Anal. Chem. 1987, 5 9 , 865-868
865
Generation of Chemiluminescence upon Reaction of Aliphatic Amines with Tris(2,2’-bipyridine)ruthenium( I I I) James B. Noffsinger and Neil D. Danielson*
Department of Chemistry, Miami University, Oxford, Ohio 45056
Ris(2,2’-bipyridine)ruthenium( II I)(Ru(bpy)?+) will undergo an electron-transfer reaction with an appropriate reducing agent to form Ru(bpy)t+, which upon achieving an excited state can result in chemiiumlnescence. Aliphatic amines with an increasing number of carbon atoms were tested between a pH of 4 and 6 and found to act as chemiluminescent reduclng agents. I n addition, some dlamines and phosphines were also found to react. Linear range and detection limit studies were done for the mono-, di-, and tri-n-propyiamlnes as well as other selected compounds. Linear range values for these amines varied between approximately 3 and 5 orders of magnitude. The lowest detection limit of 0.28 pmoi was found for tri-n-propylamine. Ionization potentials taken from photoelectron spectroscopy data for aliphatic amines were related linearly with the log of the chemiluminescent signal intensity. I n addition, It appeared that assignment of the first ionization potential from a nonbonding orbital of the heteroatom was required for chemiluminescence.
Since 1966 when Hercules and Lytle (I) first reported visible light was generated upon reduction of tris(2,2’-bipyridine)ruthenium(III), Ru(bpy),3+,with either hydrazine or hydroxide ion, there has been sustained interest in the kinetics (2)and mechanism (3-6) of this chemiluminescence process with various reducing agents. However, analytical applications that use this electrochemiluminescence system have been quite limited in number. Analytes that have been examined include hydralazine (7),oxalate (B), and peroxydisulfate (9). Previous ~ ~the + catalyst in the photostudies (10, 11) of R ~ ( b p y ) as reduction of water to hydrogen and oxygen have shown ethylenediaminetetraacetate (EDTA) and triethanolamine can act as reducing agents with R ~ ( b p y ) , ~ +We . have found that selected nitrogen and phosphorus compounds such as mono-, di-, and trialkylamines and triphenylphosphine will cause chemiluminescence upon mixing with Ru(bpy),,+. The response of these compounds as a function of p H was examined by using flow injection analysis (FIA). Linearity and detection limits of selected compounds were also determined. First ionization potential data for the compounds studied were found to correlate with the intensity of the chemiluminescence. In addition, the molecular orbital of the analyte electron corresponding to the first ionization potential was found to be an important factor for the prediction of chemiluminescence.
EXPERIMENTAL SECTION Apparatus. Because of the short lifetime of the chemiluminescent signal, mixing of the sample and the ruthenium complex at the detector was required. Figure 1A shows a schematic of the flow injection apparatus used to accomplish this work. A Gilson Co. Minipulse 2 peristaltic pump (Worthington, OH), corresponding to P1, and a Fluid Metering, Inc., Model RPSP pump (Oyster Bay, NY) designated as P2 were used to pump the carrier streams at flow rates of 1 mL/min. The sample injector (I) was a standard Tecator 5001 FIAstar injector (Tecator, Herndon, VA) with a 1O-pL loop. To minimize dispersion, the Teflon tubing
