Multidimensional Fluorescence Analysis of Cyclodextrin Solvent

Chapter 10

Multidimensional Fluorescence Analysis of Cyclodextrin Solvent—Extraction Systems Downloaded by GEORGETOWN UNIV on August 26, 2015 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0383.ch010

Lisa A. Blyshak, Gabor Patonay, and Isiah M. Warner Department of Chemistry, Emory University, Atlanta, GA 30322 The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of γ-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules pre sent in a mixture. For example, perylene is ex tracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. I n r e c e n t y e a r s , the a n a l y t i c a l u t i l i t y o f c y c l o d e x t r i n s has become i n c r e a s i n g l y e v i d e n t . These compounds, which a r e c y c l i c o l i g o s a c c h a r i d e s formed from the enzymatic d e g r a d a t i o n o f s t a r c h by b a c t e r i a , have been used i n a v a r i e t y o f a n a l y t i c a l systems. The r e s u l t i n g compounds c o n s i s t o f 6, 7, o r 8 g l u c o p y r a n o s e u n i t s a t t a c h e d by a - 1 , 4 l i n k a g e s , and they a r e r e f e r r e d t o as α - , β - , and γ-cyclodextrins respectively. These homologues a r e t o r u s - s h a p e d and have a r e l a t i v e l y n o n p o l a r i n t e r n a l c a v i t y , w h i c h r e s u l t s from the CI c h a i r c o n f o r m a t i o n o f i n d i v i d u a l g l u c o s e r e s i d u e s and the s p e c i f i c manner i n which the g l u c o s e u n i t s are l i n k e d ( I ) . P r i m a r y and secondary h y d r o x y l groups are l o c a t e d a t the c a v i t y edges, and g l y c o s i d i c oxygen b r i d g e s l i n e the i n t e r i o r o f the c a v i t y as d e p i c t e d i n F i g u r e 1. The p o s i t i o n i n g o f the h y d r o x y l groups enhances c y c l o d e x t r i n s o l u b i l i t y i n w a t e r . The g l y c o s i d i c oxygen b r i d g e s g i v e the c a v i t y a p o l a r i t y w h i c h i s about t h e same as t h a t c

0097-6156/89/0383-0167$06.00A) 1989 American Chemical Society

In Luminescence Applications; Goldberg, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Downloaded by GEORGETOWN UNIV on August 26, 2015 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0383.ch010

LUMINESCENCE APPLICATIONS

The "lining"of the cavity: glycosidic oxygen bridges, high electron density

Edge of secondary hydroxyls

Edge of primary hydroxyls

F i g u r e 1. F u n c t i o n a l s t r u c t u r a l scheme o f c y c l o d e x t r i n s . ( R e p r i n t e d w i t h p e r m i s s i o n from Réf. 1. C o p y r i g h t 1982 Akademiai K i a d o . )


10.

BLYSHAKETAL.

169

Cyclodextrin Solvent-Extraction Systems

of e t h a n o l ( 2 ) . T h i s n e a r l y n o n p o l a r i n t e r n a l environment a l l o w s c y c l o d e x t r i n s t o i n c o r p o r a t e n o n p o l a r s p e c i e s , p r o v i d e d the s i z e s o f the guest and the h o s t are c o m p a t i b l e . Some p e r t i n e n t p h y s i c a l d a t a f o r the c y c l o d e x t r i n s are g i v e n i n T a b l e I .

Table I .

Important C h a r a c t e r i s t i c s

of C y c l o d e x t r i n s

3

Type o f C y c l o d e x t r i n Parameter


α

Diameter o f c a v i t y (Â) Volume o f c a v i t y ( Â ) Number o f water m o l e c u l e s t a k e n up by c a v i t y . ^ D i f f u s i o n c o n s t a n t a t 40°C C r y s t a l form (from 60% a q . isopropanol). 3

S o l u b i l i t y i n water (g/100 mL at 25°C). Molecules per u n i t c e l l Water o f c r y s t a l l i z a t i o n (%)

972 4.7-6 176 6 3.443 Hexagonal p l a t e s or blade-shaped needles. 14.5 4 10.2

f R e p r i n t e d w i t h p e r m i s s i o n from Réf. 1. C r a i g , L . C ; P u l l e y , A . 0 . Biochemistry

β

Y

1135 8 346 11

1297 10 510 17

3.224 Monoclinic parallelograms .

3.000 Quadratic p l a t e s or prisms. 23.2

1.85 2 13.2-14.5

1961, 1,

6 8.13-17.7

89.

