Envlron. Sci. Technol. 1992, 26, 1526-1533
character could also provide a driving force for sorption to an algal surface. The physiological effects of mines on algae noted in the Introduction must have as a starting point the sorption of the amines onto the cell. The present work has shown that this sorption can occur by two processes: ion exchange of protonated amines and sorption of neutral amines, probably through hydrogen bonding. The diamine with NH2 at each end, apparently having a chain length effect, might provide a tool for exploring the distribution of surface receptor sites. Environmentally important applications may arise from results of the present sorption study. For example, pretreatment of algae with amines may create a more efficient surface for scavenging precious or toxic metals by complexation. Also, algae suspended in a solution at pH 5-6 might be useful in removing anionic metal complexes, notably AuCl,-, from aqueous solution by interaction of these anions with immobilized protonated amine groups. Finally, algae might also be used to remove amines from contaminated water. Acknowledgments We thank Dr. I. Stanovic for making the alga stock available. The help of Dr. Robert Martin in the literature study is greatly appreciated. Literature Cited (1) Smith, T. A. Phytochemistry 1975, 14, 865-890. (2) Cohen, E.; Arad, S.; Heimer, Y. H.; Mizrahi, Y. Plant Physiol. 1984, 74, 385-388. (3) Mosier, A. R. J. Environ. Qual. 1978, 7 , 237-240.
Blanck, H. Ar.h. Environ. Contam. Toxicol. 1985, 14, 609-620. Hartmann, T. Phytochemistry 1972, 11, 1327. Herrmann, V.; Juttner, F. Anal. Biochem. 1977,78,365-373. Steiner, M.; Hartmann, T. Planta 1968, 79, 113. Crist, R. H.; Oberholser, K.; Shank,N.; Nguyen, M. Environ. Sci. Technol. 1981, 15, 1212-1217. Crist, R. H.; Oberholser, K.; Schwartz, D.; Marzoff, J.; Ryder, D. Enuiron. Sci. Technol. 1988,22, 755-760. Crist, R. H.; Oberholser, K.; McGarrity, J.; Crist, D. R.; Johnson, J. K.; Brittsan, J. M. Environ. Sci. Technol. 1992, 26.496-502. Haug, A.; Lmen, B.; Smidsrod, 0. Acta Chem. Scand. 1967, 21, 691-704. Smidsrod, 0.; Haug, A. Acta Chem. Scand. 1968, 22, 1989-1997. Dodson, J. R., Jr.; Aronson, J. M. Bot. Mar. 1978, 21, 241-246. Percival, E. Br. Phycol. J. 1979, 14, 103-117. Frey, R. A.; Crist, R. H.; Oberholser, K. Proc. Penn. Acad. Sci. 1978, 52, 179-182. van Wagoner, J.; Martin, L.; Helphrey, J. D.; Meyers, R.; Hess, G . D.; Crist, R. H. Proc. Penn. Acad. Sci. 1985,59, 147-150. Crist, R. H.; Martin, J. R.; Guptill, P. W.; Eslinger, J. M.; Crist, D. R. Enuiron. Sci. Technol. 1990, 24, 337-342. Crist, R. H.; Martin, J. R.; Crist, D. R. In Mineral Bioprocessing; Smith, R. W., Misra, M., Eds.; The Minerals, Metals, and Materials Society: Warrendale, PA, 1991; pp 215-287.
Received for review December 10, 1991. Revised manuscript received March 30,1992. Accepted April 15,1992. W e express our gratitude to the J. Howard Pew Freedom Trust of the Glenmede Trust for help in funding the atomic absorption equipment.
Atmospheric Oxidation of Selected Terpenes and Related Carbonyls: Gas-Phase Carbonyl Products Daniel Grosjean,*pt Edwln L. Wllllams, I I , t and John H. Selnfeldt DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, California 93003, and Department of Chemical Engineering, California Institute of Technology, Pasadena, California 91 125
rn The gas-phase carbonyl products of a-pinene, 6-pinene, and d-limonene have been identified and their concentrations measured in experiments involving sunlight irradiations of mixtures of terpene (1-2 ppm) and NO (0.25 ppm) in air. In turn, sunlight irradiations of carbonyl-NO, mixtures have been carried out for the major high molecular weight carbonyl products of @-pinene (6,6-dimethylbicyclo[3.1.1] heptan-2-one) and d-limonene (4acetyl-1-methylcyclohexene),and the corresponding carbonyl products have been identified. The nature and yields of these carbonyl products are discussed in terms of oxidation mechanisms involving the OH-terpene, ozone-terpene, OH-carbonyl, and ozone-carbonyl reactions. Introduction Biogenic hydrocarbons, i.e., isoprene and terpenes, have recently received renewed attention for their contribution to ozone and aerosol formation in urban and rural areas 'DGA, Inc. California Institute of Technology. 1526 Envlron. Sci. Technol., Vol. 26, No. 8, 1992
(1-3). Isoprene and most terpenes react rapidly with ozone, the hydroxyl radical, and the nitrate radical; the corresponding reaction rate constants are known with reasonable certainty (4-6). For isoprene, several experimental studies of oxidation products have been carried out (7, B), and the corresponding results can be used as input data in computer kinetic models that describe the oxidation and fate of biogenic hydrocarbons in the atmosphere (9-11). Much less is known, however, regarding the gas-phase reaction products of terpenes under atmospheric conditions. As a result, the corresponding computer kinetic models are based on little or no experimental data concerning reaction products (9-1 1). Terpene oxidation products tentatively identified in laboratory studies include only a few carbonyls such as pinonaldehyde [(2,2-dimethyl-3acetylcyclobutyl)ethand]from a-pinene, 6,6-dimethylbicyclo[3.1.1]heptan-2-one from 6-pinene, and 4acetyl-1-methylcyclohexene from d-limonene (12-14). These laboratory studies involved terpene concentrations that were some 5 orders of magnitude higher than those expected in ambient air. Pinonaldehyde has also been tentatively observed as a component of airborne particulate matter (13).
