Size Exclusion Chromatography - ACS Publications - American

16 High-Efficiency Gel Permeation Chromatography Applications for the Analysis of Oligomers and Small Molecules

Downloaded by GEORGE MASON UNIV on December 20, 2014 | http://pubs.acs.org Publication Date: March 30, 1984 | doi: 10.1021/bk-1984-0245.ch016

A. KRISHEN Chemical Research and Development Division, The Goodyear Tire & Rubber Company, Akron, OH 44316

High e f f i c i e n c y columns c u r r e n t l y a v a i l a b l e for gel permeation chromatography of small molecules and oligomers provide high speed separations. The use of multiple detectors provides a d d i t i o n a l information which f a c i l i t a t e s c h a r a c t e r i z a t i o n and determination of the separated species.

H i g h e f f i c i e n c y g e l p e r m e a t i o n chromatogrphy i n t h e low m o l e c u l a r w e i g h t r a n g e i s b a s e d o n t h e same m e c h a n i s m of s e p a r a t i o n a s g e l p e r m e a t i o n chromatography f o r high molecular weight polymers. The s o l u t e components are s e l e c t i v e l y r e t a r d e d a c c o r d i n g t o the degree o f t h e i r permeation i n t o the solvent f i l l e d pores i n t h e column p a c k i n g . L a r g e r m o l e c u l e s a r e e x c l u d e d from the p o r e s o f t h e p a c k i n g due t o t h e i r p h y s i c a l s i z e and t h u s e l u t e b e f o r e t h e s m a l l e r m o l e c u l e s . B e y o n d t h i s s i m i l a r i t y however, the resemblance between t h e two i s m i n i m a l . Molecular weight d i s t r i b u t i o n s a r e the main concern f o r polymers w h i l e r e t e n t i o n volumes and d i s t i n c t s e p a r a t i o n o f i n d i v i d u a l s p e c i e s a r e o f importance i n h i g h - e f f i c i e n c y g e l permeation chromato graphy i n the low m o l e c u l a r weight range. This t e c h n i q u e has g r e a t e r s i m i l a r i t y t o both gas chromato graphy and h i g h performance l i q u i d chromatography than to g e l p e r m e a t i o n chromatography o f p o l y m e r s . Gel permeation chromatography f o r s m a l l molecules i s a r e l a t i v e l y r e c e n t development i n chromatographic techniques. I n 1968 H e n d r i c k s o n (1) p r e d i c t e d , " I t a p p e a r s l i k e l y t h a t GPC f o r s m a l l m o l e c u l e s w i l l b e come a new b a s i c t o o l t h a t c o u l d b e c a l l e d a l i q u i d phase s i z e s p e c t r o m e t e r . "

0097-6156/84/ 0245-0241 $06.00/0 © 1984 American Chemical Society

In Size Exclusion Chromatography; Provder, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

242

SIZE EXCLUSION CHROMATOGRAPHY

Advantages


In c o n t r a s t t o gas chromatography and o t h e r forms o f l i q u i d chromatography, g e l permeation chromatography i s a p p l i c a b l e e v e n when t h e r e a r e no d i f f e r e n c e s i n t h e solubility, polarity, adsorption, ionic characteristics or v o l a t i l i t y o f the m o l e c u l e s . Furthermore t h e f o l l o w i n g t h r e e c h a r a c t e r i s t i c s o f the t e c h n i q u e a r e responsible for i t s increasing u t i l i t y : 1.

Separations

are achieved

with a single solvent.

2.

E l u t i o n o f a l l the components o f a m i x t u r e takes p l a c e i n a f i n i t e volume c o n t r o l l e d column c h a r a c t e r i s t i c s .

3.

