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Room-temperature phosphorescence and fluorescence of selected model aromatic carbonyl compounds adsorbed on several solid surfaces
MICROCHEMICAL
JOURNAL
34, 56-66 (1986)
Room-Temperature Phosphorescence and Fluorescence Selected Model Aromatic Carbonyl Compounds Adsorbed on Several Solid Surfaces
of
L. A. CITTA AND R. J. HURTUBISE’ Chemistry Department, University of Wyoming. Laramie, Wyoming 82071 Received November 19. 1985: accepted March 3, 1986 Several model aromatic carbonyl compounds, which were adsorbed on various solid surfaces, were examined for room-temperature phosphorescence and fluorescence. The results showed that it was important to investigate several surfaces to obtain optimal luminescence conditions for this class of compounds. In addition, the luminescence of some of the compounds was relatively sensitive to experimental conditions. Finally, both room-temperature fluorescence and room-temperature phosphorescence were shown to be analytically USefIll.
0 1986 Academic
Press. Inc.
There has been very little data reported on the room-temperature phosphorescence (RTP) and room-temperature fluorescence (RTF) of aromatic carbonyl compounds adsorbed on various solid surfaces. However, aromatic carbonyl compounds have been examined at low temperature (77°K) in solution. Parker and Hatchard (16) reported low-temperature phosphorescence emission spectra for several aromatic carbonyl compounds. Certain carbonyl derivatives of biphenyl and naphthalene were investigated at 77°K by Ermolaev and Terenin (9). O’Donnell and Winefordner (15) presented a review of low-temperature phosphorescence spectrometry, and several of the compounds discussed were aromatic carbonyl compounds. Micelle stabilized RTP has been employed by Skrilec and Cline Love (22) to investigate the phosphorescence characteristics of functionally substituted aromatic compounds. Donkerbroek and co-workers (7, 8) studied the sensitized RTP of benzophenone and substituted benzophenones in liquid solutions. Dalterio and Hurtubise (2, 3) examined the RTP of hydroxyl aromatic model compounds adsorbed on various solid surfaces. One of the hydroxyl aromatics studied contained the carbonyl functionality. The phosphorescence lifetimes of several aromatic compounds measured at low temperature have been reported (15). Ermolaev and Terenin (9) obtained a phosphorescence lifetime of 0.97 set for 2-acetonaphthone in an ethanol-ether mixture at 77°K. Harbaugh et al. (12) have reported the phosphorescence lifetimes for benzophenone, anthrone, and anthraquinone in ethanol at 77°K as 7, 3, and 3.6 msec, respectively. The phosphorescence lifetime of benzil in an etherisopentane-ethanol mixture at 77°K was reported as 5 msec by Parker and Hatchard (16). The phosphorescence lifetimes at 77°K for benzophenone, benzil, and 2-acetonaphthone adsorbed on silica gel in isopentane were reported as 2, 1, and 80 msec, respectively (14). r To whom all correspondence should be addressed. 56 0026-265X186$1SO Copyright 0 1986 by Academic Press. Inc. All rights of reproduction in any form reserved.
PHOSPHORESCENCE
AND FLUORESCENCE
57
Little has been done with the combined use of solid-surface RTP and RTF. Ford and Hurtubise (10) employed solid-surface RTP and RTF in the characterization of phenanthridine and benzov]quinoline in shale oil. Recently, Senthilnathan and Hurtubise (18) utilized the new approach of total solid-surface luminescence analysis in the quantitative analysis of various binary and ternary mixtures containing nitrogen heterocycles and a polycyclic aromatic hydrocarbon. This approach utilized information from both RTP and RTF in the analysis. Dalterio and Hurtubise (4, 5) used second derivative solid-surface RTP and RTF in the analysis of mixtures of hydroxyl aromatics adsorbed on filter paper and in the qualitative analysis of two components in high-performance liquid chromatography fractions. Derivative solid-surface RTP and RTF were employed by Senthilnathan and Hurtubise (19) for the identification of components in mixtures of nitrogen heterocycles. General reviews on solid-surface luminescence analysis (13) and room-temperature phosphorimetry (23) have appeared in the literature which discuss in detail the compounds that have been investigated by solid-surface luminescence techniques. In this work, several aromatic carbonyl compounds were examined for RTP and RTF when adsorbed on filter paper, silica gel chromatoplates, and 0.5% poly(acrylic acid) (PAA)-NaCl mixture. The results show the analytical advantages and difficulties in solid-surface luminescence analysis for this class of compounds. EXPERIMENTAL Apparatus
RTP and RTF intensity measurements and calibration curves were obtained with a spectrodensitometer. Details of the instrument have been described elsewhere (II). Luminescence excitation and emission spectra were obtained with a Farrand MK-2 spectrofluorometer fitted with a phosphorescence rotary chopper. Roomtemperature phosphorescence lifetimes were obtained with the Farrand MK-2 spectrofluorometer and a Model 5223 Tektronix oscilloscope. The procedure for phosphorescence lifetimes was discussed earlier (20). Reagents
Absolute ethanol was purified by distillation. 5, I2-Naphthacenequinone was used as received. Benzalacetophenone was recrystallized three times from chloroform. 2-Acetonaphthone, anthraquinone, anthrone, benzil, benzophenone, (Ynaphthoflavone, and B-naphthoflavone were recrystallized three times from ethanol. Filter paper (Whatman No. 1) and plastic-backed silica gel chromatoplates (EM Laboratories, Elmsford, N.Y.) were developed three times in distilled ethanol in order to collect the impurities at one end. The poly(acrylic acid)-sodium chloride mixture (0.5% w/w) was mixed in a ball mill for 1 hr prior to use. Chloroform and 1,2-dichloroethane were used without further purification.