0013-936X/92/0926-1526$03.00/0
0 1992 American Chemical Society
In this study, we have attempted to identify the carbonyl products of terpene oxidation under simulated atmospheric conditions. Information on the nature of these carbonyls is important to elucidate terpene oxidation mechanisms and to assess their overall reactivity, which is driven to a large extent by the nature and reactivity of the first-generation carbonyl products. Since the OH-terpene and ozone-terpene reactions are closely coupled in ambient air (the former reaction produces ozone; OH is formed in the latter), we elected to carry out sunlight irradiations of terpene-NO, mixtures and carbonyl-NO, mixtures in order to approximate atmospheric conditions. The method we employed to identify carbonyl products involves off-line sampling, in-situ derivatization, positive identification of the carbonyl derivatives by liquid chromatography with ultraviolet detection (LC-UV), mass spectrometry (MS) confirmation of the derivative's structure and molecular weight, and direct comparison with authentic carbonyl derivatives synthesized in our laboratory (15-1 7). We also prepared the DNPH derivative of pinonaldehyde, whose identification in previous work has been tentative (12-14) due to the lack of a reference standard. Our study included three terpenes, a-pinene, @-pinene, and d-limonene, which are among the most abundant terpenes identified in ambient air (18-20). We also studied the oxidation of two major terpene carbonyl products identified in this study, 6,6-dimethylbicyclo[3.1.1] heptan-2-one (from @-pinene) and 4-acetyl-l-methylcyclohexene (from d-limonene). As an aid to data interpretation, peroxyacetyl nitrate [CH3C(0)OON02,PAN] was also measured in all experiments. Experimental Methods Sunlight irradiations of terpene-nitric oxide mixtures in purified air were carried out at ambient temperature in a 3.5-m3all-Teflon collapsible chamber constructed from transparent 200A FEP Teflon film (17). The use of Teflon film minimizes reactant and product loss to the chamber walls (21). The matrix air was purified by passing ambient air through large cartridges containing activated carbon, silica gel, molecular sieves, and permanganate-coated alumina. A glass fiber filter was inserted downstream of the sorbent cartridges to remove particulate matter from the purified air stream, which contained less than 1ppb of reactive hydrocarbons, ozone, oxides of nitrogen, carbonyls, PAN, and other pollutants including sulfur dioxide and organic acids. A typical experiment involved sunlight irradiation, for 2-6 h, of 1-2 ppm terpene and 0.25 ppm NO in purified air. In some (but not all) experiments, carbonyl samples were collected during three chemistry regimes: OH only (early part of the irradiation, before NO-N02 crossover, no ozone present), OH O3 (after NO-N02 crossover, ozone present), and O3 only (by continuing the experiment in the dark following sunlight irradiation of the terpene-NO, or carbonyl-NO, mixture). Ozone was measured by ultraviolet photometry using a calibrated Dasibi 1108 continuous analyzer. Oxides of nitrogen were measured by chemiluminescence using a Monitor Labs 8840 continuous analyzer calibrated by using the diluted output of a certified NOz permeation tube maintained at 30.0 A 0.1 OC in a thermostated water bath. PAN was measured by electron capture gas chromatography (22,23) using an SRI 8610 gas chromatograph and a Valco 140 BN detector. The column used was 70 X 0.3 cm Teflon-lined stainless steel column packed with 10% Carbowax on Chromosorb P, acid washed and DMCS-treated. The column and detector temperatures were 36 and 60 OC, respectively. The carrier gas was ultrahigh-purity nitrogen. The column flow rate was 58
+
'