A d d i t i o n a l i m p o r t a n t i n f o r m a t i o n on the s i z e o f t h e s e p a r a t e d compounds c a n be o b t a i n e d e a s i l y b y com p a r i s o n w i t h known compounds h a v i n g s i m i l a r c h a r a c t e r i s t i c s ; furthermore the c h a r a c t e r i z a t i o n o f t h e s e p a r a t e d compounds i s f a c i l i t a t e d b y t h e use o f m u l t i p l e d e t e c t i o n s y s t e m s .

normally by t h e

Columns The number o f s u p p l i e r s o f t h e p o l y m e r i c g e l s o f t h e p o l y s t y r e n e - d i v i n y l b e n z e n e type s u i t a b l e f o r t h e a n a l y s i s o f s m a l l m o l e c u l e s h a s been i n c r e a s i n g over the y e a r s . P a c k e d c o l u m n s - u s u a l l y 30 cm χ 8 mm i . d . o r g e l s a r e c u r r e n t l y a v a i l a b l e f r o m many s o u r c e s (2^) a l t h o u g h some o f them s e l l o n l y t h e p a c k e d c o l u m n s . Columns range i n t h e o r e t i c a l p l a t e e f f i c i e n c y from 12,000 t o 40,000 p l a t e s p e r m e t e r a s measured by chromatographing acetone a t a f l o w r a t e o f 1 ml p e r minute. The m o l e c u l a r w e i g h t r a n g e c o v e r e d b y e a c h column depends on the pore s i z e o f the g e l . I t i s q u i t e common t o u s e e i t h e r a c o m b i n a t i o n o f c o l u m n s o f d i f f e r e n t pore s i z e s o r columns w i t h beds o f mixed pore g e l s t o o b t a i n the d e s i r e d range f o r the a p p l i c a t i o n a t hand. A t y p i c a l chromatogram o b t a i n e d f o r a m i x t u r e o f n - a l k a n e s i s shown i n F i g u r e 1. A l k a n e s of s u f f i c i e n t p u r i t y t o s e r v e a s s t a n d a r d s a r e a v a i l a b l e up t o a b o u t C ^ H g g (M. W. 618) a n d l o w m o l e c u l a r weight p o l y s t y r e n e s are u s e f u l as standards i n t h e higher molecular weight range. Most o f the columns p r o v i d e s u f f i c i e n t r e s o l u t i o n t o separate the lower m o l e c u l a r weight p o l y s t y r e n e s t a n d a r d samples i n t o t h e i r i n d i v i d u a l ο1igomeric c o m p o n e n t s .


G PC of Oligomers and Small Molecules


KRISHEN

243

20 RETENTION V O L U M E

F i g u r e 1. ditions:

(ML)

G e l permeation chromatogram o f n_-alkanes.

6l0 mm χ 8 mm TSKG 2000 H8 column; and t e t r a h y d r o -

furan eluant at 0.5 mL/min.

Key: 1, n-C^gH^; 2, n-C^^H^Q ;

3, n - C H ; U, n - C ^ H ^ ; 5, n-CgH^; 6, n - C ^ ^ ; 7, l 8

Con

3 8

n-CgH^; and 8, n-C^H^.



