Pesticides Identification at the Residue Level - ACS Publications

2 Chemical Derivatization Techniques for Confirmation of Organochlorine

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Residue Identity W . P.

COCHRANE

and A . S. Y .

CHAU

Analytical Services Section, Plant Products Division, Department of Agriculture, Ottawa, Ontario

Misidentifications

in organochlorine

sis by thin-layer

and gas chromatography

of interferences

from co-extracted

naturally-occurring tion.

products

A useful technique

is chemical ment,

proper

Addition,

The sensitivity

and application

and

contamina-

of residue

and

identity rearrange-

dehydrochlorination

residues

A table

of

is given

for

con-

The

is discussed and structure

present in a 10-gram

mode of formation with reference of the parent

of some

the

reaction.

of these methods ranges from 0.01 to 0.1

-treated sample. reaction

result

compounds

of a derivatization

in terms of the parent pesticide derivatives

analy-

occur as a

oxidation,

used procedures.

tests for organochlorine choice

residue

as well as external

reduction,

most commonly

firmatory

pesticide

for confirmation

derivatization.

dechlorination,

are the

pesticide

ppm field-

chlordan

to the mechanism

of

compound.

T n r e c e n t years m u c h c o n c e r n has r i s e n , e s p e c i a l l y i n official r e g u l a t o r y circles, a b o u t t h e p r o b l e m of m i s i d e n t i f i c a t i o n o r u n c e r t a i n i d e n t i f i c a t i o n i n p e s t i c i d e r e s i d u e analysis. S i n c e t h e i n t r o d u c t i o n of t h e e l e c t r o n c a p t u r e detector

( E C ) i n 1960 ( I )

a n d its r a p i d e x p l o i t a t i o n f o r t h e

d e t e r m i n a t i o n of o r g a n o c h l o r i n e residues b y g a s - l i q u i d c h r o m a t o g r a p h y (GLC) most

( 2 ) t h e c o m b i n e d E C - G L C system has b e c o m e , f r o m 1963, t h e commonly

used

end-method

for

quantitative pesticide

residue

analysis. I t w a s q u i c k l y d i s c o v e r e d t h a t e v e n after t h e a p p l i c a t i o n o f t h e more

common

clean-up techniques

(3,

5, 4)

EC-GLC

interferences

o c c u r r e d not o n l y f r o m p e a k - o v e r l a p of the v a r i o u s pesticides themselves (6, 7)

b u t also f r o m extraneous c o n t a m i n a t i o n — e . g . , t h e l a b o r a t o r y o r 11

Biros; Pesticides Identification Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

12

PESTICIDES

t e c h n i q u e itself ( 8 ) — a n d

IDENTIFICATION

naturally-occurring components

co-extracted

from the sample. F o r e x a m p l e , artifacts ( 9 ) h a v i n g s i m i l a r G L C responses to o,p'- a n d p , p ' - D D E o n b o t h D C - 2 0 0 a n d Q F - 1 stationary phases w e r e o b t a i n e d b y u s i n g p o l y e t h y l e n e w a s h bottles ( J O ) . (II)

and di-n-butylphthalate (12)

Similarly, both elemental sulfur

h a v e b e e n i d e n t i f i e d as i n t e r f e r i n g

w i t h aldrin identification. M o r e recently, naturally-occurring components Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0104.ch002

of g r e e n p l a n t m a t e r i a l h a v e b e e n r e p o r t e d w i t h s i m i l a r r e t e n t i o n t i m e s , a g a i n o n D C - 2 0 0 a n d Q F - 1 c o l u m n s , to d i e l d r i n ( 1 3 ) .

T h i s list of i n t e r -

f e r i n g responses c a n be e x t e n d e d to i n c l u d e p r e v i o u s l y u n k n o w n d e r i v a tives or m e t a b o l i t e s s u c h as those f o u n d w i t h h e p t a c h l o r a n d h e p t a c h l o r epoxide.