mL/min. Air from the Teflon chamber was continuously pumped through a short section of 6-mm-diameter Teflon tubing connected to a 6.7-mL stainless steel sampling loop housed in the GC oven and was injected every 20 min using a timer-activated 10-port sampling valve. To calibrate the EC-GC instrument, PAN was synthesized in the liquid phase by nitration of peracetic acid, and ppb levels of PAN in the gas phase were obtained by passing purified air over a dilute solution of PAN in n-dodecane (22, 23). Calibration involved side-by-side readings with the EC-GC instrument and with the chemiluminescent NO, analyzer, which responds quantitatively to organic nitrates and peroxyacyl nitrates including PAN (24). Under the conditions employed to measure PAN, other compounds are resolved including methyl nitrate and peroxypropionyl nitrate (PPN). Both compounds were synthesized as previously described (23,25),and the EC-GC instrument was calibrated for methyl nitrate (25) and for PPN (23) as is described above for PAN. Carbonyl products were isolated as their 2,4-dinitrophenyl hydrazones by sampling the reaction mixture through small c18 cartridges coated with twice-recrystallized 2,4-dinitrophenylhydrazine (DNPH) as described previously (15). In order to minimize possible reactions between DNPH and/or hydrazones and the oxidants present in the chamber, the c18 cartridge samples were collected downstream of annular denuders coated with KI (26, 27). The sampling flow rate was 0.77 L/min. Following collection, the cartridges were eluted with HPLCgrade acetonitrile, and aliquots of the acetonitrile extracts were analyzed by liquid chromatography with ultraviolet detection (15). The DNPH derivatives were separated on a Whatman Partisphere c18 column, 110 X 4.7 mm, with 55:45 by volume CH3CN-H20 eluent at a flow rate of 1 mL/min. The detection wavelength was 360 nm. The liquid chromatograph components included a solvent delivery system equipped with 0.2-pm pore size Teflon fiiters, a SSI 300 pump, a 20-pL injection loop, a Whatman Partisphere CI8guard cartridge, and a Perkin-Elmer LC75 UV-visible detector. Quantitative analysis involved the use of external hydrazone standards, from which calibration curves, i.e., absorbance (peak height) vs concentration, were constructed. More details regarding the sampling and analytical protocols have been given elsewhere (15, 28) including collection efficiency, cartridge elution recovery, precision, accuracy, and interlaboratory comparison studies. Confirmation of the structure of the carbonyl DNPH derivatives was obtained by recording their UVvisible spectra, as dilute solutions in the CH3CN-H20 eluent, using a diode-array detector (28) or by measuring the 360/430-nm absorbance ratio as a test for dicarbonyls (17,B).Positive identification could be made by matching retention times and UV-visible spectra of sample peaks to those of the reference standards. Additional structure confirmation was obtained independently by chemical ionization mass spectrometry of both hydrazone standards and carbonyl-DNPH samples (16). The three terpenes, 6,6-dimethylbicyclo[3.l.l]heptan2-one, and 4-acetyl-l-methylcyclohexene were from commercial sources. The DNPH derivative of pinonaldehyde was synthesized by bubbling 1 ppm ozone in purified air through a solution of a-pinene in HPLC-grade ethanol, adding acidic DNPH, and drying the corresponding solid crystals in a desiccator. Dilute solutions in HPLC-grade acetonitrile were prepared for liquid chromatography analysis. DNPH derivatives of 6,6-dimethylbicyclo[3.1.1]heptan-2-one and of 4-acetyl-l-methylcyclohexene, Environ. Sci. Technol., Vol. 26, No. 8, 1992
1527
Table I. Summary of Experiments
compd, run no.
no. of carbonyl samples collected
NO-NOz crossover initial concn [NO], [NO,], [organic], ppb ppb ppm
[NO] or [NOz], PPb
start of run, min 45 85 48
max or final ppb IO,] [PAN] concni
a-pinene 2
2 2
3
1
1
225 260 1100
0 0 0
1.8 1.6 10.1
110 125 455
500 165 1080
0 15 0
1.0 1.8 10.1
a
a
0"
80 295
110 162
175 39
3 3
250 200 180 215
0 0 10 0
1.7 1.7 2.0 1.9
90 70 90 75
38 66 116 62
152 106 4 37
33 29 0.5 40
fl-pinene 1
1
2
3
3
1
d-limonene 1
2 6,6-dimethylbicyclo[3.l.l]heptan-2-one 4-acetyl-1-methylcyclohexene
3 2 2 2
120 35 45
>20 12 >36 0"
"This experiment was limited to the early part of the oxidation (OH chemistry only) before the NO-N02 crossover. Therefore, no ozone and PAN were formed.