244


Calculation

of Molecular

Sizes

The h i g h e f f i c i e n c y c o l u m n s s e p a r a t e i n d i v i d u a l com ponents as d i s t i n c t peaks s i m i l a r t o t h o s e o b t a i n e d i n gas c h r o m a t o g r a p h y . I t has been r e c o g n i z e d t h a t t h e s e p a r a t i o n i s p r e d o m i n a n t l y b a s e d on t h e s i z e t h a t t h e m o l e c u l e e x h i b i t s i n t h e e l u t i n g s o l v e n t under t h e experimental conditions. G e o m e t r i c a l shape, m o l e c u l a r a s s o c i a t i o n a n d s o l v o l y s i s due t o h y d r o g e n b o n d i n g a r e some o f t h e f a c t o r s w h i c h c o n t r o l t h e e f f e c t i v e s i z e of a m o l e c u l e . H e n d r i c k s o n a n d M o o r e (3) a n d H e n d r i c k s o n (1) c o n s i d e r e d t h e c h a i n l e n g t h o f s m o l e c u l e as t h e c o n t r o l l i n g f a c t o r f o r t h e e l u t i o n volume. The c h a i n l e n g t h s o f t h e m o l e c u l e s w e r e c a l c u l a t e d f r o m t h e bond a n g l e s and a t o m i c r a d i i . nHydrocarbons were used as s t a n d a r d s . Their chain l e n g t h s c a n a l s o be c a l c u l a t e d a s f o l l o w s : C h a i n L e n g t h ( A n g s t r o m s ) » 2.5+(1.25 χ Number o f Carbons). The c h a i n l e n g t h s o f d i f f e r e n t m o l e c u l e s w e r e t h e n compared w i t h t h e c h a i n l e n g t h s o f h y d r o c a r b o n s t o c a l c u l a t e t h e c a r b o n number w h i c h r e l a t e s t h e e l u t i o n v o l ume o f t h e compound t o t h e e l u t i o n v o l u m e o f a r e a l o r imaginary n-hydrocarbon. The " e f f e c t i v e " c a r b o n number f o r b e n z e n e b a s e d o n i t s e l u t i o n v o l u m e was e x p e r i m e n t a l l y f o u n d t o be 2.85 - i . e . i t e l u t e d near t h e e l u t i o n volume f o r propane which has a c a r b o n number o f 3.0 w h i l e t h e c a l c u l a t i o n s b a s e d o n bond a n g l e s and r a d i i o f atoms i n d i c a t e d t h a t b e n z e n e w o u l d h a v e a c a r b o n number o f 3 . 5 5 . T h u s c o r r e c t i o n s t o t h e c a l c u l a t i o n s f o r c a r b o n number w e r e r e q u i r e d . These were d e r i v e d from t h e e x p e r i m e n t a l l y o b s e r v e d e l u t i o n behavior of v a r i o u s molecules. S m i t h a n d K o l l m a n s b e r g e r (4_) i n t r o d u c e d t h e c o n cept o f molar volumes as "fundamental i n determining the degree o f s e p a r a t i o n . " M o l a r volumes were c a l c u l a t e d f o r a number o f compounds f r o m t h e i r d e n s i t y a n d w e r e e x p r e s s e d a s ml / m o l . Chang (_5 ) , G a z e s a n d G a s k i l l ( 6 , 7 ) a n d E d w a r d s a n d Ng (8_) p r o v i d e d f u r t h e r u n d e r standing of the b a s i c f a c t o r s i n v o l v e d i n the separa t i o n process i n g e l permeation chromatography. Lambert (9,10) combined t h e d a t a from v a r i o u s i n v e s t i g a t o r s and a t t e m p t e d t o r e c a l c u l a t e t h e r e s u l t s f o r a l a r g e number o f compounds on a common b a s i s . The n - h y d r o c a r b o n s were used as s t a n d a r d s and t h e i r molar volumes were found t o conform t o t h e f o l l o w i n g e q u a t i o n M o l a r Volume

(ml/mol

a t 20°C) « 33.02 + 1 6 . 1 8 χ (CAU)+ 0.0041 χ ( C A U ) 2



16.