F r o m t e c h n i c a l c h l o r d a n - t r e a t e d c a b b a g e the

dehydrochlo-

r i n a t e d p r o d u c t of f r a r w - c h l o r d a n , n a m e l y 2 - c h l o r o c h l o r d e n e w a s f o u n d to h a v e E C - G L C

(Figure 1),

and thin-layer chromatographic

characteristics s i m i l a r to h e p t a c h l o r {14).

(TLC)

T o date, n o s u i t a b l e G L C

c o l u m n has b e e n o b t a i n e d that w i l l successfully separate these t w o c o m p o u n d s , a n d f u r t h e r i t is not k n o w n w h e t h e r the 2 - c h l o r o c h l o r d e n e o r i g i n a t e d as a m i n o r constituent of t e c h n i c a l c h l o r d a n or is, i n fact, a chlordan

metabolite.

d u r i n g cis-

A

heptachlor

epoxide

artifact

(15),

trans-

observed

a n d f r a r w - c h l o r d a n f e e d i n g experiments o n rats ( 1 6 ) ,

b e e n s u b s e q u e n t l y i d e n t i f i e d as the c l o s e l y - r e l a t e d c o m p o u n d

has

1,2-dichloro-

c h l o r d e n e e p o x i d e ( 1 7 ) , w h i c h possesses one m o r e c h l o r i n e a t o m i n the 2-endo-position

than heptachlor epoxide

c h l o r d a n m e t a b o l i t e has also b e e n g e n e r a l interest is the g r o u p

itself ( F i g u r e 1 ) .

observed

in milk

of i n d u s t r i a l c o m p o u n d s

(18).

This new Of

more

k n o w n as the

p o l y c h l o r i n a t e d b i p h e n y l s ( P C B ) w h i c h , o n the c o m m o n l y u s e d G L C columns, interfere w i t h practically a l l organochlorine insecticides 20, 21).

W i t h the a d v e n t of n u m e r o u s s h o r t e n e d m e t h o d s of

(19,

residue

analysis i n w h i c h the final result is o b t a i n e d via e x t r a c t i o n p r o c e d u r e s i n c o r p o r a t i n g G L C w i t h o u t p r i o r c l e a n - u p , the s i t u a t i o n m a y b e c o m e e v e n worse. It has a l r e a d y b e e n stated t h a t " n o one m e t h o d c a n i d e n t i f y a n u n k n o w n r e s i d u e w i t h absolute c e r t a i n t y " ( 2 2 )

a n d i n this context f o u r

parameters h a v e b e e n suggested " f r o m w h i c h the c o n f i r m a t i o n o f i d e n t i t y of a r e s i d u e c a n b e i n f e r r e d w i t h reasonable a s s u r a n c e " (23).

Two

of

these parameters are the E C - G L C r e t e n t i o n t i m e ( o n a g i v e n s t a t i o n a r y p h a s e ) b e f o r e a n d after c h e m i c a l reactions. T h e pesticides o r m e t a b o l i t e s c o n c e r n e d are c o n v e r t e d b e f o r e i n j e c t i o n to d e r i v a t i v e s w i t h different r e t e n t i o n times f r o m the p a r e n t c o m p o u n d s a n d also f r o m o t h e r c o m m o n pesticides that m a y b e present. T h e other t w o parameters are R

f

( T L C or P C ) o r p-values (24)

values

and insecticidal activity.

A l t h o u g h T L C has b e e n w i d e l y a c c e p t e d as a source o f a d d i t i o n a l i n f o r m a t i o n i n c o r r o b o r a t i o n of r e s i d u e i d e n t i t y ( 9 ) , t h e use of c h e m i c a l



2.