U n l i k e o t h e r o r g a n i z e d media such as m i c e l l e s , c y c l o d e x t r i n s are r i g i d m o l e c u l e s . F o r m a t i o n o f complexes w i t h n o n p o l a r m o l e c u l e s i s based on a s t e r e o s e l e c t i v e i n t e r a c t i o n . I n c l u s i o n complexes form i f the s i z e o f the guest m o l e c u l e i s c o m p a t i b l e w i t h the CDx c a v i t y size (1/3). I f the guest i s too l a r g e t o f i t i n s i d e the c a v i t y , no complex w i l l form. In many cases an i n c l u s i o n complex may form i f some hydrophobic p o r t i o n o f the guest i s c o m p a t i b l e w i t h the c a v i t y size. U s u a l l y , the m o l e c u l e o r i e n t s i t s e l f i n o r d e r t o a t t a i n maximum c o n t a c t between the a p o l a r c a v i t y and the h y d r o p h o b i c p o r t i o n s o f the i n c l u d e d m o l e c u l e ( 4 ) . S i d e c h a i n s a f f e c t the degree o f c o m p l e x a t i o n based on t h e i r s i z e and p o l a r i t y . Each o f the t h r e e common c y c l o d e x t r i n s has a c h a r a c t e r i s t i c c a v i t y s i z e due t o the number o f g l u c o s e r e s i d u e s i n the compound, and as a r e s u l t each one i n t e r a c t s t o d i f f e r e n t degrees w i t h m o l e c u l e s o f v a r y i n g dimensions. C o m p l e x a t i o n occurs as a r e s u l t o f s e v e r a l weak i n t e r a c t i o n s , i n c l u d i n g hydrogen b o n d i n g , van der Waals f o r c e s , and h y d r o p h o b i c i n t e r a c t i o n s ; no c o v a l e n t bonds are formed d u r i n g the p r o c e s s ( 3 ) . Another f a c t o r i n f l u e n c i n g complex f o r m a t i o n i s the decrease i n r i n g s t r a i n a f f o r d e d by f o r m a t i o n o f an i n c l u s i o n complex w i t h a n o n p o l a r molecule ( I ) . The i n c l u s i o n p r o c e s s r e l e a s e s h i g h - e n e r g y water from the CDx c a v i t y .



170


C y c l o d e x t r i n s can s o l u b i l i z e h y d r o p h o b i c m o l e c u l e s i n aqueous media t h r o u g h complex f o r m a t i o n ( 5 - 8 ) . A n o n p o l a r s p e c i e s p r e f e r s the p r o t e c t i v e environment o f the CDx c a v i t y t o the b u l k aqueous solvent. I n a d d i t i o n , c y c l o d e x t r i n s c r e a t e a degree o f s t r u c t u r a l r i g i d i t y and m o l e c u l a r o r g a n i z a t i o n f o r the i n c l u d e d s p e c i e s . As a r e s u l t o f t h e s e c h a r a c t e r i s t i c s , t h e s e m a c r o c y c l e s are used i n s t u d i e s o f f l u o r e s c e n c e and phosphorescence enhancement (9-11), s t e r e o s e l e c t i v e c a t a l y s i s (12,13), and r e v e r s e - p h a s e chromatographic s e p a r a t i o n s o f s t r u c t u r a l l y s i m i l a r m o l e c u l e s (14,15). These same complexing a b i l i t i e s make c y c l o d e x t r i n s u s e f u l i n s o l v e n t e x t r a c t i o n . A l t h o u g h aqueous samples may be e a s i l y e x t r a c t e d w i t h a v a r i e t y of o r g a n i c s o l v e n t s (16), samples c o l l e c t e d i n o r g a n i c m a t r i c e s are more d i f f i c u l t t o work w i t h and o f t e n r e q u i r e l e n g t h y sample p r e p a r a tion. One method f o r e x t r a c t i n g o r g a n i c samples i s t h a t o f Rosen and Middletown ( 2 7 ) . T h i s method i s l i m i t e d because i t i s time consuming and r e q u i r e s l a r g e amounts o f s o l v e n t s . An a l t e r n a t i v e t o t h i s t e c h n i q u e p r e s e n t e d by N a t u s c h and Tomkins uses the p o l a r o r g a n i c s o l v e n t d i m e t h y l s u l f o x i d e (DMSO) t o e x t r a c t PAHs from hydrocarbon s o l v e n t ( 2 8 ) . A l t h o u g h DMSO i s u s e f u l f o r s e p a r a t i n g PAHs from n o n p o l a r o r g a n i c s o l v e n t s , s e l e c t i v e i n t e r a c t i o n s w i t h s p e c i f i c compounds are l i m i t e d . Our i n t e r e s t was t o f i n d a p o l a r s o l v e n t w h i c h c o u l d be used t o s e l e c t i v e l y e x t r a c t PAHs from an o r g a n i c - p h a s e m i x t u r e based on a p a r t i c u l a r c h a r a c t e r i s t i c o f the analyte molecules. The method d e s c r i b e d here makes use o f the a b i l i t y o f c y c l o d e x t r i n s t o i n c l u d e m o l e c u l e s based on s t e r e o s e l e c t i v e i n t e r a c t i o n s . In g e n e r a l , a p p r e c i a b l e e x t r a c t i o n o f PAHs i n t o the aqueous phase i s not f e a s i b l e because most PAHs have v e r y low s o l u b i l i t i e s i n water (29,20). The i n t e r e s t i n g f e a t u r e o f t h i s method i s t h a t the use o f an aqueous CDx m o d i f i e r enhances the e x t r a c t i o n o f s e l e c t e d s p e c i e s i n t o the aqueous l a y e r w h i l e r e t a i n i n g o t h e r s p e c i e s i n the b u l k o r g a n i c phase. The e x t r a c t i o n e f f i c i e n c y i s r e l a t e d t o the degree o f CDx c o m p l e x a t i o n and thus t o the s i z e and h y d r o p h o b i c i t y o f the compounds t o be e x t r a c t e d . T h i s method may be p a r t i c u l a r l y u s e f u l f o r s i m p l i f y i n g complex m i x t u r e s o f o r g a n i c m a t e r i a l such as o i l samples o r a i r sample a d s o r b a t e s t h a t are u s u a l l y s o l u b l e i n o r g a n i c solvents. Such samples c o n t a i n a v a r i e t y o f PAHs, w h i c h would make them amenable t o s e p a r a t i o n s by e x t r a c t i o n i n t o an aqueous phase. A few s t u d i e s on the use o f c y c l o d e x t r i n s f o r e x t r a c t i o n have been d e s c r i b e d . Most such e x t r a c t i o n s use s m a l l s o l v e n t volumes and r e q u i r e p r e c i p i t a t i o n o f the complex from the aqueous s o l u t i o n ( 2 2 ) ; then the s o l i d complex must be t r e a t e d w i t h an o r g a n i c s o l v e n t t o remove the guest from the s o l i d m a t r i x (22). A l t h o u g h the reagent volumes are s m a l l i n these e x t r a c t i o n s , the s e p a r a t i o n procedure i s tedious. In c o n v e n t i o n a l s o l v e n t e x t r a c t i o n , a s o l u t e i s p a r t i t i o n e d between two i m m i s c i b l e s o l v e n t s . H e r e , γ-CDx i s used as an aqueous-phase m o d i f i e r t o i n c r e a s e the aqueous s o l u b i l i t i e s o f s e v e r a l PAHs and thus t o i n c r e a s e t h e i r aqueous-phase e x t r a c t i o n efficiencies. I n most c a s e s , the degree o f e x t r a c t i o n depends on the f i t o f the p o t e n t i a l guest i n t o the CDx c a v i t y . Thus, the s t e r e o s e l e c t i v e b e h a v i o r o f t h e s e m a c r o c y c l e s g i v e s them the p o t e n t i a l t o d i s c r i m i n a t e between o r g a n i c - p h a s e s o l u t e s i n an e x t r a c t i o n . A f t e r e x t r a c t i o n , a n a l y t e s o f i n t e r e s t t h a t have been t r a n s f e r r e d t o the aqueous phase may be i d e n t i f i e d w i t h o u t removal from the CDx complex o r may be b a c k - e x t r a c t e d i n t o a s u i t a b l e