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w h e r e CAU i s t h e s i z e o f t h e h y d r o c a r b o n i n c a r b o n atom units. L a m b e r t ' s ( 9 , 1 0 ) summary o f t h e f a c t o r s t o be c o n s i d e r e d f o r p r e d i c t i n g the e l u t i o n volumes f o r s m a l l m o l e c u l e s i n t e t r a h y d r o f u r a n p o i n t e d out the g e n e r a l i zations . The e l u t i o n v o l u m e s f o r η-hydrocarbons show a s t r a i g h t l i n e r e l a t i o n s h i p vs the l o g a r i t h m s of t h e i r molar volumes. Molar volumes, c a l c u l a t e d from the d e n s i t i e s o f compounds o t h e r t h a n n - h y d r o c a r b o n s , must be m o d i f i e d t o h a v e t h e e l u t i o n v o l u m e s o f t h e s e com p o u n d s c o n f o r m t o t h e same c a l i b r a t i o n l i n e ( e l u t i o n v o l u m e v s l o g m o l a r v o l u m e ) as t h a t f o r t h e n - h y d r o carbons. W. W. S c h u l z ( 1 1 ) r e l a t e d t h e e l u t i o n b e h a v i o r of branched a l k a n e s i n the range of to t h e a v e r a g e numbers of gauche a r r a n g e m e n t s (Zg) w h i c h the m o l e c u l e can assume. The m o l e c u l a r w e i g h t s o f o l i g o m e r i c s p e c i e s c o r r e s p o n d i n g t o c h r o m a t o g r a p h i c p e a k s and t h e i r i d e n t i f i c a t i o n a r e u s u a l l y more u s e f u l t h a n t h e i r m o l a r volumes or t h e i r carbon numbers. The i n t e r p r e t a t i o n o f e x p e r i m e n t a l d a t a c a n be s i m p l i f i e d by u s i n g t h e l o g a r i t h m of the m o l e c u l a r w e i g h t s r a t h e r than the l o g a r i t h m s of molar volumes f o r s t a n d a r d i z a t i o n . L a r s o n (12) i n d i c a t e d t h a t the e l u t i o n v o l u m e s f o r a l i p h a t i c hydrocarbons, aromatic hydrocarbons and a l i p h a t i c a l c o h o l s formed t h r e e d i f f e r e n t p a r a l l e l s t r a i g h t 1 i n e s when p l o t t e d a g a i n s t t h e l o g a r i t h m s o f their molecular weights. These r e l a t i o n s h i p s a r e s i m i l a r t o t h o s e o b s e r v e d i n gas c h r o m a t o g r a p h y f o r d i f f e r e n t homologous s e r i e s . The l i n e f o r t h e a r o m a t i c h y d r o c a r b o n s was d i s p l a c e d • h i g h e r t h a n t h a t f o r the n-alkanes, i n d i c a t i n g t h a t the " e f f e c t i v e " m o l e c u l a r w e i g h t of the a r o r n a t i c h y d r o c a r b o n s was s m a l l e r than t h e i r a c t u a l m o l e c u l a r weight w h i l e the alcohols exhibited larger e f f e c t i v e molecular weights due t o t h e i r h y d r o g e n b o n d i n g w i t h t h e s o l v e n t , t e t r a hydrof uran. We h a v e r e c e n t l y r e p o r t e d ( 1J3 ) ) t h e u s e o f t h i s t e c h n i q u e f o r c h a r a c t e r i z a t i o n of v a r i o u s compounds. E x p e r i m e n t a l d a t a o b t a i n e d f o r a number o f compounds a r e shown i n F i g u r e 2. We c a l c u l a t e d t h e " s i z e f a c t o r s " f o r a number o f s m a l l m o l e c u l e s and o l i g o m e r s . T h i s f a c t o r i s a measure of the d e v i a t i o n of the e l u t i o n volume of a g i v e n s p e c i e s from the c a l i b r a t i o n curve f o r n-alkanes which i s assigned a s i z e f a c t o r o f 1. T h i s s i z e f a c t o r , F, i s d e f i n e d t o be e q u a l t o A/M, w h e r e M i s t h e m o l e c u l a r w e i g h t o f t h e compound and A i s t h e m o l e c u l a r w e i g h t o f a r e a l o r h y p o t h e t i c a l n - a l k a n e w h i c h w i l l e l u t e a t t h e same r e t e n t i o n v o l u m e as t h e compound. S i z e f a c t o r s f o r a number o f



246


Figure 2 . ships .

Molecular weight vs. r e t e n t i o n volume r e l a t i o n

Key: I , n-alkanes ( C ^ H ^ t o C^gH^) ; I I , toluene,

p_-xylene , and d i e t h y l p h t h a l a t e ; I I I , η-alcohols (C^H^OH t o C^gH^OH) ; IV, 2 , 6 - d i - t e r t - b u t y l - p - c r e s o l ,

dibutyladipate,

n - d i d e c y l p h t h a l a t e , and n-didodecyl phthalate ; V, nonylphenol-formaldehyde adducts; and VI, TMDQ oligomers (dimer t o hexamer).


