Chemiluminescent Reactions of Peroxyacetyl Nitrate and Ozone with Triethylamine Possible Atmospheric Monitor for Peroxyacetyl Nitrate James N. Pitts, Jr.,’ Hartmut Fuhr, Jeffrey S. Gaffney, and John W. Peters
Department of Chemistry, University of California, Riverside, Calif. 92502
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H Chemiluminescence spectra from the gas phase reactions of peroxyacetyl nitrate (PAN) (A max 650 nm) and ozone ( A max 520 nm) with triethylamine have been obtained a t atmospheric pressure. The two chemiluminescent reactions are easily distinguishable by optical filters. Concentrations of PAN as low as 6 ppb were detected by this chemiluminescence technique. The application of this method as an atmospheric monitor for PAN is discussed.
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Very sensitive chemiluminescence techniques have been developed recently to monitor atmospheric concentrations of ozone and nitric oxide. Three different chemiluminescent techniques have been employed for the measurement of ozone. Regner’s (1960, 1964) method utilizes the luminescence emission produced from the reaction of ozone with rhodamine-B adsorbed on activated silica gel. A more convenient technique for the continuous air pollution monitoring of ozone is based upon the chemiluminescence produced in the reaction between ozone and ethylene a t atmospheric pressure (Nederbragt, et al., 1965; Warren and Babcock, 1970). The low-pressure chemiluminescent reaction between nitric oxide and ozone, developed by Fontijn et al. (1970), can be used to monitor either atmospheric ozone or nitric oxide. This technique has recently been expanded by Hodgeson et al. (1971) for the measurement of total oxides of nitrogen or, with modifications, NO, plus ammonia. Furthermore, it has been suggested by Kummer et al. (1971) that it may be feasible to determine quantitatively trace amounts of sulfur-containing pollutants by means of their chemiluminescent reactions with ozone. Peroxyacetyl nitrate (PAN) is one of the key oxidants formed in photochemical smog. Ambient concentrations of PAN as high as 30 ppb are not uncommon in the eastern end of the Los Angeles basin (Darley et al., 1963). PAN is a known eye irritant (Stephens et al., 1361) and phytotoxicant; thus it has been pointed out by Taylor (1969) that acute injury occurs to sensitive plants after 4 hr of exposure to approximately 14 ppb PAN in ambient air. The most serious PAN episode reported to date occurred in Riverside in 1972 in which daily maximum PAN readings exceeding 15 ppb were recorded for 23 days (readings exceeded 40 ppb on two consecutive days) during the month of March. PAN is currently monitored in the atmosphere by gas chrOmatography on a repetitive batch basis (Stephens and Price, 1973). Presently, no chemiluminescence technique exists for atmospheric monitoring of PAN (Fontijn, 1972). A versatile chemiluminescence-monitoring technique would permit continuous determination of atmospheric levels of PAX;. Initial chemiluminescence studies with PAN and amines demonstrated that tertiary amines, when reacted
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with PAN, produced chemiluminescence. We now report the characteristic chemiluminescence spectra produced from the gas phase reactions of peroxyacetyl nitrate (PAN) and ozone with triethylamine vapor. Concentrations of PAN as low as 6 ppb were detectable with our current apparatus; consequently, emphasis will be placed on utilizing the chemiluminescence as a possible atmospheric monitor for PAN. Experimental The reaction vessel consisted of a silvered 1-liter chemiluminescence cuvette provided with two gas inlets centered above the optical window which formed the bottom of the cuvette. Light generated in the reaction cuvette was chopped mechanically a t 330 Hz and the output of the multiplier phototube (E.M.I. 9659 QD) was fed into a lock-in amplifier (Princeton Applied Research, Model HRS). Cutoff filters were mounted in a wheel arrangement
I I I
CHOPPER SYSTEM COOLED PHOTO-MULTIPLIER HIGH VOLTAGE -SIGNAL
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TO LOCK-IN AMPLIFIER
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u Figure 1. Chemiluminescencedetection unit
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0. I 0
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X (nm)
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Figure 2. Emission spectra of chemiluminescence reactions of triethylamine with PAN and ozone. Relative intensity maximum arbitrarily set at unity
between the optical window and mechanical chopper (Figure 1). Low-resolution spectra were obtained with a Bausch and Lomb monochromator (Model 33-86-03) located between the chopper and multiplier phototube. The amplified signals were displayed Qn a 100-mV potentiometric Sargent recorder (Model SRG). The monochromator-multiplier phototube unit was calibrated by use of a standard lamp (G.E. quartz iodine lamp EPI-1452, 1000 W) and the spectra were corrected for spectral sensitivity. Identical spectra were obtained whether the amine was added to the reaction cuvette in a stream of nitrogen or whether an excess of amine (liquid-vapor equilibrium) was present in the cuvette. Variable concentrations of both PAN and ozone were prepared and passed into the cuvette a t a constant flow rate (-10 cc/sec). All experiments were performed a t room temperature. Peroxyacetyl nitrate (1000 ppm, pressurized tanks) was kindly provided by the University of California Statewide Air Pollution Research Center a t Riverside. Ozone ( - 2 % V/V) was produced by passing oxygen (Matheson, ultrahigh-purity grade) through a Welsbach Model T-408 ozonizer. Triethylamine (Matheson, Coleman & Bell or Mallinckrodt gave identical results) was checked for purity by glc (>99.95%) and used without further purification.