C O C H R A N E

A N D

C H A U

Organochlorine

2-Chlorochlordene

Residue

13

Identity

3-Chlorochlordene

CI

CI

1.2-Dichlorochlordene eooxide

Figure 1. Structures and numbering for some chlordan compounds and isomers d e r i v a t i z a t i o n has b e e n a r e l a t i v e l y recent i n n o v a t i o n o w i n g p r i m a r i l y to a c h a n g e i n a p p l i c a t i o n . P r i o r to 1965, c h e m i c a l m e t h o d s w e r e u s e d as a n i n t e g r a l p a r t of t h e e x t r a c t i o n / c l e a n - u p p r o c e d u r e s m o d i f y the co-extracted m a t e r i a l ( 2 5 ) .

to r e m o v e

or

S i n c e t h a t t i m e , t h e n u m b e r of

p u b l i c a t i o n s d e a l i n g w i t h r e s i d u e c o n f i r m a t i o n has g r a d u a l l y i n c r e a s e d a n d i n p a r t i c u l a r the o r g a n o c h l o r i n e residues h a v e b e e n c o n v e r t e d

to

G L C - r e s p o n s i v e derivatives b y m a n y methods i n c l u d i n g addition, oxidat i o n , r e a r r a n g e m e n t , d e c h l o r i n a t i o n , a n d d e h y d r o c h l o r i n a t i o n reactions. I n m a n y instances, the G L C c h r o m a t o g r a m o b t a i n e d after r e a c t i o n has b e e n ' c l e a n e d - u p " of i n t e r f e r i n g or b a c k g r o u n d c o m p o n e n t s

that were

present i n the o r i g i n a l s a m p l e . C o n f i r m a t o r y tests for several groups of o r g a n o c h l o r i n e pesticides h a v e n o w b e e n e s t a b l i s h e d i n terms of specific or g e n e r a l reagents a n d the m e c h a n i s t i c p a t h w a y s b y w h i c h t h e y are derivatized.

The DDT Group S a p o n i f i c a t i o n has b e e n b y f a r the most c o m m o n l y u s e d m e t h o d f o r b o t h the i d e n t i f i c a t i o n a n d , i n m a n y instances, q u a n t i t a t i o n of D D T a n d related compounds.

D e r i v a t i v e t e c h n i q u e s h a v e b e e n a p p l i e d to b i o l o g i -


14

PESTICIDES

Table I.

Confirmatory Tests for Pesticide Reaction

Pesticide


IDENTIFICATION

Utilized

DDT

a) D e h y d r o c h l o r i n a t i o n b) D e c h l o r i n a t i o n (of p , p ' - i s o m e r )

DDE

Oxidation

DDD

Dehydrochlorination

Methoxychlor

Dehydrochlorination

Aldrin

/CI, a) A d d i t i o n ^ - B r Nert-BuOCl b) E p o x i d a t i o n 2

Dieldrin

/cleavage Epoxide^-rearrangement ^acetylation

Endrin

E p o x i d e rearrangement Dechlorination

Endosulfan

Sulfite reduction

° In ppm of parent pesticide based on a 10-gram sample. 6% Q F - 1 + 4% D C - 1 1 on Chromosorb W . Column operating at 200°C. 6

c a l extracts c o n t a i n i n g p , p ' - D D T , p , p ' - D D D , d i c o f o l ,

Perthane,

m e t h o x y c h l o r , a n d i n m a n y instances t h e i r respective o,p'-isomers.

p,p'While

the m a j o r i t y of these D D T - r e l a t e d c o m p o u n d s are c o n v e r t e d to t h e i r respective olefins ( F i g u r e 2 ) , d i c o f o l y i e l d s

p,p'-dichlorobenzophenone.

T h e s e c o n f i r m a t o r y reactions h a v e b e e n e v a l u a t e d o n s t a n d a r d i n s e c t i c i d e solutions (25, 26, 2 7 ) , v e g e t a b l e (28, 2 9 ) a n d a n i m a l tissue (27, 3 0 ) , a n d s o i l extracts (31), display R

a n d the c o r r e s p o n d i n g d e h y d r o c h l o r i n a t e d d e r i v a t i v e s

( r e t e n t i o n t i m e ) values s u b s t a n t i a l l y different f r o m the p a r e n t

t

compounds.

