2426
Anal. (?hem. 1983, 55, 2426-2427
of the (M + NO2)- peak was very poor. Inorganic salts such as NaNO,, NaN02, and Na202have also been tested as potential reagents for polycyclic aromatic hydrocarbons. In all the cases peaks corresponding to (M 15)- were observed when the inorganic salts were used. However, the intensity of the (M + 0 - H)- ion was found to be the highest when NaNO, was used as a reagent, and lowest for Na202,when the same aromatic compound is used. In experiments using coronene, the NaN03 mixture showed a more intense peak for (M + 0 - H)- than the one obtained with 1,3,5-trinitrobenzene. Thus NaN0, generally is found to be a better reagent for this ion/molecule reaction. Detailed analysis of the LMS of aromatic compounds using nitro compounds as reagents will be published separately. The cationization of organic molecules noticed earlier (5-9, often aided by the addition of alkali halides, might also be considered as solid-state chemical ionization process. However, the reported formation of (M 15)- in the present investigation is distinctly different from the others in that a fragment ion produced from the reagent compound is being used to interact with the substrate to produce a characteristic peak. To our knowledge this is the first report of this kind of chemical ionization in the solid state. We believe this type of reaction opens up new possibilities in LMS, allowing one to use suitable substances as a source of reagent ions for chemical ionization. This method has potential for obtaining structural information about organic compounds using laser mass spectrometry. We are continuing work to identify the mechanisms of the reactions reported in this paper as well
+
+
as investigating other potential reagents for solid-state chemical ionization sources. Registry No. 1,120-12-7;2,5645-3; 3,243-17-4; 4,19770-49-1; 5 , 50-32-8; 6, 192-97-2;7, 218-01-9; 8, 191-07-1;9, 191-48-0; 10, 215-58-7; 11, 53-70-3; 12, 92-24-0; 13, 85-01-8; 14, 129-00-0; 15, 217-59-4;o-dinitrobenzene,528-29-0;m-dinitrobenzene,99-65-0; p-dinitrobenzene, 100-25-4; 1,8-dinitronaphthalene, 602-38-0; l,5-dinitronaphthalenej 605-71-0; 2,3$-trinitronaphthalene, 87185-24-8; 2,3-dinitrotoluene,602-01-7;3,4-dinitrotoluene,61039-9; 1,3,5-trinitrobenzene,99-35-4.
LITERATURE CITED (1) Budzlklewlcz, H. Angew. Chem., I n f . Ed. Engl. 1981, 2 0 , 624-637. (2) Trenerry, V. C.; Bowie, J. H. Org. Mass Spectrom. 1980, 15, 367-368. (3) Vastola, F. J.; Pirone, A. J. Adv. Mass Spectrom. 1968, 4 , 107-111. (4) Honig, I?. E. J . Chem. Phys. 1954, 22, 126-131. (5) Balasanmugam, K.; Dang, T. A.; Day, R. J.; Hercules, D. M. Anal. Chem. 1981. 53. 2296-2298. (6) Zakett, D.; Schoen, A. EICooks, R. G.; Hemberger, P. H. J . Am. Chem. Soc. 1981. 103. 1295-1297. (7) Cotter, R. J. Anal. Chem. 1981, 53, 720-721.
Kesagapillai Balasanmugam Somayajula K. Viswanadham David M. Hercules* Department of Chemistry University of Pittsburgh Pittsburgh, Pennsylvania 15260
RECEIVED for review March 29, 1983. Accepted August 29, 1983. This work was supported, in part, by a grant from the Office of Naval Research.
Comparison of the Zirconia pH Sensor and the Glass Electrode Sir: It has been demonstrated that stabilized zirconia membranes can serve as pH sensors at temperatures as high as 285 “C (1-3). While such sensors will most likely find their greatest application a t temperatures that are presently unattainable by glass electrodes, it also seems possible that they will compete with the glass under other conditions. This stems from the fact that the new sensors appear to show little, if any, sensitivity to alkali ions in basic solutions and, therefore, are free from the “alkaline error” associated with the glass electrode. To illustrate this important point, I am presenting some comparison data obtained with the new sensors and with high-quality, commercially available, glass electrodes-both general purpose (GP) and high alkalinity (HA) types. EXPERIMENTAL SECTION For use in the tests, 6 in. long, 1/4 in. 0.d. yttria-stabilized zirconia tubes closed at one end were sealed to lime glass extensions to facilitate handling. Direct junction internal connections were made by adding mercury to a depth of about 2 in. and contacting with a platinum wire. The tests were conducted by introducing a sensor, a hightemperature, glass electrode (Ingold Electrodes, Inc., type GP or HA), and a high-temperature 3 M (3.3 m) silver/silver chloride, sleeve type, reference electrode (Ingold Electrodes, Inc.) into a thermostated Teflon vessel fitted with a reflux condenser and a magnetic stirrer. Provision was also made for the slow introduction of acid or base with a motor driven syringe or, more rapidly, with a pipet. Keithley Model 616 electrometershaving an input impedance of >1 X 1014s2 were employed for all of the measurements. All of the work was conducted at 95 “C. RESULTS AND DISCUSSION Data comparing the response of a zirconia sensor with that
of a GP glass electrode in the presence of 1 m sodium chloride are shown in Figure 1. They were obtained by slowly titrating an added increment of hydrochloride acid with 5 m sodium hydroxide over a period of 15 min with a motor driven syringe. The smaller response of the glass electrode undoubtedly results from the well-known “alkaline error” associated with the general purpose type of electrode. Additional comparisons of the voltage responses of zirconia sensors and a glass electrode (this time the HA type) were made over the pH range bracketed by 0.025 m HC1 and 1.0 m NaOH. Representative data are summarized in Figure 2 in which the pH values of the solution were calculated by using a value of 12.32 for pKw at 95 “C as derived from data of Naumov et al. (4). Required activity coefficients were calculated with the extended Debye-Huckel equation log y = - A d , / ( l +