Results and Discussion Corrected low-resolution spectra of the light emissions produced in the reactions of PAN (1000 ppm) and ozone (20,000 ppm) with triethylamine vapor were obtained independently and are shown in Figure 2 for comparison. The relative intensity maximum was arbitrarily set a t unity. The maxima were separated by approximately 130 nm. In control experiments, methylnitrate, ethylnitrate, ethylnitrite, and NOz, all of which are possible contaminants of PAN, were mixed with triethylamine vapor in the reaction cuvette and showed no evidence of luminescence. In a similar control experiment, the reaction of nitric oxide (1000 ppm) with triethylamine resulted in a weak luminescence which was enhanced in the presence of air. However, the emission observed from 10 ppm nitric oxide was insignificant compared to that produced from 0.4 ppm PAN. Concentrations of PAN as low as 6 ppb were detected with our current apparatus. This is nearly as sensitive as present gas chromatographic techniques (Smith et al., 1971). Improvement of the light detection system may permit measurement of PAN concentrations as low as 1 ppb or less. The reaction of PAN with triethylamine produced a slowly decaying afterglow which lasted for several minutes even a t the lowest PAN concentrations employed. This behavior is contrasted to that of the corresponding ozone reaction in which the emission rapidly decayed after the ozone flow ceased. The respective decay curves are illustrated in Figure 3. To distinguish the chemiluminescence induced by the reaction of triethylamine with concentrations of PAN and ozone found in polluted urban atmospheres, various combinations of cutoff filters were tested. A 500-nm cutoff filter (transparent: h < 550 nm) in conjunction with a 665nm cutoff filter (transparent: X > 665 nm) provided relative intensity values characteristic for both the PAN and ozone induced emissions. In the case of ozone-triethylamine reaction, a value of 1665/1550 < 1 was predicted from the monochromator spectra shown in Figure 2 ; for the PAN-triethylamine reaction, a value of 1665/1500 > 1 was predicted. The measured values of 1665/1500 were 0.35 and 3.44 for the ozone-amine and the PAN-amine reactions,
Figure 3. Decay curves of chemiluminescence reaction of triethylamine with PAN and ozone
generated in
respectively. This combination of cutoff filters affords the most appropriate means of distinguishing the two emissions a t low concentrations of PAN and 0 3 where the use of a monochromator is not feasible. To test the cutoff filter technique, the chemiluminescence produced by a mixture containing a 20-fold excess of ozone to PAN, a ratio not uncommon in polluted ambient air, was investigated. In this particular case, a value of 1665/1500 of 1.35 was found, indicating a much greater chemiluminescence efficiency for the PAN-amine reaction in contrast to the ozone-amine reaction. In an experiment designed to measure the chemiluminescence efficiency of the PAN-amine reaction relative to the corresponding Os-amine reaction, 1.5 ppm of O 3 produced the same uncorrected overall integrated light intensity as 0.4 ppm PAN in reaction with the amine. As an approximate correction for spectral sensitivity of the multiplier phototube over the integrated emission spectrum, the relative quantum efficiencies a t the Amax values of the emissions produced by the PAN and 0 3 reactions, 0.35 and 0.79, respectively, were applied. From these data, the chemiluminescence efficiency of the PAN reaction was calculated to be approximately 10 times greater than the corresponding ozone reaction. A technique is being devised for measuring atmospheric concentrations of PAN. The procedure involves measuring the 1665/1500filter intensity ratio as a function of the mole fraction of PAN relative to ozone. The percentage of PAN with respect to ozone for an unknown mixture could then be determined from this function. I t therefore would be possible, by this method, to calculate absolute concentrations of PAN in ambient air, if absolute concentrations of ozone were known from independent measurements. Alternatively, of course, the detection system could be calibrated with respect to PAN. The results of this work will be published in the near future. Although it has not been emphasized, the possible application of chemiluminescence from the ozone-amine reaction as a potential atmospheric monitor for ozone should not be disregarded. The purpose of this work was to propose a new and potentially useful method for atmospheric detection of PAN and not to identify the luminescing species or identify reaction products in either of the described chemiluminescent reactions. However, research is now in progress dealing with these aspects, in addition to a kinetic analyVolume 7, Number 6 , June 1973
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sis of the two reactions. The reaction of various tertiary amines and sulfides are also being examined for chemiluminescence efficiency.
Hodgeson, J. A., Bell, J. P. Rehme, K. A. Krost, K. J., Stevens, R. K., Joint Conference on Sensing of Environmental Pollutants, Palo Alto, Calif., November 8/10, 1971, AIAA Paper No.