16.

K RIS H EN

G PC of Oligomers and Small

compounds a l o n g w i t h c a l c u l a t e d (13).

their

Molecules

m o l a r volumes have

247 been

Applications :


W h i l e t h e m e c h a n i s m o f r e t e n t i o n f o r v a r i o u s compounds c a n be o n l y p a r t i a l l y u n d e r s t o o d , t h e a p p l i c a t i o n o f t h e t e c h n i q u e p r o v i d e s much n e e d e d i n f o r m a t i o n f o r c h a r a c t e r i z a t i o n of d i f f e r e n t types of m a t e r i a l s . Some o f t h e s e a p p l i c a t i o n s , i n c l u d i n g t h o s e r e q u i r i n g the use of m u l t i p l e d e t e c t o r s , a r e p r e s e n t e d here. Phenol - Formaldehyde Resins. Oligomeric species pro d u c e d by i n t e r l i n k i n g o f p h e n o l i c m o l e c u l e s w i t h -CH2~ m o i e t i e s r e s u l t i n complex m i x t u r e s which cannot be r e s o l v e d by gas c h r o m a t o g r a p h y . The GPC s y s t e m p r o v i d e s a m p l e i n f o r m a t i o n on t h e i n d i v i d u a l c o m p o n e n t s f o r c o m p a r i s o n of d i f f e r e n t b a t c h e s of r e s i n s s p e c i a l l y when a d u a l d e t e c t o r s y s t e m c o n s i s t i n g o f a d i f f e r e n t i a l r e f r a c t i v e i n d e x and a UV a b s o r p t i o n d e t e c t o r (254 nm) i s u s e d ( F i g u r e 3 ) . E a c h o f t h e p e a k s ob served i n the chromatogram r e p r e s e n t s i n d i v i d u a l o l i g o m e r s p r o d u c e d by a d d i t i o n o f a m o n o m e r i c u n i t c o n s i s t i n g o f t h e p h e n o l and -CU2~ s i n c e a p l o t of the r e t e n t i o n volume v e r s u s t h e logarithm of the m o l e c u l a r w e i g h t of the o l i g o m e r s p r o d u c e s a s t r a i g h t l i n e ( F i g u r e 1; V ) . 2 , 2 , 3 - T r i m e t h y l - l , 2 - D i h y d r o q u i n o 1 i n e . (TMDQ) . The a d v a n t a g e o f t h e GPC a p p r o a c h b e c o m e s e v i d e n t when e x a m i n i n g t h e c h r o m a t o g r a m o f TMDQ o l i g m e r s ( F i g u r e 4 ) . T h i s m a t e r i a l i s a common a n t i o x i d a n t made f r o m t h e r e a c t i o n o f a n i l i n e and a c e t o n e and t h e n p o l y m e r i z e d . If the observed peaks are a s s i g n e d the normal sequence - dimer, t r i m e r , t e t r a m e r e t c . , the p l o t of the r e t e n t i o n volume v e r s u s the l o g a r i t h m of the m o l e c u l a r w e i g h t s does not p r o d u c e a smooth l i n e . The p e a k s r e p r e s e n t i n g t h e n o r m a l l o i g o m e r i c s e q u e n c e c a n be s e l e c t e d by t r i a l and e r r o r and t h e n a d i f f e r e n t s e r i e s of peaks i s d i s c o v e r e d where the o l i g o m e r i z a t i o n follows a different route. The c h a r a c t e r i z a t i o n o f t h i s s e c o n d s e r i e s o f p e a k s h a s b e e n a c h i e v e d by mass s p e c t r o s c o p y and r e p o r t e d by L a t t i m e r e t . a l . ( 1 4 ) . Butylated p-Cresol-Dicyclopentadiene Product. A com p l e x n o n - s t a i n i n g o l i g o m e r i c a n t i o x i d a n t m a r k e t e d by G o o d y e a r as " W i n g s t a y L" i s t h e b u t y l a t e d r e a c t i o n p r o d u c t o f p - c r e s o l and d i c y c l o p e n t a d i e n e . After t r y i n g v a r i o u s a n a l y t i c a l t e c h n i q u e s , we f o u n d t h a t GPC p r o v i d e s the best approach f o r f o l l o w i n g the r e a c t i o n

American Cfiemfcaf Society library 1Î55

1 5 * Si.

