Environ. Sci. Technol. 1993, 27, 2814-2820

Evaluation of Ozone and Water Vapor Interferences in the Derivatization of

Atmospheric Aldehydes with Dansylhydrazine

Daniel R. Rodler, Lubos Nondek,? and John W. Blrks’

Department of Chemistry and Biochemistry and Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado 80309-02 16

The dansylhydrazine (DNSH) and 2,4-dinitrophenylhy- drazine (DNPH) techniques for the determination of carbonyl compounds are both susceptible to interferences from ozone oxidation and water vapor hydrolysis. Here we report the results of an investigation of these potential interferences for a new DNSH microcatridge technique and describe means of minimizing or completely elimi- nating them. Studies were carried out using both silanized, controlled-pore, glass beads and octadecylsilane (CIS) particles as the reagent support. All intereferences were minimized by the use of CIS particles. Ozone was found to cause partial oxidation of the DNSH reagent but had no significant effect on the hydrazone products for mixing ratios up to 300 ppbv 03, with or without the presence of up to 100% relative humidity. Thus, ozone is not a significant interference so long as DNSH is in substantial excess over the carbonyl compounds being derivatized. Water vapor provides an interference by shifting the equilibrium between the hydrazones and an alcohol intermediate. Addition of trichloroacetic acid to the microcartridge was found to reduce this interference at 100% RH to <lo% for the hydrazone of propanal and to negligible levels for other aldehydes.

Introduction

Recently, there has been considerable concern about regional increases in tropospheric concentrations of ozone and other oxidants derived from ozone. Although the general mechanism of oxidant formation in the reactions of carbon monoxide, hydrocarbons, and the oxides of nitrogen (NO,) in the presence of sunlight is reasonably well understood, further development of emissions reg- ulations requires an understanding of the relative con- tributions by these natural and anthropogenic chemical species to oxidant formation. One approach to obtaining a better understanding of the relative contributions of anthropogenic and natural hydrocarbons to oxidant for- mation is to measure the atmospheric concentrations of specific aldehydes and ketones. As the first stable oxidation products of hydrocarbons, these carbonyl com- pounds may serve as indicators of which hydrocarbons are contributing to ozone formation in a particular air mass. Such measurements require high detection sensi- tivity (low part-per-trillion detection limits) and short sampling times.

We recently reported a highly sensitive microcartridge technique for the measurement of atmospheric aldehydes and ketones at the sub-ppbv level based on derivatization ~ ~ ~~

t Present address: Water ResearchInstitute,Podbabska30,16000, Prague, Czechoslovakia.

2814 Envlron. Sci. Technol., Vol. 27, No. 13, 1993

with dansylhydrazine (DNSH) (I, 2) . Limits of detection for 10-min sampling times (1 L of air) are determined by the blank and are -50 pptv for formaldehyde and acetaldehyde and even lower for other aldehydes.

The - 2 orders of magnitude greater sensitivity of the DNSH microcartridge technique over the commonly employed 2,4-dinitrophenylhydrazine (DNPH) method is due to two factors. The first is the inherently greater sensitivity provided by fluorescence detection (DNSH) relative to detection by UV absorption (DNPH). The second sensitivity enhancement is realized through the use of microcartridges to collect and derivatize the air samples. These cartridges are capable of withstanding the high pressures necessary in high-performance liquid chromatography (HPLC), thus enabling them to be connected in-line with the HPLC system and permitting the transfer of the entire sample to the head of the HPLC column. By using an appropriate focusing technique, it is possible to perform the transfer in a manner which effectively eliminates the peak broadening associated with large injection volumes. For a silanized glass bead sorbent, we are able to elute the analyte from the cartridge with water, thereby focusing the relatively nonpolar analyte onto the head of the column (a process hereafter referred to as “retention focusing”). A more detailed explanation of this technique is presented in earlier papers (I, 2).