which have not been prepared before, were synthesized by reaction of the carbonyl with DNPH as described earlier for other carbonyl-DNPH derivatives (15). The corresponding UV-visible and mass spectra were recorded, and calibration curves (Figure 1) were constructed in the concentration range that bracketed those found in the DNPH cartridge samples collected from the terpene-NO, and carbonyl-NO, experiments. Results and Discussion The compounds studied and the corresponding initial concentrations are listed in Table I along with other pertinent information including the maximum concentrations of ozone and PAN formed during the terpene-NO sunlight irradiation experiments. The carbonyl products positively identified and their concentrations are listed in Table 11. The distribution of these products is discussed below for each terpene and carbonyl studied. Limonene. Carbonyls positively identified as reaction products of limonene included 4-acetyl-1-methylcyclohexene and formaldehyde, along with small amounts of glyoxal. Two other carbonyls were tentatively identified (no hydrazone standards were available), 3-oxobutanal (CH3COCH2CHO)and a Clo dicarbonyl, CH3CO(CH2),CH(C(CH3)=CH2)CH2CH0.A sixth carbonyl was present but could not be identified. Formaldehyde, 4-acetyl-lmethylcyclohexene, and the Clo carbonyl are the major products expected to form in the OH-limonene reaction. This is shown in Figure 2, which summarizes the reaction sequence of OH addition on the two unsaturated carboncarbon bonds, reaction of the corresponding hydroxyalkyl radicals with 02,peroxy radicals reaction with NO, and unimolecular decomposition of the corresponding alkoxy radicals. As is shown in Figure 3, the same carbonyls may also form (along with formic acid and C8and C9 carboxylic acids) by reaction of limonene with ozone. The reaction of terpenes with ozone, and more specificallythe pathways involving disubstituted Criegee biradicals, are discussed in more detail below for a-pinene. Subsequent reactions of the high molecular weight carbonyls with OH lead to smaller carbonyls including formaldehyde, glyoxal, and 3-oxobutanal, as we indeed observed in the experiment involving 4-methyl-lmethylcyclohexene as the starting material. These reactions are shown in Figure 4. Several of the reaction pathways shown in Figure 4 (and similar pathways for the Clo carbonyl, not shown) involve the production of acetyl radicals, which lead to PAN, as we observed using either 1528 Envlron. Scl. Technol., Vol. 26, No. 8, 1992
Table 11. Summary of Carbonyl Reaction Product Concentrations compd, run a-pinene 1 before* 1 afterb 2 before 2 after 3 after &pinene 1 before 2 before 2 after 1 h 2after2h 3 after 6,6-dimethylbicyclo[3.l.l]heptan-2-one before after d-limonene 1 before lafterlh 1 dark' 2 after 1 dark' 4-acetyl-1-methylcyclohexene before after
carbonyl," ppb form. acet; pinon DMBH AMCH 26 21 10 15 2
5 34 5 20 a7
13
4 2 15 34 76
4 3 12 37 120
4 3
832 672
6 15 82 1 13
20 6 112 171 82 137 13 26
2 9 10 9
8 550 400
form., formaldehyde; acet, acetone; pinon, pinonaldehyde; DMBH, 6,6-dimethylbicyclo[3.1.1] heptan-2-one; AMCH, 4-acetyl1-methylcyclohexene. * Collected before or after NO-N02 crossover. See Table I for initial concentrations and experimental conditions. Reactant and product concentrations measured in the dark following sunlight irradiation of the limonene-NO, mixture.
limonene or 4-acetyl-1-methylcyclohexeneas the starting material. @-Pinene. Several carbonyls were isolated (as their 2,4-DNF" derivatives) as oxidation products of a-pinene. Of these, four were positively identified: formaldehyde, acetone, pinonaldehyde, and glyoxal. Two were tentatively identified as being a Clo carbonyl and a Cl0 hydroxy dicarbonyl, respectively. The last carbonyl product observed is a monofunctional, small carbon chain compound (from its HPLC retention time and 360/430-nm absorbance ratio) but could not be identified. The reaction of OH with a-pinene leads to pinonaldehyde according to the pathways summarized in Figure
1000
ooH
Go. +
800
C C H O 600
+
HO,
A
r: d
5
r Y
8
400
L 0 2 , NO
200
0 20
40
60
80
100
6
Concentration, pg I rnL
1600
-I- HCHO
+
HO,
Flgure 2. Carbonyl products of the OH-limonene reaction: formaldehyde, 4acetyi-l-methylcyclohexene, and the Cl0 carbonyl. Pathways leading to organic nitrates omitted for clarity; u.d., unimolecular decomposition. 1200
E E
r:
f
d
5
800
r Y
8
a
400
A
'
6,
+
H,COO
and
Qo6
+
HCHO
0 20
40
60
80
100
120
Concentration, pg / rnL
Figure 1. Calibration curves (absorbance vs carbonyl concentratlon) for the 2,Minitrophenyi hydrazones of 6,6dlmethylbicycio[3.1.1]heptan-2one (a, top) and rlacetyl-1-methylcyclohexene (b, bottom). Linear regression parameters (slope f one SD, Intercept f one SD, peak height, mm, attenuation setting 6 vs carbonyl concentration, pg/mL) are 12.99 f 0.09, 4.1 f 4.2 ( R 2 > 0.999) for 6,6dimethylbicyclo[3.l.l]heptan-2-one and 8.69 f 0.02, 0.0 f 0.9 (R2 > 0.999) for &cetyl-1-methyicyclohexene.