10.

BLYSHAKETAL


171

s o l v e n t , such as c y c l o h e x a n e . T h i s t e c h n i q u e i s s i m p l e r than p r e v i o u s CDx e x t r a c t i o n methods because the aqueous-phase complex i s amenable t o a v a r i e t y o f m a n i p u l a t i o n s . The scheme d e s c r i b e d here may enhance e x i s t i n g knowledge o f CDx b e h a v i o r i n two-phase systems and may a l s o s e r v e as a s a m p l e - p r e p a r a t i o n t e c h n i q u e f o r r e v e r s e phase chromatography. In t h i s s t u d y , a γ-CDx m o d i f i e r was used t o e x t r a c t s e v e r a l PAHs as s i n g l e components and t o e x t r a c t s e v e r a l b i n a r y m i x t u r e s . The data were c o l l e c t e d u s i n g f l u o r e s c e n c e measurements, which a l l o w b o t h i d e n t i f i c a t i o n and q u a n t i t a t i o n o f the f l u o r o p h o r e i n s o l v e n t extraction. Important e x p e r i m e n t a l c o n s i d e r a t i o n s such as s o l v e n t c h o i c e , t e m p e r a t u r e , and c o n c e n t r a t i o n s o f the m o d i f i e r and the a n a l y t e s are d i s c u s s e d . The u t i l i t y o f t h i s method as a means o f s i m p l i f y i n g complex PAH m i x t u r e s i s a l s o e v a l u a t e d . In a d d i t i o n , the c o u p l i n g o f c y c l o d e x t r i n - m o d i f i e d s o l v e n t e x t r a c t i o n w i t h luminescence measurements f o r q u a l i t a t i v e e v a l u a t i o n o f components i n m i x t u r e s w i l l be d i s c u s s e d b r i e f l y . Experimental