To achieve analyte focusing in the case of octadecyl silica (CIS) sorbent, we have developed a dual-injector technique. This technique uses two injection valves connected in series. The first injection loop contains a nonpolar solvent, and the second contains the sampling cartridge. When the injections are made, the solvent elutes the analyte from the octadecylsilica sorbent as a narrow band, focussing as it elutes (hereafter referred to as “elution focusing”). Through the development of this technique and aminor change in the ordinary HPLC solvent gradient, we are able to obtain more than adequate chromatographic resolution of derivatized atmospheric carbonyl compounds. A complete description of the dual-injector technique will be described elsewhere (3).

In the conventional DNPH procedure the air sample typically is collected on a low-pressure, nonpolar sorbent cartridge, which subsequently is eluted with -1 mL of solvent into a vessel where the derivatization reaction is completed. A small fraction of the collected sample (about 1-5%) is then injected onto the HPLC column and analyzed. The use of high-pressure sampling cartridges increases the overall sensitivity of our method relative to the conventional cartridge technique by more than 1 order of magnitude by permitting the transfer of the entire sample to the HPLC column. The technique also min- imizes the possibility of sample contamination from

0013-936X/93/0927-2814$04.00/0 0 1993 American Chemlcal Society

exposure to additional solvents, glassware, laboratory air, etc. Additionally, the increased sensitivity permits a smaller sample volume, thereby minimizing interferences and reducing the possibility of sample breakthrough.

The twoderivatization methods utilize thesame reaction mechanism, a highly selective reaction of the hydrazine compounds with aldehydes and ketones to form hydra- zones. The principal difference, in terms of the chemistry involved, between our method and the well-characterized DNPH procedure is the microenvironment in which the derivatization reaction occurs. In the technique we have developed, the reaction is performed on the surface of the sampling cartridge sorbent. In contrast, the DNPH derivatization has typically been carried out homoge- neously in the liquid phase.

In our previous work using the DNSH microcartridge technique (2), a potential interference by ozone was identified. The purpose of the work described here was to evaluate the ozone and water vapor intereferences for a broad range of reaction conditions and to identify conditions under which they are minimized or eliminated altogether. We examined the stahility of various hydra- zones on silanized glass heads and octadecyl silica (C18) sorbents, in the presence and absence of an acid catalyst, when exposed to air samples containing a wide range of relative humidities and ozone concentrations. Also, a preliminary investigation of in-cartridge isoprene oxidation was carried out by sampling a gas-phase isoprene standard in the presence of various levels of relative humidity and ozone.

Experimental Section

Chemicals. The aldehydes, isoprene, and dansylhy- drazine were obtained from Aldrich, Milwaukee, WI. Acetic, trichloroacetic (TCA), and hydrochloric acids were purchased from Mallinckrodt, Paris, KY. The hydrazones were prepared by introducing the aldehydes to an ace- tonitrile solution containing the dansylhydrazine and allowing 24 h to ensure complete derivatization. The HPLC mobile phase consisted of acetonitrile and water, hothfromBwdickandJackson,Muskegon,MI. The water was buffered with 1.6 g/Lmonohasic potassium phosphate obtained from EM Science, Cherry Hill, NJ. The hy- drocarbon-free air used as zero air was ohtained from Denver Welding Supply, Denver, CO. Controlled-pore glass heads (PG-1000-120,80-120 mesh, 22.7 mVg) were ohtained from Sigma, St. Louis, MO. The glass heads were silanized with a mixture of trimethylchlorosilane and hexamethyldisilazane, also obtained from Sigma. The octadecyl silica (Cle) used to pack the sampling cartridges was obtained from Sep-Pak CIS cartridges purchased from Waters, Milford, MA.

