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Room-temperature luminescence of benzo[f]quinoline, p-aminobenzoic acid, phenanthrene, and 4-phenylphenol on a variety of solid surfaces
MICROCHEMICAL
JOURNAL
39, 33&335 (1989)
Room-Temperature Luminescence of Benzo[flquinoline, p-Aminobenzoic Acid, Phenanthrene, and 4-Phenylphenol Variety of Solid Surfaces BARBARA B. PURDY Chemistry
Department,
on a
ANDROBERT J. HURTUBISE'
University
of Wyoming, Laramie,
Wyoming 82071
Received January 9, 1989; accepted January 30, 1989 Analytical figures of merit for the room-temperature luminescence of four model compounds with quite different chemical structures were compared. The compounds were adsorbed on four different surfaces that have been employed recently in solid-surface luminescence analysis. The solid materials investigated were silica gel with a polyacrylate binder, filter paper, 1% polyacrylic acid-NaBr, and 80% o-cyclodextrin-NaCl. The experimental conditions were optimized to give enhanced luminescence signals. In some cases, filter paper and 80% a-cyclodextrin-NaCl gave comparable analytical results. However, fflter paper gave the best overall results. 8 1989 Academic press, IN.
Solid-surface room-temperature phosphorescence (RTP) and room-temperature fluorescence (RTF) have become important analytical techniques for trace determination of various organic compounds (1, 2). The interactions responsible for solid-surface RTP, in particular, have not been fully developed. However, the physical aspects and analytical considerations of RTP have been reviewed (24). Several authors reported the use of various types of solid surfaces for analytical RTP and RTF. Filter paper has been the most widely used surface to induce RTP from organic compounds. Dalterio and Hurtubise (5) used several spectral techniques to study the interactions of hydroxyl aromatics and aromatic hydrocarbons with filter paper. Ramasamy and Hurtubise (6, 7) studied the effects of temperature on the solid-surface luminescence properties of 4-phenylphenol and benzov]quinoline adsorbed on filter paper. The RTF of nitrogen heterocycles adsorbed on silica gel samples was investigated by Burrell and Hurtubise (8, 9). Also, several polymer-salt mixtures were examined as solid surfaces under different conditions (10, II). A qualitative comparison of conditions for RTP of nitrogen heterocycles and aromatic amines on silica gel, filter paper, and polyacrylic acid (PAA)-salt mixtures were presented by Ramasamy and Hurtubise (12, 23). RTP analysis of phosphors in polyacrylic acid solutions spotted onto filter paper has also been reported (14, 15). Bello and Hurtubise (26-18) showed that several compounds of various sizes and functionalities exhibited RTP and RTF from an a-cyclodextrin-NaCl matrix. Very little work has been done on the comparison of solid surfaces as substrates for inducing RTP and RTF. However, Citta and Hurtubise (14) have compared the RTF and RTP of aromatic carbonyl compounds adsorbed on several solid sur’ To whom correspondence
should be addressed. 330
0026-265X/89 $1.50 Copyright 8 1989 by Academic Press. Inc. All rights of reproduction m any form reserved.