I n some cases, m i s l e a d i n g results c a n b e o b t a i n e d b y the

less t h a n astute analyst b e c a u s e of p e a k - o v e r l a p of t h e e x p e c t e d d e r i v a t i v e w i t h a n o r g a n o c h l o r i n e p e s t i c i d e r e s i d u e a l r e a d y present b u t unaffected b y the a l k a l i c o n d i t i o n s u s e d . U s i n g a c o l u m n c o n t a i n i n g C h r o m o s o r b coated w i t h 4 % S E - 3 0 +

6%

Q F - 1 , the d e r i v a t i v e s D D M U

W

(Figure 2)

a n d o , p ' - D D E , from p , p ' - D D D a n d o , p ' - D D T , respectively, overlap w i t h h e p t a c h l o r e p o x i d e w h i c h is unaffected u n d e r m i l d b a s i c c o n d i t i o n s

(28).

S i m i l a r l y , p , p ' - D D E a n d d i e l d r i n c o i n c i d e u s i n g D C - 2 0 0 as s t a t i o n a r y phase

(31).

Although

potassium

tert-butoxide

(f-BuOK),

sodium

methylate

( N a O C H ) , sodium ethylate ( N a O Q j H s ) , alcoholic potassium hydroxide, 3

a n d s o d i u m h y d r o x i d e solutions h a v e b e e n u s e d , t h e u t i l i z a t i o n of t h e


2.

C O C H R A N E

A N D

Organochlorine

C H A U

Residue

Identity

15

Residues; The D D T Group and Some Cyclodienes


Limit of Detectability

a

Pesticide Interference

Reference

b

0.02 0.03

DDE p,p'-DDD

27 32

0.05

many

29

0.03

-

27

0.1

p,p'-DDT

27

0.03 0.04 0.04 0.01

p,p'-DDD

30 U u

-

-

Dieldrin

0.01 0.05 0.04

Endrin Endrin

30 36 39

Dieldrin

36

-

0.04 0.04

-

0.02

40

o,p'-DDE

53

stronger n u c l e o p h i l i c reagents—e.g., f - B u O K — c a n s i m u l t a n e o u s l y i d e n t i f y DDT

a n d analogues a n d some c y c l o d i e n e

series

insecticides of the c h l o r d a n

(14).

N o r m a l l y , p , p ' - D D T occurs together w i t h its m e t a b o l i t e p , p ' - D D E , w h i c h c a n interfere w i t h d e h y d r o c h l o r i n a t i o n c o n f i r m a t i o n unless i t has b e e n p r e v i o u s l y r e m o v e d , for e x a m p l e , b y T L C ( T a b l e I ) . O n e c h e m i c a l

\

—c— -C—CI

/

p.p'- D D T

>

/"

C,«,

R

S

/ "

H — C - - C — C I

»/

DDMU

P.P- DDD

base

baae

c = c , /

X

H

DDNU

+

>

7

o ,

-C

p,p'- - D D E

:c

DDMU

DCS

Figure 2. Reaction products of p , p ' - D D T and p , p ' - D D D with basic and aqueous chromous chloride reagents (where R = Cl@-)


16

PESTICIDES

IDENTIFICATION

r e a c t i o n t h a t c i r c u m v e n t s this a d d i t i o n a l step is d e c h l o r i n a t i o n

with

c h r o m o u s c h l o r i d e ( C r C l ) s o l u t i o n . C h r o m o u s c h l o r i d e reacts p r e f e r e n 2

t i a l l y w i t h the p , p ' - i s o m e r to g i v e p r i m a r i l y p , p ' - D D D ( F i g u r e 2 ) o n l y 45 m i n u t e s at 6 0 ° C ( T a b l e I ) .

after

Prolonged reaction ( F i g u r e 2) fur-

t h e r converts p , p ' - D D D to D D N U , D D M U , a n d f r a n s - p , p ' - d i c h l o r o s t i l bene ( D C S )

(32).

On a 4%

DC-11 +

6%

Q F - 1 on Chromosorb

c o l u m n , p , p ' - D D E a n d D C S h a v e i d e n t i c a l r e t e n t i o n times.

W

A l s o , the


f u r t h e r p h o t o i s o m e r i z a t i o n p r o d u c t of D C S , the c o r r e s p o n d i n g cis-isomer ( 3 3 ) , D D N U , a n d h e p t a c h l o r h a v e t h e same R v a l u e ( F i g u r e 3 ) .