5. In turn, pinonaldehyde may photolyze and react with OH. The reaction of pinonaldehyde with OH may involve H atom abstraction from the carbonyl carbon (pathway C in Figure 5) or from the two tertiary carbons (pathways A and B in Figure 5). As is shown in Figure 5, the corresponding alkoxy radicals (pathways A and B) and acyl radicals (pathway C) are expected to yield smaller frag-
Figure 3. Simplified mechanism for the ozone-limonene reaction. Several fragmentation and rearrangement pathways for the Crlegee biradicals omltted for clarity.
ments including CH,CHO, which leads to glyoxal, and CH,CO, which leads to PAN. In the oxidation of a-pinene, pinonaldehyde may also form by reaction with ozone as is shown in Figure 6. Of the two Criegee biradicals formed, one is expected to yield 2,2-dimethyl-3-acetylcyclobutaneaceticacid (pinonic acid), which we did not observe in the gas phase and did not expect to observe on account of its very low vapor pressure. Pinonic acid has been identified before as a condensed product, i.e., as a component of a-pinene aerosol (29,30). The other Criegee biradical is a disubstituted biradical, of which one substituent is a methyl group. In recent product studies of the reaction of ozone with simple alEnviron. Sci. Technol., Vol. 26, No. 8, 1992
1529
fb
OH
O2,NO
+OH------
8 OH/ CH,CO CH,CH,C
@
\OH
COCH3
O
.
PINONALDEHYDE
COCH3
1 PATHWAYS SIMILAR TO
0 CH,COCH&H2C
H
I
/Oz.NO
I
G
CH,CO(CH~),CHCH,CO
CHSHO I
@
CH,CHO
I
COCH3
''7 D + CH,CO
E
CH3COON02(PAN) II 0
D
I u , d. t
F
CHpHO
H02
t
CHOCHO (GLYOXAL)
t
CHJCOCHz&!2
HOz
t
CHJXH2CHO II 0
= CH,CO(CH~,COCH&HO
i
E = CHgO + CH3CO(CH&C0 F = C H ~ O t C H ~ H Ot
CH3C0 (+
co
Flgwe 4. Reactions of 4-acetyCl-methylcyclxenewith OH involving H atom abstraction from the tertiary carbon (pathway A) and the carbonyl carbon (pathway B). Organic nitrate formation pathways omttted for clarity.
kenes, it has been shown that methyl-substituted Criegee biradicals may form carbonyl, dicarbonyl, and hydroxy carbonyl products (17): RC(CH3)00 RCOCH3 (carbonyl) CH2=C(R)COOH (hydroperoxide) (dicarbonyl) CH,==C(R)OOH RCOCHO + H2 (RCOCHZOH)'
--
(RCOCH20H)'
-+
RCOCHzOH (hydroxy carbonyl) RCO CH2OH
+
Under the conditions of our experiments, the hydroxymethyl and acyl radicals lead to formaldehyde and to a peroxyacyl nitrate, respectively: CH2OH + 0 2 HCHO + HOz RCO O2 RC03 RC03 + NO2 is RC(0)OON02 -+
+
-
The Cloproducts tentatively identified in our experiments are consistent with the above sequence of pathways for the ozone-a-pinene reaction. Formaldehyde was also observed, but the peroxyacyl nitrate was not. The EC-GC conditions we employ to measure PAN are suitable to observe other low molecular weight peroxyacyl nitrates (C,-C,) and organic nitrates (c&) but may not be suitable to detect the higher molecular weight members of these two functional groups, e.g., C9-Cl0,that are expected to form in the oxidation of terpenes. &Pinene. Carbonyl products identified in the oxidation of @-pineneincluded 6,6-dimethylbicyclo[3.1.1]heptan-2one, formaldehyde, and acetone. Four other carbonyls, three c446 including two dicarbonyls (from their retention times and 360/430-nm absorbance ratios), and one com1530
Environ. Sci. Technol., Vol. 26, No. 8, 1992
PAN)
CH,COCH, C&CHO
(--GLYOXAL)
OTHER FRAGMENTS
Flgwe 5. OH-a-pinene reaction and subsequent reactions of OH with pinonaldehyde. Pathways A-C originate with H atom abstraction from the two tertiary carbons (A, B) and from the carbonyl carbon (C). Pathways leading to organic nitrates are omitted for clarity.
pound eluting after 6,6-dimethylbicyclo[3.l.l]heptan-2-one were detected but could not be identified. The carbonyl products of 6,6-dimethylbicyclo[3.l.l]heptan-2-one included formaldehyde, acetone, and the three unknown low molecular weight carbonyls that are also products of @pinene. PAN was observed to form in small amounts, 3 ppb or less from @-pinene and 0.5 ppb from 6,6-dimethylbicyclo[ 3.1.11heptan-2-one. The reactions of OH and ozone with @-pineneinvolve addition on the unsaturated carbon-carbon bond. As is shown in Figure 7, the major products of the OH reaction are 6,6-dimethylbicyclo[3.l.l]heptan-2-oneand formaldehyde, which are formed via unimolecular decomposition of the two Clo @ hydroxy alkoxy radicals. Reaction of one of these radicals with 02,if important relative to unimolecular decomposition, leads to the Clo hydroxy carbonyl shown in Figure 7. This compound may be the unidentified carbonyl which elutes after 6,6-dimethylbicyclo[3.l.l]heptan-2-oneunder our HPLC conditions. One of the Criegee biradicals formed in the ozone reaction is disubstituted. We assume from the general reaction scheme discussed earlier that its major decomposition pathway involves loss of an oxygen atom to form 6,6-dimethylbicyclo[3.1.1]heptan-2-one. The reaction of 6,6-dimethylbicyclo[3.l.l]heptan-2-one with OH (ita reaction with O3 is negligibly slow) may lead to a number of carbonyls, as is shown in Figure 8. TWO alkoxy radicals are formed following H atom abstraction from the two tertiary carbons. Their subsequent reactions may involve unimolecular decomposition and/or reaction
o +
G
H
1
O
I G
H
OH
O
PlNONlC ACID + OTHER PRODUCTS
PINONALDEHYDE
0 2 , NO. 0 2
J
4
\ CH, OH
1
C=O
CH,OH
+
G
HCHO +
H
O
G C H O
OONO,
I
H 4
0
G C H O
Flgure 6. Ozone-a-pinene reaction: carbonyl products of the disubstituted Criegee biradical containing one methyl group.