H.

w.

In Size Exclusion Chromatography; Provder, T.; Washington. 0. C. Society: 20038 ACS Symposium Series; American Chemical Washington, DC, 1984.


NONYLPHENOL:

HCHO ADDUCTS

ι ·

{ I


M.W. 1

7:6

1614.6

2

5:4

1149.8

3

4:3

917.5

F i g u r e 3 . G e l permeation chromatogram o f nonylphenolformaldehyde adducts w i t h dual d e t e c t o r s .

4

L/ 6

1

5

.

10

1

1

.

15 V

R

i

20

(mL of THF)

F i g u r e k. G e l permeation chromatogram o f polymerized a c e t o n e - a n i l i n e condensation products. Key: 3 , 5 - and 6-TMDQ oligomers ; and 1 , 2 - and U-oligomeric s e r i e s from a d i f f e r e n t addition route. In Size Exclusion Chromatography; Provder, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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Molecules

249


products. B o t h t h e u n b u t y l a t e d and b u t y l a t e d o l i g o m e r s a r e w e l l s e p a r a t e d ( F i g u r e 5) and t h e y a l l f a l l on a s i m p l e s t r a i g h t l i n e when t h e i r r e t e n t i o n v o l u m e s a r e p l o t t e d a g a i n s t the l o g a r i t h m of t h e i r m o l e c u l a r weights. In t h i s case both the d i f f e r e n t i a l r e f r a c t i v e i n d e x and t h e UV 254 nm d e t e c t o r s p r o v i d e e s s e n t i a l l y t h e same i n f o r m a t i o n . Fiasticizers. Some o f t h e common p l a s t i c i z e r s u s e d f o r PVC a p p l i c a t i o n s c o n s i s t of e s t e r s of p h t h a l i c a c i d , e p o x i d i z e d s o y a o i l s and e s t e r s o f d i b a s i c a l k y l a c i d s . W h i l e gas c h r o m a t o g r a p h y c a n r e s o l v e some o f t h e l o w e r b o i l i n g m a t e r i a l s , a c o m p l e t e a n a l y s i s c a n be o b t a i n e d by GPC u s i n g two d e t e c t o r s . When a c o m p l e t e c h a r a c t e r i z a t i o n of the m i x t u r e of p l a s t i c i z e r s i s r e q u i r e d , the u s e o f a UV 254 nm and a d i f f e r e n t i a l r e f r a c t i v e i n d e x detector i s essential. While a l l the p l a s t i c i z e r s i n c l u d i n g e p o x i d i z e d o i l s r e s p o n d i n the RI d e t e c t o r , d e t e c t i o n of e s t e r s w i t h p h t h a l a t e a r o m a t i c m o i e t i e s i s a c h i e v e d w i t h t h e UV 254 nm d e t e c t o r . In a recent p r o b l e m where p l a s t i c i z e r s were e x t r a c t e d from a p o l y mer w e r e b e i n g e x a m i n e d by GPC, we o b s e r v e d a p e a k c o r r e s p o n d i n g to d i - 2 - e t h y l h e x y l p h t h a l a t e . T h e r e was n o t h i n g u n u s u a l and t h e i d e n t i f i c a t i o n was c o n f i r m e d by GC. A c a r e f u l e x a m i n a t i o n o f t h e UV and R I responses, h o w e v e r , showed t h a t t h e UV r e s p o n s e was l o w e r t h a n expected. The UV/RI r a t i o f o r d i - 2 - e t h y l - h e x y l - p h t h a l a t e i s a b o u t 2.0 b u t t h e samp l e p e a k g a v e a r a t i o o f only about 1.0. T h i s i n f o r m a t i o n s u g g e s t e d t h e p r e s e n c e o f an a d d i t i o n a l component c o - e l u t i n g w i t h d i - 2 - e t h y l h e x y l phthalate. W i t h t h e i n f o r m a t i o n a t h a n d i t was p o s s i b l e t o s u r m i z e t h a t t h i s c o m p o n e n t had t h e fο 1 l o w ing c h a r a c t e r i s t i c s : 1.