Section

Reagents. P e r y l e n e was o b t a i n e d from Sigma Chemical Company ( S t . Louis, Missouri). A l l o t h e r PAHs were s u p p l i e d by A l d r i c h Chemical Company ( M i l w a u k e e , W i s c o n s i n ) and were r e p o r t e d t o c o n t a i n l e s s t h a t 3% i m p u r i t i e s . A l l PAHs were used w i t h o u t f u r t h e r p u r i f i c a t i o n . I s o p r o p y l e t h e r (99%) f o r e x t r a c t i o n work was a l s o purchased from Aldrich. Hydroquinone, a f l u o r e s c e n t s t a b i l i z e r p r e s e n t i n the e t h e r , was removed p r i o r t o s o l u t i o n p r e p a r a t i o n by r o t a r y evapo ration. F l u o r o m e t r i c - g r a d e 1-butanol was s u p p l i e d by F i s h e r S c i e n t i f i c Company ( F a i r Lawn, New J e r s e y ) . A l l solutions for extractions of PAHs were p r e p a r e d by e v a p o r a t i n g p o r t i o n s o f a s t o c k c y c l o h e x a n e s o l u t i o n and d i l u t i n g t o the a p p r o p r i a t e volume w i t h i s o p r o p y l e t h e r . F l u o r e s c e n c e measurements were performed on 1:10 d i l u t i o n s o f the s t o c k and f i n a l o r g a n i c phase s o l u t i o n s . The e f f e c t o f d i s s o l v e d CDx on the f l u o r e s c e n c e i n t e n s i t y o f the o r g a n i c phase PAH was m i n i m i z e d by d i l u t i o n w i t h i s o p r o p y l e t h e r . C y c l o d e x t r i n s o l u t i o n f o r e x t r a c t i o n s t u d i e s was p r e p a r e d a t a c o n c e n t r a t i o n o f 1.00 x 10~ if by d i s s o l v i n g s o l i d γ-CDx i n d e i o n i z e d water ( C o n t i n e n t a l Water Systems, A t l a n t a , G e o r g i a ) . F r e s h s o l u t i o n was p r e p a r e d d a i l y t o p r e v e n t b a c t e r i a l growth and CDx d e c o m p o s i t i o n from i n t e r f e r i n g w i t h c o m p l e x a t i o n and e x t r a c t i o n . C y c l o d e x t r i n was purchased from Advanced S e p a r a t i o n T e c h n o l o g i e s , I n c . (Whippany, New J e r s e y ) and was used as r e c e i v e d . S o l i d CDx from one l o t number was used f o r a l l e x t r a c t i o n s . Samples f o r s t u d i e s o f CDx e f f e c t s on f l u o r e s c e n c e enhancement i n o r g a n i c s o l u t i o n were p r e p a r e d u s i n g p y r e n e , because pyrene p o s s e s s e s a l o n g l i f e t i m e and i s v e r y s u s c e p t i b l e t o quenching and enhancement i n s o l u t i o n ( 2 3 ) . An a l i q u o t o f pyrene s t o c k s o l u t i o n i n cyclohexane was p l a c e d under a n i t r o g e n purge t o evaporate the cyclohexane. Samples were r e d i s s o l v e d i n a 1:4 m i x t u r e o f i s o p r o p y l e t h e r and 1 - b u t a n o l , w h i c h was s a t u r a t e d w i t h aqueous CDx s o l u t i o n . Pyrene samples were a l s o p r e p a r e d i n w h i c h the o r g a n i c s o l v e n t was not s a t u r a t e d w i t h CDx s o l u t i o n . The mixed s o l v e n t was used i n o r d e r t o m i n i m i z e the e f f e c t s o f e t h e r e v a p o r a t i o n and thus a l l o w more a c c u r a t e q u a n t i t a t i o n . F l u o r e s c e n c e measurements were made on d i l u t e d samples o f t h e s e s o l u t i o n s . The s o l v e n t used t o make up the 2


172


f i n a l volume f o r the d i l u t i o n s o f b o t h sample types was the mixed solvent. T h i s procedure was f o l l o w e d i n o r d e r t o mimic the c o n d i t i o n s used f o r the p r e p a r a t i o n o f e x t r a c t i o n samples f o r f l u o r e s cence a n a l y s i s . Peak areas o f the r e s u l t i n g f l u o r e s c e n c e s p e c t r a from b o t h s a t u r a t e d and u n s a t u r a t e d samples were compared t o d e t e r mine the e f f e c t o f CDx on PAH f l u o r e s c e n c e i n the o r g a n i c phase. Extraction Procedure and Apparatus. E x t r a c t i o n s were performed by v i g o r o u s l y s h a k i n g e q u a l volumes o f aqueous 1Q~ M v-CDx and 10~ J»f PAH s o l u t i o n s f o r 2 min a t room t e m p e r a t u r e . The two l a y e r s were separated i n a separatory funnel. S i n c e f l u o r e s c e n c e enhancement i s o f t e n observed f o r luminophores i n aquenous CDx m e d i a , f l u o r e s c e n c e measurements were made on the o r g a n i c phase. Fluorescence i n organic media i s not expected t o be s t r o n g l y a f f e c t e d by CDx because o f the g e n e r a l l y low s o l u b i l i t y o f the o l i g o s a c c h a r i d e s i n n o n p o l a r media ( 2 ) . E x t r a c t i o n s were a l s o performed w i t h o u t CDx t o ensure t h a t no a p p r e c i a b l e e x t r a c t i o n o c c u r r e d i n the absence o f CDx. I n a d d i t i o n , an o r g a n i c - p h a s e volume change was noted f o r some e x t r a c t i o n s . These changes are r e f l e c t e d i n the d a t a c a l c u l a t i o n s . To ensure t h a t t o t a l f l u o r e s c e n c e was l i n e a r l y r e l a t e d t o PAH c o n c e n t r a t i o n , b o t h the i n i t i a l 10~ Μ o r g a n i c phase s o l u t i o n and the o r g a n i c phase a f t e r e x t r a c t i o n were d i l u t e d w i t h more o f the i n i t i a l o r g a n i c s o l v e n t t o a c o n c e n t r a t i o n t o 10~ Af b e f o r e measurements were made. T h i s d i l u t i o n d i m i n i s h e s the e f f e c t o f d i s s o l v e d c y c l o d e x t r i n on f l u o r e s c e n c e i n t e n s i t i e s o f PAHs. E x t r a c t i o n e f f i c i e n c i e s were e v a l u a t e d by m o n i t o r i n g the f l u o r e s c e n c e o f the d i l u t e d o r g a n i c samples. Since the f l u o r e s c e n c e peak area i s p r o p o r t i o n a l t o c o n c e n t r a t i o n , peakarea v a l u e s were s u b s t i t u t e d i n t o the e q u a t i o n f o r the d i s t r i b u t i o n r a t i o D: 5


2

5

6

[P] u

=

(1)

—

where [ P ] i s the f i n a l PAH c o n c e n t r a t i o n i n the aqueous phase and A

[P]

q

i s the f i n a l PAH c o n c e n t r a t i o n i n the o r g a n i c phase.

efficiencies

r e p o r t e d here were determined a c c o r d i n g t o the

Extraction equation,

100D

V

=

(2) D + V /V ο w

where D i s the d i s t r i b u t i o n r a t i o , V /V

i s the volume r a t i o o f

the

o r g a n i c and aqueous p h a s e s , and %E i s the p e r c e n t e x t r a c t e d i n t o the aqueous phase. A l l samples were m o n i t o r e d u s i n g a P e r k i n - E l m e r 650-10S Fluorescence Spectrophotometer. F l u o r e s c e n c e e x c i t a t i o n and e m i s s i o n wavelengths f o r the PAHs i n t h i s s t u d y were o b t a i n e d from Berlman ( 2 4 ) . The r e s u l t i n g s p e c t r a were a n a l y z e d u s i n g an Apple 11+ computer by i n t e g r a t i n g peak areas to determine t o t a l changes i n



10.