ROOM-TEMPERATURE
LUMINESCENCE
STUDIES
331
faces. In this work, four solid matrices, namely, silica gel, filter paper, polyacrylic acid (PAA)-NaBr mixture, and 80% cw-cyclodextrin (CD)-NaCl mixture, were used to obtain RTP and RTF analytical data for the four model compounds. The model compounds were selected because of their widely different functionalities. The compounds investigated were benzov]quinoline [BV]Q], p-aminobenzoic acid (PABA), phenanthrene, and 4-phenylphenol. EXPERIMENTAL
All RTP and RTF intensity data were obtained with a Schoeffel SD 3000 spectrodensitometer, and details of the instrument were described earlier (10). Reagents
Ethanol was purified by distillation. Absolute methanol (spectra grade, Fisher Scientific) was used as received. PABA, phenanthrene, and 4-phenylphenol (Aldrich Chemical Co.) were recrystallized from distilled ethanol. BV]Q (Gold Label, Aldrich Chemical Co.) was used as received. a-Cyclodextrin hydrate (Aldrich Chemical Co.) and NaCl (AR grade, Baker Chemical Co.) were washed with distilled ethanol prior to use. Polyacrylic acid (secondary standard, Scientific Polymer Products) was used as received; NaBr (AR grade, Aldrich Chemical Co.) was used without further purification. Each polymer-salt mixture was ground to a homogeneous powder in a ball mill. Filter paper (Whatman No. 1) and aluminum-backed silica gel chromatoplates (EM Laboratories) were developed in distilled ethanol to collect impurities at one end. The helium gas (high-purity grade) for use with the 80% cx-CD-NaCl mixture was passed through an Oxytrap (Alltech Associates) to remove oxygen. Procedures
Solutions of the compounds for RTP and RTF measurements were prepared in their respective solvents (Table 3). One-microliter (~1) aliquots of sample solutions were spotted with a lo-~1 Hamilton syringe onto filter paper and silica gel chromatoplate and then dried at 80°C for 30 min, as noted elsewhere (5). The procedure for the adsorption of samples onto 1% PAA-NaBr mixture was described earlier (10). The procedure for the adsorption of samples onto 80% a-CD-NaCl was also described elsewhere (16). On the basis of earlier work (IO, 15,16) the excitation and emission wavelengths used for each compound on the different surfaces are as follows: BMQ, 370 and 510 nm for RTP, 280 nm and UV filter 7-37 for RTF (silica gel and filter paper), 290 and 440 nm (1% PAA-NaBr), 290 nm and UV filter 7-60 (80% a-CDNaCl) for RTF; PABA, 300 and 440 nm for RTP, 295 nm and UV filter 7-60 for RTF; phenanthrene, 300 and 500 nm for RTP, 295 nm and UV filter 7-37 for RTF; 4-phenylphenol, 275 and 480 nm for RTP, 280 nm and UV filter 7-60 for RTF. Background signals were subtracted for the appropriate sample-substrate system.
332
PURDY AND HURTUBISE
RESULTS AND DISCUSSION
Tables 1 and 2 list the limits of detection, percentage relative standard deviations, and linear ranges for the four compounds adsorbed on silica gel which contained a polyacrylate binder, filter paper, 1% PAA-NaBr and 80% a-CIXNaCl for RTF and RTP, respectively. Table 3 lists the solvent systems used to adsorb the model compounds on the different solid surfaces. The experimental conditions used for the compounds adsorbed on 80% a-CD-NaCl were based on earlier work of Bello and Hurtubise (16). Bv]Q is a nitrogen heterocycle which, when protonated, gives favorable RTP and RTF signals (29). For all the surfaces, HBr-ethanol or HBr-methanol solutions were used to provide an acid medium for the protonated form of Bv]Q. With respect to the highest RTP and RTF intensities, the 1% PAA-NaBr surface gave the strongest RTF and RTP signals. The best reproducibility was obtained with the filter paper surface. The lowest limit of detection with RTF was obtained with filter paper, whereas, with RTP, the lowest limits of detection were obtained with both silica gel and 1% PAA-NaBr. The linear range was lower for RTF and RTP on silica gel and filter paper but was the same for RTF and RTP on PAA-NaBr and a-CD-NaCl surfaces. It is notable that for all four surfaces, the RTF signals were stronger than their corresponding RTP signals. PABA is an amino aromatic carboxylic acid, and it gives fairly good RTP and RTF signals from neutral ethanol or methanol solutions on all four surfaces. Ethanol solutions containing dilute HBr or HCl yielded lower RTF and RTP signals and poorer reproducibility than the neutral solutions for PABA adsorbed on the silica gel surface. Filter paper induced the strongest RTP and RTF intensities. The RTF signals were also consistently stronger than the corresponding TABLE 1 RTF Analytical Figures of Merit Surface
BVIQ
PABA
Phenanthrene
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCl
0.75 0.50 2.00 1.50
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCl
RTF percentage relative standard deviation 4.18 2.49 8.26 3.66 3.13 4.51 4.61 5.74 6.15 5.14 4.60 5.59
3.67 3.53 4.23 5.87
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCI
O-40 O-40 O-100 t&100
RTF linear range (ng) CblOO O-80 O-100 0-100
O-100 O-140 O-100 O-140
RTF limit of detection (ng) 0.40 14.0 0.40 0.50 2.00 0.35 0.60 1.50
O-300 O-140 O-100 O-100
4-Phenylphenol 10.0 0.50 4.00 1.50
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STUDIES
TABLE 2 RTP Analytical Figures of Merit Phenanthrene
4-Phenylphenol
Surface
NtlQ
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCl
0.50 2.00 0.50 0.70
8.0 2.50 0.15 0.30
15.0 3.50 0.50 0.10
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCI
RTP percentage relative standard deviation 6.56 5.78 6.71 3.39 5.40 5.09 5.99 5.46 5.78 5.84 6.17 4.81
