Anal. Chem. 1983, 55, 1809-1810 1809

accuracy in the biological matrix being stuldied is proved. One such test of accuracy wlould be the ability to accurately de- termine potassium in the presence of the substances isolated from Sephadex G-10 chromatographs of concentrated urine as described in Figure 2.

(12) Morf, W. E.; Ammann, D.; Simon, W. Chlmla 1974, 28, 65-67. (13) Jenny, H.-B.; Riess, C.; Ammann, D.; Magyar, B.; Asper, R.; Simon, W.

Mikrochim. Acta 1980, 11, 309-315. (14) Civan, M. M.; Shporer, M. In "Biological Magnetic Resonance"; Beriin-

er, L. J., Reubin, J., Eds.; Plenum Press: New York, 1978; pp 1-32.

' Present address: Department of Pathology and Laboratory Medicine, Center for Health Sciences, Room B4/212, University of Wisconsin- Madison, Madison, WI 53792.

Registry No. Potassium, 7440-09-7.

LITEIRATURE CITED Pioda, L. A. R.; Stanitova, V.; Simon, W. Anal. Leff. 1969, 2, 665-674. Frant, M. S.; Ross, J. W., Jr. Science 1970, 167, 987-988. Ladenson, J. H. Clin. Chem. (Wlnsfon-Salem, N.C.) 1977, 23, 191 2-19 16. Ladenson, J. H. Clin. Chem. (Wlnsfon-Salem, N . C . ) W79, 25, 757-763. Peiieg, A.; Levy, G. 6. CYn. Chem. (Wlnsfon-Salem, N . C . ) 1975, 21, 1572-1574. Biumenfeld, T. A.; Griffibh, B. Clln. Chem. (Winsfon-Salem, N . C . )

Hebert, N. C. In "Glass Microelectrodes"; Lavaiiee, M., Schanne, 0. F., Hebert, N. C., Eds.; Wiley: New York, 1969; p 25. Walker, J. L. Anal. Chslm. 1971, 43, 89A-93A. Oehme, M.; Simon, W. Anal. Chlm. Acta. 1078, 86, 21-25. Thomas, R. C.; Moody, W. J. Trends B/ochem. Scl. 1980, 5, 86-87. Djamgoz, M. 8. A.; Laming, P. J. TrendsNeurascl. 1981, 4 , 280-283.

1980, 26, 1883-1886.

David D. Koch' Jack H. Ladenson*

Division of Laboratory Medicine Departments of Pathology and Medicine Washington University School of Medicine Box 8118 St. Louis, Missouri 63110

RECEIVED for review April 1, 1983. Accepted May 19, 1983. Presented in part a t the National Meeting of the American Association for Clinical Chemistry, July 1981, Kansas City, MO. D.D.K. wa3 supported by a postdoctoral fellowship from Nova Biomedical Inc.

Chemiluminescent Detection of Arsine Oxidation

Sir: Chemiluminescence with ozone is now recognized as a fast and sensitive technique for detection of traces of arsine in air ( I ) or of arsine generated from the borohydride reduction of aqueous arsenic compounds (2). A chemiluminescent arsine detector is already commercially available (3). The literature, however, is lacking infoirimation regardin,g the nature of the reactions between arsine and ozone or oxygen. The reaction mechanism, rate of react ion, and pressure dependence of the chemiluminescent intensity, all of which may be relevant to instrument optimization, are unknown.

EXPERIMENTAL SECT'ION These studies were performed with adapted chemiluminescent

NO detectors, Columbia Scientific Instruments (CSI) Model 1600, an instrument operating close to atmospheric pressure, and a Thermo Electron Corp. (TECO) Model 12A, 1x1 instrument which operates with the reactor under vacuum (aE low as 20 torr with the present pump and reagent flows).

The radical enhancement experiments were performed by use of the TECO 12A with a aiilent discharge ozonizer (Maximum 3 mol % O3 in O2 output) and another ozonizer maintained at tho reactor pressure. The latter ozonizer provided free radicals from a stream of oxygen that had passed through an impinger con- taining a 30% H202 solution. The output f ~ o m the radical gen- erator entered the sample inlet line just upstream of the reactor. Variable reactor pressure was achieved by a valve between the vacuum pump and the reactor and was measured with a ma. nometer. Several other radical generation techniques were at. tempted including moist ozone photolysis, but the discharged 02/H202/H20 system was the most successful. Discharged H? + NO2 was not used due to the operating pressures (>20 torr) and the background which would have ariiien from NO + 03. Calibrations were perfornied by static and flow dilution either of pure AsH3 samples or From a calibrated (cylinder containing 50 ppm by volume AsH3 in argon (Matheson gas, sold as 100 ppm).

The rate of oxidation reactions was measured by introducing arsine (to an initial concentration -40 ppb in air) into Tedlar bags (50-100 L). The decay of these mixtures of arsine in oxygen, air, and moist air exposed to sunlight was measured by using the CSI Instrument calibrated by static and dynamic dilution between

1 and 100 ppb. In the final study, ASH, decay was measured in the presence of excess ozone (10-40 ppm). The initial zone concentrations were determined with a Dasibi (UV absorption) ozone monitor.

RESULTS AND DISCUSSION Previous studies ( 4 ) have suggested that the chemilumi-

nescent reaction between arsine and ozone can be described in part by the following steps:

ASH, + O3 - products including O H

ASH, + OH - A S H ~ + HzO (a)

(b) ASH, + O3 -

light emission and further radical generation (c)

I t was suggested that the overall mechanism includes a slow initial reaction (a) followed by a branched chain reaction probably involving initiation by the odd hydrogen radical OH, reaction (b). Studies of the light emission (5) have shown that the quantum yield for the reaction is approximately 3 X photons per AsH3 input, indicating that light production is a minor channel in the overall reaction.