58
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Procedures Luminescence spectra. Low-temperature solution spectra were obtained with the Farrand MK-2 spectrofluorometer. Room-temperature luminescence spectra were obtained for samples adsorbed on solid supports using sample holders described earlier (6, II). Room temperature measurements. Stock solutions of the compounds in distilled ethanol were used to prepare four different spotting solutions (ethanol, 0.1 M HBr, 0.1 it4 HCl, and 0.1 M NaOH) of each compound (100 ng/pl) with the exceptions of anthraquinone and 5,12-naphthacenequinone. Anthraquinone and 5,12-naphthacenequinone were prepared in 1,2-dichloroethane/ethanol (1 + 1) solutions (100 ng/pl). A l-p1 aliquot of the sample solution was spotted onto the filter paper and the silica gel chromatoplates. The filter paper and silica gel chromatoplates were handled as described previously (6, II). Filter paper and silica gel chromatoplates spotted with 2-acetonaphthone and benzophenone were dried in the oven for 45 min at 44°C. The other samples were dried at 80°C for 30 min. The procedure for the adsorption of compounds onto PAA-NaCl powders was described earlier (17). The dried PAA-NaCl mixture was handled as described previously (2). 2-Acetonaphthone and benzophenone adsorbed on 0.5% PAANaCl were dried at 44°C for 2 hr because of the volatility of the compounds. A stock solution of PAA in ethanol (1 g/25 ml) was prepared as described previously (21). The appropriate aliquot of the PAA stock solution was transferred to a volumetric flask to yield a phosphor solution which contained 20 kg of PAA per 1 ~1 of solution. The procedure for spotting this type of solution and the syringe used were discussed previously by Senthilnathan et al. (21). Samples adsorbed on filter paper with PAA were dried for 30 min at 80°C with the exceptions of 2-acetonaphthone and benzophenone which were dried at 44°C for 45 min. In order to compensate for the variation in the RTP intensity of the compounds due to the use of different gain settings, the RTP data were normalized to the gain setting used for the RTP from 5,6-benzoquinoline. The RTF data were normalized to the gain setting used for the RTF from 5,6-benzoquinoline. RESULTS AND DISCUSSION
Luminescence Spectra Low temperature. Uncorrected luminescence solution excitation and emission spectra were obtained at liquid-nitrogen temperature for model compounds. Table 1 lists the names, structures, and the results of the low-temperature study for the nine model compounds. Benzalacetophenone did not exhibit low-temperature fluorescence or phosphorescence in the wavelength region scanned (350 to 600 nm). 2-Acetonaphthone, ol-naphthoflavone, and l3-naphthoflavone exhibited both fluorescence and phosphorescence at low temperature. The other compounds exhibited only phosphorescence in the wavelength region studied (350 to 600 nm) at liquid-nitrogen temperature. The information in Table 1 indicated the possibility of a given compound yielding RTF and/or RTP. Just because a compound gives a low-temperature fluorescence or phosphorescence signal in solution does not
59
PHOSPHORESCENCE AND FLUORESCENCE
TABLE 1 Compound Investigated and Low-Temperature Spectral Results LTP
Structure
Compound
LTFb
+ cd
+e
+d
+e
3. 5,12-Naphthacenequinone
id
-d
4. 2-Acetonaphthone
+d
+e
1. B-Naphthoflavone
I’
O :I
I
0
%
/ 1’
0
2. a-Naphthoflavone :I
'/ 6%
I
O
3
5. Anthrone
-e
6. Anthraquinone
i-d
-d
7. Benzalacetophenone
-d
-d
+d
-c
8. Benzophenone
9. Benzil
n Low-temperature phosphorescence. b Low-temperature fluorescence. c Signal observed (+ 1; signal not observed (-). d Wavelength region scanned from 3.50to 600 nm. e Wavelength region scanned from 300 to 600 nm.
60
CITTA
AND HURTUBISE
necessarily mean that the compound will yield a RTF or RTP signal when adsorbed on a solid surface. However, it is important to initially determine if the compound gives low-temperature fluorescence and/or phosphorescence in solution because not all compounds are luminescent. Thus, if a compound does not give a low-temperature fluorescence signal or phosphorescence signal, it is highly improbable that the compound would yield RTF or RTP when adsorbed on a solid surface. The phosphorescence characteristics of some aromatic carbonyl compounds can be relatively complex such as the assignment of the triplet state to a n,n* or n,r* state (I). However, in this work the emphasis was on the analytical applicability of the luminescence phenomena. The particular aromatic compounds studied showed well-defined fluorescence and/or phosphorescence spectra. Room temperature. Benzalacetophenone was not examined at room temperature since it did not give fluorescence or phosphorescence at low temperature. It was attempted to record the uncorrected phosphorescence excitation and emission spectra at room temperature for the remaining eight compounds adsorbed on the several surfaces investigated. The solid surfaces used were silica gel EM chromatoplates, filter paper, 0.5% PAA-NaCl, and filter paper containing PAA. Anthraquinone, benzil, and anthrone did not exhibit RTP on any of the four surfaces. RTP was not observed from 2-acetonaphthone and benzophenone adsorbed on silica gel chromatoplates and filter paper. 2-Acetonaphthone gave RTP when adsorbed on 0.5% PAA-NaCl and filter paper containing PAA. RTP was detected for benzophenone adsorbed on 0.5% PAA-NaCl; however, the intensity of the signal was too low to be analytically useful. Benzophenone adsorbed on filter paper with PAA did not give RTP. 5,12-Naphthacenequinone, a-naphthoflavone, and B-naphthoflavone exhibited RTP on all of the surfaces, and 2-acetonaphthone, o-naphthoflavone, and B-naphthoflavone yielded RTF on all of the surfaces. RTP Measurements
Listed in Table 2 are the excitation and emission wavelengths and the RTP relative intensities of the compounds spotted from the solutions (neutral, acidic, or basic) which gave the strongest RTP signal when adsorbed on the respective solid surface. Since 5,12-naphthacenequinone had a limited solubility in ethanol, this compound was prepared in 1,2-dichloroethane/ethanol (1 + 1) solution. Anthrone, benzil, a-naphthoflavone, and B-naphthoflavone formed a precipitate in basic solution. The phosphoroscope assembly was not used with the spectrodensitometer for the RTP measurements from 5,12-naphthacenequinone adsorbed on the various surfaces. Table 1 shows that no low-temperature fluorescence was observed from this compound. In addition, none of the surfaces investigated induced a roomtemperature fluorescence signal from 5,12-naphthacenequinone. Thus, phosphorescence could be measured without interference from flourescence. a-Naphthoflavone and B-naphthoflavone exhibited stronger RTP when adsorbed onto silica gel chromatoplates from an ethanolic solution of 0.1 M HCl than from 0.1 M HBr. For both compounds adsorbed on silica gel chromato-
II* 86 27+ -f
500 490 510
350 350 300
B-Naphthoflavone a-Naphthoflavone 5,12-Naphthacenequinone 2-Acetonaphthone
a One hundred nanograms adsorbed, average of duplicate samples. b Compound dissolved in 0.1 M HCl-ethanol. c Compound dissolved in ethanol. d Phosphoroscope was not used. e Compound dissolved in l,2-dichloroethane/ethanol (I + I) solution. r No RTP observed.
