Anal. Chem. 1989, 6 1 , 1768-1772
1768
The Laplace inversion transform of eq A8 and A9 by use of the relation ( 5 )
L[CR] = C R O E / S s-l" sinh {s'/'(l -
1) sech (sl/z){L[iL/nFAD] - CR'/S) (A171
L-'[s-'iZ t a n h (as'/2)] = u-'O,(O;T/U~) (a, constant) (A10) yields eq 12 and 13, respectively. In the above equation, L-' is the inverse Laplace transform operator. Appendix 2. Applying Laplace transformation to eq 14 and rearranging, we have
L [ ~ ( T ) L / ~ F A=DS-'/' ] coth ( s ' / ' ) s ~ [ c R 0 (+ ~ exp(-{))-l] (All) Inverse transform of eq A l l is obtained by making use of relations (5) s L [ f ( ~ ) 1= L ( d f ( ~ ) / d r I+ f ( 0 )
L[c,] = C R O ( 1 - E ) / s + s-'/'sinh (s'/'(l - E ) ) sech ( S ' / ~ ) ( L [ ~ L / ~ F CAR OD/ S]]
(A181 Letting 6 = 0 in eq A17 and A18 and inverse transforming by use of eq A10 gives eq 28 and 29.
ACKNOWLEDGMENT Helpful discussion with Dr. J. F. Cassidy is gratefully acknowledged. Registry No. Fe(CN)6*-,13408-63-4;Fe(CN)63-,13408-62-3; KFe(CN)G,13943-58-3;dipotassium sulfate, 7778-80-5.
LITERATURE CITED
and
L-'[S-'/~coth (as'/2)]= a-'O3(0;T/a2) (a, constant) (A121
(1) (2) (3) (4)
and we have eq 19. Appendix 3. Application of the Laplace transformation with respect to T to eq 7 , 25, and 27 using eq 24 yields
(6)
d 2 L [ C ~ ] / d E= 2 (S/D)L[CR] - cRoE/D
(A13)
(7)
d2L[co]/dF2 = (S/D)L[co] - C R o ( l - C;)/D (A14)
(8) (9) (10) (11)
with d L [ c ~ ] / d [ = -dL[co]/dt = L [ i L / n F A D ]for
5 =0 (A15)
L[cR] = CRo/S, L[c,] = 0 for
6
= 1
(A16)
Following the procedure similar to Appendix 1, we obtain
(5)
(12)
Morita, K.; Shimizu, Y. Anal. Cbem. 1989, 67, 159. Shimizu, Y.; Morita, K., submitted for publication in Anal. Chem. Morita, K.; Sugiyama, T.; Ohaba, M., unpublished results. Bond, A. M.: Luscombe, D.; Oldham, K. B.; Zoski, C. G. J. Elechoanal. Chem. 1988, 249, 1. Roberts, G. E.; Kaufrnan, H. Table of Laplace Transforms; W. B. Saunders Company: Philadelphia, PA, 1966. Spanier, J.; Oldham, K. B. An At&s of Functions; Hemisphere Publishing Corporation: Washington, DC, 1987; Chapter 27. Aoki, K.; Tokuda, K.; Matsuda. H. J. Electroanal. Chem. 1983, 746, 417. Daruhizi, L.; Tokuda, K.; Farsang, G. J . Electroanal. Chem., in press. Matsuda, H.; Ayabe. Y. 2.Elektrocbem. 1955, 59,494. Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706. Bruckenstein, S.; Tokuda, K.; Albery, W. J. J. Cbem. Soc. Faraday Trans. 7 1977, 7 3 , 823. Sawyer, D. T.; Roberts, J. L., Jr. Experimental Electrocbemistry for Chemists: John Wiley: New York, 1974; p 153.
RECEIVED for review December 28, 1988. Accepted May 9, 1989.