from the injector to the detector was 10 cm X 0.3 mm. The photomultiplier tube (PMT) used was a Hamamatsu Model R 372 photomultiplier (Hamamatsu Corp., Middlesex, NJ) powered at 800 V with a Model EU-701-30 GCA/McPherson Instrument photomultiplier module (Acton, MA). A homemade Pyrex spiral T-flow cell (Figure 1B) was constructed similar to the one described by Pacey and co-workers (12) and was mounted directly across from the PMT window. The entire photomultiplier unit was enclosed in a blackened woodsn box tq minimize stray light. The photomultiplier currents were measured and converted to voltages with a Keithley 617 programmable electrometer (Keithley Instruments, Cleveland, OH). A Fisher Recordall Series 5000 (Houston Instruments, Austin, TX) Model D5117-5AQ strip chart recorder was used to record the voltage output of the electrometer. Chemicals. All chemicals used were of reagent grade or better. Ru(bpy),Cl,.GH,O was obtained from the GFS Chemical Co. (Columbus,OH) and was used without further purification. The water used was obtained from a Barnstead Nanopure distillation unit (Sybron/Barnstead Corp., Boston, MA). All the amines and phosphines examined were obtained from commercial sources. Two of the amines used, dipentylamine and dihexylamine, are highly toxic and should be handled with due caution. Procedure. All solutions were made fresh before use. The carrier phase buffers used were 0.07 M H2S04at pH 0.84,lO mM NaH2P04at pH 2.5, 10 mM sodium acetate at pH 3.8, 10 mM sodium acetate at pH 4.6, 10 mM sodium acetate at pH 5.8, and 10 mM Na2HP04at pH 7.0. Solutions with a pH above 7.0 were not investigated since hydroxide ion will produce a signal. A 1 mM Ru(bpy):+ solution prepared in the desired buffer was placed on a stir plate inside the blackened wooden box. Prior deoxygenation of the Ru(bpy):+ solution was found not to be required. The solution was oxidized at +1.35 V to Ru(bpy)? by using an IBM Model EC/225 voltammetric analyzer (IBM Instruments, Danbury, CT) with a standard three-electrode arrangement (working, Pt gauze; auxiliary, Pt wire; reference, SCE). Oxidation was initially allowed to take place for 45 min for each 150 mL of the reagent solution before use; however the potential was held constant at +1.35 V during the entire time of the experiment. After the Ru(bpy)$+ has been formed, it is pumped by P2 to the upper inlet of the T-flow cell. The other pump, P1, delivers the injected sample plug to the lower inlet of the T-flow cell to be mixed in front of the photomultiplier by using a carrier phase consisting of the same buffer chosen for the Ru(bpy)t+ solution. Most of the analytical measurements were made with the elctrometer set between the 1 >: lo4 and 1 X A scale. It was noted that the R ~ ( b p y ) , ~solution + did have a background chemiluminescence; however it was rather small at 7 X A. Measurement of peak height was found to be satisfactory for quantitation.
RESULTS AND DISCUSSION Initially, it was discovered that upon mixing of R ~ ( b p y ) ~ , + with a wide variety of aliphatic amines, a yellow-orange light was generated with a lifetime of less than a second. A previous electrochemical study (13)of the oxidation of tertiary amines has postulated the formation of a short-lived radical cation, which .then loses a proton, e.g., (C3H7)3N’+ (C3H7),NCHC2H,. This chemiluminescence observed by us is likely due to the ability of the amine radical formed upon reduction of R ~ ( b p y ) to ~ ~react + with either R u ( b p ~ ) , ~or+ additional Ru(bpy),3+ to form the excited state Ru(bpy)?+* complex, which can then emit light upon returning to the ground state. An analogous mechanism involving the oxalate
0003-2700/87/0359-0~65$01.50/0 0 1987 American Chemical Society
-
866
ANALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987
A Dl
Buf'er
n
I
U
" W
B
0
4
2 Buffer
w Figure 1. (A) Schematic diagram of the flow injectlon system. (B) Schematic diagram of the Pyrex spiral T-flow cell (top view). The ceii Is approxlmately 2 X 3 cm and is constructed from 2-mm4.d. tubing. The two Inlets of the cell are shown in the center of the diagram. W = waste.