Rel. intensity”
Aelll,“Ill
ACX,“lll
Compound
Silica gel chromatoplate A,,,,, 350 350 300
A,,,,, 510 510 510
530
330
-f
9d.e
A,,,,, 510 490 510
A,,,,, 350 350 300
I=
Rel. intensity” 12’ 6’ l5da’
0.5% PAA-NaCl
Rel. intensity” 18’ 3’
Filter paper
TABLE 2 Excitation and Emission Wavelengths and Relative RTP Intensities of Model Compounds Adsorbed on Several Surfaces
F3
0 Ifi in 8 3
62
CITI’A
AND HURTUBISE
plates, the neutral solution gave the lowest RTP signal. Apparently the heavy atoms from HBr did not have an important influence on the RTP for a-naphthoflavone and B-naphthoflavone. RTP and RTF Analytical
Data
Tables 3 and 4 list RTP and RTF analytical data for several compounds adsorbed on silica gel chromatoplates, filter paper, filter paper with PAA, and 0.5% PAA-NaCl. Useful analytical data could not be obtained for the other compounds which are not listed in Tables 3 and 4. Although RTP and RTF were observed from 2-acetonaphthone adsorbed on 0.5% PAA-NaCl, nonreproducible results were obtained. For this compound, a lower drying temperature had to be used which necessitated a long period of time (2 hr) to evaporate the solvent. This most likely contributed to the nonreproducible results which were obtained. Therefore, no analytically useful data were reported for 2-acetonaphthone adsorbed on 0.5% PAA-NaCl (Tables 3 and 4). 2-Acetonaphthone exhibited only RTF when adsorbed on silica gel chromatoplates (Table 4) and both RTP and RTF when adsorbed on filter paper with PAA (Tables 3 and 4). For the data in Table 3, the phosphoroscope was not used with the spectrodensitometer for the RTP data for 2-acetonaphthone and 5,12-naphthacenequinone. As discussed in the previous section, it was not necessary to use a phosphoroscope for the RTP measurements of 5,12-naphthacenequinone because no fluorescence was observed from this compound. For 2-acetonaphthone, its RTP lifetime was determined to be 4 msec. Experiments with and without the chopper indicated that the rotation rate of the chopper was too slow for a strong RTP signal to be observed for 2-acetonaphthone. Thus, its RTP was measured without the phosphoroscope. Since 2acetonaphthone also exhibited RTF, an appropriate RTP emission wavelength had to be chosen from a region where there was no interference from RTE Therefore, the emission wavelength chosen for RTP was not the maximum emission wavelength for 2-acetonaphthone adsorbed with PAA on filter paper; however, the emission wavelength gave minimum interference from RTF. The maximum RTP emission wavelength was used for 5,12-naphthacenequinone since only RTP was observed from this compound adsorbed on the surfaces studied. RTP and RTF were both observed from a-naphthoflavone and B-naphthoflavone. For these two compounds, the phosphoroscope was used when the RTP data was obtained. Dalterio and Hurtubise (2) have reported the linear range and the limit of detection for the RTP from ol-naphthoflavone adsorbed on filter paper from an ethanol/water (80 + 20) solution which contained NaBr. In Tables 3 and 4, RTP and RTF analytical data were obtained for a-naphthoflavone adsorbed on filter paper from an ethanolic 0.1 M HCl solution. Improved limits of detection were obtained for a-naphthoflavone and 5,12-naphthacenequinone adsorbed on filter paper containing PAA as compared to filter paper without PAA (Table 3). Also, with the addition of PAA to filter paper, the linear ranges increased for the RTP from u-naphthoflavone and B-naphthoflavone and the relative standard deviations improved for 5,12-naphthacenequinone and B-naphthoflavone compared to untreated filter paper. Senthilnathan et al. (21) have reported a general improvement in the sensitivity, limits of detection, and relative standard deviation
0.4-50
350/500
0.4
0.8
0.8-75
-c
350/490
-c 0.4
-e
350/510 0.4-50
1.4d
1.7-50
350/510
300/510 1.7-55
-c
3.2“
l.lf
-c
A,,,,
0.5
350/410 0.5-75
1.2
0.3
1.2-125
2.9
1.9
1.0
350/420
350/430
-c
linear range, ng LOD’ RSD, %* A,,,,
3501430 0.3-75
350/420
-
Aex.nm
0.7-125
0.6-50
-c
0.7
0.6
-c
4.3
4.6
-c
0.5-55
0.8-75
350/510
2.1-100
3501500 0.9-100
300/510
350/570
2.1
0.9
0.5
0.8
3.5d
4.2d
2.5f
4.66
Aexnm
350/400
0.5-100
-d
350/410 0.7-75 -d
Aexpn
350/510
350/490
300/510
-I
0.5
-d
0.7
-c 350/400 3501420
3.9 -d 3.8
linear range, ng LOD” RSD, %* A,,.,
Filter paper with PAA
Adsorbed on Several Surfaces
4.7d
3.5d
4.11
-e
linear range, ng LOD” RSD, %b A,,.,
Filter paper
a LOD = limit of detection (ng); amount of sample needed to give a S/N of 3. b Relative standard deviation calculated from 6 spots of 100 ng each. c No data reported due to poor analytical results. d No data obtained due to overlap of RTP spectrum with RTF spectrum.
2-Acetonaphthone (Ethanol) u-Naphthoflavone (0.1 M HCI-ethanol) S-Naphthoflavone (0.1 M HBr-ethanol)
Compound and solution
Analytical
0.4
1.7
1.7
-c
TABLE 4 Data for RTF from Model Compounds
Silica gel chromatoplate
Aernm
Filter paper with PAA
0.5% PAA-NaCI
0.2
0.5
0.2
-c
5.7d
5.4d
3.3"
-c
0.3-75
0.3-100
-c
0.3
0.3
-c
4.5
4.3
-c
linear range, ng LOD” RSD, %b
0.5% PAA-NaCI
0.2-75
0.5-50
0.2-45
-e
Aer,nm Acr.nm Aci.nm linear linear linear linear a range, ng LOD RSD, % A,,,,, range, ng LOD” RSD, % A,,,, range, ng LOD@ RSD, % A,,., range, ng LOD” RSD, %
300/510 0.4-60
-c
A,,,,
Aei.nm
’ LOD = limit of detection (ng); amount of sample needed to give a S/N of 3. * Phosphoroscope was not used. c No RTP observed. ’ Relative standard deviation calculated from 6 spots of 100 ng each. ’ No data reported due to nonreproducible results. ‘Relative standard deviation calculated from 9 spots of 100 ng each.
2-Acetonaphthoneb (Ethanol) 5,12-Naphthacenequinoneb (1,2-Dichloroethane-ethanol) u-Naphthoflavone (0.1 M HCl-ethanol) &Naphthoflavone (0.1 M HBr-ethanol)
Compound and solution
-
Filter paper
TABLE 3 Data for RTP from Model Compounds Adsorbed on Several Surfaces
Silica gel chromatoplate
Analytical
!2 G
6
E
2
;
k
ci
64
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AND HURTUBISE
for the RTP from compounds with the addition of PAA to filter paper. In this work, RTF results showed improvement in the limit of detection and relative standard deviation for P-naphthoflavone adsorbed on filter paper containing PAA (Table 4). In Table 3, the RTP limit of detection for P-naphthoflavone adsorbed on filter paper with PAA was higher than the limits of detection obtained for this compound adsorbed on the other surfaces. When the sample of P-naphthoflavone adsorbed with PAA on filter paper from an ethanolic 0.1 A4 HBr solution was removed from the oven, the sample spots were quite dark. The ethanol/PAA/O. 1 M HBr treated filter paper blank was of the same dark intensity as the sample spots. The spots were not dark for 2-acetonaphthone, 5,12-naphthacenequinone, and cx-naphthoflavone adsorbed on PAA treated filter paper from ethanol, 1,2dichloroethane/ethanol (1 + l), and ethanolic 0.1 A4 HCl solutions, respectively. RTP excitation and RTF and RTP emission spectra were obtained from pnaphthoflavone adsorbed on filter paper and filter paper with PAA (dark spot). The spectra showed that P-naphthoflavone was not altered with the addition of PAA to the filter paper. The higher limit of detection for @naphthoflavone is attributed to the darkening of the sample spots due to the blank. The maximum RTP emission wavelengths were used for a-naphthotlavone and p-naphthoflavone adsorbed on the solid surfaces since the phosphoroscope was used and thus fluorescence would not interfere (Table 3). However, data for RTF from a-naphthoflavone adsorbed on filter paper with PAA were not collected. The fluorescence and phosphorescence spectra for a-naphthoflavone adsorbed on filter paper with PAA showed overlap of the RTP spectrum into the RTF region. The total luminescence spectrum indicated that the phosphorescence signal was of the same magnitude as fluorescence and thus the fluorescence data obtained would be influenced by the phosphorescence. Therefore, under these experimental conditions, filter paper treated with PAA could not be used to obtain RTF data for cY-naphthoflavone. For the compounds, cw-naphthoflavone and p-naphthoflavone, it was important to obtain RTF data in a wavelength region where RTP was not observed so interference from RTP was minimized. The RTF emission wavelengths used for IXnaphthoflavone adsorbed on 0.5% PAA-NaCl and for /3-naphthoflavone adsorbed on filter paper and filter paper with PAA were not the maximum emission wavelengths. A small amount of RTP was present at the maximum RTF emission wavelengths for these two compounds. This is illustrated in Fig. 1 for the RTF and RTP emission spectra for P-naphthoflavone adsorbed on filter paper with PAA. The maximum RTF emission wavelength for l3-naphthoflavone adsorbed on filter paper with PAA was 452 nm; however, the RTF analytical data were obtained at an emission wavelength of 400 nm where RTP was not present (Fig. 1). In related work, emission spectra for a-naphthoflavone adsorbed on 0.5% PAANaCl and P-naphthoflavone adsorbed on filter paper showed the RTF maximum emission wavelengths were 420 and 465 nm, respectively. Because of possible interference from phosphorescence, the maximum RTF emission wavelengths were not used for these two compounds; however, acceptable analytical data were acquired (Table 4).