Fiber-optic Time-Resolved Fluorescence Sensor for the Simultaneous Determination of AI3+ and Ga3+ or In3+ Mary K. Carroll, Frank V. Bright,' and Gary M. Hieftje*
Department of Chemistry, Indiana University, Bloomington, Indiana 47405
A fiber-optic fluorescence sensor for simultaneous two-elemental determlnatlons has been developed. The sensor is based on the formation of a complex between specific metal ions and a metal ion chelator. Several chelator-ion systems and several means of chelator immobilization were studied. The successful fiber-optic sensor design Is based on a pool of chelator solution trapped behind a membrane made of Naflon. The chelator uitlmately chosen, lumogallion, forms strongly fluorescent complexes with trivalent aluminum, gallium, and indium ions. Because of the difference in fiuorescence lifetimes of the various lumogaliion complexes, timeresolved fluorometry enables simultaneous determination of two of these ions.
* Author
t o w h o m correspondence should b e addressed. C u r r e n t address: Department o f Chemistry, State University of N e w York a t Buffalo, Buffalo, NY.
INTRODUCTION Many chelators form strongly fluorescent complexes with metal ions. Often, the fluorescence of the chelator itself is weaker than that of its complexes. As a result, the extent of complexation and, thus, the concentration of an ion in solution can be found from a measurement of fluorescence intensity. However, a chelator will frequently form complexes with several different ions, and the emission spectra of the different complexes are sometimes similar. Hence, interferences plague the determination of any particular metal ion in the presence of one or more of the others. This report describes the development of a fiber-optic-based fluorescence sensor capable of simultaneous two-element determinations under the conditions described above. Others have developed fiber-optic sensors for the determination of metal ions (1-5). Generally, these sensors are fabricated by immobilizing a metal indicator or chelator on
0003-2700/89/0361-1768$01.50/0 0 1989 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 61, NO. 15, AUGUST 1, 1989
the distal end of the fiber and measuring the fluorescence of the complex formed when the optrode contacts an appropriate ion-containing solution. Seitz and co-workers have published data on sensors of this type based on the complexes of morin, calcein, and quinolin-8-01 sulfonate (1-4). Unfortunately, these sensors are subject to severe interferences from ions other than the one targeted. In this paper, we avoid these interferences through the use of time-resolved fluorometry. Lytle and co-workers have shown that this method can be used to determine two or more metal ions in solution when the lifetimes of their fluorescent complexes are different (6, 7). Vitense and McGown have performed simultaneous determinations of metal ions through We have comthe use of phase-resolved fluorometry (8,9). bined the advantages of fiber-optic sensors with the method of time-resolved fluorometry to create a sensor that is capable of simultaneously determining the concentrations of A13+and Ga3+or A13+ and In3+ions in solutions containing a mixture of these ions. Detection limits obtained for aluminum, gallium, 2 x lo-', and indium ions by using this sensor are 2 X and 3 x lo4 M, respectively, and dynamic ranges are between 2 and 3 orders of magnitude. Relative errors encountered when mixtures of ions are determined range from 4 to 20%. Response times of a new chelator-pool sensor lie in the range of 4-5 min. THEORY The method employed to determine fluorescence lifetimes is called the phase-plane method, described in detail by Demas and co-workers (10, 11). When applied to a mixture of chelator-ion complexes with overlapping fluorescence spectra, the phase-plane method utilizes simultaneous equations and the fluorescence lifetime for each complex to calculate the contribution of each complex to the observed emission intensity (11). EXPERIMENTAL SECTION Reagents. Lumogallion was purchased from Pfalz and Bauer. Perfluorinated ion-exchange powder, 5% solution by weight, and morin hydrate were purchased from Aldrich Chemical Co. Gallium(II1)chloride and indium(II1) chloride were obtained from Aesar; aluminum(II1) nitrate nonahydrate was obtained from Fisher Scientific Co. All of the above reagents were used without further purification. Mordant Blue 31 was synthesized following the procedure outlined by Hiraki (12). Fluorescein (Sigma Chemical Co.) and Rhodamine 6G (Exciton) were used as reference fluorophores for the time-resolved measurements. Solutions were prepared by using distilled, deionized water, spectral grade acetone (Fisher Scientific),absolute ethanol (Aaper Alcohol and Chemical Co.), or a combination of these solvents. Commercial buffers (Fisher Scientific) were used for the pH study. Immobilization Procedures. Morin and the morin-A13+ complex were immobilized on microcrystalline cellulose (J. T. Baker Chemical Co.) following the procedure of Saari and Seitz (2, 3). The immobilized morin was compared with a sample donated by W. R. Seitz and was found to have the same emission spectrum. Lumogallion, its aluminum, gallium, and indium complexes, and morin and its complexes were immobilized by soaking AGl-X4 ion-exchange resin (Bio-Rad) in a solution of chelator or complex. Conventional Fluorescence Measurements. The instrument used for conventional fluorescence measurements is shown in Figure 1. The beam (150-250 mW of the 514.5, 488.0-, or 457.9-nm line) from a Spectra-Physics Model 171 argon ion laser is reflected from two mirrors, M1 and M2, passes through an iris, I, and is focused by lens L1 into one end of a 0.5-m-longbifurcated optical fiber (200-pm diameter, donated by Galileo Electro-optics). Fluorescence from the sample is collected by the other end of the optical fiber and is carried 0.5 m to a Spex double monochromator (Model 1680B). A Hamamatsu R928 photomultiplier tube in a Pacific Model 3150,s PMT housing collects the emission signal. The PMT is powered by a Pacific Photometric Instruments Model 203 high-voltage power supply, operated at -1000 V dc, and its
1769
IiI
I
I
U SAMPLE
MlNC 11/23
SUPPLY
Figure 1. Schematic design of instrument used for conventional fluorescence measurements: M, mirror; I, iris; L, lens.
I
i
1
I
I
-+L2
---Y
Argon-ion Laser
Mode-locker
x,y,z
Fiberoptic
t!-
Sample
I
Chopper
1
'-1/-
Flgure 2. Schematic design of instrument used for time-resolved fluorescence measurements: M, mirror; L, lens; xyz, translation mount; PM, photomultiplier tube. output is sent to a Keithley 414s picoammeter. The output of the picoammeter is connected to a DEC MINC-11/23 computer. The computer also functions to drive the monochromator. No attempt was made here to improve signal-to-noise ratios in the steady-state spectra by means of computer-based time averaging. Indeed, if the spectra were plotted on a strip chart recorder the apparent signal-to-noise ratio would be higher. Time-Resolved Fluorescence Measurements. Figure 2 shows the instrument us& for fluorescence lifetime measurements. A similar instrument has been described previously (13),and only its general features will be outlined here. The 514.5-,488.0-, or 457.9-nm output of a mode-locked Spectra-Physics Model 171 argon ion laser (Spectra-Physics Model 342 mode-locker, Model 452 mode-locker driver) is reflected from two mirrors, M1 and M2, mechanically chopped, and focused by L1 into one end of a bifurcated optical fiber (200 pm diameter, Galileo Electro-Optics). The beam travels 0.5 m through the fiber to the sample (either an optrode or a solution). The resulting fluorescence is collected through another 0.5-m length of fiber and carried to a Kratos Model GM100-1 monochromator set to the wavelength of maximum emission for the compound being studied. Detection of this fluorescence is accomplished with a Hamamatsu R928 PMT in a Pacific Model 3150,s PMT housing. The output of the PMT is sent to a sampling oscilloscope (Tektronix Model 7844 mainframe, Model S4 sampling head, Model 7Sll sampling unit), which is triggered by the mode-locker driver. The fluorescence decay of the sample is recorded by the oscilloscope, the output of which is sent t o an EG&G Princeton Applied Research Model 5101 lock-in amplifier. The lock-in amplifier, used to reduce noise introduced by the sampling oscilloscope, is referenced to the mechanical chopping frequency. The output of the lock-in amplifier is sent to a MINC-11/23 computer for data collection. The computer controls the scan rate of the oscilloscope time base; thus,
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ANALYTICAL CHEMISTRY, VOL. 61, NO. 15, AUGUST 1, 1989
Table I. Fluorescence Lifetimes of Selected Chelator-Ion Complexes
41
4 i
TEFLON TAPE
GLASS TUBING I 'I/
\ I '
2\
PIPETTE TIP
/
FILM Figure 3. Chelator pool optrode; original design. Not to scale. NAFION
TEFLON TAPE GLASS TUBING PlPElTE TIP SEGMENT CHELATOR SOLUTION NAFION FILM
4
Figure 4. Improved version of chelator pool optrode. Not to scale.