anion radical which decomposes to the COz'- species before reacting with the ruthenium complexes has been reported previously [ 4 ] . Quantitative studies with respect to reaction pH and analytical utility for many of these amines and some phosphines were carried out by using FIA. The FIA system was able to achieve a sample throughput of 150 injections per hour. pH Studies. Recently, Bard and co-workers reported that the observed chemiluminescence for sodium oxalate is dependent upon pH, with a maximum signal at a p H of approximately 6.0 ( 4 ) . In addition, we found t h e response for hydrazine reaches a maximum at a p H of 4.6. Therefore, the maximum chemiluminescent response could vary with pH, depending upon the compound studied. The pH investigation was directed to include a wide variety of primary, secondary, and tertiary aliphatic amines. Figure 2 shows the chemiluminescent response for the trialkylamines as a function of pH. Trimethylamine through tri-n-hexylamine all showed a maximum response at between pH 4.0 and pH 6.0. The class of trialkylamines exhibited the most intense chemiluminescence as compared to any of the other classes of compounds investigated. A general trend followed by each of the classes studied was an increase in signal response between pH 4.5 and pH 6.0. A study of the rate of reaction of R ~ ( b p y ) , +with ~ EDTA as a function of p H shows a similar profile from p H 2 to 6 (11). The chemiluminescent responses of the analogous dialkylamines and the two cyclic secondary amines piperidine and piperazine as a function of pH were investigated. Except for dimethylamine and diethylamine, all the remaining dialkylamines showed a maximum response at pH 4.0 or pH 6.0. Dimethylamine and diethylamine showed an optimum but diminished response a t p H 7.0. The overall signal intensity of the dialkylamines was about a factor of 7 lower than their trialkylamine analogues. The response profiles for piperidine and piperazine were similar to that of the dialkylamines in both pH range and signal intensity. Both cyclic amines had a response maximum with R ~ ( b p y ) , ~a+t about pH 5.8. However, the signal intensity of piperazine was nearly 10 times less than that of piperidine. The response of the primary alkylamines with increasing carbon number from methylamine through n-hexylamine were also studied as a function of pH. Again, as with the trialkylamines, their intensity of chemiluminescence increased
6
pH
Figure 2. Chemiluminescence response plot for trlmethylamlne (CI, O ) ,triethylamine (C2, +), trl-n-propyiamine (C3, O ) ,trl-n-butylamine (C,, A),trl-n-pentylamine (C X), and trl-n-hexylamlne (C8, V)as a functlon of pH. The Ru(bpy)p concentratlon was 1 mM in a 10 mM buffer and the trialkylamines compounds were 10 mM in concentration.
with pH up to about p H 6.0. Methylamine and ethylamine again showed an optimum but diminished response at pH 7.0. The signal strength overall was about a factor of 60 lower in intensity than the trialkylamine analogues. The chemiluminescence formed upon reaction of n-butylamine, sec-butylamine, isobutylamine, and tert-butylamine with the metal complex were compared to examine branching effects. The response for tert-butylamine was approximately a third of the response of n-butylamine. The signals from sec-butylamine and isobutylamine were close to the response generated by n-butylamine. The tert-butyl group is believed to help stabilize the formed intermediate cation better than the other isomers and as a result hinders the reaction that produces the chemiluminescent signal. The p H investigation was expanded to incorporate the following diamines: hydrazine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, and 1,6-diaminohexane. In general, their response was improved with increasing pH up to about pH 6.0. Except for hydrazine, 1,4-diaminobutane, and 1,6diaminopentane, the response of the diaminoalkanes was maximum a t about pH 5.8. 1,4-Diaminobutane and 1,Bdiaminopentane showed a maximum signal at pH 7.0. The signal intensity for the diaminoalkanes was generally 20 times lower than the trialkylamines signal. Hydrazine's signal was twice as intense as the signal from any of the other diaminoalkanes. A few phosphines were examined to see if substituting a phosphorus for nitrogen would still generate chemiluminescence. Triethylphosphine and tributylphosphine did produce a Chemiluminescent signal with R ~ ( b p y ) , ~ +However, . the intensity of the signals was about 12 times less than their amine analogues. In addition, the pH of the maximum response was shifted to a lower pH, as shown in Figure 3. The maximum signal intensity for triethylphosphine was around pH 4.6 and for tri-n-butylphosphine around pH 4.0. Triphenylphosphine generated an intense signal with Ru(bpy)p, approximately as intense as the signal for tri-n-butylamine in Figure 2. The signal intensity reached a maximum at about pH 5.0. The fact that triphenylphosphine chemiluminesced was surprising. In general, aromatic substituted amines such as aniline, diphenylamine, and triphenylamine generated no chemiluminescence at any of the pHs examined. Quenching of the R ~ ( b p y ) ~ excited ~ + * complex by aromatic amines has been reported previously (14). Detection Limit a n d Linear Range. Oxalic acid, triphenylphosphine, 1,3-diaminopropane, piperidine, and piperazine as well as the primary, secondary, and tertiary pro-
ANALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987
,
60
I
Table 11. First Ionization Potential and Molecular Orbital Data chemical IP, eV MO chemical IP, eV MO hydrazine4 methylamineb
,
ethylamine* propylamine' n-butylamineb isobutylamined tert-butylamined amylamined dimethyl-
4
10 -
A
/
0
dipropylaminec
4
2 Buffer
6
pH
Figure 3. Chemiluminescence response plot for triethylphosphine (A, A),tri-n-butylphosphine (6,O ) , and triphenylphosphine (C, 0 )as a function of pH. Conditions are the same as those given in Figure 2.
