Anal. Chem. 1983, 55, 1809-1810
accuracy in the biological matrix being stuldied is proved. One such test of accuracy wlould be the ability to accurately determine potassium in the presence of the substances isolated from Sephadex G-10 chromatographs of concentrated urine as described in Figure 2. Registry No. Potassium, 7440-09-7.
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(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";Beriiner, 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 WisconsinMadison, Madison, W I 53792.
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, 1912-19 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 . ) 1980, 26, 1883-1886. 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.
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, 1x1instrument 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 containing a 30% H202solution. The output f ~ o mthe radical generator 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/H20system 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 (cylindercontaining 50 ppm by volume AsH3in 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 chemiluminescent reaction between arsine and ozone can be described in part by the following steps:
-+ -
ASH, + O3
ASH,
ASH, + O3
products including O H
(a)
A S H ~+ HzO
(b)
OH
light emission and further radical generation (c) It 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 continuum (360-700 nm) it was shown that the nonlinear calibration 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 resulting from reactions (a) and (c) which under these conditions
0003-2700/83/0355-1809$01.50/0 0 1983 Amerlcan Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 11, SEPTEMBER 1983
1.0
-
0 0
200
400
600
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-
3
6 9 1 Time minutes
2
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
