Chapter 9
Applications and Interactions in Solid-Surface Luminescence Analysis
Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0383.ch009
Robert J. Hurtubise, S. M. Ramasamy, Job M. Bello, Greg J. Burrell, and Linda A. Citta Chemistry Department, University of Wyoming, Laramie, WY 82071 Solid-surface room-temperature phosphorescence (RTP) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTP are only partly understood. To clarify some of the interactions re quired for strong RTP, organic compounds adsorbed on several surfaces are being studied. Fluorescence quan tum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodium acetate-sodium chlo ride mixtures and on α-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet forma tion efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTP from organic compounds adsorbed on sodium acetate-sodium chloride and α-cyclodextrin -sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid -surface luminescence analysis. S o l i d - s u r f a c e luminescence a n a l y s i s i n v o l v e s the measurement o f f l u o r e s c e n c e and phosphorescence o f o r g a n i c compounds adsorbed on s o l i d materials. S e v e r a l s o l i d m a t r i c e s such as f i l t e r p a p e r , s i l i c a w i t h a p o l y a c r y l a t e b i n d e r , sodium a c e t a t e , and c y c l o d e x t r i n s have been used i n t r a c e o r g a n i c a n a l y s i s . Recent monographs have c o n s i d e r e d the d e t a i l s o f s o l i d - s u r f a c e luminescence a n a l y s i s ( 2 , 2 ) . Solids u r f a c e room-temperature f l u o r e s c e n c e (RTF) has been used f o r s e v e r a l years i n organic trace a n a l y s i s . However, s o l i d - s u r f a c e roomtemperature phosphorescence (RTP) i s a r e l a t i v e l y new t e c h n i q u e , and the e x p e r i m e n t a l c o n d i t i o n s f o r RTP are more c r i t i c a l t h a n f o r RTF. I n a d d i t i o n , the fundamental i n t e r a c t i o n s needed f o r RTP a r e o n l y 0097-6156/89/0383-0155$06.00/0 c 1989 American Chemical Society
Goldberg; Luminescence Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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156
LUMINESCENCE APPLICATIONS
p a r t l y understood. Von Wandruszka and H u r t u b i s e (3) employed s e v e r a l s p e c t r a l t e c h n i q u e s t o show t h a t the a n i o n o f p - a m i n o b e n z o i c a c i d was h e l d by two sodium a c e t a t e m o l e c u l e s , w h i c h was one a s p e c t t h a t a l l o w e d RTP t o be d e t e c t e d . The RTP l i f e t i m e s and the i n t e n s i t i e s o f the a n i o n o f p - a m i n o b e n z o i c a c i d absorbed on sodium a c e t a t e - s o d i u m c h l o r i d e m i x t u r e s were a l s o i n v e s t i g a t e d ( 4 ) . S h o r t - and l o n g d e c a y i n g phosphorescent components were observed from the a n i o n adsorbed on sodium a c e t a t e and on sodium a c e t a t e - s o d i u m c h l o r i d e mixtures. F i l t e r paper has been used e x t e n s i v e l y as a m a t r i x t o o b t a i n RTP from o r g a n i c compounds. N e v e r t h e l e s s , l i t t l e i s known about the i n t e r a c t i o n s t h a t cause RTP from o r g a n i c compounds adsorbed on f i l t e r paper. Schulman and P a r k e r (5) p o s t u l a t e d t h a t hydrogen bonding o f i o n i c o r g a n i c m o l e c u l e s t o h y d r o x y l groups o f the f i l t e r paper was the main i n t e r a c t i o n w h i c h p r o v i d e d a r i g i d sample m a t r i x f o r RTP. Lue-Yen Bower and Winefordner (6) r e p o r t e d t h a t RTP by the heavy-atom e f f e c t f o r a r o m a t i c hydrocarbons adsorbed on f i l t e r paper was caused by s i l v e r i o n f o r m i n g a π - c o m p l e x w i t h the 7 t - e l e c t r o n c l o u d o f the aromatic hydrocarbons. Andino e t a l . (7) employed X - r a y p h o t o e l e c t r o n s p e c t r o s c o p y t o u n d e r s t a n d the s u r f a c e p r o c e s s e s