11.15 5.10 3.81 6.11
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCI
O-80 O-80 o-loo o-loo
PABA
RTP limit of detection (ng) 4.50 0.30 2.50 0.15
RTP linear range (ng) O-80 O-80 0-100 O-80
O-140 O-140 O-100 &lo0
6100 O-140 Cl50 O-200
0 Contained a polyacrylate binder which was necessary for RTP signals (19).
RTP signals. For RTF measurements, the limits of detection were the same for silica gel and filter paper. However, the lowest limit of detection for RTP was obtained on 80% oL-ClSNaCl. The best RTF reproducibility was obtained with silica gel, and filter paper gave the best RTP reproducibility. Phenanthrene is a polycyclic aromatic hydrocarbon which gave different RTP and RTF signals with each type of surface and solvent used. On silica gel, better signals were obtained using 0.1 M HBr-ethanol, than using the following solvents: neutral ethanol, 0.5 M NaOH-ethanol, NaCl-ethanol, NaBr-ethanol, and 0.1 M HCl-NaCkthanol. On filter paper, a neutral ethanol solvent containing 200 ng NaCl/p,l gave the best signals, while on 1% PAA-NaBr and 80% c&D-NaCl, neutral ethanol or methanol was the best solvent to use. The PAA-NaBr surface gave the strongest RTP and RTF signals. Except for the filter paper surface, all the RTP signals were stronger than the corresponding RTF signals. The heavy atom effect was important in enhancing the RTP of phenanthrene. The best reproTABLE 3 Solutions Used for Adsorbing Samples on the Solid Surfaces Surface
WIQ
PABA
Phenanthrene
4-Phenylphenol
Silica gel Filter paper 1% PA A-NaBr 80% a-CD-NaCI
0.1 M HBr-EtOH” 0.1 M HBr-EtOH 0.1 M HBr-EtOH 0.001 M HBr-MeOHb
EtOH EtOH EtOH MeOH
0.1 M HBr-EtOH 200 ng NaCl-EtOH EtOH MeOH
0.1 M HBr-EtOH 200 ng NaCl-EtOH EtOH MeOH
0 EtOH represents ethanol. b MeOH represents methanol
334
PURDY
AND
HURTUBISE
ducibility was obtained using filter paper as a surface, and the lowest limit of detection was obtained on PAA-NaBr surface. The corresponding RTP and RTF linear ranges were the same for filter paper, PAA-NaBr, and (r-CD-NaCl surfaces. 4-Phenylphenol gave different RTP and RTF intensities for each surface and solvent used. On the silica gel surface, stronger signals were obtained using 0.1 M HBr-ethanol than using the solvents 0.5 M NaOH-ethanol, NaCl-ethanol, NaBrethanol, and 0.1 M HCl-NaCl-ethanol. On filter paper, a neutral ethanol solvent containing 200 ng NaCl/p,l yielded the best signal, while neutral ethanol or methanol solvents gave the best signal for 1% PAA-NaBr and 80% a-CD-NaCl. Again, the heavy atom effect played a role in enhancing the RTP of 4-phenylphenol. The PAA-NaBr surface gave the highest RTP and RTF intensities. The best RTF reproducibility was obtained with filter paper and, for RTP, PAA-NaBr gave the best reproducibility. The lowest limit of detection was obtained with a-CD-NaCl for RTP, and for RTF the lowest limit of detection was obtained with filter paper. A variety of linear ranges was obtained for RTF and RTP from the different surfaces. Under the experimental conditions used, silica gel and filter paper surfaces gave lower background readings than 1% PAA-NaBr and 80% a-CD-NaCl surfaces. With respect to sample preparation, silica gel and filter paper surfaces were easier to work with and allowed quicker sample preparation than (w-CwNaCl and PAANaBr powder mixtures, The transfer of the powder mixtures to the sample holder also affected the reproducibility. However, the overall average reproducibility for the four samples on filter paper was 3.71%, whereas on 80% u-CD-NaCl the overall average RTF reproducibility was 3.83%. Thus, the RTF reproducibility for 80% (w-CD-NaCl is close to that of filter paper. Filter paper gave the best overall average RTF reproducibility. In addition, filter paper gave the best overall average RTP reproducibility (4.75%). For limits of detection, filter paper gave the lowest overall average RTF limit of detection (0.48 ng), and 80% a-CD-NaCl gave the lowest overall average RTP limit of detection (0.31 ng). In summary, of the four surfaces investigated, tilter paper and 80% o-CD-NaCl showed the better analytical figures of merit. The use of 80% c&D-NaCl involves more sample preparation time; however, it gave the lowest average limits of detection for RTP. Another advantage of 80% a-CD-NaCl over filter paper is that its luminescence emission bands are frequently better defined. ACKNOWLEDGMENT Financial support for this project was provided by the Department of Energy, Division of Basic Energy Sciences, Grant DE-FG02-86ER13547.