Bad0
(1)
where I is the ionic strength and where values of a = 9.0 8, for the hydrogen ion and 3.0 A for the hydroxide ion (5) were employed. Values of A = 0.59385 and B = 0.34255 were derived by interpolation from tabulations in ref 4. It is seen that even the HA type glass electrode deviates significantly from a linear response at high pH, while the response of the zirconia sensor is linear over the entire range. In the worst case at 1 m NaOH the glass electrode shows a deviation of about 0.8 pH unit from the calculated value. It was also found that in the absence of large excesses of sodium ion the correlation between the zirconia sensor and the HA glass electrode was excellent over the range of pH from 1.2 to 11.2 (0.0875 m NaOH), and no hysteresis was observed in
0003-2700/83/0355-2426$01.50/00 1963 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983 2427 o
0
GLASS ELECTRODE ZIRCONIA SENSOR
OPEN POINTS FOLLOW AGING I N ACID CLOSED POINTS FOLLOW AGING I N BASE
700
t,/
CALCULATED RESPONSE
t ZIRCONIA SENSOR
L BASE ADDED
-
Figure 1. Titration curves obtained with a zirconia sensor and a GP type glass electrode at 95 O C ; solution inltiaily 0.1 rn in HCI and 1.0 rn in NaCi. 600
800 0
I
GLASS ELECTRODE ZIRCONIA SENSOR
L T 0
REPLACE ELECTROLYTE WITH FRESH ACID I
I
I
I
I
I
I
I
IO
I
I
I
I
4t0
20
2
ADDITION
Figure 3. Comparison of responses of a zirconia sensor and an HA type glass electrode during aging of both for 1 month at 95 O C .
L
DAY 2
OAY 30
DAY 30 -AFTER REPLACING SOWTION
Figure 4. Comparlson of responses of a zlrconla sensor and an HA type glass electrode to rapid changes In pH at 95 O C .
-300
I
0
I 2
I
I
4
6
I
8 1 PH
0
1
2
1
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Figure 2. Comparison of the responses of a zirconia sensor and an HA type glass electrode from 0.025 rn HCI to 1.0 rn NaOH at 95 O C . going from acidic to basic pH and back. Further data indicating the behavior of the zirconia sensor and the HA type glass electrode at 95 OC were obtained over a period of a month. Starting with 1L of a solution that was 0.025 m in HC1, 25-mL aliquots of 5 m NaOH and 5 m HCI were added alternately to cause step changes in pH. Normally two or three such additions were made over a period of about 1h, and then the electrodes were allowed to age for a longer period in either the acidic or alkaline solution before another set of transients was undertaken. The aging periods varied from 1 to 8 days. In Figure 3 the responses of the two types of pH sensor are compared with the theoretical during successive cycles as sodium chloride accumulated in the solution. The theoretical responses were calculated allowing for the dilutions that occurred with each increment of added acid or base and for the accumulation of sodium chloride in the electrolyte. It is evident that even with the HA electrode employed in this test its behavior is more erratic than that of the zirconia sensor, and as sodium accumulated in the solutions some loss of response occurred. Upon replacing the solution with fresh, the full response of the glass electrode was again obtained. As seen from the data in Figure 4, the response rate of the zirconia sensor remained comparable with that of the glass electrode throughout the test period.
It should be mentioned that these data are representative of those obtained with the six to eight better ceramics that we have tested. All were fabricated from high-purity powders, and care was taken to minimize surface pores and defects. A similar number of earlier tubes prepared with less attention to such details developed the full voltage response to pH changes, but with much longer response times. We are presently investigating the cause of such sluggish performances. ACKNOWLEDGMENT S. Prochazka of General Electric Corporate Research and Development was extremely helpful by fabricating several high-density zirconia tubes for use in some of this work. Highly purified, yttria-stabilized zirconia powder was kindly prepared by C. Scott of the General Electric Lighting Research Laboratory, Cleveland, OH, for this purpose. Registry No. Zirconia, 1314-23-4.
LITERATURE CITED (1) Nledrach, L. W. Sclence 1880, 207, 1200. (2) Niedrach, L. W. J . Electrochem. SOC.1880, 727, 2122. (3) Nledrach, L. W.; Stoddard, W. H. "The Development of a High Temperature pH Electrode for Geothermal Flulds. Final Report-Task 111 and Year-End Summary"; prepared for the Pacific Northwest Laboratory operated by Battelle Memorial Institute under prime contract No. DE-AC-06-76-RLO-1830 for the United States Department of Energy, Divlsion of Geothermal Energy, Report No. PNL 4651, Feb 1983. (4) Naumov, 0. B.; Ryzhenko, B. N.; Khcdakovsky, I. L. "Handbook of Thermodynamlc Data"; Transl. U.S. Geological Survey, USGS-WRD74-001 (1974). (5) Butler, J. N. "Ionic Equillbrlum-A Mathematical Approach"; AddlsonWesley: Readlng, MA. 1964; p 434.
L. W.Niedrach General Electric Corporate Research and Development P.O. Box 8 Schenectady, New York 12301 RECEIVED for review May 27,1983. Accepted August 3,1983.