65
300
350
400
460 WAVELENGTH
500
5io
600’
(nm)
FIG. 1. RTF (-) and RTP (- - -) emission spectra of 500 ng of B-naphthoflavone adsorbed from an ethanol/PAA/O. 1 M HBr solution onto filter paper. The RTP spectra were obtained at a slightly different sensitivity setting. RTF excitated at 300 nm; RTP excitated at 350 nm.
Overall, good analytical data were obtained for the model compounds adsorbed on the surfaces investigated. The results in Tables 3 and 4 indicate that no one surface gave the optimum RTP and RTF analytical data for every compound studied. Rather, Tables 3 and 4 show that the use of a variety of surfaces provides more information about RTP and RTF from the compounds. For example, if filter paper had been the only surface employed, then data for RTP and RTF from 2-acetonaphthone would not have been obtained. Conditions for a specific surface had to be carefully selected when obtaining RTP and RTF data such that there was no interference from the unwanted luminescence. In many cases through the combined use of RTP and RTF, more useful analytical information was obtained. ACKNOWLEDGMENTS Financial support for this project was provided by the Department of Energy, Division of Basic Energy Sciences, Contract DE-AC0280ER10624. The authors thank S. M. Ramasamy for obtaining the lifetime data for 2-acetonaphthone.
REFERENCES 1. Becker, R. S., “Theory and Interpretation of Fluorescence and Phosphorescence,” pp. 156-167. Wiley, New York, 1969. 2. Dalterio, R. A., and Hurtubise, R. J., Room-temperature phosphorescence of hydroxyl-substituted aromatics adsorbed on solid surfaces. Anal. Chem. 54, 224-228 (1982). 3. Dalterio, R. A., and Hurtubise, R. J., External conditions and interactions in room-temperature phosphorescence of hydroxyl aromatics adsorbed on solid surfaces containing poly(acrylic acid). Anal. Chem. 55, 1084-1089 (1983). 4. Dalterio, R. A., and Hurtubise, R. J., Zeroth and second derivative fluorescence and phosphorescence analysis of mixtures of hydroxyl aromatics adsorbed on filter paper. Anal. Chem. 56, 819-821 (1984). 5. Dalterio, R. A., and Hurtubise, R. J., Second derivative solid surface luminescence analysis of two-component liquid chromatography fractions. Anal. Chem. 56, 1183-1186 (1984).
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6. Dalterio, R. A., and Hurtubise, R. J., Interactions of phosphors and solid supports in room-temperature phosphorescence of aromatic compounds. Anal. Chem. 56, 336-341 (1984). 7. Donkerbroek, J. J., Elzas, J. J., Gooijer, C., Frei, R. W., and Velthorst, N. H., Some aspects of room-temperature phosphorescence in liquid solutions. Talanta 28, 717-723 (1981). 8. Donkerbroek, J. J., Gooier, C., Velthorst, N. H., and Frei, R. W., Sensitized room temperature phosphorescence in liquid solutions with 1,4-dibromonaphthalene and biacetyl as acceptors. Anal. Chem. 54, 891-895 (1982). 9. Ermolaev, V. L., and Terenin, A. N., Intramolecular energy transfer between triplet levels. Sov. Phys. Usp. (Engl. Trunsf.) 3, 423-426 (1960). 10. Ford, C. D., and Hurtubise, R. J., Separation of benzo[flquinoline and phenanthridine from shale oil and characterization by room temperature phosphorescence. Anal. Left. 13(A6), 485-496 (1980). 11. Ford, C. D., and Hurtubise, R. J., Design of a phosphoroscope and the examination of room temperature phosphorescence of nitrogen heterocycles. Anal. Chem. 51, 659-663 (1979). 12. Harbaugh, K. F., O’Donnell, C. M., and Winefordner, J. D., Pulsed source, time resolved phosphorimetry determination of phosphorescence lifetimes. Anal. Chem. 45, 381-382 (1973). 13. Hurtubise, R. J., “Solid Surface Luminescence Analysis: Theory, Instrumentation, Applica-
tions.” Dekker, New York, 1981. 14. Nicholls, C. H., and Leermakers, P. A., Photochemical and spectroscopic properties of organic
15.
16. 17. 18.
19. 20.
21.
molecules in adsorbed or other perturbing polar environments. In “Advances in Photochemistry” (J. N. Pitts, Jr., G. S. Hammond, and W. A. Noyes, Jr., eds.), Vol. 8, pp. 315-336. Wiley-Interscience, New York, 1971. O’Donnell, C. M., and Winefordner, J. D., The potential of phosphorescence spectrometry in clinical chemistry-the new generation of instrumentation and methodology. Clin. Chem. 21, 285-299 (1975). Parker, C. A., and Hatchard, C. G., The possibilities of phosphorescence measurement in chemical analysis: tests with a new instrument. Analyst 87, 664-676 (1962). Ramasamy, S. M., and Hurtubise, R. J., Matrix and solvent effects on the room-temperature phosphorescence of nitrogen heterocycles. Anal. Chem. 54, 2477-2481 (1982). Senthilnathan, V. P., and Hurtubise, R. J., Total solid-surface room-temperature luminescence for analysis of mixtures. Anal. Chem. 56, 913-918 (1984). Senthilnathan, V. P., and Hurtubise, R. J., Solid-surface derivative room-temperature luminescence spectrometry of mixtures. Anal. Chim. Actu 170, 177-185 (1985). Senthilnathan, V. P., and Hurtubise, R. J., Room-temperature phosphorescence lifetimes and intensities of p-aminobenzoic acid adsorbed on sodium acetate-sodium chloride mixtures. And. Chem. 57, 1227-1230 (1985). Senthilnathan, V. P., Ramasamy, S. M., and Hurtubise, R. J., Effects of polyacrylic acid on the room-temperature phosphorescence of selected compounds. Anal. Chim. Actu 157, 203-206 (1984).
22. Skrilec, M., and Cline Love, L. J., Room temperature phosphorescence characteristics of substituted arenes in aqueous thallium lauryl sulfate micelles. Anal. Chem. 52, 1559-1564 (1980). 23. Vo-Dinh, T., “Room Temperature Phosphorimetry for Chemical Analysis.” Wiley-Interscience, New York, 1984.