Apparatus. The HPLC apparatus was comprised of a Spectra-Physics SP8800 ternary gradient pump, Rheo- dyne 7335 column inlet filter, Rheodyne 7125 six-port injection valves, Alltech Hypersil ODS (CIS) column (15 cm, 4.6 mm i.d.), Rainin Microsorh MV column (15 cm, 4.6 mm i.d.), Kratos FS 970 fluorometer, and a Hewlett- Packard HP3396A integrator. Supelco SP-13P sampling pumps were employed in sample collection. Sampling cartridges and cartridge shells were obtained from Tessek (Prague, Czechoslovakia) and have been described pre- viously (I, 2). Ozone concentrations in the range 0-300 pphv were obtained from a UV ozonizer (Figure 1) of our

Flgure 1. Duakange. UV ozonizer. Variable levels of ozone are obtained by adjusting the length of shielding of the lamp.

Exponentla1 Dllul lon rI83L

taa chromatcqraph - Flgure 2. Schematic diagram of the apparatus used In evaluating the stability of dansyihydrazlne and dansylhydrazones and the potential for in-cartridge Isoprene oxhiation

own construction (described below). Relative humidities from 0 to nearly 100% were generated by passing dry zero airthrough a humidifier tube of our own construction and diluting as necessarywith dry zeroair. Gas-phase isoprene standards were generated with an exponential dilution apparatus of our own construction; it is contained within the temperature-controlled oven of a Hewlett-Packard 5730A gas chromatograph. Tylan mass flow controllers (FC 260) were used to control the gas flow rates.

Ozone Generator. A simple UV ozone generator was constructed (Figure 1) for the purpose of evaluating the effect of ozone on dansylhydrazine and the dansylhydra- zones. It consists of a Pen-Ray mercury lamp housed within a movable Pyrex sheath (4) . A stream of zero air is passed through a '/a-in. quartz tube located adjacent to the lamp. This system employs a secondary mercury emission line a t 185 nm which photolyzes oxygen to form ozone. This wavelength is blocked by the Pyrex sheath hut is able to pass through the quartz tube. Therefore, the intensity of this wavelength reaching the airstream and the concentration of the ozone produced varies with the length of the lamp not covered by the sheath. The generator output was calibrated with a Teco Model 49 photometric ozone analyzer and was found to he linear as a function of the exposed length of the lamp over the range 50-300 pphv.

Exponential Dilution Apparatus. We constructed an exponential dilution generator for the creation of gas- phase standards of isoprene (Figure 2) in order to evaluate the possibility of isoprene oxidation within the sampling

En~Iron. Scl. Technol.. VoI. 27. NO. 13. 1993 2815

cartridge. The exponential dilution apparatus was con- nected downstream from the ozonizer and humidifier. A wide range of conditions may be achieved by adjusting the ozonizer output and regulating the flow rates through the three portions of the system. The concentration of the standard exiting the dilution flask at time t is given by

where CO is the initial concentration, F is the flow rate (mL/min), t is the time (rnin), and Vis the volume of the dilution flask (mL). The integrated average concentration for a sample begun at tl and completed at tz is given by

A 1000-mL exponential dilution flask was connected to the injection port of a gas chromatograph (GC). In this arrangement, the dilution gas may be routed through a mass flow controller to the conventional carrier gas inlet on the GC. This arrangement also permits the introduc- tion of the standard solution ( -5 pL of dilute liquid phase) to the system via the heated injection port ( d 5 0 "C), where it is vaporized and transported to the dilution flask maintained at 60 "C in the GC oven. The vaporized standard is flushed from the dilution flask at a flow rate of 17 mL/min. At this flow rate, -40 min is required for dilution by a factor of 2. The collection of a standard sample generally begins -15 min after the dilution is started. This is done to minimize surface effects by providing time for equilibration with the surfaces. The measurements presented are based on the sum of the peak areas of the cis and trans isomers of the hydrazones.

