1200
Anal. Chem. 1982. 54. 1200-1201
to determine. In the case of t ( A t , AE),it is not necessary to know E , and t , values beforehand. This is a completely different point from all other definitions of response times. The discussion presented here for Cu(I1) ISEs should also hold true for other types of ISEs.
The results of the response times according to a new definition are shown in Table 11. Each magnitude of A t is properly short and AE is small. The results indicate that the dependence of the response time on the magnitude of the concentration jump is very small as compared with those of tW,tB5, etc. For example, the value t (2,0.3) shows that the magnitude of the potential change between 2.8 and 4.8 min after the concentration change is at most 0.3 mV independent of the magnitude of the concentration jump. This result is similar to that oft* and indicates that the response speed of the electrode near the equilibrium potential depends little on the magnitude of the preceding concentration change. Some advantages of the new definition of response time are (1)it is one realistic measure of the practical performance of the electrode, (2) it can be applied to ISEs whose response speed is slow so that the final value is not determined readily, (3) it is concentration independent when At is chosen properly short and AE is small, and (4) it would also be used for some mechanistic discussion on the very final stage of responses where the precise c w e fitting is rather difficult. On the other hand, it has some disadvantages. It does not necessarily indicate precisely to what extent the electrode response approaches the equilibrium state, while t, theoretically gives such information. In addition, this new definition has no direct relation to mathematical formulation of response curves like the time constant in an exponential or a hyperbolic equation as t , does. However, this latter condition for t , holds only for ideal cases where the response curve can be fitted with a single exponential or hyperbolic. If the equilibrium potential E , is easily obtainable, it is no more necessary to define such parameters as t, or t*; instead, the value of E , and t , (time needed to get equilibrium potential) could simply be reported. However, a logical paradox raised here is that we cannot determine t, and t* values without knowing E , and t,, which are not necessarily easy
ACKNOWLEDGMENT The authors gratefully acknowledge S. Fujiwara for his support toward this study. LITERATURE CITED Fleet, B.; Ryan, T. H.; Brand, M. J. D. Anal. Chem. 1974, 46, 12-15. Rangarajan, R.; Rechnitz, G. A. Anal. Chem. 1975, 47, 324-326. Mertens, J.; den Winkle, P. V.; Massart, D. L. Anal. Chem. 1976, 4 8 ,
272-277. IUPAC Pure Appl. Chem. 1976. 48, 127-132. IUPAC I n f . Bull. 1978, NO. 1 , 69-74. Shatkay, A. Anal. Chem. 1976, 48, 1039-1050. Umezawa, Y.; Nagata, M.; Sawatari, K.; FuJlwara, S. Bull. Chem. SOC. Jpn. 1979, 52, 241-242. Alexander, P. W.; Rechnltz, G. A. Anal. Chem. 1974, 4 6 , 250-254. Rechnitz, G. A.; Kresz, M. R.; Zamochnlck, S. B. Anal. Chem. 1966, 3 8 , 973-976. Rechnitz, G. A.; Kresz, M. R. Anal. Chem. 1966, 3 8 , 1786-1788. Blaedel, W. J.; Dlnwlddie, D. E. Anal. Chem. 1975, 47, 1070-1073. Sawatari, K.; Imanishi. Y.; Umezawa, Y.; Fujlwara, S. Bunseki Kagaku ~ 7 8 ~ 2 180-183. 7 ,
’
Present address: Department of Chemlstry, College of General Education, The University of Tokyo, Komaba, Meguroku 153,Japan.
Isamu Uemasu’ Yoshio Umezawa* Department of Chemistry Faculty of Science The University of Tokyo Hongo, Tokyo 113, Japan
RECEIVED for review December 7, 1981. Accepted March 8, 1982.
-. .. . . . ... Gas rnase memiluminescence ot Arsine Mixea with wzone A
A.