I t had

only

2.

I t had

a molecular

minimal

3.

I t was

too

high

response i n w e i g h t of

boiling

UV.

about

f o r gas

400.

chromatography.

I t was t h e n p o s s i b l e t o s c r e e n some p o s s i b l e c a n d i d a t e s and come up w i t h t h e p r o b a b l e p r e s e n c e o f a chlorinated paraffin. T h i s m a t e r i a l was f o u n d t o e l u t e a t t h e same r e t e n t i o n v o l u m e as d i - 2 - e t h y l h e x y l - p h t h a l a t e and showed no r e s p o n s e a t 254 nm ( F i g u r e 6 ) . For q u a n t i t a t i o n UV/RI r e s p o n s e r a t i o p r o v i d e d a l l t h e data r e q u i r e d . However, i n o r d e r to c o n f i r m the p r e s e n c e o f t h i s a d d i t i o n a l c o m p o n e n t , t h e s a m p l e was h y d r o l y z e d and t h e a c i d c o n v e r t e d t o i t s d i m e t h y l e s t e r . The products were then examined by GPC. The UV r e sponse f o r the peak of i n t e r e s t was completely




R I.

U V.

F i g u r e 5» Gel permeation chromatogram o f b u t y l a t e d ] D - c r e s o l - d i c y c l o p e n t a d i e n e r e a c t i o n products.



16.

KRISHEN


Rl

DETECTOR

UV

DETECTOR

251

Β

Rl

DETECTOR

UV

DETECTOR

Figure 6. Gel permeation chromâtograms w i t h dual d e t e c t o r s . Key: A, d i - 2 - e t h y l h e x y l p h t h a l a t e ; and B, c h l o r i n a t e d paraffin.


252



e l i m i n a t e d but the R l r e s p o n s e due t o u n h y d r o l y z a b l e c h l o r i n a t e d p a r a f f i n was s t i l l t h e r e . The d i m e t h y l e s t e r o f p h t h a l i c a c i d e l u t e d l a t e r a n d showed t h e e x p e c t e d UV r e s p o n s e . Quinones and H y d r o q u i n o n e s . I n the a n a l y s i s o f q u i n o n e s a n d h y d r o q u i n o n e s , t h e u s e o f two d i f f e r e n t d u a l d e t e c t o r s y s terns was r e q u i r e d . The r e t e n t i o n d a t a f o r h y d r o q u i n o n e s shows t h e n o r m a l b e h a v i o r o f h y d r o x y 1 g r o u p s associâting w i t h t h e s o l v e n t , THF. Thus o c t y l q u i n o n e a n d h y d r o q u i n o n e élute a l m o s t t o g e t h e r . S i m i l a r l y d i o c t y l q u i n o n e and o c t y l hydroquinone e l u t e together (Figure 7). The UV/RI r e s p o n s e r a t i o f o r b e n z o q u i n o n e i s 3.75. Hydroquinone and d i o c t y l q u i n o n e show s i m i l a r d i s p a r i t i e s i n t h e UV/RI r e s p o n s e s . This i n f o r m a t i o n p r o v i d e s a v e r y good m e t h o d f o r d e t e c t i n g i m p u r i t i e s i n diocty1 hydroquinone. The r e v e r s e p r o b l e m o f d e t e c t i n g h y d r o q u i n o n e i m p u r i t i e s i n quinones r e q u i r e s the u s e o f an e l e c t r o chemical detector. The h y d r o q u i n o n e s a r e o x i d i z e d a t 1.2V t o quinones t o give very strong responses. The q u i n o n e s h a v e no r e s p o n s e i n t h i s d e t e c t o r . Poly Chlorinated BiphenyIs. The p h o t o c o n d u c t i v i t y d e t e c t o r p r o v i d e s good r e s p o n s e s f o r p o l y c h l o r i n a t e d b i p h e n y I s s e p a r a t e d b y GPC. The n o r m a l m a t r i x compon e n t s a r e d e t e c t e d b y R l a n d UV d e t e c t o r s w h i l e t h e p o l y c h l o r i n a t e d s p e c i e s show h i g h r e s p o n s e s i n t h e e l e c t r o c h e m i c a l d e t e c t o r ( F i g u r e 8) . A comprehensive l i s t i n g o f the a p p l i c a t i o n s of t h i s t e c h n i q u e i n the c o a t i n g s indus t r y has been presented i n r e c e n t p u b l i c a t i o n s (15 ,16) . Conclusions H i g h - e f f i c i e n c y gel permeation chromatography o f f e r s a very u s e f u l technique f o r the c h a r a c t e r i z a t i o n and a n a l y s i s o f οligomers a n d s m a l l m o l e c u l e s p a r t i c u l a r l y when m u l t i p l e d e t e c t o r s y s t e m s a r e u s e d .