Reduc-

t

tive dechlorination w i t h C r C l related compounds.

2

does not a p p e a r to b e c o m m o n to a l l D D T -

F o r e x a m p l e , o , p ' - D D T reacts f a i r l y q u i c k l y a n d

p , p ' - m e t h o x y c h l o r not at a l l . U n p r e d i c t a b l y , p r e f e r e n t i a l d e c h l o r i n a t i o n p a t h w a y s h a v e also b e e n o b s e r v e d i n t h e d e g r a d a t i o n of D D T a n d a n a logues i n some b i o l o g i c a l systems b u t n o t i n others

(34).

C h r o m i c a c i d o x i d a t i o n has b e e n e m p l o y e d f o r t h e q u a n t i t a t i o n of p , p ' - D D E (35)

a n d c a n b e successfully a p p l i e d to its c o n f i r m a t i o n o n

t h e r e s i d u e scale ( T a b l e I ) . D D T - r e l a t e d compounds

S i n c e this r e a c t i o n is a p p l i c a b l e to other

a n d m e t a b o l i t e s , the p o s s i b l e sources of i n t e r -

f e r e n c e h a z a r d s i n a D D T - c o n t a i n i n g b i o l o g i c a l extract are m a n y . W h e n i n c o r p o r a t e d i n t o r e g u l a t o r y r e s i d u e p r o c e d u r e s , these m e t h ods w o r k satisfactorily w i t h v a r i o u s p l a n t a n d a n i m a l extracts d o w n to levels of 0.02-0.1 p p m , d e p e n d i n g o n t h e p e s t i c i d e c o n c e r n e d ( T a b l e I ) .

The Aldrin Group T a k i n g a d v a n t a g e of t h e o b s e r v a t i o n that e n d r i n is r e a d i l y r e a r r a n g e d t o a p e n t a c y c l i c ketone b y m i n e r a l acids (36)

a n d also b o r o n t r i f l u o r i d e

( B F ) ( 3 7 ) , a n u m b e r of c o n f i r m a t o r y tests h a v e b e e n d e v i s e d .

Concen-

3

trated sulfuric acid minutes

at

room

(H S0 ) 2

4

temperature.

achieves

complete

Similarly,

conversion

hydrobromic

in

acid

10-15 (HBr),

chromic acid ( C r 0 ) , a n d hydrochloric acid ( H Q ) under various condi3

tions h a v e b e e n u t i l i z e d f o r the p o s i t i v e i d e n t i f i c a t i o n of e n d r i n f o u n d i n s o i l , vegetable, forage c r o p , a n d fat extracts. A l t h o u g h t h e use of m i n e r a l acids is c o n v e n i e n t a n d q u i c k , d i e l d r i n also reacts u n d e r s i m i l a r c o n d i tions.

With B F

3

i n m e t h a n o l , c o n c e n t r a t e d H S 0 , or p e r c h l o r i c a c i d , 2

4

d i e l d r i n is r e a r r a n g e d to a " d i e l d r i n k e t o n e , " t h e exact structure of w h i c h is s t i l l not k n o w n . U s i n g c o n c e n t r a t e d H C 1 i n e t h a n o l , the c o r r e s p o n d i n g a l d r i n c h l o r o h y d r i n has b e e n i d e n t i f i e d as the d e r i v a t i v e p r o d u c e d e p o x i d e cleavage (38).

by

P r e s u m a b l y H B r y i e l d s the c o r r e s p o n d i n g b r o m o -

h y d r i n p r o d u c t a n d , i f g l a c i a l acetic a c i d is present, the c o r r e s p o n d i n g bromoacetate.

I n one instance (21),

concentrated H S 0 2

4

has b e e n u s e d

f o r t h e d e t e c t i o n of s m a l l a m o u n t s of the m o r e v o l a t i l e c o m p o u n d s — e . g . , a l d r i n a n d l i n d a n e — b y " r e m o v a l " of t h e o x y g e n - c o n t a i n i n g residues s u c h


2.