Procedure for Interference Studies. A sampling cartridge, packed with silanized porous glass or octadecyl silica particles, was loaded with an acetonitrile solution containing 0.1 mg/mL trichloroacetic acid when appro- priate and 0.1 mg/mL DNSH and DNS hydrazones. The loading was accomplished by connecting a syringe to the cartridge and drawing the spiked reagent solution into the cartridge. The hydrazones of formaldehyde, acetal- dehyde) and propanal were present a t levels comparable to those seen in 1-L air samples; Le., several hundred picomoles. After the cartridges were loaded with the reagent, they were dried with helium at a flow rate of 100 mL/min for 3 min. A 1-L air sample containing 0-300 ppbv ozone and 0-r100% RH was then taken at a rate of 100mL/min by connecting the cartridge to a small battery- powered pump. The reagent solution, purge gas, and air sample were all passed through the cartridge in the same direction. After the sample was collected, the cartridges were wrapped in two sheets of aluminum foil, sealed in a vial, heated at 60 "C for 10 min, and inserted in-line with the HPLC system. The entire sample was injected onto the column and eluted with a solvent gradient a t 1 mL/ min. Gradient elution greatly reduces the time required to perform the analysis and enhances the detectability of the later elutingderivatives. There area few small changes to the conventional gradient that are beneficial to the chromatographic resolution when C18 microcartridges are used. Because the Cla cartridge requires a nonpolar solvent to elute the analyte, the initial aqueous fraction of the mobile phase is held at 90% for the first minute to

Table I. Solvent Elution Programs Used for Silanized Glass Beads and (218 Silica

HzO:CH&N time, min silanized glass beads CIS silica

0 1 8

43

63:37 63:37 63:37 25:75

9O:lO 63:37 63:37 25:75

maintain resolution by enhancing the degree of retention focusing at the head of the column. By comparison, the solvent program begins with 63 % water for cartridges packed with silanized glass beads. The solvent gradients used in this work are provided in Table I.

Sampling Cartridges. The octadecyl silica sampling cartridges were prepared by filling the cartridge cases with octadecyl silica obtained from a Waters Sep-Pak Cle cartridge. The reagent loading and sampling procedures were identical to the loading of the silanized glass bead cartridges. However, the method of cartridge elution used for the silanized glass bead sorbent is not effective for the octadecyl silica. The octadecyl silica is very nonpolar and hydrophobic, and thus the relatively nonpolar hydrazine and hydrazones are not eluted with water. In order to remove them from the sampling cartridge, it is necessary to elute the analytes with a nonpolar solvent. This is easily accomplished, but in the process, the retention focusing of the analyte a t the head of the column is lost and the loss of resolution in the chromatogram is apparent (Figure 3). However, through the use of dual six-port injection valves, as shown in Figure 4, we are able to achieve satisfactory cartridge elution without excessive peak broadening. This is accomplished by filling the 50-pL injection loop with acetonitrile. After the loop is filled, the pump is turned off and the valves are turned to inject. The pump is then turned on, and the analysis proceeds analogous to the procedure used with silanized glass bead cartridges. This method allows the cartridge to be eluted by a narrow band of hydrophobic solvent which transfers the analyte to the column. Elution focussing is accom- plished by the narrow band of nonpolar solvent as it strips the analyte from the octadecyl silica. The resulting narrow band profiles (Figure 5) are maintained by dilution of the hydrophobic stripping solvent with the high water content of the mobile phase. Thus, the elution procedure accom- plishes the same goal as water elution from silica or silanized glass beads (I, 2).

Results and Discussion

Water Vapor as an Interference. In one set of experiments, we examined the effects of sampling an airstream with high relative humidity. First, a study was undertaken using silanized glass beads as the sorbent (Figure 6a,b). No significant interference was found for DNSH or the hydrazone of formaldehyde. However, at a relative humidity of -loo%, about two-thirds of the acetaldehyde hydrazone and -90% of the propanal hydrazine were destroyed in the absence of TCA. This observation is consistent with the reported behavior of the DNPH derivative of acetaldehyde for cartridge sam- pling (5). With the addition of 0.1 mg/mL trichloroacetic acid to the microcartridge, the water vapor effect was reduced. There was still no significant intereference for

2818 Environ. Scl. Technol., Vol. 27, No. 13, 1983

I . I ' I ' I '

0 5 1 0 1 5 2 0

Time (min) Flgure 3. Sample chromatogram illustrating the peak broadening caused by eluting the octadecyl silica cartridge with 150 pL of cyclohexane. The chromatogram was obtained using a normal slngle- valve injection.