Acknowledgment
Kummer, W. A., Pitts, J. N., Jr., Steer, R. P., Enuiron. Sci. Technol., 5 , 1045 (1971). Nederbragt, C . W., Van der Horst, A., Van Duijn, T., Nature,
The authors thank 0. Clifton Taylor, Raymond Tenorio, and Eugene A. Cardiff for the preparation and a generous supply of PAN. Note Added in Proof. Chemiluminescence generated by bubbling PAN through a solution of triethylamine in acetone (1%V/V) was approximately twice as intense as that produced in the vapor phase reaction. The results were more reproducible in the liquid phase than in the vapor phase. Therefore, the liquid phase chemiluminescence seems to be more suitable for atmospheric monitoring applications. Literature Cited Darley, E. F., Kettner, K. A,, Stephens, E. R., Anal. Chem., 35, 591 (1963).
Fontijn, A., International Conference on Chemiluminescence, University of Georgia, Athens, Ga., October 10-13, 1972. Fontijn, A , , Sabadell, A. J., Ronco, R. J., Anal. Chem., 42, 575 (1970).
71-1067.
206,87 (1965).
Regner, V. H., J . Geophys. Res., 65, 3975 (1960). Reener. V. H.. ibid.. 69.3795 (1964). S z t h , ’ R . G.,’ Bryan, R. J., Feldstein, M., Levadie, B., Miller, F. A , . SteDhens. E. R.. Health Lab. Sci., 8,48 (1971). Stephens, E. R., Darley, E. F., Taylor, 0. C., Scott, W. E., Int. J. Air WaterPoll., 4, 79 (1961). SteDhens. E. R.. Price. M. A , . J. Chem. Ed., in mess (1973). Tailor, 0. C., J. Air Poll. Control Assoc., 19, 34? (1969). Warren, G. J., Babcock, F., Rev. Sci. Instrum., 41, 280 (1970) Received for review October 24, 1972. Accepted February 2, 1973. This project has been financed in part with federal funds from the Environmental Protection Agency under grant number 800649. The contents d o not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. H. F. thanks the Deutsche Forschungsgemeinschaft for financial assistance.
NOTES
Removal of Mercury from Aqueous Solutions by Nitrogen-Containing Chemically Modified Cotton Earl J. Roberts’ and Stanley
P. Rowland
Southern Regional Research Laboratories, New Orleans, La. 701 79
Four chemically modified cotton celluloses were investigated for effectiveness in sorbing mercury (Hgz) from aqueous solutions. Effectiveness of these compositions was due to amine units of the following types: ethylenimine network polymer formed in the fibers, polyethylenimine sorbed on the filters, 2-diethylaminoethyl substituents in the cellulose, and 2-aminoethyl substituents in the cellulose. Cotton celluloses modified with 2-diethylaminoethyl or 2-aminoethyl substituents were the more effective compositions at concentrations of mercury above 1000 ppb. Cotton cellulose containing ethylenimine network polymer was most effective on the basis of the weight of the cellulosic composition. Sorbed mercury can be readily removed from the chemically modified cottons for recovery of the former and reuse of the latter. Mercury may be removed from aqueous media by precipitation as the sulfide (Deriaz, 1963), by use of ion exchange resins (Koch and Biebing, 1969; Scholten and Prielipp, 1963; and Law, 1971), by reduction and separation as metallic mercury (C&EN, 1970), and by sorption on proteins such as wool (Friedman and Waiss, 1972). This paper describes the effectiveness of four different chemically modified cotton celluloses for the removal of mercury from aqueous solutions. Unmodified cellulose is ineffective. 1 To whom
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Environmental Science & Technology
Experimental
Preparation of Cotton Impregnated with Crosslinked Polyethylenimine (CPEI). A prepolymer was prepared by allowing a, mixture of 25 grams (0.25 mole) of 1,2-dichloroethane and 75 grams (1.75 moles) of ethylenimine to react for 16 hr in a water bath maintained a t 25°C. Caution is exercised to control polymerization at this stage by efficient removal of heat, Cotton fabric impregnated with ethylenimine network polymer formed in situ was prepared as described by Roberts and Rowland (1971). The fabric was subjected to two cycles of immersion in a 20% ethanolic solution of the prepolymer and passed through squeeze rolls to a wet pickup of 95%. The impregnated fabric was allowed to dry and cure for 16 hr a t room temperature. The cured fabric was washed in flowing t a p water for 30 min and line-dried a t room temperature. The add-on was 16%; the moisture content was 7.5570, and the nitrogen content was 2.75% on the dry basis. Aqueous solutions of the prepolymer may be used in place of ethanol solutions with similar results. Boiling the final fabric in water for 5-10 min increases its efficiency in removing mercury from aqueous solutions. Preparation of 0-(2-Diethylamino)ethyl (DEAE) Cotton. The DEAE cotton was prepared by subjecting cotton fabric to two cycles of immersion in a 1.OM solution of N,N-diethylaziridinium chloride (DAC), prepared as described by Roberts et al. (1971), and by passing the resultant material through squeeze rolls to a wet pickup of