JOURNAL
34, 56-66 (1986)
Room-Temperature Phosphorescence and Fluorescence Selected Model Aromatic Carbonyl Compounds Adsorbed on Several Solid Surfaces
of
L. A. CITTA AND R. J. HURTUBISE’ Chemistry Department, University of Wyoming. Laramie, Wyoming 82071 Received November 19. 1985: accepted March 3, 1986 Several model aromatic carbonyl compounds, which were adsorbed on various solid surfaces, were examined for room-temperature phosphorescence and fluorescence. The results showed that it was important to investigate several surfaces to obtain optimal luminescence conditions for this class of compounds. In addition, the luminescence of some of the compounds was relatively sensitive to experimental conditions. Finally, both room-temperature fluorescence and room-temperature phosphorescence were shown to be analytically USefIll.
0 1986 Academic
Press. Inc.
There has been very little data reported on the room-temperature phosphorescence (RTP) and room-temperature fluorescence (RTF) of aromatic carbonyl compounds adsorbed on various solid surfaces. However, aromatic carbonyl compounds have been examined at low temperature (77°K) in solution. Parker and Hatchard (16) reported low-temperature phosphorescence emission spectra for several aromatic carbonyl compounds. Certain carbonyl derivatives of biphenyl and naphthalene were investigated at 77°K by Ermolaev and Terenin (9). O’Donnell and Winefordner (15) presented a review of low-temperature phosphorescence spectrometry, and several of the compounds discussed were aromatic carbonyl compounds. Micelle stabilized RTP has been employed by Skrilec and Cline Love (22) to investigate the phosphorescence characteristics of functionally substituted aromatic compounds. Donkerbroek and co-workers (7, 8) studied the sensitized RTP of benzophenone and substituted benzophenones in liquid solutions. Dalterio and Hurtubise (2, 3) examined the RTP of hydroxyl aromatic model compounds adsorbed on various solid surfaces. One of the hydroxyl aromatics studied contained the carbonyl functionality. The phosphorescence lifetimes of several aromatic compounds measured at low temperature have been reported (15). Ermolaev and Terenin (9) obtained a phosphorescence lifetime of 0.97 set for 2-acetonaphthone in an ethanol-ether mixture at 77°K. Harbaugh et al. (12) have reported the phosphorescence lifetimes for benzophenone, anthrone, and anthraquinone in ethanol at 77°K as 7, 3, and 3.6 msec, respectively. The phosphorescence lifetime of benzil in an etherisopentane-ethanol mixture at 77°K was reported as 5 msec by Parker and Hatchard (16). The phosphorescence lifetimes at 77°K for benzophenone, benzil, and 2-acetonaphthone adsorbed on silica gel in isopentane were reported as 2, 1, and 80 msec, respectively (14). r To whom all correspondence should be addressed. 56 0026-265X186$1SO Copyright 0 1986 by Academic Press. Inc. All rights of reproduction in any form reserved.
PHOSPHORESCENCE
AND FLUORESCENCE
57
Little has been done with the combined use of solid-surface RTP and RTF. Ford and Hurtubise (10) employed solid-surface RTP and RTF in the characterization of phenanthridine and benzov]quinoline in shale oil. Recently, Senthilnathan and Hurtubise (18) utilized the new approach of total solid-surface luminescence analysis in the quantitative analysis of various binary and ternary mixtures containing nitrogen heterocycles and a polycyclic aromatic hydrocarbon. This approach utilized information from both RTP and RTF in the analysis. Dalterio and Hurtubise (4, 5) used second derivative solid-surface RTP and RTF in the analysis of mixtures of hydroxyl aromatics adsorbed on filter paper and in the qualitative analysis of two components in high-performance liquid chromatography fractions. Derivative solid-surface RTP and RTF were employed by Senthilnathan and Hurtubise (19) for the identification of components in mixtures of nitrogen heterocycles. General reviews on solid-surface luminescence analysis (13) and room-temperature phosphorimetry (23) have appeared in the literature which discuss in detail the compounds that have been investigated by solid-surface luminescence techniques. In this work, several aromatic carbonyl compounds were examined for RTP and RTF when adsorbed on filter paper, silica gel chromatoplates, and 0.5% poly(acrylic acid) (PAA)-NaCl mixture. The results show the analytical advantages and difficulties in solid-surface luminescence analysis for this class of compounds. EXPERIMENTAL Apparatus
RTP and RTF intensity measurements and calibration curves were obtained with a spectrodensitometer. Details of the instrument have been described elsewhere (II). Luminescence excitation and emission spectra were obtained with a Farrand MK-2 spectrofluorometer fitted with a phosphorescence rotary chopper. Roomtemperature phosphorescence lifetimes were obtained with the Farrand MK-2 spectrofluorometer and a Model 5223 Tektronix oscilloscope. The procedure for phosphorescence lifetimes was discussed earlier (20). Reagents
Absolute ethanol was purified by distillation. 5, I2-Naphthacenequinone was used as received. Benzalacetophenone was recrystallized three times from chloroform. 2-Acetonaphthone, anthraquinone, anthrone, benzil, benzophenone, (Ynaphthoflavone, and B-naphthoflavone were recrystallized three times from ethanol. Filter paper (Whatman No. 1) and plastic-backed silica gel chromatoplates (EM Laboratories, Elmsford, N.Y.) were developed three times in distilled ethanol in order to collect the impurities at one end. The poly(acrylic acid)-sodium chloride mixture (0.5% w/w) was mixed in a ball mill for 1 hr prior to use. Chloroform and 1,2-dichloroethane were used without further purification.