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Sir: We have observed a room-temperature gas phase chemiluminescence between arsine (ASH,) and ozone. Arsine was generated via sodium borohydride reduction of arsenic trioxide using a small amount of Nz carrier and allowed to react with a 2% ozone/oxygen mixture produced by passing pure oxygen through an electrodeless discharge. The gases mixed in a Pyrex reaction vessel producing a bluish white chemiluminescence. A 0.25-m McPherson monochromator with an EM1 9526B photomultiplierand Keithley electrometer were used to obtain the spectra. Figure 1 shows a low-resolution spectrum of the chemiluminescence of arsine with ozone observed a t a reduced pressure of 22 torr. The UV bands from 300 to 331 nm arise from the As0 y system (A22 X21T) (I). The origin of the diffuse apparent continuum is unknown, but by analogy to the similar phosphorus “phosphorescence” discussed by VanZee and Khan (2) it may be due to an excimer, thus A s O ( ~ ~ )A s 0 e (ASO)~* 2As0 hu
-
+
-
+
The UV bands of As0 have previously been observed in diffusion flames (3-5) and discharge systems (6-8). In only one of these studies, however, was a similar visible continuum observed (3). The suggestion of the (ASO)~* excimer to account for the visible continuum is based on three considerations. Firstly, if the excimer has a bound excited state and a dissociative ground state, the excimer emission would be
I
I .
-
expected to be a continuum, red shifted relative to the forbidden AsO(~~T X2n)transition which would occur with 0 0 at 3378 A (7). Secondly, the spectral characteristics are very similar to those found for the chemiluminescent reaction of P4with moist oxygen examined by VanZee and Kahn (2). On the basis of their experimental evidence, the analogous (PO),* excimer was assigned as the emitting species in the continuum. Finally, we have obtained experimental evidence consistent with this proposition. Spectra have been taken at higher pressures in which the continuum increased in intensity relative to the UV band emission. In a flow tube constructed to study the kinetics of this chemiluminescence we have found that the intensity of the visible bands increases markedly with increasing pressure and also that the maximum visible intensity can occur down stream from the initial mixing zone. A model involving excimer formation can be constructed which has these properties.
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RESULTS AND DISCUSSION The primary technique for analysis of arsenic compounds is reduction to arsine using sodium borohydride followed by atomic absorption spectrometry (AAS) (9-11) or atomic fluorescence spectrometry (AFS) (12). The determination of arsenic by AAS of its near-vacuum UV resonance line has been reported to encounter difficulties with stability of the light source as well as absorption interfence from oxygen-containing
0003-2700/82/0354-1200$01.25/00 1982 American Chemlcal Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 7, JUNE 1982
1
1201
Table 11. Investigation of Interferences at 100 ppbv of the Listed Molecules Relative to ASH, = 100 potential interferent AH3
H2s KO
signal
potential interferent
signal
100 0.5
PH, SbH,
4.8 134
3.3
s, a pulse containing as little as 0.2 ng of arsine in the gas phase 310
370 430 WAVEL ENG T H
49 0
550
(nm)
Uncorrected photoelectric spectrum obtained from the chemiluminescencis generated by mixing 70 mL min-' of 2% O3in O2 with 120 mL min-' of 10% ASH, in N, at a total pressure of 22 torr. At the high pressures used in the detector described herein the As0 band system becomes much less intense than the continuum and thus was not observed by Fujiwara et al. (76). Figure 1.
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Table I. Arsine Calibration Data arsine amine concn, response concn, ppbv (;as ppm N O ) a ppbv 14 18 30 43 55 70
0.22 0.40 0.65 1.00 1.37 2.04
92 106 120 138 158
response (as ppm NO)a 2.50 2.95 3.34 3.93 4.52
could be observed. Optimization of such parameters as reaction vessel geometry, flows, total pressure, and choice of photomultiplier tube could markedly improve both detection limit and response time. We anticipate no interference from common atmospheric gases since Oz, Nz,COP, HzO, CO, NOz, and SOz do not chemiluminesce with ozone. Table I1 shows the relative interference posed by several substances introduced at 100 ppb mixing ratio and expressed relative to the arsine response at 100 ppb. The results obtained for stibine indicate that this substance is also readily detected by chemiluminescence with ozone. The data for stibine differ significantly from the concurrent work of Fujiwara et al. (16) who found that antimony interference in the detection of arsenic in solution by borohydride reduction and subsequent room temperature chemiluminescencewith ozone was over an order of magnitude less than we observe in our direct measurements of gas phase species.