independent monitoring of individual points on the fluorescence decay curve can be performed.
OPTRODE DESIGN Figure 3 is a schematic diagram of a new kind of chemical sensor based on a pool of chelator solution trapped behind an ion-permeable membrane. A solution of anionic chelator, placed behind a plug of Nafion film, cannot pass through the film into the sampled metal ion solution, because Nafion contains anionic "pores". In contrast, the positively charged metal ions can diffuse through the membrane into the chelator pool where complexation occurs. To prepare the optrode of Figure 3, a drop of Nafion solution is suspended in the tip of an inverted 250-pL plastic disposable pipet tip (Rainin, Inc.). The solvent is allowed to evaporate, leaving a plug of Nafion in the tip. A razor is then used to cut through the Nafion plug to obtain a thinner film of Ndion. I t is necessary to cut the plug at an angle to avoid shattering the rather brittle Nafon film. The pipet tip is then righted and a pool of chelator solution added to it (typically, 125 pL is added). The optrode is fixed onto the end of the bifurcated fiber optic by Teflon plumbing tape. A hole is punched out of the side of the pipet to relieve back pressure and to enable ions to traverse through the membrane without producing a pressure differential. This preliminary design suffered from sensor-to-sensor irreproducibility, as discussed later. A modified chelator pool optrode was therefore designed (see Figure 4). The top segment of a 250-pL plastic disposable pipet tip is set upright on a Parafilm-covered microscope slide. The Nafion film is then formed by adding a fixed amount, generally 50 or 60 pL, of Nafion solution to the pipet tip segment and letting the solvent evaporate. The Nafion film thus prepared is about 35 pm in thickness. The sensor is peeled off the Parafilm, leaving the Nafion film intact across the end of the pipet tip segment.
complex
lifetime, ns
std dev, ns
morin-Al(II1) morin-Ga(II1) morin-In(II1) lumogallion-Al(II1) lumogallion-Ga(II1) lumogallion-In( 111) Mordant Blue 31-AI(III) Mordant Blue 31-Ga(III) Mordant Blue 31-Mg(II)
4.11
0.13
4.07 3.92
0.21 0.24 0.10
2.41
1.33 0.94 1.65 0.96 1.54
0.20 0.16 0.16 0.13 0.08
RESULTS AND DISCUSSION Several chelator-ion chemical systems have been tested. The requirements are that the chelator be relatively nonfluorescent and that it form complexes with metal ions that are strongly fluorescent. The fluorescence lifetimes of the various complexes must be sufficiently different to allow distinction among their individual contributions to a total fluorescence signal. We have found that, for our instrumental system, the lifetimes must differ by a t least 1 ns to meet this criterion. In addition, the 12.2-11s interpulse spacing of the mode-locked laser renders examination of lifetimes greater than 10 ns difficult. Morin. Morin is a metal ion chelator that has been used successfully in previous fiber-optic sensors (2, 3). Morin is known to form complexes with a variety of metal ions, including AI3+,Ga3+,and In3+. These specific complexes, in 5 pM concentration, visibly fluoresce when exposed to ordinary room lighting. Morin is itself only weakly fluorescent when excited with the 457.9-nm argon ion laser line. The AI3+,Ga3+, and In3+ complexes of morin all show emission maxima a t about 525 