BLYSHAKETAL.

173


fluorescence. F l u o r e s c e n c e peak areas were used because t o t a l f l u o r e s c e n c e peak areas are i n s e n s i t i v e t o peak s h i f t s and peak r a t i o changes and, t h u s , a c c u r a t e l y r e f l e c t changes i n a n a l y t e concentration. B i n a r y m i x t u r e s o f two PAH s p e c i e s were q u a n t i t a t e d u s i n g f l u o r e s c e n c e i n t e n s i t y measurements i n r e g i o n s o f s o l e e m i s s i o n f o r each compound and comparing t h e s e data t o c a l i b r a t i o n curves a l s o based on f l u o r e s c e n c e i n t e n s i t y a t the wavelengths chosen f o r s o l e e m i s s i o n . The m i x t u r e s q u a n i t a t i v e l y s t u d i e d were a n t h r a c e n e - p e r y l e n e , p y r e n e - p e r y l e n e and p y r e n e - c o r o n e n e . The wavelengths chosen f o r s o l e e m i s s i o n f o r t h e s e s t u d i e s were 385 nm f o r a n t h r a c e n e , 375 nm f o r p y r e n e , 475 nm f o r p e r y l e n e , and 480 nm f o r coronene. S e v e r a l t w o - d i m e n s i o n a l s p e c t r a o f PAH m i x t u r e s were o b t a i n e d u s i n g a v i d i c o n - b a s e d v i d e o f l u o r o m e t e r which p r o v i d e s m u l t i p l e e m i s s i o n s p e c t r a as a f u n c t i o n o f m u l t i p l e e x c i t a t i o n wavelengths ( 2 5 ) . Results

and

Discussion

The e x t r a c t i o n e f f i c i e n c i e s f o r the PAHs s t u d i e d are g i v e n i n T a b l e I I a l o n g w i t h the dimensions o f each PAH. As e x p e c t e d , the l a r g e r PAHs showed l a r g e r e x t r a c t i o n e f f i c i e n c i e s because they c o u l d more a d e q u a t e l y f i l l the 9 . 5 - Â c a v i t y o f γ-CDx. Comparative e x t r a c t i o n s u s i n g pure d e i o n i z e d water r a t h e r t h a n CDx d i d not r e s u l t i n a p p r e c i a b l e e x t r a c t i o n e f f i c i e n c i e s f o r any o f the PAHs s t u d i e d . In the CDx e x t r a c t i o n s , p y r e n e , p e r y l e n e , and coronene were e x t r a c t e d from i s o p r o p y l e t h e r w i t h r e s p e c t i v e e x t r a c t i o n e f f i c i e n c i e s o f 38.2%, 95.1%, and 93.7%. R e l a t i n g t h i s i n f o r m a t i o n t o the r e l a t i v e dimensions o f each compound i n d i c a t e s t h a t the e x t r a c t i o n procedure i s r e l a t e d t o the b u l k i n e s s o f the PAH and the t i g h t n e s s o f i t s f i t i n the CDx c a v i t y . L a r g e , b u l k y guest m o l e c u l e s such as p e r y l e n e and coronene are capable o f f i t t i n g t i g h t l y i n γ-CDx because t h e i r m o l e c u l a r dimensions c l o s e l y approximate the d i a m e t e r o f the c y c l o dextrin. Thus, t h e s e compounds g i v e v e r y l a r g e e x t r a c t i o n efficiencies.

Table I I .

Compound

Anthracene Pyrene Perylene Coronene

E x t r a c t i o n E f f i c i e n c i e s (%) f o r S e v e r a l PAHs u s i n g Cyclodextrin-Modified Extraction Molecular Dimensions (angstroms) 5.0 7.1 9.1 9.2

x x x x

3

%Extracted^

0.60 38.2 95.1 93.7

9.2 8.9 9.2 9.2

± ± ± ±

2.0 1.9 2.6 4.0

E s t i m a t e based on bond l e n g t h s . E x t r a c t e d from i s o p r o p y l e t h e r i n t o 10~ flf γ-CDx. 2

The s m a l l e r m o l e c u l e s do not e x t r a c t a p p r e c i a b l y when the CDx m o d i f i e r i s used. Even though anthracene i s r e p o r t e d t o complex w i t h γ-CDx, i t s f o r m a t i o n c o n s t a n t may not be l a r g e enough t o p e r m i t