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Procedures Luminescence spectra. Low-temperature solution spectra were obtained with the Farrand MK-2 spectrofluorometer. Room-temperature luminescence spectra were obtained for samples adsorbed on solid supports using sample holders described earlier (6, II). Room temperature measurements. Stock solutions of the compounds in distilled ethanol were used to prepare four different spotting solutions (ethanol, 0.1 M HBr, 0.1 it4 HCl, and 0.1 M NaOH) of each compound (100 ng/pl) with the exceptions of anthraquinone and 5,12-naphthacenequinone. Anthraquinone and 5,12-naphthacenequinone were prepared in 1,2-dichloroethane/ethanol (1 + 1) solutions (100 ng/pl). A l-p1 aliquot of the sample solution was spotted onto the filter paper and the silica gel chromatoplates. The filter paper and silica gel chromatoplates were handled as described previously (6, II). Filter paper and silica gel chromatoplates spotted with 2-acetonaphthone and benzophenone were dried in the oven for 45 min at 44°C. The other samples were dried at 80°C for 30 min. The procedure for the adsorption of compounds onto PAA-NaCl powders was described earlier (17). The dried PAA-NaCl mixture was handled as described previously (2). 2-Acetonaphthone and benzophenone adsorbed on 0.5% PAANaCl were dried at 44°C for 2 hr because of the volatility of the compounds. A stock solution of PAA in ethanol (1 g/25 ml) was prepared as described previously (21). The appropriate aliquot of the PAA stock solution was transferred to a volumetric flask to yield a phosphor solution which contained 20 kg of PAA per 1 ~1 of solution. The procedure for spotting this type of solution and the syringe used were discussed previously by Senthilnathan et al. (21). Samples adsorbed on filter paper with PAA were dried for 30 min at 80°C with the exceptions of 2-acetonaphthone and benzophenone which were dried at 44°C for 45 min. In order to compensate for the variation in the RTP intensity of the compounds due to the use of different gain settings, the RTP data were normalized to the gain setting used for the RTP from 5,6-benzoquinoline. The RTF data were normalized to the gain setting used for the RTF from 5,6-benzoquinoline. RESULTS AND DISCUSSION
Luminescence Spectra Low temperature. Uncorrected luminescence solution excitation and emission spectra were obtained at liquid-nitrogen temperature for model compounds. Table 1 lists the names, structures, and the results of the low-temperature study for the nine model compounds. Benzalacetophenone did not exhibit low-temperature fluorescence or phosphorescence in the wavelength region scanned (350 to 600 nm). 2-Acetonaphthone, ol-naphthoflavone, and l3-naphthoflavone exhibited both fluorescence and phosphorescence at low temperature. The other compounds exhibited only phosphorescence in the wavelength region studied (350 to 600 nm) at liquid-nitrogen temperature. The information in Table 1 indicated the possibility of a given compound yielding RTF and/or RTP. Just because a compound gives a low-temperature fluorescence or phosphorescence signal in solution does not
59
PHOSPHORESCENCE AND FLUORESCENCE
TABLE 1 Compound Investigated and Low-Temperature Spectral Results LTP
Structure
Compound
LTFb
+ cd
+e
+d
+e
3. 5,12-Naphthacenequinone
id
-d
4. 2-Acetonaphthone
+d
+e
1. B-Naphthoflavone
I’
O :I
I
0
%
/ 1’
0
2. a-Naphthoflavone :I
'/ 6%
I
O
3
5. Anthrone
-e
6. Anthraquinone
i-d
-d
7. Benzalacetophenone
-d
-d
+d
-c
8. Benzophenone
9. Benzil
n Low-temperature phosphorescence. b Low-temperature fluorescence. c Signal observed (+ 1; signal not observed (-). d Wavelength region scanned from 3.50to 600 nm. e Wavelength region scanned from 300 to 600 nm.
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necessarily mean that the compound will yield a RTF or RTP signal when adsorbed on a solid surface. However, it is important to initially determine if the compound gives low-temperature fluorescence and/or phosphorescence in solution because not all compounds are luminescent. Thus, if a compound does not give a low-temperature fluorescence signal or phosphorescence signal, it is highly improbable that the compound would yield RTF or RTP when adsorbed on a solid surface. The phosphorescence characteristics of some aromatic carbonyl compounds can be relatively complex such as the assignment of the triplet state to a n,n* or n,r* state (I). However, in this work the emphasis was on the analytical applicability of the luminescence phenomena. The particular aromatic compounds studied showed well-defined fluorescence and/or phosphorescence spectra. Room temperature. Benzalacetophenone was not examined at room temperature since it did not give fluorescence or phosphorescence at low temperature. It was attempted to record the uncorrected phosphorescence excitation and emission spectra at room temperature for the remaining eight compounds adsorbed on the several surfaces investigated. The solid surfaces used were silica gel EM chromatoplates, filter paper, 0.5% PAA-NaCl, and filter paper containing PAA. Anthraquinone, benzil, and anthrone did not exhibit RTP on any of the four surfaces. RTP was not observed from 2-acetonaphthone and benzophenone adsorbed on silica gel chromatoplates and filter paper. 2-Acetonaphthone gave RTP when adsorbed on 0.5% PAA-NaCl and filter paper containing PAA. RTP was detected for benzophenone adsorbed on 0.5% PAA-NaCl; however, the intensity of the signal was too low to be analytically useful. Benzophenone adsorbed on filter paper with PAA did not give RTP. 5,12-Naphthacenequinone, a-naphthoflavone, and B-naphthoflavone exhibited RTP on all of the surfaces, and 2-acetonaphthone, o-naphthoflavone, and B-naphthoflavone yielded RTF on all of the surfaces. RTP Measurements
Listed in Table 2 are the excitation and emission wavelengths and the RTP relative intensities of the compounds spotted from the solutions (neutral, acidic, or basic) which gave the strongest RTP signal when adsorbed on the respective solid surface. Since 5,12-naphthacenequinone had a limited solubility in ethanol, this compound was prepared in 1,2-dichloroethane/ethanol (1 + 1) solution. Anthrone, benzil, a-naphthoflavone, and B-naphthoflavone formed a precipitate in basic solution. The phosphoroscope assembly was not used with the spectrodensitometer for the RTP measurements from 5,12-naphthacenequinone adsorbed on the various surfaces. Table 1 shows that no low-temperature fluorescence was observed from this compound. In addition, none of the surfaces investigated induced a roomtemperature fluorescence signal from 5,12-naphthacenequinone. Thus, phosphorescence could be measured without interference from flourescence. a-Naphthoflavone and B-naphthoflavone exhibited stronger RTP when adsorbed onto silica gel chromatoplates from an ethanolic solution of 0.1 M HCl than from 0.1 M HBr. For both compounds adsorbed on silica gel chromato-
II* 86 27+ -f
500 490 510
350 350 300
B-Naphthoflavone a-Naphthoflavone 5,12-Naphthacenequinone 2-Acetonaphthone
a One hundred nanograms adsorbed, average of duplicate samples. b Compound dissolved in 0.1 M HCl-ethanol. c Compound dissolved in ethanol. d Phosphoroscope was not used. e Compound dissolved in l,2-dichloroethane/ethanol (I + I) solution. r No RTP observed.