nm when excited with 457.9-nm light and in a 1:l morin:ion concentration ratio in absolute ethanol. These spectra all overlap strongly, and the morin complexes are therefore difficult or impossible to distinguish by conventional fluorometric techniques. Lifetime measurements for the three morin complexes in solution were obtained with time-resolved fluorometry. The fluorescence lifetimes of the species, calculated from the decay curves, are listed in Table I. Our instrument cannot be used to determine one ion in the presence of either of the others, because the lifetimes of the three species are so similar (within 0.2 ns). Morin immobilized on cellulose ( 2 , 3 )produces a relatively weak fluorescence signal. Moreover, the fluorescence lifetimes of the morin-ion complexes do not change appreciably when the complexes are immobilized. Thus, a sensor based on morin and the formation of its complexes with AI3+, Ga3+,and In3+ is not suitable for multielemental determinations using time-resolved fluorometry. Lumogallion. Lumogallion (LMG) by itself can be excited by using the 488.0-nm argon ion laser line. In pH 5.0 acetate buffer solution, the wavelength of maximum emission is found to be about 595 nm (Figure 5 ) . Although lumogallion itself fluoresces, it forms complexes with group IIIA elements (9, 14-20) that are at least 2 orders of magnitude more strongly fluorescent. The LMG-A13+ complex exhibits the greatest intensity, followed by the LMG-Ga3+ complex and the LMG-In3+ complex. The fluorescence spectra of all three complexes are quite similar (see Figure 6), so determination of one ion in the presence of the others is difficult or impossible by conventional fluorescence measurements. Fluorescence decay curves for the 20-pM lumogallion complexes are shown in Figure 7 and the corresponding lifetimes collected in Table I. The fluorescence lifetime of the L M G A13+ complex, 2.41 ns, is at least 1ns longer than that of either
ANALYTICAL CHEMISTRY, VOL. 61, NO. 15, AUGUST 1, 1989
1771
Table 11. Determination of Mixtures of Aluminum and Gallium" prepared, pM Al(II1) Ga(II1) 1 1 2
10 20 5
found, pM A1(III)b Ga(III)C 1.3 1.2 1.8
9.2 18.6 5.1
" Conditions: lumogallion concentration, 30 p M , pH 5; excitation wavelength, 457.9 nm; emission wavelength, 600 nm; laser average power, 160 mW. bAverage relative error for Al(II1) was 20%. Average relative error for Ga(II1) was 4%. 1
I
520
I
I
556
I
I
I
582
I
628
I
I
J 700
664
(nm)
WAVELENGTH
Flgure 5. Fluorescence spectrum of lumogallion in pH 5.0 acetate buffer. Excitation wavelength = 488.0 nm.
Table 111. Determination of Mixtures of Aluminum and Indium" prepared, p M Al(II1) In(II1)
found, pM Al(III)b In(III)c
LUMOQALLION COMPLEXES
I
1 1
I
2
40 90 20
1.06 0.90 1.92
43 97 23
" Conditions:
lumogallion concentration, 30 rM, pH 5.0; excitation wavelength, 457.9 nm; emission wavelength, 600 nm; laser average power, 160 mW. *Average relative error for Al(II1) was 7%. Averaee relative error for In(II1) . . was 9%. I
I 520
I 556
I
I
I
I
592
626
WAVELENGTH
I
I 664
I
I 700
(nm)
Figure 6. Fluorescence spectra of lumogallion-ion complexes in pH 5.0 buffer: excltation wavelength, 488.0 nm; lumogalllon concentration, 2.5 X lo3 M; cation concentration, 5 X lo4 M; relative vertical scale, 30: 100 1000 1n:Oe:Al complexes, taking intensity of LMG alone .equal to 1 (in Figure 5).