Figure 8. OH-6,6dimethylblcyclo[3.l.l] heptan-Bone reaction. Pathways shown as examples are two of the three unimolecular decomposition pathways possible for one of the two alkoxy radicals formed following H atom abstraction from tertiary carbon atoms. Organic nitrates omltted for clarity.
Table 111. Reaction Rate Constants and Fraction of Terpene or Carbonyl Reacted 102.
NO
6CH,
CH,OH I
I
G
HO,
+
O
H
gH
63
+
HCHO
+
HO,
rate const," cm3 fractn reacted after 1 h molecule-' s-l [OH]= 106 03, OH, molecules [O,] = 100 compd 10'8k 10"k cmd PPb a-pinene 0.52 84 6.0 0.19 pinonaldehyde slow 1.6, 2.4 0.07 0 0.17 21 7.8 0.24 8-P'inene 6,6-dimethylbicyclo- slow 1.5 0.05 0 [ B,l,l]heptan2-one d-limonene 640 14.2 0.40 0.99 4-acetyl-1-methyl100b 10 0.30 0.59 cyclohexene a Measured (4-6) or estimated (12, 14). Estimated from structure-reactivity relationships (33, 34).
00
0
I
-
OTHER PRODUCTS
Figure 7. Carbonyl products of the OH-&pinene (top) and ozone-& pinene reactions (bottom).
with oxygen. Several of these pathways are shown in Figure 8 and lead to acetone, formaldehyde, and a number of six-membered cyclic compounds that bear up to three carbonyl functional groups. These products, if indeed
formed, may account for the unidentified carbonyl products we observed in both @-pinene-NO, and 6,6-dimethylbicyclo[3.1.1]heptan-2-one-NOX experiments. Acetone (slow reaction with OH) is one of the precursors to PAN in both systems. Reactivity Considerations. Measured and estimated rate constants for the reaction of OH and ozone with the terpenes studied and for their major high molecular weight products are summarized in Table 111. Also included in Table I11 are the fractions of terpene or carbonyl that have reacted after 1h for two typical examples of electrophile concentrations, i.e., [OH] = lo6 molecules cm-, and [O,] = 100 ppb. These examples illustrate that the importance of the ozone reaction relative to the OH reaction increases as the overall reactivity of the terpene (or carbonyl) toward Environ. Sci. Technol., Vol. 26, No. 8, 1992
1531
~~~
Table IV. NO, Consumed and Accounted for As PAN
compd, run no.
[NOZl, PPb finala consumed
PAN, % of NO, consumed
a-pinene 1 2
3 @-pinene 1 2
3 d-limonene 1 2
6,6-dimethylbicyclo[3.1.11heptan-2-one 4-acetyl-1-methylcyclohexene
70 80 350
155 180 750
13 7 >5
380 50
120 130
0 2
200
880
0.3
50
20 160
200 180 30
17 16 2
5
210
19
Measured by chemiluminescence and corrected for PAN; initial NO, concentrations are listed in Table I. a
electrophiles increases. While carbonyl products in terpene-NO, systems are due to both OH and ozone reactions, the carbonyl product distribution for the more reactive terpenes reflects an increasing contribution of the ozone reaction. The concentration-time profiles of NO, NOz,03, and PAN in our experiments are consistent with reactivity considerations; i.e., limonene, 4-acetyl-1-methylcyclohexene, and a-pinene were the most reactive, followed by 8-pinene (intermediate) and 6,6-dimethylbicyclo[3.1.1]heptan-Zone (slowest). Examination of the data in Table I11 indicates that in most cases the first-generation products are as reactive toward OH and ozone as the parent terpene. The one exception, 6,6-dimethylbicyclo[3.1.1]heptan-Bone, indeed accumulated in our 8-pinene-NO, experiments and is most likely to be present at measurable concentrations in the atmosphere where it could possibly serve as an indicator of biogenic terpene emissions. Carbon and Nitrogen M a s s Balance Considerations. Product yields could be estimated from the measured carbonyl concentrations and from measured or estimated rate constants to account for their removal by reaction with OH, reaction with 03, and photolysis. However, these yields and those reported in earlier studies (12, 14) may have limited relevance since the initial terpene concentrations employed, 1ppm or more, were some 4-5 orders of magnitude higher than terpene concentrations in the atmosphere. In addition, many of the high molecular weight compounds observed in this study may be distributed