i n RTP where heavy-atom i o n s were u s e d . They commented t h a t the e x t e n t o f p e n e t r a t i o n o f the heavy atom o r i o n s appeared t o exceed t h a t o f the o r g a n i c compound. I f the f i l t e r paper i s packed w i t h s a l t s o r s u g a r s , the m a t r i x can h o l d the phosphor r i g i d , and r e l a t i v e l y s t r o n g RTP s i g n a l s can be o b t a i n e d ( 8 ) . McAleese and Dunlap (9) c o n s i d e r e d a m a t r i x - i s o l a t i o n mechanism f o r RTP from c e l l u l o s e paper samples which was based on the s w e l l i n g p r o p e r t y o f c e l l u l o s e i n the presence of s t r o n g l y p o l a r s o l v e n t s . F o r example, a f t e r the m a t r i x was d r i e d , the m o l e c u l e s became t r a p p e d between c e l l u l o s e c h a i n s , and t h i s p e r m i t t e d the n e c e s s a r y r i g i d i t y f o r the phosphor. I n o t h e r work, D a l t e r i o and H u r t u b i s e (10) used s e v e r a l s p e c t r a l t e c h n i q u e s and showed t h a t s e v e r a l hydrogen-bonding i n t e r a c t i o n s c o u l d o c c u r between phosphors and f i l t e r p a p e r . Ramasamy and H u r t u b i s e ( I I ) i n v e s t i g a t e d the e f f e c t s o f temperature on the RTF and RTP p r o p e r t i e s o f the a n i o n of p - a m i n o b e n z o i c a c i d adsorbed on sodium a c e t a t e . T h e i r r e s u l t s supported a r i g i d l y h e l d mechanism f o r the RTP o f the a n i o n o f p - a m i n o b e n z o i c a c i d adsorbed on sodium a c e t a t e . I n l a t e r work, they s t u d i e d the room-temperature luminescence p r o p e r t i e s o f the a n i o n o f p - a m i n o b e n z o i c a c i d adsorbed on sodium a c e t a t e - s o d i u m c h l o r i d e m i x t u r e s ( 1 2 ) . The r e s u l t s r e v e a l e d t h a t s e v e r a l f a c t o r s were i m p o r t a n t f o r maximum RTP from t h i s a n i o n . Short
Historical
Survey
S a w i c k i (13) used s o l i d - s u r f a c e f l u o r e s c e n c e t e c h n i q u e s e x t e n s i v e l y i n the I 9 6 0 ' s f o r a i r p o l l u t i o n r e s e a r c h . I n 1967, R o t h (14) r e p o r t e d the RTP o f s e v e r a l p h a r m a c e u t i c a l s adsorbed on f i l t e r p a p e r . Schulman and W a l l i n g (15) showed t h a t s e v e r a l o r g a n i c compounds gave RTP when adsorbed on f i l t e r p a p e r . P a y n t e r e t a l . (16) r e p o r t e d the f i r s t d e t a i l e d a n a l y t i c a l data f o r RTP and gave l i m i t s o f d e t e c t i o n , l i n e a r dynamic r a n g e s , and r e p r o d u c i b i l i t i e s f o r the compounds. S i n c e p u b l i c a t i o n o f these two s t u d i e s (15,16), s e v e r a l r e s e a r c h e r s have used s o l i d - s u r f a c e luminescence a n a l y s i s i n t r a c e o r g a n i c analysis (1,2).
Goldberg; Luminescence Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0383.ch009
9.
HURTUBISE ET AL.
Solid-Surface Luminescence Analysis
157
Recent Uses of Solid-Surface Luminescence Analysis in Environmental Analysis. V o - D i n h and coworkers have shown v e r y e f f e c t i v e l y how s o l i d - s u r f a c e luminescence t e c h n i q u e s can be used f o r e n v i r o n m e n t a l l y i m p o r t a n t samples ( 2 7 - 2 2 ) . RTP has been used f o r the s c r e e n i n g of ambient a i r p a r t i c u l a t e samples ( 2 7 , 2 8 ) . I n a d d i t i o n , RTP has been employed i n c o n j u n c t i o n w i t h a r a n k i n g i n d e x t o c h a r a c t e r i z e p o l y n u c l e a r a r o m a t i c p o l l u t a n t s i n e n v i r o n m e n t a l samples ( 2 9 ) . A unique a p p l i c a t i o n o f RTP r e p o r t e d r e c e n t l y i s a p e r s o n a l d o s i m e t e r badge based on m o l e c u l a r d i f f u s i o n and d i r e c t d e t e c t i o n by RTP o f p o l y n u c l e a r a r o m a t i c p o l l u t a n t s ( 2 0 ) . The d o s i m e t e r i s a p e n - s i z e d e v i c e t h