I I

I - C 1 8 Ssmpllng

In jec t ion Cartridge

Column Flgure 4. Dual-Inlector system used in the evaluation of sampling cartridges packed wlth octadecyl sllica sorbent.

DNSH or the formaldehyde hydrazone, and the water vapor effect for acetaldehyde and propanal was reduced

c .- v) S al c

al 0 c al 0 v )

0 3 U

c -

2 -

L 1

0 5 1 0 1 5 2 0

Time (min) Flgure 5. Sample chromatogram depicting the focusing effect of the dual-valve injection technlque for eluting octadecyl sllica cartridges.

to depletions of about 20 and 70%, respectively. In order to further reduce the water vapor interference,

we conducted the same set of experiments using octadecyl silica, which is very hydrophobic, as the sorbent (Figure 6c,d). In the absence of TCA, high relative humidity had no appreciable effect on DNSH or the formaldehyde and acetaldehyde hydrazones. Also, the water vapor effect for the propanal hydrazone was reduced to a depletion of -50%. Loading of the microcartridge with 0.1 mg/mL TCA further improves the situation by reducing the depletion of the propanal hydrazone to less than 10%.

Acetic and hydrochloric acids also were investigated as a means of reducing the water vapor interference. With these acids it was difficult to achieve an acceptable level of reproducibility. This is caused in part by the higher vapor pressures of these acids, relative to TCA, which may allow the acids to leave the cartridge during solvent removal, sampling, and derivatization steps. Also, the hydrochloric acid presumably is completely dissociated in a thin film of water adsorbed to the surface. Since the amount of water adsorbed differs significantly over a broad range of relative humidities, the pH at which the deriva- tization occurs may vary considerably. Data obtained by using 0.1 mL of HCl/mL of reagent solution with the silanized glass bead sorbent are shown in Figure 6e. The general trend in the magnitude of the water vapor

Environ. Sci. Technol., Vol. 27. No. 13, 1993 2817

Glass Beads Without Trichloroacetic Acid a C18 Silica with Trichloroacetic Acid d

Glass Beads With Trichloroacetic Acid b Glass Beads with HCI

i C 2 L 1 O N S H C 1 C Z C 3 C 4 L

C18 Silica Without Trichloroacetic Acid C . 1 . 2 ,

Zero Air l O O % R H 3oOppbvO3

H lOO4RH.3Wppbv03

e

Cii>" :;, C 2 C:

Flpure 6. Normallzed peak areas showing water vapor and ozone Interferences for dansylhydrazine and the hydrazones of formaldehyde. acetaldehyde. and propanal (a) on Silanlzed glass bead Sorbent In the absence of trichloroacetic acld (n = 5); (b) on silanized glass bead sorbent in the presence of trichloroacetic acid. (n = 5); (c) on octadecyl sillca sorbent in the absence of trichloroacetic acM (n = 5): (d) on octadecyl silica sorbent in the presence of trlchloroacetk acM (n = 4). The error bars represent one standard deviation. (e) Normalized peak areas showing water vapor interferences for dansylhydrazine and hydrazones of straight chain aldehydes through hexanal and benzaldehyde on silanized glass bead sorbent in the presence of hydrochloric acM (n = 3).

interference illustrated in this figure is consistent with observations made using both sorbents, regardless of the presence or absence of an acid; i.e., the propanal hydrazone is the most affected by water vapor.

The water vapor interference is dependent on the relative humidity of the sample, the acidity of the reagent solution used to load the cartridge, and the type of sorbent. This is believed to be primarily, if not entirely, due to the changing pH of the microenvironment in which the reaction occurs. The initial level of acidity is determined by the conditions used when the microcartridge is loaded. During sampling, water vapor is adsorbed onto the sor- bent and presumably reaches equilibrium with the air- stream that flows through the cartridge. The amount of water adsorbed is related to the extent to which the airstream is humidified, with the hydrophilic glass beads adsorbing much more water than the hydrophobic octa- decyl silica. The amount of water adsorbed determines the volume in which the acid is solvated, and thus the acidity and pH.