Rel. intensity”
Aelll,“Ill
ACX,“lll
Compound
Silica gel chromatoplate A,,,,, 350 350 300
A,,,,, 510 510 510
530
330
-f
9d.e
A,,,,, 510 490 510
A,,,,, 350 350 300
I=
Rel. intensity” 12’ 6’ l5da’
0.5% PAA-NaCl
Rel. intensity” 18’ 3’
Filter paper
TABLE 2 Excitation and Emission Wavelengths and Relative RTP Intensities of Model Compounds Adsorbed on Several Surfaces
F3
0 Ifi in 8 3
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plates, the neutral solution gave the lowest RTP signal. Apparently the heavy atoms from HBr did not have an important influence on the RTP for a-naphthoflavone and B-naphthoflavone. RTP and RTF Analytical
Data
Tables 3 and 4 list RTP and RTF analytical data for several compounds adsorbed on silica gel chromatoplates, filter paper, filter paper with PAA, and 0.5% PAA-NaCl. Useful analytical data could not be obtained for the other compounds which are not listed in Tables 3 and 4. Although RTP and RTF were observed from 2-acetonaphthone adsorbed on 0.5% PAA-NaCl, nonreproducible results were obtained. For this compound, a lower drying temperature had to be used which necessitated a long period of time (2 hr) to evaporate the solvent. This most likely contributed to the nonreproducible results which were obtained. Therefore, no analytically useful data were reported for 2-acetonaphthone adsorbed on 0.5% PAA-NaCl (Tables 3 and 4). 2-Acetonaphthone exhibited only RTF when adsorbed on silica gel chromatoplates (Table 4) and both RTP and RTF when adsorbed on filter paper with PAA (Tables 3 and 4). For the data in Table 3, the phosphoroscope was not used with the spectrodensitometer for the RTP data for 2-acetonaphthone and 5,12-naphthacenequinone. As discussed in the previous section, it was not necessary to use a phosphoroscope for the RTP measurements of 5,12-naphthacenequinone because no fluorescence was observed from this compound. For 2-acetonaphthone, its RTP lifetime was determined to be 4 msec. Experiments with and without the chopper indicated that the rotation rate of the chopper was too slow for a strong RTP signal to be observed for 2-acetonaphthone. Thus, its RTP was measured without the phosphoroscope. Since 2acetonaphthone also exhibited RTF, an appropriate RTP emission wavelength had to be chosen from a region where there was no interference from RTE Therefore, the emission wavelength chosen for RTP was not the maximum emission wavelength for 2-acetonaphthone adsorbed with PAA on filter paper; however, the emission wavelength gave minimum interference from RTF. The maximum RTP emission wavelength was used for 5,12-naphthacenequinone since only RTP was observed from this compound adsorbed on the surfaces studied. RTP and RTF were both observed from a-naphthoflavone and B-naphthoflavone. For these two compounds, the phosphoroscope was used when the RTP data was obtained. Dalterio and Hurtubise (2) have reported the linear range and the limit of detection for the RTP from ol-naphthoflavone adsorbed on filter paper from an ethanol/water (80 + 20) solution which contained NaBr. In Tables 3 and 4, RTP and RTF analytical data were obtained for a-naphthoflavone adsorbed on filter paper from an ethanolic 0.1 M HCl solution. Improved limits of detection were obtained for a-naphthoflavone and 5,12-naphthacenequinone adsorbed on filter paper containing PAA as compared to filter paper without PAA (Table 3). Also, with the addition of PAA to filter paper, the linear ranges increased for the RTP from u-naphthoflavone and B-naphthoflavone and the relative standard deviations improved for 5,12-naphthacenequinone and B-naphthoflavone compared to untreated filter paper. Senthilnathan et al. (21) have reported a general improvement in the sensitivity, limits of detection, and relative standard deviation
0.4-50
350/500
0.4
0.8
0.8-75
-c
350/490
-c 0.4
-e
350/510 0.4-50
1.4d
1.7-50
350/510
300/510 1.7-55
-c
3.2“
l.lf
-c
A,,,,
0.5
350/410 0.5-75
1.2
0.3
1.2-125
2.9
1.9
1.0
350/420
350/430
-c
linear range, ng LOD’ RSD, %* A,,,,
3501430 0.3-75
350/420
-
Aex.nm
0.7-125
0.6-50
-c
0.7
0.6
-c
4.3
4.6
-c
0.5-55
0.8-75
350/510
2.1-100
3501500 0.9-100
300/510
350/570
2.1
0.9
0.5
0.8
3.5d
4.2d
2.5f
4.66
Aexnm
350/400
0.5-100
-d
350/410 0.7-75 -d
Aexpn
350/510
350/490
300/510
-I
0.5
-d
0.7
-c 350/400 3501420
3.9 -d 3.8
linear range, ng LOD” RSD, %* A,,.,
Filter paper with PAA
Adsorbed on Several Surfaces
4.7d
3.5d
4.11
-e
linear range, ng LOD” RSD, %b A,,.,
Filter paper
a LOD = limit of detection (ng); amount of sample needed to give a S/N of 3. b Relative standard deviation calculated from 6 spots of 100 ng each. c No data reported due to poor analytical results. d No data obtained due to overlap of RTP spectrum with RTF spectrum.
2-Acetonaphthone (Ethanol) u-Naphthoflavone (0.1 M HCI-ethanol) S-Naphthoflavone (0.1 M HBr-ethanol)
Compound and solution
Analytical
0.4
1.7
1.7
-c
TABLE 4 Data for RTF from Model Compounds
Silica gel chromatoplate
Aernm
Filter paper with PAA
0.5% PAA-NaCI
0.2
0.5
0.2
-c
5.7d
5.4d
3.3"
-c
0.3-75
0.3-100
-c
0.3
0.3
-c
4.5
4.3
-c
linear range, ng LOD” RSD, %b
0.5% PAA-NaCI
0.2-75
0.5-50
0.2-45
-e
Aer,nm Acr.nm Aci.nm linear linear linear linear a range, ng LOD RSD, % A,,,,, range, ng LOD” RSD, % A,,,, range, ng LOD@ RSD, % A,,., range, ng LOD” RSD, %
300/510 0.4-60
-c
A,,,,
Aei.nm
’ LOD = limit of detection (ng); amount of sample needed to give a S/N of 3. * Phosphoroscope was not used. c No RTP observed. ’ Relative standard deviation calculated from 6 spots of 100 ng each. ’ No data reported due to nonreproducible results. ‘Relative standard deviation calculated from 9 spots of 100 ng each.
2-Acetonaphthoneb (Ethanol) 5,12-Naphthacenequinoneb (1,2-Dichloroethane-ethanol) u-Naphthoflavone (0.1 M HCl-ethanol) &Naphthoflavone (0.1 M HBr-ethanol)
Compound and solution
-
Filter paper
TABLE 3 Data for RTP from Model Compounds Adsorbed on Several Surfaces
Silica gel chromatoplate
Analytical
!2 G
6
E
2
;
k
ci
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for the RTP from compounds with the addition of PAA to filter paper. In this work, RTF results showed improvement in the limit of detection and relative standard deviation for P-naphthoflavone adsorbed on filter paper containing PAA (Table 4). In Table 3, the RTP limit of detection for P-naphthoflavone adsorbed on filter paper with PAA was higher than the limits of detection obtained for this compound adsorbed on the other surfaces. When the sample of P-naphthoflavone adsorbed with PAA on filter paper from an ethanolic 0.1 A4 HBr solution was removed from the oven, the sample spots were quite dark. The ethanol/PAA/O. 1 M HBr treated filter paper blank was of the same dark intensity as the sample spots. The spots were not dark for 2-acetonaphthone, 5,12-naphthacenequinone, and cx-naphthoflavone adsorbed on PAA treated filter paper from ethanol, 1,2dichloroethane/ethanol (1 + l), and ethanolic 0.1 A4 HCl solutions, respectively. RTP excitation and RTF and RTP emission spectra were obtained from pnaphthoflavone adsorbed on filter paper and filter paper with PAA (dark spot). The spectra showed that P-naphthoflavone was not altered with the addition of PAA to the filter paper. The higher limit of detection for @naphthoflavone is attributed to the darkening of the sample spots due to the blank. The maximum RTP emission wavelengths were used for a-naphthotlavone and p-naphthoflavone adsorbed on the solid surfaces since the phosphoroscope was used and thus fluorescence would not interfere (Table 3). However, data for RTF from a-naphthoflavone adsorbed on filter paper with PAA were not collected. The fluorescence and phosphorescence spectra for a-naphthoflavone adsorbed on filter paper with PAA showed overlap of the RTP spectrum into the RTF region. The total luminescence spectrum indicated that the phosphorescence signal was of the same magnitude as fluorescence and thus the fluorescence data obtained would be influenced by the phosphorescence. Therefore, under these experimental conditions, filter paper treated with PAA could not be used to obtain RTF data for cY-naphthoflavone. For the compounds, cw-naphthoflavone and p-naphthoflavone, it was important to obtain RTF data in a wavelength region where RTP was not observed so interference from RTP was minimized. The RTF emission wavelengths used for IXnaphthoflavone adsorbed on 0.5% PAA-NaCl and for /3-naphthoflavone adsorbed on filter paper and filter paper with PAA were not the maximum emission wavelengths. A small amount of RTP was present at the maximum RTF emission wavelengths for these two compounds. This is illustrated in Fig. 1 for the RTF and RTP emission spectra for P-naphthoflavone adsorbed on filter paper with PAA. The maximum RTF emission wavelength for l3-naphthoflavone adsorbed on filter paper with PAA was 452 nm; however, the RTF analytical data were obtained at an emission wavelength of 400 nm where RTP was not present (Fig. 1). In related work, emission spectra for a-naphthoflavone adsorbed on 0.5% PAANaCl and P-naphthoflavone adsorbed on filter paper showed the RTF maximum emission wavelengths were 420 and 465 nm, respectively. Because of possible interference from phosphorescence, the maximum RTF emission wavelengths were not used for these two compounds; however, acceptable analytical data were acquired (Table 4).