REFERENCES I. Hurtubise, R, J., Solid Surface Luminescence Analysis: Theory, Instrumentation, Applications. Dekker, New York, 1981. 2. Vo-Dinh, T., Room Temperature Phosphorimetry for Chemical Analysis. Wiley-Interscience, New York, 1984. 3. Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chim. Acta, 1980, 119, 189-205. 4. Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chim. Acta, 1980, 120, 1-17.
ROOM-TEMPERATURE
5. 6. 7. 8. 9. 10. Il. 12. 13. 14. 15. 16. 17. 18. 19.
LUMINESCENCE
STUDIES
335
Dalterio, R. A.; Hurtubise, R. J. Anal. Chem., 1984, 56, 336-341. Ramasamy, S. M.; Hurtubise, R. J. Talanta, in press. Ramasamy, S. M.; Hurtubise, R. J. Appl. Spectrosc., in press. Burrell, G. J.; Hurtubise, R. J. Anal. Chem., 1987, 59, 965-970. Burrell, G. J.; Hurtubise, R. J. Anal. Chem., 1988, 60, X4-568. Dalterio, R. A.; Hurtubise, R. J. Anal. Chem., 1982, 54, 224-228. Dalterio, R. A.; Hurtubise, R. J. Anal. Chem., 1983, 55, 1084-1089. Ramasamy, S. M.; Hurtubise, R. J. Anal. Chem., 1982, 54, 1642-1644. Ramasamy, S. M; Hurtubise, R. J. Anal. Gem., 1982, 54, 2477-2481. Citta, L. A.; Hurtubise, R. J. Microchem. J., 1986, 34, 56-66. Senthilnathan, V. P.; Ramasamy, S. M.; Hurtubise, R. J. Anal. Chim. Acta, 1984, 157, 203-206. Bello, J. M.; Hurtubise, R. J. Anal. Lett., 1986, 19, 775-796. Bello, J. M.; Hurtubise, R. J. Appl. Spectrosc., 1986, 40, 790-794. Bello, J. M.; Hurtubise, R. J. Anal. Chem., 1988, 60, 1291-1296. Ford, C. D.; Hurtubise, R. J. Anal. Chem., 1980, 52, 656-662.
JOURNAL
39, 33&335 (1989)
Room-Temperature Luminescence of Benzo[flquinoline, p-Aminobenzoic Acid, Phenanthrene, and 4-Phenylphenol Variety of Solid Surfaces BARBARA B. PURDY Chemistry
Department,
on a
ANDROBERT J. HURTUBISE'
University
of Wyoming, Laramie,
Wyoming 82071
Received January 9, 1989; accepted January 30, 1989 Analytical figures of merit for the room-temperature luminescence of four model compounds with quite different chemical structures were compared. The compounds were adsorbed on four different surfaces that have been employed recently in solid-surface luminescence analysis. The solid materials investigated were silica gel with a polyacrylate binder, filter paper, 1% polyacrylic acid-NaBr, and 80% o-cyclodextrin-NaCl. The experimental conditions were optimized to give enhanced luminescence signals. In some cases, filter paper and 80% a-cyclodextrin-NaCl gave comparable analytical results. However, fflter paper gave the best overall results. 8 1989 Academic press, IN.