Table I. Detection Limit and Linear Range Data
chemical oxalic acid triphenylphosphine propylamine dipropylamine piperidine 1,3-diaminopropane piperazine tripropylamine
10.02 9.64 9.50
n
9.37 9.40 9.29
n n
n n
9.24
n n
9.30
n
8.89
n
8.59
n
dibutylamined piperidinef trimethylamine8 triethylaming tripropylamine8
tributylaming triphenylphosphineh anilineh diphenylamineh triphenylamineh
8.49
n
8.64
n n n
8.53 8.08 7.92 7.90
7.88 8.02 7.35 6.99
n n n ?r
71
r
aminee
B
0 -
867
detection limit" ppb ng pmol 31 222 2220 244 180
0.31
2.4
2.22 22.2 2.44 1.8
8.5 370
913 1390 4.0
9.13 13.9 0.04
24 21 120
160 0.28
upper linear pmol
range,b
X10-3
14 6.3
67 857 73 11 25 150
a The detection limit was calculated as 3 times the signal from the standard deviation of the background noise. bThe upper limit of the linear range was determined to be the point at which the deviation from the line was 10%.
pylamines were considered for this study. Table I shows the detection limits and linear range found for each compound. The precision of the data was based on at least five trials for each data point, with the relative standard deviation range of 2 to 8%. The linear range determined on the basis of plots of four or more points for the selected compounds varied from approximately 2 orders of magnitude for 1,3-diaminopropane to over 5 orders of magnitude for tripropylamine. Our detection limit for oxalate of 0.25 X lo4 M was comparable to 1 X lo4 M cited previously (€9,which was obtained by using R ~ ( b p y ) ~ chemiluminescence. I+ Triphenylphosphine was found to be detectable at a low level as well, about 1 x M. For the aliphatic amines, the detection limits can be ordered tertiary < secondary < primary. The detection limits for the propylamines are characteristic of the other aliphatic amines in each class with the exception of methyl and ethylamine. These amines have detection limits about 10 times higher. There are a wide variety of methods that can determine primary and/or secondary amines. In particular, amino acids, after derivatization and HPLC separation, can be monitored by using UV (15),fluorescence (16),electrochemical (In,or chemiluminescence (18)detection at the low or subpicomole range. Therefore, this R ~ ( b p y )chemiluminescence ~~+ method could not be considered a competitive technique for amino acid analysis. However, few methods have been reported for the derivatization of tertiary amines. One, involving the reaction of aconitic acid and acetic anhydride with tertiary amines to produce a green fluorescence, cannot be done in aqueous solution and must be incubated for 20 min (19). The detection limit for tri-n-propylamine was only 2-10 Kg. Our detection
Literature sources for the first vertical ionization potentials, that of hydrazine found in reference 22. bReference 23. Reference 24. Reference 25. e Reference 26. f Reference 27. g Reference 28. Reference 29. limit for the same amine was 0.04 ng. The chemiluminescent emission upon oxidation of aliphatic secondary and tertiary amines by benzoyl peroxide permits the detection of these analytes at the 0.5 Kmol/mL level (20). However, this reaction must be done in a dry nonaqueous solvent due to the decomposition of the peroxide by water. Therefore, the Ru(bpy):+ chemiluminescent method can be considered very complementary to existing schemes for the determination of aliphatic amines with respect to detection limits. Electron Energy and Source. Since the mechanism for the chemiluminescence process is a charge-transfer reaction (21), then examination of the energy and source of the electron from the reducing agent should indicate some basis for predicting the reactivity of additional reducing agents. Table I1 lists the first vertical ionization potential as measured by UV photoelectron spectroscopy and the electronic assignment for each compound as reported in the literature. For the alkylamines, the lowest ionization potentials originate from