a t does n o t r e q u i r e sample e x t r a c t i o n p r i o r t o a n a l y s i s . The d o s i m e t e r can d e t e c t v a r i o u s p o l y n u c l e a r a r o m a t i c s a t the ppb l e v e l a f t e r 1 hour o f e x p o s u r e . I t has been shown t h a t the RTP o f a z a - a r e n e s can be enhanced by u s i n g m e r c u r y ( I I ) c h l o r i d e as a heavy atom ( 2 2 ) . A l s o , s e n s i t i z e d f l u o r e s c e n c e s p e c t r o m e t r y w i t h a s o l i d o r g a n i c s u b s t r a t e can be used t o d e t e c t t r a c e amounts o f p o l y n u c l e a r a r o m a t i c compounds ( 2 2 ) . Experimental
Considerations
S e v e r a l s o l i d s u r f a c e s , such as f i l t e r p a p e r , sodium a c e t a t e , and s i l i c a g e l c h r o m a t o p l a t e s w i t h a p o l y a c r y l a t e b i n d e r , have been used i n s o l i d - s u r f a c e luminescence work ( 2 , 2 ) . E x p e r i m e n t a l l y i t i s r e l a t i v e l y easy t o p r e p a r e samples f o r a n a l y s i s . W i t h f i l t e r p a p e r , f o r example, a s m a l l volume o f sample s o l u t i o n i s s p o t t e d onto the s u r f a c e , the f i l t e r paper i s d r i e d , and t h e n the measurement i s made. In many c a s e s , an i n e r t gas i s passed o v e r the s u r f a c e d u r i n g the measurement s t e p t o enhance the RTP s i g n a l . F o r powdered samples, the sample p r e p a r a t i o n procedure i s somewhat more i n v o l v e d . Com m e r c i a l i n s t r u m e n t s can be r e a d i l y used t o measure the luminescence s i g n a l s , and a v a r i e t y o f r e s e a r c h i n s t r u m e n t s have been developed t o o b t a i n the s o l i d - s u r f a c e luminescence data ( 2 , 2 ) . Solid-Surface Luminescence with α-Cyclodextrin-NaCl Mixtures. I t was r e c e n t l y r e p o r t e d t h a t an 80% O f - c y c l o d e x t r i n - N a C l m i x t u r e c o u l d be employed as a m a t r i x t o o b t a i n RTF and RTP a n a l y t i c a l data (23,24). C y c l o d e x t r i n s are c y c l i c o l i g o s a c c h a r i d e s c o n s t r u c t e d from a - ( 1 , 4 ) l i n k e d glucose u n i t s arranged i n a t o r u s . C y c l o d e x t r i n s have been shown t o form i n c l u s i o n compounds w i t h m o l e c u l e s t h a t f i t i n t o t h e i r h y d r o p h o b i c c a v i t y ( 2 5 ) . They are c o m m e r c i a l l y a v a i l a b l e as α - , β - , and v - c y c l o d e x t r i n s , and r e s e a r c h e r s have shown t h a t they have many uses (25,26). I n t h i s work, we showed t h a t i t was r e l a t i v e l y easy t o d e t e c t nanogram amounts o f m i x t u r e s o f b e n z o ( a ) p y r e n e and b e n z o ( e ) p y r e n e u s i n g RTF and RTP. I t was found t h a t b e n z o ( a ) p y r e n e gave RTF on 80% α - c y c l o d e x t r i n - N a C l , whereas benzo(e)pyrene gave b o t h RTF and RTP on the m i x t u r e . A l s o , the RTF i n t e n s i t y o f b e n z o ( e ) p y rene was 16 times l e s s than the RTF i n t e n s i t y o f b e n z o ( a ) p y r e n e . F i g u r e l a shows the RTF e m i s s i o n s p e c t r a f o r s e v e r a l m i x t u r e s o f benzo(a)pyrene and benzo(e)pyrene adsorbed on 80% a - c y c l o d e x t r i n N a C l , and F i g u r e l b g i v e s a s t a n d a r d RTF e m i s s i o n spectrum f o r benzo(a)pyrene adsorbed on the c y c l o d e x t r i n m a t r i x . As a comparison of the two f i g u r e s shows, b e n z o ( a ) p y r e n e can be r e a d i l y d e t e c t e d i n the presence o f d i f f e r e n t amounts o f b e n z o ( e ) p y r e n e . Figure 2 gives the RTP s p e c t r a f o r benzo(e)pyrene i n the presence o f b e n z o ( a ) p y r e n e .
Goldberg; Luminescence Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
LUMINESCENCE APPLICATIONS
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Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0383.ch009
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