Solid-surface room-temperature phosphorescence (RTP) and room-temperature fluorescence (RTF) have become important analytical techniques for trace determination of various organic compounds (1, 2). The interactions responsible for solid-surface RTP, in particular, have not been fully developed. However, the physical aspects and analytical considerations of RTP have been reviewed (24). Several authors reported the use of various types of solid surfaces for analytical RTP and RTF. Filter paper has been the most widely used surface to induce RTP from organic compounds. Dalterio and Hurtubise (5) used several spectral techniques to study the interactions of hydroxyl aromatics and aromatic hydrocarbons with filter paper. Ramasamy and Hurtubise (6, 7) studied the effects of temperature on the solid-surface luminescence properties of 4-phenylphenol and benzov]quinoline adsorbed on filter paper. The RTF of nitrogen heterocycles adsorbed on silica gel samples was investigated by Burrell and Hurtubise (8, 9). Also, several polymer-salt mixtures were examined as solid surfaces under different conditions (10, II). A qualitative comparison of conditions for RTP of nitrogen heterocycles and aromatic amines on silica gel, filter paper, and polyacrylic acid (PAA)-salt mixtures were presented by Ramasamy and Hurtubise (12, 23). RTP analysis of phosphors in polyacrylic acid solutions spotted onto filter paper has also been reported (14, 15). Bello and Hurtubise (26-18) showed that several compounds of various sizes and functionalities exhibited RTP and RTF from an a-cyclodextrin-NaCl matrix. Very little work has been done on the comparison of solid surfaces as substrates for inducing RTP and RTF. However, Citta and Hurtubise (14) have compared the RTF and RTP of aromatic carbonyl compounds adsorbed on several solid sur’ To whom correspondence
should be addressed. 330
0026-265X/89 $1.50 Copyright 8 1989 by Academic Press. Inc. All rights of reproduction m any form reserved.
ROOM-TEMPERATURE
LUMINESCENCE
STUDIES
331
faces. In this work, four solid matrices, namely, silica gel, filter paper, polyacrylic acid (PAA)-NaBr mixture, and 80% cw-cyclodextrin (CD)-NaCl mixture, were used to obtain RTP and RTF analytical data for the four model compounds. The model compounds were selected because of their widely different functionalities. The compounds investigated were benzov]quinoline [BV]Q], p-aminobenzoic acid (PABA), phenanthrene, and 4-phenylphenol. EXPERIMENTAL
All RTP and RTF intensity data were obtained with a Schoeffel SD 3000 spectrodensitometer, and details of the instrument were described earlier (10). Reagents
Ethanol was purified by distillation. Absolute methanol (spectra grade, Fisher Scientific) was used as received. PABA, phenanthrene, and 4-phenylphenol (Aldrich Chemical Co.) were recrystallized from distilled ethanol. BV]Q (Gold Label, Aldrich Chemical Co.) was used as received. a-Cyclodextrin hydrate (Aldrich Chemical Co.) and NaCl (AR grade, Baker Chemical Co.) were washed with distilled ethanol prior to use. Polyacrylic acid (secondary standard, Scientific Polymer Products) was used as received; NaBr (AR grade, Aldrich Chemical Co.) was used without further purification. Each polymer-salt mixture was ground to a homogeneous powder in a ball mill. Filter paper (Whatman No. 1) and aluminum-backed silica gel chromatoplates (EM Laboratories) were developed in distilled ethanol to collect impurities at one end. The helium gas (high-purity grade) for use with the 80% cx-CD-NaCl mixture was passed through an Oxytrap (Alltech Associates) to remove oxygen. Procedures
Solutions of the compounds for RTP and RTF measurements were prepared in their respective solvents (Table 3). One-microliter (~1) aliquots of sample solutions were spotted with a lo-~1 Hamilton syringe onto filter paper and silica gel chromatoplate and then dried at 80°C for 30 min, as noted elsewhere (5). The procedure for the adsorption of samples onto 1% PAA-NaBr mixture was described earlier (10). The procedure for the adsorption of samples onto 80% a-CD-NaCl was also described elsewhere (16). On the basis of earlier work (IO, 15,16) the excitation and emission wavelengths used for each compound on the different surfaces are as follows: BMQ, 370 and 510 nm for RTP, 280 nm and UV filter 7-37 for RTF (silica gel and filter paper), 290 and 440 nm (1% PAA-NaBr), 290 nm and UV filter 7-60 (80% a-CDNaCl) for RTF; PABA, 300 and 440 nm for RTP, 295 nm and UV filter 7-60 for RTF; phenanthrene, 300 and 500 nm for RTP, 295 nm and UV filter 7-37 for RTF; 4-phenylphenol, 275 and 480 nm for RTP, 280 nm and UV filter 7-60 for RTF. Background signals were subtracted for the appropriate sample-substrate system.