Pressure Effect and Radical Enhancement. Previous studies ( I , 2) have shown that the calibration curves from arsine chemiluminescence with ozone are linear at atmospheric pressure. Reduction of pressure in the chemiluminescent reaction between NO and O3 gives increased sensitivity while maintaining linearity (6). In the case of arsine, however, we have observed increased nonlinearity and decreased sensitivity (particularly a drastic loss of intensity at lower concentrations) of the calibration curves as the pressure is reduced from 1 atm to 20 torr. By use of optical filters to discriminate between the As0 band emission (295-345 nm) from the visible con- tinuum (360-700 nm) it was shown that the nonlinear cali- bration curves are unaffected by viewing only the visible continuum. The nonlinearity a t reduced pressures and low concentrations is believed to be a kinetic phenomenon re- sulting from reactions (a) and (c) which under these conditions

0003-2700/83/0355-1809$01.50/0 0 1983 Amerlcan Chemical Society

1810 ANALYTICAL CHEMISTRY, VOL. 55, NO. 11, SEPTEMBER 1983

0 2 0 0 4 0 0 6 0 0

PRESSURE (TORR)

Figure 1. Normalized instrument response (arbitrary units) for arsine at 50 ppm and 300 ppb using the radical generation system as a function of reactor prer +sure.

Log ASH, Concentration (PPm)

Figure 2. Calibration curves for arsine with ozone (A) and for arsine with ozone with radical enhancement (B), both at a total pressure of 300 torr using flows of sample of 500 mL min-I, ozonized 0, 165 mL min-', and radical source 22 mL min-'. Plotted is the log of the instrument response (arbitrary units) vs. log of the arsine concentration in ppm.

produce insufficient radicals necessary for efficient photon production.

Other investigators have shown that the chemiluminescent response from the reaction of reduced sulfur compounds with ozone may be improved by passing air through the ozonizer rather than oxygen (7). When tried with arsine, the response significantly decreases. Since we believe that OH radicals figure prominently in the path to light emission, we attempted to enhance the chemiluminescent signal from arsine reaction with ozone by adding OH radicals as described. Figure 1 shows the normalized instrument response to 300 ppb and 50 ppm arsine with the radical generation system as a function of reactor pressure. This figure shows the optimum pressure region (for maximum response) to both concentrations to be in the 200-300 torr range. Figure 2 shows two calibration curves using the apparatus described at 300 torr, one without and one with radical generation. The radical enhanced curve shows linearity over 5 orders of magnitude and enhanced sensitivity a t reduced concentrations. The reduction in in-

1.0 -

0 3 6 9 1 2 Time minutes

Figure 3. Variation of the arsine decay with ozone concentration plotted as log instrument response ( I ) vs. time for various (indicated) ozone concentrations.

tensity at higher arsine concentrations is probably due to intensity lost by reaction in the tubing prior to reaching the reactor (-20 ms). We have performed absolute calibrations for arsine and demonstrated calibration curve linearity to concentrations as low as 10 ppb. Based on the observed instrument noise when calibrated at 10 ppb, the detection limit is 0.2 ppb with a measured response time of <5 s.

Kinetic Studies. In pure 02, at room temperature, the initial arsine concentration was found to be unchanged over a period of several days. Similar results were found by using air and moist air exposed to sunlight.

To determine the rate constant for the initial reaction with ozone at room temperature, the decay of arsine signal in excess ozone was measured. Figure 3 shows logarithmic decays in excess ozone concentrations between 10 and 40 ppm. As expected for a bimolecular reaction, the data show faster decays (greater slopes) at higher concentrations of ozone. When the slopes were plotted against ozone concentration, a straight line was obtained, the slope of which is the apparent bimolecular initial rate constant. With propagation of both random and systematic errors the rate constant obtained is (5.0 f 2.0) X cm3 molecule-1 s-l. This rate constant indicates that the expected lifetime of low concentrations of arsine in ambient air a t room temperature (-50 ppb 0,) is about 2 days.

Registry No. AsH3, 7784-42-1; OH, 3352-57-6; Os, 10028-15-6; HZOz, 7722-84-1.

LITERATURE CITED (1) Fraser, M. E.; Stedman, D. H. Anal. Chem. 1982, 5 4 , 1200. (2) Fuiiwara, K.; Watanabe, Y.; Fuwa, K.; Winefordner, J. D. Anal. Chem. . .

19'82, 54 , 125. (3) L'air liquid, Alphagaz gaseous hydrldes detector. Product Release

Brochure, Paris, F;ance, Feb 1982. (4) Fraser, M. E.; Stedman, D. H. J. Chem. SOC., Faraday Trans. 1

1983. 78 . 527. (5) Fraser. M'. E.: Stedman. D. H.: Dunn, T. M. J. Chem. SOC., Faraday ~I

Trans. 1 , in press.

1983, 55, 135.

(6) Fontljn, A.; Sabadell, A. J.; Ronco, R. J. Anal. Chem. 1970, 42, 575. (7) Kelly, T. J.; Gaffney, J. S.; Phillips, M. F.; Tanner, R. L. Anal. Chem.

Mark E. Fraser Donald H. Stedman*

Musaddiq Nazeeri Marcel1 Nelson

Department of Chemistry The University of Michigan Ann Arbor, Michigan 48109

RECEIVED for review March 10,1983. Accepted May 17,1983. M. Nazeeri and M. Nelson were participants in the University of Michigan program in scholarly research for urban/minority high school students during the summer of 1982.