0
TIME
12 ("3)
Figure 7. Fluorescence decay curves for lumogallion-ion complexes: concentration of LMG, 8.0 X lo-' M; of AI3+, 3.1 X lo4 M; of Ga3+, 7.7 X lo4 M; and of In, 3.7 X lo-' M.
the Ga3+ or In3+complexes. Thus, the contributions of the individual complexes should be discernible with our instrument through time-resolved fluorometry. Immobilization of Lumogallion. Although lumogallion can be immobilized on BiceRad AGl-X4 anion-exchange resin, the immobilized LMG does not then form complexes with Al(III), Ga(III), or In(II1) ions. Presumably, the active chelating site is sequestered by immobilization. Alternatively, lumogallion complexes can be immobilized on AGl-X4 resin and the metal ions subsequently removed by immersion of the resin in a basic solution. Even then, the chelating agent
remaining on the resin will not form complexes with the trivalent ions when it is subsequently immersed in a buffered solution containing them. I t is for these reasons that the pool optrodes of Figures 3 and 4 were designed. They are inexpensive and relatively easy to prepare. One optrode can be used many times and is readily regenerated simply by rinsing out the pool of lumogallion and soaking the optrode in acid to remove any ions that remain in the membrane. The optrode is very sensitive and gives steady-state (single-ion) detection limits of 2 X lo4, 2 X and 3 X lo4 M for aluminum, gallium, and indium ions, respectively. (The detection limit is defined here as the concentration of analyte that yields a signal equal to 3 times the standard deviation of the background fluctuation.) A linear dynamic range of 3 orders of magnitude is obtained for both aluminum and indium complexes, and a range of 2 orders of magnitude is obtained for gallium. The principal disadvantage of the design of Figure 3 is its slow response time. Figure 8A shows that its response begins to level off only after 20 min of immersion is a metal-ioncontaining solution. Another disadvantage of the sensor design of Figure 3 is that a reproducible Ndion film thickness could not be guaranteed. The design of Figure 4 performs as well as the sensor shown in Figure 3 but has a response time of under 5 min (see Figure 8B) and exhibits good sensor-to-sensor film thickness reproducibility. A previous study has described the pH-dependence of fluorescence intensities and lifetimes of the lumogallion-ion complexes (9). Here, the effect of pH on the chelator pool optrode is minimal. Buffered solutions covering the range from pH 3.0 to 8.0 were used as the matrix for both the lumogallion pool optrode and the aluminum-ion-containing sample solution. In all cases, the ions traverse the Nafion membrane and form fluorescent complexes with lumogallion. The response time of the sensor is less than 10 min at every pH. No leakage of lumogallion is noted at any pH. Thus, the sensor is useful over a wide range of solution pH. Multielemental Determinations. It can be seen in Table I1 that the values calculated by using the time-resolved fluorometry technique are within 2-20% of the true values for the aluminum and gallium mixture. Results for the si-
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ANALYTICAL CHEMISTRY, VOL. 61, NO. 15, AUGUST 1, 1989
tained from an unknown concentration of Mordant Blue 31 and excess metal ions agree well with those reported in the literature (12). Also, measurements of the fluorescence lifetimes of the Mordant Blue 31 complexes indicate that timeresolved fluorometry could be used to determine aluminum and either gallium or magnesium in a mixture (see Table I). Further purification will be necessary before simultaneous determination of the ions is possible; the concentrations of the Mordant Blue 31 solutions are as yet unknown. Nonetheless, the Mordant Blue 31 system appears to be well-suited for use in the chelator pool optrodes.
ACKNOWLEDGMENT 0
2
4
6
8
10
12
14
16
18
20
TIME (mln)
We are grateful to Dean Geraci and Galileo Electro-optics for donating the optical fibers used in this investigation. We thank W. R. Seitz (Universityof New Hampshire) for donating samples of morin immobilized on cellulose.