332
PURDY AND HURTUBISE
RESULTS AND DISCUSSION
Tables 1 and 2 list the limits of detection, percentage relative standard deviations, and linear ranges for the four compounds adsorbed on silica gel which contained a polyacrylate binder, filter paper, 1% PAA-NaBr and 80% a-CIXNaCl for RTF and RTP, respectively. Table 3 lists the solvent systems used to adsorb the model compounds on the different solid surfaces. The experimental conditions used for the compounds adsorbed on 80% a-CD-NaCl were based on earlier work of Bello and Hurtubise (16). Bv]Q is a nitrogen heterocycle which, when protonated, gives favorable RTP and RTF signals (29). For all the surfaces, HBr-ethanol or HBr-methanol solutions were used to provide an acid medium for the protonated form of Bv]Q. With respect to the highest RTP and RTF intensities, the 1% PAA-NaBr surface gave the strongest RTF and RTP signals. The best reproducibility was obtained with the filter paper surface. The lowest limit of detection with RTF was obtained with filter paper, whereas, with RTP, the lowest limits of detection were obtained with both silica gel and 1% PAA-NaBr. The linear range was lower for RTF and RTP on silica gel and filter paper but was the same for RTF and RTP on PAA-NaBr and a-CD-NaCl surfaces. It is notable that for all four surfaces, the RTF signals were stronger than their corresponding RTP signals. PABA is an amino aromatic carboxylic acid, and it gives fairly good RTP and RTF signals from neutral ethanol or methanol solutions on all four surfaces. Ethanol solutions containing dilute HBr or HCl yielded lower RTF and RTP signals and poorer reproducibility than the neutral solutions for PABA adsorbed on the silica gel surface. Filter paper induced the strongest RTP and RTF intensities. The RTF signals were also consistently stronger than the corresponding TABLE 1 RTF Analytical Figures of Merit Surface
BVIQ
PABA
Phenanthrene
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCl
0.75 0.50 2.00 1.50
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCl
RTF percentage relative standard deviation 4.18 2.49 8.26 3.66 3.13 4.51 4.61 5.74 6.15 5.14 4.60 5.59
3.67 3.53 4.23 5.87
Silica gel Filter paper 1% PAA-NaBr 80% a-CD-NaCI
O-40 O-40 O-100 t&100
RTF linear range (ng) CblOO O-80 O-100 0-100
O-100 O-140 O-100 O-140
RTF limit of detection (ng) 0.40 14.0 0.40 0.50 2.00 0.35 0.60 1.50
O-300 O-140 O-100 O-100
4-Phenylphenol 10.0 0.50 4.00 1.50
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STUDIES
TABLE 2 RTP Analytical Figures of Merit Phenanthrene
4-Phenylphenol
Surface
NtlQ
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCl
0.50 2.00 0.50 0.70
8.0 2.50 0.15 0.30
15.0 3.50 0.50 0.10
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCI
RTP percentage relative standard deviation 6.56 5.78 6.71 3.39 5.40 5.09 5.99 5.46 5.78 5.84 6.17 4.81