The water vapor interference may be attributed to hydration of thecarbon-nitrogen double bond. Hydrazine derivatization of carbonyl compounds occurs in two stages, addition and dehydration (6):

2818 Environ. Sd. Technol.. VoI. 27. No. 13. 1993

S %N + H,O

I H

'N-DNS H/

3

Under neutral or mildly acidic conditions, the equilibrium between 2 and 3 is located more toward 2 due to hydration. However, under more strongly acidic conditions, dehy- dration (2 - 3) is enhanced, and the equilibrium between 2 and 3 is shifted toward 3. The addition of water to the reaction microenvironment shifts the equilibrium back toward 2 by diluting the acid and possibly by increasing the activity of water. Cis and Trans Isomers. In the chromatograms

obtained, it is apparent that the chromatographic process is capable of separating the cis and trans (with respect to the C=N bond) isomers of the dansylhydrazones (Figure

5 and refs 1 and 2), e.g., for the propanal hydrazone:

I4

The exception of this is formaldehyde, the only symmet- rical aldehyde. The trans isomers are the preferred products of the derivatization reaction. The trans:& ratio is greater than 3 for all the aldehydes we have analyzed. This is to be expected since the cis derivatization product is more sterically hindered than the trans product. The trans isomer is more elongated and permits greater interaction between the alkyl chain of the hydrazone and the octadecyl silica of the column, translating into a greater retention time for the trans isomer versus the cis isomer. It is interesting to consider the relative impact of hydrolysis on the two isomers. By comparing chromatograms in which the hydrazones were exposed to 1 L of dry air to chromatograms in which the hydrazones were exposed to 1 L of air containing 100 % RH, it is readily apparent that the cis isomers were hydrolyzed to a very small extent, while the trans isomers were extensively hydrolyzed. In fact, the transcis ratio decreases to roughly unity. This finding permits detection of any water vapor interference by following the transxis ratio.

The dependences of extent of hydrolysis on length of the alkyl chain (C3 most strongly affected) and on the isomeric structure (trans more susceptible to hydrolysis than cis) are not readily explained in terms of mechanistic organic chemistry. Differences in reaction rates of isomers are often due to differences in steric hindrance in formation of the transition state. The large difference in reactivity of cis and trans isomers found for the dansyl hydrazones could be explained by steric hindrance if the lone electron pair of the S-N nitrogen catalyzes the nucleophilic attack of water on the carbon of the C=N bond. However, both the isomeric and alkyl chain length effects may involve surface interactions and have complex explanations.

Ozone as an Interference. A negative interference for ozone has been reported for the DNPH method (7,8) and identified in a preliminary study for DNSH (2). The effects of exposing the hydrazine and hydrazones to an air sample containing high levels of ozone, with and without water vapor, are shown in Figure 6a-d. It is apparent that regardless of the humidity and presence or absence of the catalyst, there is no net oxidation of the hydrazones. However, a t 300 ppbv ozone, there was -40% reduction in the hydrazine reagent when the silanized glass bead sorbent was used. This is improved to -25% by using the octadecyl silica sorbent. Interferences of this mag- nitude are not severe enought to have an impact on sample

derivatization, because we typically work with at least a 10-fold excess of hydrazine.