C O C H R A N E

A N D

Organochlorine

C H A U

17

Residue Identity


D D N U + cis— DCS

2

4

6

8

10

12

Retention T i m e (in M i n u t e s )

Figure 3. Chromatogram showing the products obtained reaction of p,p'-DDT with CrCl after 24 hours at 60°C ( and subsequent standing in fluorescent light or sunlight ( 2

as d i e l d r i n , e n d r i n , a n d h e p t a c h l o r e p o x i d e .

from ) )

Unlike endrin and dieldrin,

the d i s a p p e a r a n c e of h e p t a c h l o r e p o x i d e is n o t r e a d i l y e x p l a i n e d since this r e s i d u e is a p p r e c i a b l y resistant to a c i d t r e a t m e n t . I r r e s p e c t i v e of t h e a c i d i c reagent e m p l o y e d , i f a D C - 2 0 0 o r m i x e d D C - l l / Q F - 1 c o l u m n is u s e d i n t h e final G C a n a l y s i s , i n c o m p l e t e r e s o l u t i o n of the e n d r i n a n d d i e l d r i n d e r i v a t i v e peaks is o b s e r v e d (36, 3 8 ) . T h i s o v e r l a p p r o b l e m has b e e n o v e r c o m e b y u s i n g e i t h e r 1 5 % Q F - 1 a n d 1 0 % D C - 2 0 0 as s t a t i o n a r y phase f o r o n - c o l u m n r e s o l u t i o n o r a n a c e t y l a t i o n procedure

to g i v e e a s i l y G C r e s o l v a b l e d e r i v a t i v e s w h e n e n d r i n a n d

d i e l d r i n residues o c c u r together.

I n the f o r m e r case, this p a r t i c u l a r c o l -

u m n w a s u s e d to separate e n d r i n ketone a n d the a l d r i n c h l o r o h y d r i n ; i n t h e l a t t e r case a n a c e t i c a n h y d r i d e - s u l f u r i c a c i d reagent (36, 3 9 )

pro-

d u c e d the e x p e c t e d e n d r i n ketone a n d a d i e l d r i n d i a c e t a t e d e r i v a t i v e h a v i n g s i g n i f i c a n t l y different R values. t

A n a l t e r n a t i v e c o n f i r m a t o r y test f o r e n d r i n i n the presence of d i e l d r i n has b e e n a c h i e v e d b y p r e f e r e n t i a l r e d u c t i v e d e c h l o r i n a t i o n . A l t h o u g h b o t h e n d r i n a n d d i e l d r i n react w i t h C r C l , e n d r i n is s u b s t a n t i a l l y m o r e 2

l a b i l e ( F i g u r e 4 ) to this p a r t i c u l a r reagent to g i v e a p e n t a c h l o r o k e t o n e w h i c h has a different r e t e n t i o n t i m e f r o m t h e m o r e c o m m o n c h l o r i n e pesticides

organo-

(40).

S e l e c t i v e h a l o g e n a t i o n of a l d r i n to the c o r r e s p o n d i n g d i c h l o r i d e o r d i b r o m i d e constitutes one a p p r o a c h to its c o n f i r m a t i o n (30, 41).

How-

ever, c a r e f u l r e m o v a l of r e s i d u a l traces of c h l o r i n e or b r o m i n e m u s t b e p e r f o r m e d to g i v e G C - i n t e r p r e t a b l e d e r i v a t i v e - c o n t a i n i n g extracts. A l s o ,


18

PESTICIDES

Heptachlor

Lindane

I D E N T I F I C A T I O N

H e p t a c h l o r epoxide

P,p'~DDT


- C —

>

CI

frarw-Chlordane

cw-Chlordane

0

X

II I C — C —

I

I

CCI,

CCI,

o,p'—DDT

CH, II

2-Chlorochlordene

3-Chlorochlordene

X I

> — C —

C — > t e r t — X > aec — - I

X = I , B r , CI

(OV-CH

II

I

>-Br

X > primary — X >

VO/~

B

r

*

I I

— C = C — X

>-CI

B r — C H , B r > C H , C H B r - C H Br C H , > Br C H - C H . B r ~ CI CI

CH, CHCI-CHCI C H , > C H , - C H , %

p,p'—DDE

CH,-CBr-CH,Br

BrCH=CHBr

>

Reference C3

^Rr

Figure 4.