between gas and condensed (aerosol) phases, thus leading to erroneous yield estimates. Indeed, substantial amounts of aerosols, as high as 5040% on a carbon basis for the pinene isomers, are formed from terpenes at initial concentrations comparable to those employed in this study (12,13,29-32). Some of the products we have identified here in the gas phase have been reported as components of the aerosol phase as well (13,31,32). Finally, some of the "second-generation" carbonyl products we observed, while providing insight into the terpene oxidation mechanisms, are not expected to accumulate in the atmosphere but rather to undergo rapid oxidation to yield CO (12) and free radicals. For all terpene-NO, systems studied, a large fraction of the initial NO, was consumed. PAN accounted for 16-19% of the consumed NO, for limonene and for its carbonyl product Cacetyl-1-methylcyclohexene,7-13% for a-pinene, and 12% for @-pineneand its carbonyl 6,6-dimethylbicyclo[3.1.1]heptan-2-one(Table IV). Some of the 1532
Environ. Scl. Technol., Voi. 26, No. 8, 1992
"missing" NO, may be accounted for by nitric acid (which was not measured) produced by reaction of OH with NO2 and by loss on the Teflon chamber walls. Another and possibly large fraction of the NO, not accounted for in our experiments may consist of two categories of nitrogencontaining products, the high molecular weight alkyl nitrates and peroxyacyl nitrates. In turn, a large fraction of these high molecular weight products, especially the Clo alkyl nitrates, may be present as aerosol rather than as gas-phase components (12, 30). Acknowledgments We thank Eric Grosjean for his assistance in carrying out the experiments and the carbonyl analyses. Ms. Denise Yanez prepared the draft and final versions of the manuscript. Literature Cited Rasmussen, R. A. J. Air. Pollut. Control Assoc. 1972,22, 537-543. Lamb, B.; Guenther, A,; Gay, D.; Westberg, H. Atmos. Enuiron. 1987,21, 1695-1705. Chameides, W. L.; Lindsay, R. W.; Richardson, J.; Kiang, C. S. Science 1988,241, 1473-1475. Atkinson, R. J. Phys. Chem. Ref. Data 1989, Monograph 1, 1-246. Atkinson, R.; Hasegawa, D.; Aschmann, S. M. Znt. J. Chem. Kinet. 1990, 22, 871-887. Barnes, I.; Bastian, V.; Becker, K. H.; Tong, Z. J . Phys. Chem. 1990,94, 2413-2419. Tuazon, E. C.; Atkinson, R. Znt. 9.Chem. Kinet. 1990,22, 1221-1236. Paulson, S. E.; Flagan, R. C.; Seinfield, J. H. Znt. J. Chem. Kinet. 1992,24, 79-101. Jacob, D. J.; Wofsy, S. C. J. Geophys. Res. 1988, 93, 1477-1486. Atherton, C. S.; Penner, J. E. J. Geophys. Res. 1990, 95, 14027-14038. Hov, 0.;Schjoldager, J.; Wathne, B. M. J. Geophys. Res. 1983,88,10679-10688. Hatakeyama, S.; Izumi, K.; Fukuyama, T.; Akimoto, H.; Washida, N. J. Geophys. Res. 1991, 96, 947-958. Yokouchi, Y.; Ambe, Y. Atmos. Environ. 1985, 19, 1271-1276. Arey, J.; Atkinson, R.; Aschmann, S. M. J. Geophys. Res. 1990,95, 18539-18546. Grosjean, D. Enuiron. Sci. Technol. 1991, 25, 710-715. Grosjean, D. Anal. Chem. 1983, 55, 2436-2439. Grosjean, D. Enuiron. Sci. Technol. 1990,24, 1428-1432. Graedel, T. E. Rev. Geophys. Space. Phys. 1979, 17, 937-947. Roberts, J. M.; Fehsenfeld, F. C.; Albritton, D. L.; Sievers, R. E. J. Geophys. Res. 1983,88, 10667-10678. Petersson, G. Atmos. Environ. 1988, 22, 2617-2619. Grosjean, D. Environ. Sci. Technol. 1985,19, 1059-1065. Williams, E. L., 11.; Grosjean, D. Atmos. Environ. 1990, MA, 2369-2377. Williams, E. L., II;Grosjean, D. Environ. Sci. Technol. 1991, 25, 653-659. Grosjean, D.; Harrison, J. Environ. Sci. Technol. 1985,19, 749-752. Grosjean, D.; Parmar, S. S.; Williams, E. L., I1 Atmos. Enuiron. 1990,24A, 1207-1210. Parmar, S . S.; Grosjean, D. Atmos. Environ. 1990, 24A, 2699-2702. Williams, E. L., II;Grosjean, D. Environ. Sci. Technol. 1990, 24, 811-814. Druzik, C. M.; Grosjean, D.; Van Neste, A.; Parmar, S. S. Znt. J . Enuiron. Anal. Chem. 1990. 38. 495-512. Hatakeyama, S.; Izumi, K.; Fukuyaka, T.; Akimoto, H. J. Geophys. Xes. 1989, 94, 13013-13024. Schueltze, D.; Rasmussen, R. A. J. Air Pollut. Control Assoc. 1986,28, 236-240.