Isoprene Oxidation within the Cartridge. We carried out a preliminary investigation of the effects of sampling an airstream containing 10 ppbv isoprene, which is comparable to levels observed in a forest atmosphere during the warmer seasons (9, IO), along with various levels of ozone and relative humidity. At high concentrations of O3 and HzO, 300 ppbv ozone, and =loo% RH, the oxidation of isoprene produced the expected formaldehyde, methylvinyl ketone, and methacrolein for both glass beads and CIS. In addition, a mixture of Crj-C~o aldehydes and several unknown peaks were produced. This likely oc- curred as a result of free-radical polymerization of isoprene initiated by the Criegee biradical intermediate. I t was also observed that at high levels of ozone and relative humidity (300 ppbv, ~ ~ 1 0 0 % RH) the hydrazine and hydrazones disappeared almost completely from the chromatogram when TCA was not used. Initially, it was thought that the radicals might have reacted at the dimethylamino group, thereby quenching the fluorescence. However, it was determined that under these conditions all of the hydrazine and hydrazone peaks were destroyed in UV absorbance chromatograms as well. This leads us to believe that either a polymer product, which incorpo- rated the DNSH into its structure, was formed and did not elute from the cartridge or, less likely, the radicals produced in the cartridge destroyed the aromatic ring system. Additional work to further characterize the potential in-cartridge reactions of isoprene and other reactive species of interest, including acrolein, methac- rolein, and methyl vinyl ketone, with ozone is in progress. A more thorough understanding of this potential inter- ferences is important to any cartridge sampling method, including the DNPH method, for atmospheric carbonyl compounds.

Conclusions

Water vapor is a serious interference in the DNSH derivatization technique that can be almost entirely eliminated through the use of octadecyl silica as the sorbent in combination with trichloroacetic acid. Ozone is not a significant interference, for mixing ratios up to 300 ppbv, provided that an excess of hydrazine is present. The destruction of the hydrazine reagent by ozone is less for octadecyl silica than for silanized glass beads. Artifact peaks may be created when the air sample contains 10 ppbv isoprene and high levels of ozone and relative humidity, and this effect requires further investigation for the DNPH technique as well.

Acknowledgments

We thank Paul Goldan and Bill Kuster for their contributions to the designs of the ozonizer and humidifier, David Parrish and John Holloway for assistance in calibration of the ozonizer, Shelley Copley for helpful discussions of the hydrolysis mechanism, and Fred Feh- senfeld and Jim Roberts for a number of helpful sugges- tions. This work was supported by a grant from the Global Change Program of the National Oceanic and Atmospheric Administration (Grant GC91135). D.R.R. thanks CIRES for a Graduate Student Research Assistantship during part of this work.

Environ. Sci. Technol., Vol. 27, No. 13, 1993 2819

Literature Cited (7)

Nondek, L.; Milofsky, R. E.; Birks, J. W. Chromatographia (8) ~.

1993, 32, 33. Nondek, L.; Rodier, D.; Birks, J. W. Environ. Sci. Technol. (9) . , lY92,26, 1174. Rodier, D.; Birks, J. W., University of Colorado, Boulder, CO, submitted for publication 1993. Goldan, P. D.; Kuster, W. @. NOAA Aeronomy Laboratory,

(10)

. , lY92,26, 1174. Rodier, D.; Birks, J. W., University of Colorado, Boulder, CO, submitted for publication 1993. Goldan, P. D.; Kuster, W. @. NOAA Aeronomy Laboratory,

(10)

Smith, D. F.; Kleindeinst, T. E.; Hudgens, E. E. J . Chromatogr. 1989,483, 431. Arnts, R. R.; Tejada, S. B. Enuiron. Sci. Technol. 1989,23, 1428. Pierotti, D.; Wofsy, S. C.; Jacob, D. J. Geophys. Res. 0 2 1990, 95, 1871. Martin, R. S.; Westberg, H.; Allwine, E.; Ashman, L.; Farmer, J. C.; Lamp, B. J. Atmos. Chem. 1991, 13, 1.

Boulder, CO, personal communication, 1993. Grosjean, D.; Fung, K. Anal. Chem. 1982,54, 1221.

Hydronitrogens Having N-N bonds; Benjamin/Cum- mings: Reading, MA, 1983; p 15.

Received for review March 4, 1993. Revised manuscript re- Smith, p. A. S. Derivatives of Hydrazine and other ceived August 31, 1993. Accepted September 13, 19933.'

a Abstract published in Advance ACS Abstracts, October 15,1993.

2820 Envlron. Scl. Technol., Vol. 27, No. 13, 1993