Relative order of reactivity of organochlorine pesticides and some halogenated compounds to Cr * reagents 2

c H c h l o r o a l d r i n m a y interfere w i t h p , p ' - D D D w h i c h is unaffected b y t h e c h l o r i n a t i o n c o n d i t i o n s . A d d i t i o n to the u n h i n d e r e d d o u b l e b o n d of a l d r i n has also b e e n a c c o m p l i s h e d u n d e r v a r i o u s conditions. undergoes r e a c t i o n

to

with

terf-butyl

hypochlorite

(tert-BuOCl)

U s i n g f e r r - b u t y l a l c o h o l as solvent, o n l y a l d r i n

give

the c o r r e s p o n d i n g

chloro-tert-butyl

ether,

Table II. Reaction

Pesticide Heptachlor

The

Utilized

/acetylation a) A l l y l i c ^ h y d r o x y l a t i o n ^dechlorination b) A d d i t i o n c)

Epoxidation

Heptachlor epoxide

Epoxide

cis- a n d transChlordan

Dehydrochlorination

rearrangement

Nonachlor a)

Dechlorination

b)

Dehydrochlorination


2.

C O C H R A N E

A N D

Organochlorine

C H A U

Residue

19

Identity

whereas i n glacial acetic a c i d both heptachlor a n d aldrin give their res p e c t i v e c h l o r o a c e t a t e d e r i v a t i v e s (14).

T h e most c o n v e n i e n t m e t h o d ,

h o w e v e r , is the e x p o x i d a t i o n of a l d r i n to d i e l d r i n b y p e r a c i d s o r C r 0 . 3

A l t h o u g h p e r a c e t i c (42), a c i d s (14)

performic, perbenzoic, and monoperphthalic

are a p p l i c a b l e for this e p o x i d a t i o n ,

ra-chloroperbenzoic

acid

w i l l p r o b a b l y b e t h e reagent of c h o i c e b e c a u s e of its a v a i l a b i l i t y , e v e n t h o u g h i t has b e e n p o i n t e d out that b a c k g r o u n d E C - G L C Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0104.ch002

m a y be an a d d e d complication

interferences

(43).

T h e s e n s i t i v i t y r a n g e of these c o n f i r m a t o r y c h e m i c a l tests f o r a l d r i n , d i e l d r i n , a n d e n d r i n is 0.01 to 0.05 p p m i n terms of the p a r e n t pesticides in

field-treated

samples ( T a b l e I ) .

The Chlordan Group A v a r i e t y of m e t h o d s has b e e n d e v i s e d f o r t h e c o n f i r m a t i o n of h e p t a c h l o r residues ( T a b l e I I ) .

T h e presence

i n the heptachlor molecule

( F i g u r e 1) of a r e a c t i v e a l l y l i c c h l o r i n e a t o m has b e e n t h e basis of t h r e e c o n f i r m a t o r y tests b a s e d o n its ease of r e p l a c e m e n t . R e a c t i o n w i t h a s i l v e r a c e t a t e - g l a c i a l a c e t i c a c i d m i x t u r e p r o d u c e d 1-acetoxychlordene w h i c h , w i t h the G L C c o n d i t i o n s u s e d , h a d a r e t e n t i o n t i m e close t o h e p t a c h l o r e p o x i d e (44).