KRISHEN

GPC of Oligomers and Small

Molecules


16.

F i g u r e 7. G e l permeation chromatograms w i t h dual d e t e c t o r s . Key: t o p , d i o c t y l quinone; and bottom, o c t y l hydroquinone.


253

SIZE EXCLUSION C H R O M A T O G R A P H Y

Ί


i

ii ii Μ ii !i ιi ij i i

uv

_

m

j ν

f i g u r e 8. G e l permeation chromatograms with r e f r a c t i v e index, UV 25k, and p h o t o c o n d u c t i v i t y d e t e c t o r s . Key: t o p , p - c h l o r o b i p h e n y l ; and bottom, decachlorobiphenyl.


16.

KRISHEN


255

Acknowledgment The p e r m i s s i o n o f T h e G o o d y e a r T i r e & R u b b e r Company to p u b l i s h t h i s paper i s g r a t e f u l l y appreciated.

Literature Cited


1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Hendrickson, J . G.,Anal. Chem. 40: 49-53 (1968) Majors, R. E. J., Chromatog. Sci. 18: 488-511 (1980). Hendrickson, J . G. and Moore, J . C., J . Polym. Sci. Part A-1 4:167-88 (1966). Smith, W. B. and Kollmansberger, K., J. Phys. Chem. 69: 4157-61 (1965). Chang, Teh-Liang, Anal. Chim. Acta. 39: 519-21 (1967). Cazes, J . and Gaskill, D. R., Sep. Sci. 2: 421-30 (1967). Cazes, J and Gaskill, D. R., Sep. Sci. 4: 15-24 (1969) Edwards, G. D., and Ng, Q. Y . , J . Polym. Sci. Part C. 21: 105-17 (1968). Lambert, A . , J . Appl. Chem. 20: 305-306 (1970). Lambert, A, Anal. Chim. Acta. 53 : 63-72 (1971). Schulz, W. W., J . Chromatog. 55: 73-81 (1971). Larsen, F. Ν., App. Polym. Symp. 8: 111-24 (1969) Krishen, A. and Tucker, R. G., Anal. Chem. 49: 898-902 (1977). Lattimer, R. P., Hooser, Ε. R., and Zakriski, P. M. Rubber Chem Technol. 53: 346-356 (1980) Kuo, C . , and Provder, Τ. ACS Symposium Series, No. 138: 207-224 (1980). Kuo, C . , Provder, Τ.,and Kah, A. F . , Paint & Resin, March/April 1983: 26-33.

RECEIVED

October 13, 1983


Size Exclusion Chromatography - ACS Publications - American

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