174


e x t r a c t i o n i n t h i s system. Roughly 100% o f the anthracene remained i n the o r g a n i c l a y e r . The d a t a o b t a i n e d thus f a r suggest t h a t the PAH must not o n l y f i t i n s i d e the c a v i t y , but must a l s o form a s t r o n g complex i n o r d e r t o t r a n s f e r s a t i s f a c t o r i l y t o the aqueous p h a s e . Thus, e x t r a c t i o n e f f i c i e n c y i s r e l a t e d t o the c o m p a t i b i l i t y o f the CDx and PAH d i m e n s i o n s , as i s seen by comparing %E t o PAH d i m e n s i o n s . E x t r a c t i o n may a l s o be i n h i b i t e d by the f o r m a t i o n o f t e r n a r y com p l e x e s between s m a l l PAHs, o r g a n i c s o l v e n t m o l e c u l e s , and CDx. The p r e s e n c e o f o r g a n i c s o l v e n t i n the CDx c a v i t y would change the p o l a r i t y o f the c a v i t y , making the c a v i t y environment s i m i l a r t o t h a t o f the b u l k o r g a n i c s o l v e n t . Should t h i s o c c u r , the d r i v e f o r c o m p l e x a t i o n would be l e s s e n e d s i n c e c o m p l e x a t i o n i s promoted by the p o l a r i t y change e x p e r i e n c e d by the guest m o l e c u l e . The more t a p e r e d m o l e c u l e s , such as anthracene and p y r e n e , which cannot f i l l the c a v i t y as w e l l as l a r g e r s p e c i e s , would l e a v e room i n the c a v i t y f o r s o l v e n t m o l e c u l e s t o e n t e r and, t h u s , would have s m a l l e r e x t r a c t i o n efficiencies. I n a d d i t i o n t o the s i z e o f the p o t e n t i a l guest s p e c i e s , o t h e r f a c t o r s may i n f l u e n c e the degree o f e x t r a c t i o n p o s s i b l e f o r p a r t i c u l a r PAHs. F o r example, temperature i s known t o a f f e c t the f o r m a t i o n c o n s t a n t s f o r i n c l u s i o n complexes ( I ) . A t lower t e m p e r a t u r e s , the s t a b i l i t y o f c e r t a i n complexes i s i n c r e a s e d . Thus, l o w e r i n g the temperature a t w h i c h e x t r a c t i o n s are performed may i n c r e a s e e x t r a c t i o n e f f i c i e n c i e s . The s o l v e n t c h o i c e may a l s o be u s e f u l i n e s t a b l i s h i n g the degree t o w h i c h c e r t a i n PAHs e x t r a c t . I f t e r n a r y complex f o r m a t i o n i s a problem d u r i n g the s o l v e n t e x t r a c t i o n p r o c e s s , the p o l a r i t y o f the o r g a n i c s o l v e n t may a l s o p r o v i d e a means o f a l t e r i n g e x t r a c t i o n e f f i c i e n c i e s . As the s o l v e n t p o l a r i t y approaches the p o l a r i t y o f the c y c l o d e x t r i n c a v i t y , the e x t r a c t i o n e f f i c i e n c i e s f o r PAHs may d e c r e a s e . The e f f e c t s o f s o l v e n t p o l a r i t y are c u r r e n t l y under s t u d y . S i n c e many o f the o r g a n i c s o l v e n t s form i n s o l u b l e complexes w i t h c y c l o d e x t r i n ( I ) , s o l v e n t c h o i c e was c r u c i a l i n d e s i g n i n g the s o l v e n t - e x t r a c t i o n scheme. W i s h n i a and L a p p i r e p o r t e d the complex a t i o n o f v a r i o u s o r g a n i c s o l v e n t s w i t h the c y c l o d e x t r i n s ( 2 6 ) . Thus, s o l v e n t c h o i c e must be based upon a knowledge o f CDx c o m p l e x a t i o n behavior. I n p r e l i m i n a r y e x t r a c t i o n s t u d i e s , s o l v e n t s such as c y c l o h e x a n e and c h l o r o f o r m formed such s t a b l e complexes w i t h v-CDx t h a t , when shaken, a w h i t e p r e c i p i t a t e formed i n the aqueous p h a s e , and the o r g a n i c phase volume decreased a p p r e c i a b l y . Any PAH p r e s e n t i n t h e s e systems was c o m p l e t e l y e x t r a c t e d from the o r g a n i c p h a s e , p o s s i b l y as a s o l i d t e r n a r y complex. T h i s method, however, i s not t r u e s o l v e n t e x t r a c t i o n , s i n c e a s o l i d s p e c i e s forms d u r i n g the separation. To a v o i d t h i s p r o b l e m , we used a s m a l l s o l v e n t m o l e c u l e w h i c h d i d not complex a p p r e c i a b l y w i t h γ-CDx. I s o p r o p y l e t h e r was chosen as the o r g a n i c s o l v e n t because i t d i d not p r e c i p i t a t e when mixed w i t h aqueous CDx. V a r i o u s o t h e r o r g a n i c s o l v e n t s may a l s o be used f o r t h i s type o f e x t r a c t i o n , but most o f t h e s e are v o l a t i l e and, t h u s , not s u i t a b l e f o r a q u a n t i t a t i v e s t u d y . E t h e r s appear t o be e s p e c i a l l y amenable t o use i n c y c l o d e x t r i n - m o d i f i e d e x t r a c t i o n . It i s i m p o r t a n t t o remember, however, t h a t the use o f α-CDx and β-CDx may r e q u i r e o t h e r s o l v e n t systems, s i n c e the CDx c a v i t y s i z e a f f e c t s the f o r m a t i o n o f c r y s t a l l i n e t e r n a r y complexes.


10.