O f the c o m m o n organochlorine pesticides, only heptachlor

r e a c t e d q u a n t i t a t i v e l y . E n d r i n reacts to a s m a l l extent w i t h t h e g l a c i a l acetic a c i d to g i v e a s e c o n d a r y e n d r i n k e t o n e p e a k . W h e n t h e r e a c t i o n of h e p t a c h l o r w i t h silver salts w a s e x t e n d e d t o silver c a r b o n a t e i n a q u e ous a l c o h o l , 1 - h y d r o x y c h l o r d e n e w a s o b t a i n e d w h i c h c a n e a s i l y b e c o n v e r t e d to t h e m o r e v o l a t i l e a n d G C - r e s p o n s i v e s i l y l ether. U n f o r t u n a t e l y , this s i l y l ether has a R i d e n t i c a l to a l d r i n . W i t h s i l v e r c a r b o n a t e , h e p t a t

Chlordan Group Limit of Detectability

Pesticide Interference

-A l d r i n

0.01 0.01 0.01 0.03 0.05

Chlordene

-H e p t a c h l o r epoxide

Reference

44 u 45 14

29

0.01

-

52

0.01

-

14

0.01 0.01

ciVChlordan Aldrin

53


20

PESTICIDES

I D E N T I F I C A T I O N

c h l o r w a s the o n l y c h l o r i n a t e d p e s t i c i d e t o u n d e r g o m o d i f i c a t i o n , a n d t o date this r e a c t i o n is t h e most specific c o n f i r m a t o r y test o b s e r v e d f o r a n y of t h e c o m p o u n d s i n v e s t i g a t e d . S i n c e b o t h t h e s i l v e r salt reactions i n v o l v e r e f l u x i n g for a m i n i m u m of 30 m i n u t e s , a m o r e c o n v e n i e n t t e c h n i q u e is the use of C r C l

2

h e p t a c h l o r to c h l o r d e n e (45).

laboratory

s o l u t i o n for the a l l y l i c d e c h l o r i n a t i o n of T h i s is e a s i l y a c c o m p l i s h e d b y r e a c t i o n at

5 0 ° - 6 0 ° C for 30 m i n u t e s . T o g e t h e r w i t h t h e m a j o r r e d u c t i v e d e c h l o r i n a Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 8, 2017 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0104.ch002

tion pathway, t w o minor products, a dimer a n d 1-hydroxychlordene,

are

obtained probably b y bimolecular reduction and hydroxyl insertion res p e c t i v e l y , w h e n the r e a c t i o n is c a r r i e d out i n aqueous m e d i a ( F i g u r e 5 ) . U n d e r s u c h c o n d i t i o n s , i t c a n also b e p o s t u l a t e d t h a t

1-hydroxychlordene

is f o r m e d b y h y d r o l y s i s of h e p t a c h l o r as has b e e n p r e v i o u s l y (46,

47).

O n t h e r e s i d u e scale, these s e c o n d a r y

observed

p r o d u c t s present

no

o b s e r v a b l e G C interference. C h l o r d e n e has b e e n o b t a i n e d b y d e c h l o r i n a t i o n of h e p t a c h l o r b y b a c t e r i a a n d subsequent m i c r o b i a l e p o x i d a t i o n t o c h l o r d e n e e p o x i d e i n soils (48);

therefore, interference c a n o c c u r i n s u c h

samples d e p e n d i n g u p o n the extent of c h l o r d e n e d e g r a d a t i o n . T w o f u r t h e r tests for h e p t a c h l o r i n v o l v e a d d i t i o n to the s t e r i c a l l y hindered double bond.

N o r m a l l y , c h l o r i n e does n o t a d d to h e p t a c h l o r

unless a n i n i t i a t o r , s u c h as a n t i m o n y p e n t a c h l o r i d e , is present.

Hepta-

c h l o r is resistant to e p o x i d a t i o n b y p e r a c i d s b u t b o t h a d d i t i o n a n d e p o x i dation can readily be achieved chemically b y

terf-BuOCl/HOAc

o x i d a t i o n , r e s p e c t i v e l y ( T a b l e I I ) . F o r the a d d i t i o n of

and C r 0

terf-BuOCl

Dimer

1 -Hydroxychlordene

Chlordene

Figure 5.

Reaction

pathways of heptachlor with CrCl solution

aqueous

g


3

to p r o -


2.

C O C H R A N E

A N D

01

fr

Pesticides Identification at the Residue Level - ACS Publications

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