LITERATURE CITED (1) Saari, L. A.; Seitz, W. R. Anal. Chem. 1984, 56, 810-813. (2) Saari, L. A.; Seitz, W. R. Anal. Chem. 1983, 55, 667-670. (3) Saari, L. A.; Seitz, W. R. Analyst 1984, 109, 655-657. (4) Zhujun, Z.; Seitz, W. R. Anal. Chim. Acta 1985, 171, 251-258. (5) Zhujun. 2 . ; Muiiin, J. L.; Seitz, W. R . Anal. Chim. Acta 1986, 184, 25 1-258. (6) Craven, T. L.; Lytle, F. E. Anal. Chim. Acta 1979, 107, 273-278. (7) Craven, T. L.;Lytle, F. E. Specfrosc. Lett. 1979, 12, 559-586. (8) Vitense, K. R.; McGown, L. B. Anal. C h h . Acta 1987, 193, 119-125. (9) Vitense, K. R.; McGown, L. B. Analyst 1987. 112, 1273-1277. (IO) Demas, J. N. Excited State Lifetime Measurements; Academic Press: New York, 1983; pp 130-134. (11) Carraway, E. R.; Hauenstein, B. L., Jr.; Demas, J. N.; DeGraff, B. A. Anal. Chem. 1985. 57, 2304-2308. (12) Hiraki, K. Bull. Chem. Soc. Jpn. 1972, 45, 789-793. (13) Briaht. F. V.; Vickers. G. H.; Hieftje, G. M. Anal. Chem. 1988. 58. 1215-1 227. (14) CRC Handbook of Organic Analytical Reagents; Cheng, K. L., Ueno, K., Imamura, T., Eds.; CRC Press, Inc.: Boca Raton, FL. 1982; pp 139- 157.
I 0
2
4
6
8
10
12
14
16
18
20
TIME (mln)
Figure 8. (A) Time response of a typical chelator pool optrcde of the design shown in Figure 3. (B) Time response of a lyprCal chelator pool optrode of the design shown in Figure 4.
multaneous determination of aluminum and indium ions are even better (all within lo%), as seen in Table 111. Application to Other Chemical Systems. The chelator pool optrode described here for lumogallion should be useful for other complexing reactions that involve an anionic chelator. For example, Mordant Blue 31 is similar in structure to lumogallion. As a result, it is likely to undergo a conformational change when it forms a complex with metal ions such as Al(III), Ga(III), and Mg(I1). Unfortunately, synthesis of Mordant Blue 31 in our laboratory has resulted in a very impure product, due to significant amounts of NaCl contamination. Nonetheless, conventional fluorescence spectra ob-
(15) F&nandez-Gutierrez, A.; Munoz de la Pena, A. In Molecular Lumlnescence Spectroscopy: Methods and Applications : Part 1 ; Schulman, S. G., Ed.; "Chemical Analysis"; Eking, P. J., Winefordner, J. P., Koithoff, I. M., Eds.; John Wiley and Sons: New York, 1985; Vol. 77, Chapter 4. (16) Haugen, G. R.; Steinmetz, L. L.; Hirschfeld, T. B.: Klainer, S. M. Appi. S ~ C ~ O S1981, C . 35, 568-571. (17) Imasaka, T.; Harada, T.; Ishibashi, N. Anal. Chim. Acta 1981, 129, 195-203. (18) Ishibashi, N.; Kina, K.; Goto, Y. Anal. Chim. Acta 1980, 114, 325-328. (19) Hydes, D. J.; Liss, P. S.Analyst 1976, 10 1 , 922-931. (20) Kina, K.; Ishibashi, N. Microchem. J . 1974, 19, 26-31.
RECEIVED for review August 19,1988. Revised April 20,1989. Accepted May 1, 1989. The authors acknowledge financial support of this work by the Office of Naval Research, the Upjohn Company, and the National Science Foundation through Grant CHE 87-22639. This material is based upon work supported under a National Science Foundation Graduate Fellowship, granted to M.K.C., who also acknowledges support by an Indiana University Graduate Fellowship.