BLYSHAK ET AL.


ns

The u t i l i t y o f CDx s o l v e n t e x t r a c t i o n f o r s e p a r a t i n g m i x t u r e s was e v a l u a t e d by measuring the i n d i v i d u a l e x t r a c t i o n e f f i c i e n c i e s o f the components i n s e v e r a l b i n a r y PAH m i x t u r e s . The r e s u l t s o f t h e s e m i x t u r e a n a l y s e s are shown i n T a b l e I I I .

Table I I I .

E x t r a c t i o n E f f i c i e n c i e s (%E) o f Components i n B i n a r y PAH M i x t u r e s


Components o f Binary Mixture Anthracene-perylene Pyrene-perylene Pyrene-coronene

%E f o r Component 1 0.0 ± 3.1 40.9 ± 4 . 2 42.3 ± 8.4

%E f o r Component 2 8 9 . 6 ± 5.4 93.5 ± 3.1 9 2 . 3 ± 0.9

The d a t a i n d i c a t e t h a t the e x t r a c t e d p e r c e n t a g e s o f components i n t h e s e m i x t u r e s were independent o f one a n o t h e r . Of the t h r e e m i x t u r e s e x t r a c t e d , s e p a r a t i o n o f PAHs was r e l a t i v e l y good f o r o n l y one o f them. T h i s m i x t u r e o f anthracene and p e r y l e n e was e a s i l y s e p a r a t e d because anthracene d i d not e x t r a c t i n t o aqueous γ-CDx s o l u t i o n but p e r y l e n e e x t r a c t e d r e a s o n a b l y w e l l . F o r those m i x t u r e s i n w h i c h b o t h s p e c i e s had a r e a s o n a b l e e x t r a c t i o n i n t o the m o d i f i e d aqueous phase, s e p a r a t i o n o f the two compounds was not p o s s i b l e . S i n c e excess CDx was a v a i l a b l e f o r c o m p l e x a t i o n , the e x t r a c t i o n o f one component d i d not i n t e r f e r e w i t h the e x t r a c t i o n o f the o t h e r . T h i s problem might be r e s o l v e d by d e c r e a s i n g the CDx c o n c e n t r a t i o n so t h a t the PAHs would compete w i t h one another i n the c o m p l e x a t i o n process. F i g u r e s 2 and 3 show the t o t a l - l u m i n e s c e n c e c o n t o u r p l o t s of two b i n a r y PAH m i x t u r e s b e f o r e and a f t e r e x t r a c t i o n w i t h aqueous γ-CDx. The second o f t h e s e m i x t u r e s , anthracene-coronene ( F i g u r e 3 ) , a g a i n i l l u s t r a t e s the p o t e n t i a l f o r s e p a r a t i n g m i x t u r e s when one component has a low e x t r a c t i o n e f f i c i e n c y . The u t i l i t y o f e x t r a c t i o n w i t h aqueous CDx m o d i f i e r appears t o l i e i n the p o t e n t i a l f o r s i m p l i f y i n g complex m i x t u r e s o f PAHs. I n t e r p r e t a t i o n o f the data suggests t h a t e x t r a c t i o n s o f t h i s type are u s e f u l f o r s e p a r a t i n g l a r g e PAHs from s m a l l ones based on the s t r e n g t h o f complex f o r m a t i o n . Only t h o s e s p e c i e s t h a t are o f the r i g h t s i z e t o form s t r o n g complexes w i t h c y c l o d e x t r i n are c a p a b l e o f being extracted. T h i s t e c h n i q u e i s u s e f u l f o r d i s c r i m i n a t i n g among a n a l y t e s p r e s e n t i n an o r g a n i c m a t r i x . Combining c y c l o d e x t r i n m o d i f i e d s o l v e n t e x t r a c t i o n w i t h a v a i l a b l e luminescence t e c h n i q u e s may p r o v i d e a n a l y s t s w i t h a u s e f u l t e c h n i q u e f o r i d e n t i f i c a t i o n o f components i n complex m i x t u r e s . A f t e r e x t r a c t i o n , each phase may be s t u d i e d i n d e p e n d e n t l y i n o r d e r t o o b t a i n a u s e f u l q u a l i t a t i v e e v a l u a t i o n o f the components i n the o r i g i n a l sample. The s e l e c t i v i t y and s p e c i f i c i t y o f f l u o rescence a n a l y s i s can be e s p e c i a l l y b e n e f i c i a l i n i d e n t i f i c a t i o n o f PAHs. F o r example, some components c o u l d be i d e n t i f i e d by exam i n i n g the f l u o r e s c e n c e s p e c t r a o f the o r g a n i c and aqueous p h a s e s . C h a r a c t e r i s t i c peak shapes may r e v e a l i d e n t i t i e s o f the components. F o r more c o m p l i c a t e d systems i n which the s p e c t r a o v e r l a p , l i f e t i m e measurements may be used t o i d e n t i f y components ( 2 7 ) .




F i g u r e 2 . T o t a l - l u m i n e s c e n c e c o n t o u r p l o t s o f an a n t h r a c e n e - p e r y l e n e m i x t u r e p r i o r t o e x t r a c t i o n (a) and f o l l o w i n g e x t r a c t i o n (b) w i t h v - c y c l o d e x t r i n .




BLYSHAK ET AL.

F i g u r e 3. T o t a l - l u m i n e s c e n c e c o n t o u r p l o t s o f an a n t h r a c e n e - c o r o n e n e m i x t u r e p r i o r t o e x t r a c t i o n (a) and f o l l o w i n g e x t r a c t i o n (b) w i t h γ - c y c l o d e x t r i n .