11.15 5.10 3.81 6.11
Silica gel” Filter paper 1% PAA-NaBr 80% a-CD-NaCI
O-80 O-80 o-loo o-loo
PABA
RTP limit of detection (ng) 4.50 0.30 2.50 0.15
RTP linear range (ng) O-80 O-80 0-100 O-80
O-140 O-140 O-100 &lo0
6100 O-140 Cl50 O-200
0 Contained a polyacrylate binder which was necessary for RTP signals (19).
RTP signals. For RTF measurements, the limits of detection were the same for silica gel and filter paper. However, the lowest limit of detection for RTP was obtained on 80% oL-ClSNaCl. The best RTF reproducibility was obtained with silica gel, and filter paper gave the best RTP reproducibility. Phenanthrene is a polycyclic aromatic hydrocarbon which gave different RTP and RTF signals with each type of surface and solvent used. On silica gel, better signals were obtained using 0.1 M HBr-ethanol, than using the following solvents: neutral ethanol, 0.5 M NaOH-ethanol, NaCl-ethanol, NaBr-ethanol, and 0.1 M HCl-NaCkthanol. On filter paper, a neutral ethanol solvent containing 200 ng NaCl/p,l gave the best signals, while on 1% PAA-NaBr and 80% c&D-NaCl, neutral ethanol or methanol was the best solvent to use. The PAA-NaBr surface gave the strongest RTP and RTF signals. Except for the filter paper surface, all the RTP signals were stronger than the corresponding RTF signals. The heavy atom effect was important in enhancing the RTP of phenanthrene. The best reproTABLE 3 Solutions Used for Adsorbing Samples on the Solid Surfaces Surface
WIQ
PABA
Phenanthrene
4-Phenylphenol
Silica gel Filter paper 1% PA A-NaBr 80% a-CD-NaCI
0.1 M HBr-EtOH” 0.1 M HBr-EtOH 0.1 M HBr-EtOH 0.001 M HBr-MeOHb
EtOH EtOH EtOH MeOH
0.1 M HBr-EtOH 200 ng NaCl-EtOH EtOH MeOH
0.1 M HBr-EtOH 200 ng NaCl-EtOH EtOH MeOH
0 EtOH represents ethanol. b MeOH represents methanol
334
PURDY
AND
HURTUBISE
ducibility was obtained using filter paper as a surface, and the lowest limit of detection was obtained on PAA-NaBr surface. The corresponding RTP and RTF linear ranges were the same for filter paper, PAA-NaBr, and (r-CD-NaCl surfaces. 4-Phenylphenol gave different RTP and RTF intensities for each surface and solvent used. On the silica gel surface, stronger signals were obtained using 0.1 M HBr-ethanol than using the solvents 0.5 M NaOH-ethanol, NaCl-ethanol, NaBrethanol, and 0.1 M HCl-NaCl-ethanol. On filter paper, a neutral ethanol solvent containing 200 ng NaCl/p,l yielded the best signal, while neutral ethanol or methanol solvents gave the best signal for 1% PAA-NaBr and 80% a-CD-NaCl. Again, the heavy atom effect played a role in enhancing the RTP of 4-phenylphenol. The PAA-NaBr surface gave the highest RTP and RTF intensities. The best RTF reproducibility was obtained with filter paper and, for RTP, PAA-NaBr gave the best reproducibility. The lowest limit of detection was obtained with a-CD-NaCl for RTP, and for RTF the lowest limit of detection was obtained with filter paper. A variety of linear ranges was obtained for RTF and RTP from the different surfaces. Under the experimental conditions used, silica gel and filter paper surfaces gave lower background readings than 1% PAA-NaBr and 80% a-CD-NaCl surfaces. With respect to sample preparation, silica gel and filter paper surfaces were easier to work with and allowed quicker sample preparation than (w-CwNaCl and PAANaBr powder mixtures, The transfer of the powder mixtures to the sample holder also affected the reproducibility. However, the overall average reproducibility for the four samples on filter paper was 3.71%, whereas on 80% u-CD-NaCl the overall average RTF reproducibility was 3.83%. Thus, the RTF reproducibility for 80% (w-CD-NaCl is close to that of filter paper. Filter paper gave the best overall average RTF reproducibility. In addition, filter paper gave the best overall average RTP reproducibility (4.75%). For limits of detection, filter paper gave the lowest overall average RTF limit of detection (0.48 ng), and 80% a-CD-NaCl gave the lowest overall average RTP limit of detection (0.31 ng). In summary, of the four surfaces investigated, tilter paper and 80% o-CD-NaCl showed the better analytical figures of merit. The use of 80% c&D-NaCl involves more sample preparation time; however, it gave the lowest average limits of detection for RTP. Another advantage of 80% a-CD-NaCl over filter paper is that its luminescence emission bands are frequently better defined. ACKNOWLEDGMENT Financial support for this project was provided by the Department of Energy, Division of Basic Energy Sciences, Grant DE-FG02-86ER13547.
REFERENCES I. Hurtubise, R, J., Solid Surface Luminescence Analysis: Theory, Instrumentation, Applications. Dekker, New York, 1981. 2. Vo-Dinh, T., Room Temperature Phosphorimetry for Chemical Analysis. Wiley-Interscience, New York, 1984. 3. Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chim. Acta, 1980, 119, 189-205. 4. Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chim. Acta, 1980, 120, 1-17.
ROOM-TEMPERATURE
5. 6. 7. 8. 9. 10. Il. 12. 13. 14. 15. 16. 17. 18. 19.
LUMINESCENCE
STUDIES
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