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(34) Grosjean, D.; Williams, E. L., I1 Atmos. Environ. 1992,26A, 1395-1405.
(31) Pandie, S.; Paulson, S. E.; Seinfeld, J. H.; Flagan, R. C. Atmos. Environ. 1991,25A, 997-1008. (32) Grosjean, D., Seinfeld, J. H. Atmos. Environ. 1989, 23, 1601-1606. (33) Grosjean, D. J . Air Waste Manage. Assoc. 1990, 40, 1397-1402.
Received for review January 15, 1992. Revised manuscript received April 3, 1992. Accepted April 21, 1992. This work was supported by National Science Foundation Grant ATM-901)3186.
Enantioselective Determination of Chlordane Components Using Chiral High-Resolution Gas Chromatography-Mass Spectrometry with Application to Environmental Samples Hans-Rudolf Buser' and Markus D. Muller
Swiss Federal Research Station, CH-8820 Wadenswil, Switzerland Christoffer Rappe Institute of Environmental Chemistry, University of Umei, S-90187 Umei, Sweden
Technical chlordane was examined using both achiral and chiral high-resolution gas chromatography (HRGC) with detection by electron capture, negative ionization mass spectrometry (ECNI-MS). The enantiomer separation of several chiral octachlordanes including cis- and trans-chlordane was achieved and enantiomeric ratios of approximately 1:l were determined using a modified 8cyclodextrin as the chiral selector. The method was then applied to tissue extracts of several aquatic vertebrate species collected from the Baltic Sea (herring, salmon, and seal) and from Antarctica (penguin). The isomer profiles of the 6and nonachlordanes observed in the biological samples using achiral HRGC-MS differed from those observed in a technical chlordane mixture, with some minor components of the technical mixture showing much higher abundance in the aquatic samples. Chiral HRGC now showed enantiomeric ratios of several chiral octachlordanes differing from 1:l in each of these aquatic species. The changed enantiomeric compositions likely result from enantioselective biological processes and not from abiotic processes such as chemical, distribution, or transport processes in the environment. The results reinforce previous data showing the presence of these contaminants in biota from the most remote area on earth, Antarctica. 4
Introduction Chlordane is among the most prevalent and important toxic environmental contaminants. It was used as a pesticide for both residential and agricultural applications over several decades (1,2).By 1988, the use of chlordane has stopped in the United States, Japan, and most European countries, but consumption in other countries continues. The global occurrence of chlordane has been well documented, and nowadays chlordane or its metabolites are readily found at all trophic levels, in specimens from such remote areas as the Arctic and Antarctic. It is even present in human adipose tissue and milk (3-7). Residues found in biological and environmental samples include components from technical chlordane and their metabolites such as oxychlordane (8). Chlordane is now considered a possible human carcinogen (9). Technical chlordane is a complex mixture of various chemically similar components derived from hexachlorocyclopentadiene. Detailed analysis of the technical mixture revealed up to 120 components (2,10-12). However, in most of these reports the chirality of some of the chlordane 0013-936X/92/0926-1533$03.00/0
components, including those of the main constituen%. cisand trans-chlordane, has hardly ever been considcrdd. Enantiomers (optical isomers) of chiral compounds may show different biological behavior and properties such as uptake, metabolism, and excretion (13,15). Transformation reactions in biological systems and in the environment may thus show stereoselectivity (16-18). In contrast, abiotic processes such as chemical, distribution, or transport processes will be the same for both enantiomers, and enantiomeric composition will thus remain unchanged. h enantioselective determination of chiral compounde in environmental and biological samples may thus give additional information on possible degradation pathways a-ld may allow a distinction of enantioselective biotic from nonenantioselective abiotic processes. In this respect, however, only minor progress has been made because of the unavailability of analytical techniques, particularily so at the trace concentration levels required for environmental analyses. Recently, the enantiomer separations of cis- and tram-chlordane were reported using a high-resolution gas chromatography (HRGC) column coated with a pure Pcyclodextrin (P-CD) derivative (19). These columns, however, have some limitations for general use including low thermal stability and poor inertness. These deficiencies often lead to excessive retention times and high background signals, which preclude their use for trace environmental and biological applications. Recently, HRGC columns prepared by dilution of high-melting 0-CD derivatives in apolar polysiloxane stationary phases were described (20,21).These columns show somewhat reduced chiral selectivity, but are more suitable for chiral analyses of real biological samples. The enantioselective determination by use of this technology of a-HCH enantiomers in environmental samples was recently reported (18). We report here the first application of chiral HRGCmass spectrometry (MS) toward the enantioselective determination of chiral chlordane components in a technical product and in environmental biological samples. Various chlordane components were first assigned in a technical chlordane mixture using achiral HRGC-MS and then enantiomeric ratios of chiral components were determined using chiral HRGC-MS. The information thus obtained was then used to assign these components in aquatic vertebrate species from the Baltic Sea and from the Antarctic. Interestingly, several chiral chlordane compo-
0 1992 American Chemical Society
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