65
300
350
400
460 WAVELENGTH
500
5io
600’
(nm)
FIG. 1. RTF (-) and RTP (- - -) emission spectra of 500 ng of B-naphthoflavone adsorbed from an ethanol/PAA/O. 1 M HBr solution onto filter paper. The RTP spectra were obtained at a slightly different sensitivity setting. RTF excitated at 300 nm; RTP excitated at 350 nm.
Overall, good analytical data were obtained for the model compounds adsorbed on the surfaces investigated. The results in Tables 3 and 4 indicate that no one surface gave the optimum RTP and RTF analytical data for every compound studied. Rather, Tables 3 and 4 show that the use of a variety of surfaces provides more information about RTP and RTF from the compounds. For example, if filter paper had been the only surface employed, then data for RTP and RTF from 2-acetonaphthone would not have been obtained. Conditions for a specific surface had to be carefully selected when obtaining RTP and RTF data such that there was no interference from the unwanted luminescence. In many cases through the combined use of RTP and RTF, more useful analytical information was obtained. ACKNOWLEDGMENTS Financial support for this project was provided by the Department of Energy, Division of Basic Energy Sciences, Contract DE-AC0280ER10624. The authors thank S. M. Ramasamy for obtaining the lifetime data for 2-acetonaphthone.
REFERENCES 1. Becker, R. S., “Theory and Interpretation of Fluorescence and Phosphorescence,” pp. 156-167. Wiley, New York, 1969. 2. Dalterio, R. A., and Hurtubise, R. J., Room-temperature phosphorescence of hydroxyl-substituted aromatics adsorbed on solid surfaces. Anal. Chem. 54, 224-228 (1982). 3. Dalterio, R. A., and Hurtubise, R. J., External conditions and interactions in room-temperature phosphorescence of hydroxyl aromatics adsorbed on solid surfaces containing poly(acrylic acid). Anal. Chem. 55, 1084-1089 (1983). 4. Dalterio, R. A., and Hurtubise, R. J., Zeroth and second derivative fluorescence and phosphorescence analysis of mixtures of hydroxyl aromatics adsorbed on filter paper. Anal. Chem. 56, 819-821 (1984). 5. Dalterio, R. A., and Hurtubise, R. J., Second derivative solid surface luminescence analysis of two-component liquid chromatography fractions. Anal. Chem. 56, 1183-1186 (1984).
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6. Dalterio, R. A., and Hurtubise, R. J., Interactions of phosphors and solid supports in room-temperature phosphorescence of aromatic compounds. Anal. Chem. 56, 336-341 (1984). 7. Donkerbroek, J. J., Elzas, J. J., Gooijer, C., Frei, R. W., and Velthorst, N. H., Some aspects of room-temperature phosphorescence in liquid solutions. Talanta 28, 717-723 (1981). 8. Donkerbroek, J. J., Gooier, C., Velthorst, N. H., and Frei, R. W., Sensitized room temperature phosphorescence in liquid solutions with 1,4-dibromonaphthalene and biacetyl as acceptors. Anal. Chem. 54, 891-895 (1982). 9. Ermolaev, V. L., and Terenin, A. N., Intramolecular energy transfer between triplet levels. Sov. Phys. Usp. (Engl. Trunsf.) 3, 423-426 (1960). 10. Ford, C. D., and Hurtubise, R. J., Separation of benzo[flquinoline and phenanthridine from shale oil and characterization by room temperature phosphorescence. Anal. Left. 13(A6), 485-496 (1980). 11. Ford, C. D., and Hurtubise, R. J., Design of a phosphoroscope and the examination of room temperature phosphorescence of nitrogen heterocycles. Anal. Chem. 51, 659-663 (1979). 12. Harbaugh, K. F., O’Donnell, C. M., and Winefordner, J. D., Pulsed source, time resolved phosphorimetry determination of phosphorescence lifetimes. Anal. Chem. 45, 381-382 (1973). 13. Hurtubise, R. J., “Solid Surface Luminescence Analysis: Theory, Instrumentation, Applica-
tions.” Dekker, New York, 1981. 14. Nicholls, C. H., and Leermakers, P. A., Photochemical and spectroscopic properties of organic
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19. 20.
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molecules in adsorbed or other perturbing polar environments. In “Advances in Photochemistry” (J. N. Pitts, Jr., G. S. Hammond, and W. A. Noyes, Jr., eds.), Vol. 8, pp. 315-336. Wiley-Interscience, New York, 1971. O’Donnell, C. M., and Winefordner, J. D., The potential of phosphorescence spectrometry in clinical chemistry-the new generation of instrumentation and methodology. Clin. Chem. 21, 285-299 (1975). Parker, C. A., and Hatchard, C. G., The possibilities of phosphorescence measurement in chemical analysis: tests with a new instrument. Analyst 87, 664-676 (1962). Ramasamy, S. M., and Hurtubise, R. J., Matrix and solvent effects on the room-temperature phosphorescence of nitrogen heterocycles. Anal. Chem. 54, 2477-2481 (1982). Senthilnathan, V. P., and Hurtubise, R. J., Total solid-surface room-temperature luminescence for analysis of mixtures. Anal. Chem. 56, 913-918 (1984). Senthilnathan, V. P., and Hurtubise, R. J., Solid-surface derivative room-temperature luminescence spectrometry of mixtures. Anal. Chim. Actu 170, 177-185 (1985). Senthilnathan, V. P., and Hurtubise, R. J., Room-temperature phosphorescence lifetimes and intensities of p-aminobenzoic acid adsorbed on sodium acetate-sodium chloride mixtures. And. Chem. 57, 1227-1230 (1985). Senthilnathan, V. P., Ramasamy, S. M., and Hurtubise, R. J., Effects of polyacrylic acid on the room-temperature phosphorescence of selected compounds. Anal. Chim. Actu 157, 203-206 (1984).
22. Skrilec, M., and Cline Love, L. J., Room temperature phosphorescence characteristics of substituted arenes in aqueous thallium lauryl sulfate micelles. Anal. Chem. 52, 1559-1564 (1980). 23. Vo-Dinh, T., “Room Temperature Phosphorimetry for Chemical Analysis.” Wiley-Interscience, New York, 1984.