178


Modern i n s t r u m e n t s c a p a b l e o f o b t a i n i n g e x c i t a t i o n - e m i s s i o n m a t r i c e s (EEMs) a l l o w use o f new d a t a - a n a l y s i s t e c h n i q u e s t o r e s o l v e o v e r l a p p e d s p e c t r a . R e s o l u t i o n t e c h n i q u e s such as t h e r a t i o method (28) and o t h e r s (29,30) may p r o v i d e f u r t h e r d i f f e r e n t i a t i o n o f t h e components p r e s e n t i n the phases s e p a r a t e d by s o l v e n t e x t r a c t i o n .


Conclusion C y c l o d e x t r i n - m o d i f i e d s o l v e n t e x t r a c t i o n has been used t o e x t r a c t s e v e r a l PAHs from e t h e r t o an aqueous phase. Data e v a l u a t i o n shows t h a t t h e degree o f e x t r a c t i o n i s r e l a t e d t o the s i z e o f the p o t e n t i a l guest m o l e c u l e and t h a t t h e method s u c c e s s f u l l y s e p a r a t e s s i m p l e b i n a r y m i x t u r e s i n which one component does n o t complex s t r o n g l y w i t h CDx. The most u s e f u l a p p l i c a t i o n o f c y c l o d e x t r i n - m o d i f i e d s o l v e n t e x t r a c t i o n i s f o r the s i m p l i f i c a t i o n o f complex m i x t u r e s . The combined use o f CDx m o d i f i e r and d a t a - a n a l y s i s t e c h n i q u e s may s i m p l i f y t h e q u a l i t a t i v e a n a l y s i s o f PAH m i x t u r e s .

Literature Cited 1. Szejtli, J. Cyclodextrins and Their Inclusion Complexes; Akademiai Kiado: Budapest, Hungary, 1982. 2. Schlenck, W.; Sand, D. M. J. Am. Chem. Soc. 1961, 83, 2312. 3. Saenger, W. Angew. Chem. Int. Ed. Engl. 1980, 19, 344-362. 4. Bender, M. L.; Komiyama, M. Cyclodextrin Chemistry; Springer -Verlag: New York, 1978. 5. Cline Love, L. J.; Weinberger, R. Spectrochim. Acta, Part Β 1983, 38(11/12), 1421-1433. 6. Lach, J. L.; Chin, T. F. J. Pharm. Sci. 1964, 53, 924. 7. Hamanda, Y.; Nambu, N.; Nagai, T. Chem. Pharm. Bull. 1975, 23, 1205. 8. Cohen, J . ; Lach, J. L. J. Pharm. Sci. 1963, 52, 132. 9. Jules, O.; Scypinski, S., Cline Love, L. J. Anal. Chim. Acta 1985, 169, 355-360. 10. Scypinski, S.; Cline Love, L. J. Anal. Chem. 1984, 56, 322-327. 11. Cline Love, L. J . ; Grayeski, M. L.; Noroski, J . ; Weinberger, R. Anal. Chim. Acta 1985, 170, 3-12. 12. Breslow, R.; Kohn, U.; Siegel, B. Tetrahedron Lett. 1976, 1645-1646. 13. Kitaura, Y.; Bender, M. L. Bioorg. Chem. 1975, 4, 237-249. 14. Armstrong, D. W.; DeMond, W.; Czech, B. D. Anal. Chem. 1985, 57, 481-484. 15. Armstrong, D. W.; DeMond, W. J. Chrom. Sci. 1984, 22, 411-415. 16. Caton, J. E.; Barnes, Ζ. K.; Kubota, H.; Griest, W. H.; Maskarinec, M. P. Adv. Identif. Anal. Org. Pollut. Water 1981, 1, 329-344. 17. Rosen, Α. Α.; Middletown, F. M. Anal. Chem. 1955, 27, 790. 18. Natusch, D. F. S.; Tomkins, B. A. Anal. Chem. 1978, 50(11), 1429-1434. 19. Pearlman, P. S.: Yalkowsky, S. H.; Banerjee, S. J. Phys. Chem. Ref. Data 1984, 13(2), 555-562. 20. Schwarz, F. P. J. Chem. Eng. Data 1977, 22, 273-277. 21. Matsunaga, K.; Imanaka, M.; Ishida, T.; Oda, T. Anal. Chem. 1984, 56, 1980-1982. 22. Harangi, J . ; Nanasi, P. Anal. Chim. Acta 1984, 156, 103-109.



10.

BLYSHAK ET AL.


179

23. Kalyanasundaram, K.; Thomas, J. K. J. Am. Chem. Soc. 1977, 99, 2039-2044. 24. Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic Molecules, 2nd ed.; Academic: New York, 1971. 25. Warner, I. M.; Fogarty, M. P.; Shelley, D. C. Anal. Chim. Acta 1979, 109, 361-372. 26. Wishnia, Α.; Lappi, S. J. J. Mol. Biol. 1974, 82, 77. 27. Warner, I. M.; Patonay, G.; Thomas, M. P. Anal. Chem. 1985, 57, 463A-483A. 28. Fogarty, M. P.; Warner, I. M. Anal. Chem. 1981, 53, 259-265. 29. Moran, M. G.; Kowalski, B. R. Anal. Chem. 1979, 51, 776A-789A. 30. Appellof, C. J.; Davidson, E. R. Anal. Chem. 1981, 53, 2053-2056. RECEIVED August 18, 1988


Multidimensional Fluorescence Analysis of Cyclodextrin Solvent

Recommend Documents