem. 1981, 53, 1627-1632. . - - . . - - -. (8) Bruner, F.; Crescentinl, G.; Mangani, F.; Petty, R. L. Anal. Chem. W83, 55, 793-795. (9) Grlest, W. H.; Towklns, B. A., Environ. Sci. Techno/. 1986, 2 0 , 291-295. (IO) Butler,-J. D.; Crossley, P. Atmos. Environ. 1981, 15, 91-94.
RECEIVED for review October 7,1985.
Resubmitted April 15,
1987. Accepted April 28, 1987.
Desorption Characteristics of Four Polyimide Sorbent Materials Using Supercritical Carbon Dioxide and Thermal Methods James H. Raymer,*Edo D. Pellizzari, and Stephen D. Cooper Analytical a n d Chemical Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709 “C-Labeled 1,2,3,4,5,6hexachiorocyciohexane, hexachlorobiphenyl, anthracene, and parathion were used to study the desorption of four polyimide-based sorbent materials using both supercritical carbon dioxlde and thermal methods. Supercrltlcal fkkl desorption was found to be superior to thermal desorption. Both types of desorption were more difficult from the polylmides than from Tenax-GC used in previous work. This work helps to define the appilcablilty of supercrltical desorption of polylmides. The identities of the compounds desorbed with supercritical COPwere verified by using thinlayer chromatography and mass spectrometry. Resuits were compared to those from Tenax-GC studies.
The identification and quantification of organic compounds
in ambient air are problems that are complicated both by the wide range of molecular weights and polarities of these com-
pounds and by the trace levels a t which these compounds are present. One of the most useful methods to overcome the problem of low analyte concentration is to use a sorbent such as Tenax-GC (I,2). In such an analysis, an air stream is drawn through a cartridge packed with the sorbent material and the organic compounds are selectively retained. The trapped compounds are subsequently thermally desorbed and cryogenically focused onto the head of a gas chromatographic column for analysis. Although such chromatographic preconcentration techniques are very powerful, they do have limitations. One such limitation is the poor retention of certain compounds on the sorbent itself. For example, Tenax-GC retains nonpolar compounds much more efficiently than polar compounds such as methanol or vinyl chloride (2). This results in the “breakthrough” of the polar compounds while the nonpolar materials are still being effectively concentrated and the inability to quantify such poorly retained, polar materials. If,
0003-2700/87/0359-2069$01.50/00 1987 American Chemical Society