electrons in the n orbital. In general, the ionization potentials of the alkylamines can be ordered primary > secondary > tertiary. The ionization potentials also decrease in magnitude as the alkyl chain length increases within each group of primary, secondary, and tertiary amines. The nitrogen nonbonding orbital in the phenylamines is more tightly bound than the phenyl a orbitals and therefore the first ionization potentials for these compounds correspond to the a electrons (29). However, for triphenylphosphine, destabilization of the n orbital and stabilization of the a orbitals occur due to the shift in electron density from the phenyl groups to the heavy phosphorus atom caused by likely participation of the d orbitals in the molecular bonding. The question of why the aromatic amines do not chemiluminescence but triphenylphosphine does must be considered. The first ionization potential for aniline falls in the range of energies for the chemiluminescent aliphatic amines (7.8-10 eV) and the ionization potentials for the T electrons of diphenylamine and triphenylamine are even lower (Table 11). Therefore the loss of a a electron for the charge-transfer reaction appears to be unfavored compared to a nonbonding electron. The first ionization potential for triphenylphosphine is 7.88 eV from an n orbital and a strong chemiluminescent signal is seen. The energy of the first n orbital for triphenylamine is 10.27 eV (third ionization potential) (29); however, it is apparently too high in magnitude to be involved with the R ~ ( b p y ) chem~~+ iluminescence mechanism. Figure 4 shows a plot of the log of the chemiluminescence response at the optimum pH for the aliphatic amines and triphenylphosphine vs. the energy of their first ionization potential. It is not surprising that a linear relationship would exist between the log of the chemiluminescent signal intensity
868
ANALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987
chromophore, but have a trialkyl amine group, could be determined in aqueous solutions by using this detection scheme.
ACKNOWLEDGMENT The authors acknowledge Walter Dressick of IGEN, Inc., for his insights regarding the possible reaction mechanism, William C. Herndon of the University of Texas at El Paso for this comments concerning UV photoelectron spectroscopic ionization potentials, and James W. Herschberger of Miami University for his helpful discussions about linear free-energy relationships.
* c
m f u
3.8
8 E
m
9
C
LITERATURE CITED 0
1 8 ;7-7--
7 8
T- T
8
8 2
8 4
a6
88
First lonlzation P o t e n t i a l
9
92
T
T
9 4
,- -I
9 6
( eV )
Flgwe 4. Plot of the log of chemiluminescent signal intensity at the optimum pH against the compound’sfirst ionization potential. Aliphatic amines listed in Table I1 and triphenylphosphine are represented. Conditions are the same as those glven in Figure 2.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
Hercules, D. M.; Lytle, F. E. J. Am. Chem. SOC. 1988, 88, 4745. Lytle, F. E.; Hercules, D. M. Photochem. Photobiol. 1971, 73, 123. Tokel, N. E.; Bard, A. J. J. Am. Chem. Soc.1972, 9 4 , 2862. Rubinstein, I.; Bard, A. J. J . Am. Chem. Soc. 1981, 103, 512. Rublnstein, I.; Bard, A. J. J. Am. Chem. SOC. 1981, 703, 5007. White, U. S.;Bard, A. J. J. Am. Chem. Soc. 1982, 104, 8891. Nonldez, W. K.; Leyden, D. E. Anal. Chlm. Acta 1978, 96, 401. Martin, C. R.; Bard, A. J. Anal. Chem. 1983, 5 5 , 1580. Rublnstein, I.; Ege, D.; Becker, W. G.; Bard, A. J. Anal. Chem. 1984, 56, 2413. Chan, Sifi; Chow, M.; Creutz, C.; Matsubara, T.; Sitin, N. J. Am. Chem. Soc. 1981, 103, 369. Miller, D.; McClendon, G. Inorg. Chem. 1981, 20, 950. Hollowell, D. A.; Gord, J. R.; Gordon, G.; Pacey, G. E. Anal. Chem. 1988, 58, 1524. Smith, P. J.; Mann, C. K. J. Org. Chem. 1969, 3 4 , 1821. Bock, C.R.; Connor, J. A.; Gutiemez, A. R.; Meyer, R. J.; Whitten, D. G.; Sulllvan, B. P.; Nagle, J. K. J. Am. Chem. SOC. 1979, 701, 4815. Stone, K. L.; Willlmas, K. R. J. Chromatogr. 