LITERATURE CITED
a Response from CSI 1600 NO detector with red filter removed.
gases such as HzO, NO, and O2(3). Detection by chemiluminescence, where applicable, is often the method of choice because of its inherent simplicity, low cost, sensitivity, and relative freedom from interference (13, 14). Fujiwara et al. (3), studied the analytical applicability of arsine chemiluminescence in a furnaceflame system. They found an ultimate sensitivity of 10 ppb to aqueous solutions. Because their experimental system employed a hot hydrogen diffusion flame they had to contend with a high background signal as well a8 spectral interference with some of the important As0 peaks from emission of other molecular species. The present chemiluminescence method does not show high background or simultaneous spectral interferences. Potential chemical interferences are discussed later. In order to test the sensitivity of this novel chemiluminescenceas an analytical technique, we employed a commercial NO detector. The only adaptation was removal of the red filter. Table I shows the data obtained om calibration with dilute mixtures of ASH, in air. Typical operating conditions were a sample flow of 600 mL m i d , O3/0:!flow of 125 mL min-l, and a reaction chamber pressure near atmospheric. The response represents the read-out as ppni NO. There is an apparent linear response to arsine concentration in the range around the threshold limit value specified for industrial exposure (50 ppb) (15). Calibration was achieved by both static and exponential dilution of arsine samples generated and purified on a vacuum system. If the linearity observed in Table I is extrapolated down to the observed noise level, then with a response time of 50
Pearse, R. W. B.; Gaydon, A. G. "The Identification of Molecular Spectra", 3rd ed.; Chapman and Hall Ltd.: London, 1965; p 66. VanZee, R. ,J.; Khan, A. U. J. Chem. Phys. 1976, 65, 1764. Fujiwara, K.; Bower, J. N.; Bradshaw, J. D.; Winefordner, J. D. Anal. Chim. Acta 1979, 109, 229. Kushawaha, V. S.; Asthana, E. P.;Pathak, C. M. J. Mol. Spectrosc. 1972, 4 1 , 577. Asthana, B. P.;Pathak, C. M. Spectrosc. Left. 1980, 13, 7. Mrozowski, 5.; Santaram, C. J. Opt. SOC. Am. 1968, 56, 1174. Callomon, J. H.; Morgan, J. E. Proc. Phys. SOC.,London 1965, 86, 1091. Anderson, V. M.; Callomon, J. H. J , Pbys. B 1973, 6, 1664. Schmidt, F. J.; Royer, J. L. Anal. Lett. 1973, 6 , 17. Smith, R. G.;Van Loon, J. C.; Knechtel, J. R.; Fraser, J. L.; Pitts, A. E.; Hodges, A. E. Anal. Chim. Acta 1977, 9 3 , 61. Siemer, D. [I.; Koteel, P.; Jariwala, V. Anal. Chem. 1976, 4 8 , 836. Heithmar, E. M.; Plankey, F. W. Appl. Spectrosc. 1978, 32, 208. Fontijn, A.; Golomb, D.; Hodgeson, J. A. In "Chemiluminescenceand Bioluminescence";Cormier, M. J., Hercules, D. M., Lee, J., Eds.; Plenum Press: New York, 1973; pp 393-424. Fontijn, A. In "Modern Fluorescence Spectrometry"; Wehry, E. L., Ed.; Plenum Press: New York, 1976; Vol. I,pp 159-192. Natlonal Institute lor Occupatlonal Safety and Health, 1974, Publication Number (NIOSH) 75-149. Fujiwara, K.; Watanabe, Y.; Fuwa, K.; Wlnefordner, J. 0.Anal. Chem. 1982, 5 4 , 125.
'
Present address: Kernron Environmental Services, Farrnington Hills, M I 48018.
Mark E. Fraser Donald H. Stedman* Michael J. Henderson' Department of' Chemistry The University of Michigan Ann Arbor, Michigan 48109
RECEIVED for review November 30,1981. Accepted February 18, 1982.