1988, 359, 203. Bhown, A. S.;Cornelius, T. W.; Bennett, J. C. LC Mag. 1983, 1 , 50. Allison, L. A.; Mayer, G. S.; Shoup, R. E. Anal. Cbem. i984, 56, 1089. Miyaguchi, K.; Honda, K.; Imai. K. J. Chromatogr. 1984, 303, 173. Pesez, M., Bartos. J. Colorimetric and Nuorlrnetric Analysls of Organic Compounds and Drugs; Marcel Dekker: New York. 1974; pp 174- 180. Burguera, J. L.; Townsherd, A. Talanta 1979, 2 6 , 795. Kalyanasundaram, K. C w r d . Chem. Rev. 1982, 46, 159. Rademacher, P. Angew. Chem., Int. Ed. Engl. 1973, 12, 408. Katsumata, S.;Iwai, T.; Kimura, K. Bull. Chem. SOC.Jpn. 1973, 4 6 , 3391. Peel, J. B.; Willett, G. D. Aust. J . Chem. 1977, 3 0 , 2571. Takahashi, M.; Iwao, W.; Ikeda, S.J. phvs. Chem. 1983, 8 7 , 5059. Katrib, A. Libyan J. Sci. 1975, 4 8 , 35. Yoshikawa, K.; Hashimoto, M.; Morlshima, I. J. Am. Cbem. SOC. 1974, 9 6 , 268. Neisen, S.F. J. Org. Chem. 1984, 4 9 , 1891. Debies, T. P.; Rabalals, J. W. Inorg. Chem. 1974, 73, 308. Amouyal, E.; Zdler, B.; Keiler, P.; Moradpour, A. Chem. fhys. Lett. 1980, 74, 314. Marcus, R. A. J. Phys. Chem. 1983, 6 7 , 853. KJingler, R. J.; Kochi, J. K. J. Am. Cbem. SOC. 1980, 702, 4790. Gassman, P. G.;Mulllns, M. J.; Richtsmeler, S.; Dixon, D. A. J. Am. Chem. SOC. 1979, 707, 5793. Ogata, H.; Onizuka, H.;Yoshimasa, N.; Kamada, H. Bull. Chem. SOC. Jpn. 1973, 46, 3036. Noffsinger, J. B.; Danielson, N. D. J. Chromatogr., in press.
and ionization potential of the amine. For a series of struc(12) turally and chemically similar compounds which undergo (13) endergonic or weakly exergonic electron-transfer (ET) pro(14) cesses, the activation free energy, AGIET, is nearly a linear (15) function of the free energy of the electron transfer, AGOET. (16) The former parameter is inversely related to the logarithm (17) of the rate constant for electron transfer (intensity of the (18) chemiluminescence) (30) according to the Erying equation (19) (31). Because the ionization potential of the amines is expected to correlate linearly with AGOm (32,33), it is reasonable (20) to expect an inverse linear relationship between ionization (21) (22) potential of the amine and the logarithm of the chemilumi(23) nescent signal intensity, as observed in Figure 4. The correlation coefficient for this plot was 0.9368. No such corre(24) (25) lation was found between chemiluminescent signal and pK,. (26) Even though Table I1 is not complete for all the compounds (27) reported in t h i paper, the trend appears to be that compounds (28) with lower energy n electrons also produce the most intense (29) (30) signals. This scheme can be used to predict the reactivity of sulfur (31) compounds as well. The first ionization potential of the al(32) (33) iphatic mercaptans is the n electron, which falls at around 9.4-9.0 eV and is assigned to the “lone pair” on the sulfur atom (34) (34). Therefore, the mercaptans would be expected to reduce (35) R ~ ( b p y ) 3 to ~ +generate chemiluminescence with a detection limit similar to the primary alkylamines. for review June 27,1986. Accepted November 18, In conclusion, the analytical potential of this R ~ ( b p y ) ~ ~ +RECEIVED chemiluminescent FIA detector appears very promising. This 1986. The authors thank the Miami University Faculty Research Committee and Sigma Xi, The Scientific Research instrumental system has been adapted as a HPLC postcolumn Society, for funding this project. J.B.N. is grateful for a detedor for triaikylamines (35).This class of compounds does Dissertation Fellowship awarded by the Graduate School of not absorb light well in the UV-visible region since the molar Miami University. This work was presented, in part, at the absorptivities are very low (less than 50 for tripropylamine 37th Pittsburgh Conference on Analytical Chemistry and in aqueous solution) and are extremely difficult to derivatize. Spectroscopy, Atlantic City, NJ, March 13, 1986. In addition, drugs such as erythromycin, which possess no good
