Past, Present, and Future Application of Paper and Thin-Layer

8 Past, Present, and Future Application of Paper and Thin-Layer Chromatography for Determining Pesticide Residues

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MELVIN

E. GETZ

Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md. 20705

The past and present uses of paper and thin-layer tography fication

have been confined and semiquantitative

optical

scanning

techniques analysis

have endeavored

can be

tographic

uniform

application

tative

method

residue

The

in

precision

and

upon uniformity

spotting

of samples

of chromogenic

were undertaken

of analysis

Developments

and refinements

are dependent

new investigations

identiin

spotting

to show that these methods

quantitative.

layer, uniform

chroma-

to qualitative

estimation.

instrumentation

of this approach and

largely

would

of

and

reagents.

so an alternate be available

for

of

accuracy chromastandards, These quantipesticide

analysis.

* T p h e effect o n the e n v i r o n m e n t of pesticides a n d t h e i r residues has b e c o m e a g r o w i n g c o n c e r n of the scientific c o m m u n i t y a n d the g e n e r a l public ( J ) .

Pesticides e m b r a c e a l a r g e v a r i e t y of c h e m i c a l s , i n c l u d i n g

insecticides, f u n g i c i d e s , h e r b i c i d e s , r o d e n t i c i d e s , n e m a t o c i d e s , a n d m o l luscicides.

S i n c e these c o m p o u n d s

are toxic i n n a t u r e , m a n y countries

regulate t h e i r use b y l a w a n d specify h o w m u c h r e s i d u e c a n b e left i n a food product.

I n o r d e r to enforce s u c h r e g u l a t i o n s , s o p h i s t i c a t e d a n a -

l y t i c a l m e t h o d s h a v e h a d to b e d e v e l o p e d . I n a d d i t i o n to f o o d analysis, the e n v i r o n m e n t is m o n i t o r e d to m e a s u r e the degree of c o n t a m i n a t i o n that m i g h t b e c a u s e d b y the use of pesticides. T h e s e projects

e n t a i l s a m p l i n g of w i l d life, w a t e r sources, a n d soils.

W e a l t h y countries c a n u t i l i z e h i g h l y s o p h i s t i c a t e d a n d expensive e q u i p m e n t , s u c h as gas c h r o m a t o g r a p h y c o u p l e d w i t h mass s p e c t r o m e t r y , f o r r e s i d u e d e t e r m i n a t i o n a n d i d e n t i f i c a t i o n . H o w e v e r , since there is i n t e r 119

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

120

PESTICIDES

IDENTIFICATION

n a t i o n a l c o n c e r n a b o u t the use of p e s t i c i d e s , there is a n e e d f o r a r e l i a b l e a n a l y t i c a l m e t h o d t h a t is s i m p l e a n d i n e x p e n s i v e . P a p e r a n d t h i n - l a y e r c h r o m a t o g r a p h y are t w o s u c h a p p r o a c h e s .

The

t e c h n i q u e s are s i m p l e a n d r e q u i r e i n e x p e n s i v e e q u i p m e n t . I f one chooses the p r o p e r solvents, adsorbents, a n d c h r o m o g e n i c reagents, residues c a n b e i s o l a t e d o n a sheet of c h r o m a t o g r a p h i c p a p e r or a t h i n l a y e r of a d sorbent. T h e t y p e of r e s i d u e c a n t h e n b e d e t e r m i n e d b y c o m p a r i s o n w i t h reference s t a n d a r d s . T h e a p p l i c a t i o n s of these t e c h n i q u e s are r e v i e w e d i n this p a p e r . T h e a u t h o r s p e r s o n a l experiences are p r e s e n t e d w i t h a l o o k i n t o f u t u r e a p p l i Downloaded by TUFTS UNIV on October 2, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0104.ch008

cations, i n p a r t i c u l a r , q u a n t i t a t i v e d e t e r m i n a t i o n s b y o p t i c a l s c a n n i n g methods.

Review Paper Chromatography.

T h e first i m p o r t a n t step for a n y p e s t i c i d e

r e s i d u e m e t h o d o l o g y is to extract the r e s i d u e f r o m the substrate a n d i s o late i t i n a p u r e e n o u g h state so that i t c a n b e i d e n t i f i e d a n d m e a s u r e d . T h i s p u r i f i c a t i o n step is c a l l e d " c l e a n - u p , " a n d there is a great q u a n t i t y of l i t e r a t u r e c o n c e r n i n g the different a p p r o a c h e s ( 2 , 3, 4, 5,

6).

O n c e the r e s i d u e has b e e n i s o l a t e d i n a f a i r l y p u r e state, i t c a n b e further resolved and identified b y chromatography.

Paper chromatog-

r a p h y , w h i c h w a s i n t r o d u c e d b y C o n s d e n et al. ( 7 ) i n 1944, w a s the first technique used.

I n i t i a l l y , i t w a s chiefly a n art, since i t d e p e n d e d

on

m a n i p u l a t i o n s of t h e i n d i v i d u a l investigators. B y 1957, s u p p l i e r s of c h r o m a t o g r a p h i c p a p e r s s t a r t e d to m a n u f a c t u r e a h i g h - q u a l i t y p r o d u c t .

It

w a s at this t i m e that M i t c h e l l ( 8 ) d e v e l o p e d p a p e r c h r o m a t o g r a p h y i n t o a s c i e n c e b y s e t t i n g u p a systematic a p p r o a c h for d e t e r m i n i n g o p t i m u m c o n d i t i o n s for r e s o l u t i o n a n d s e n s i t i v i t y . H i s w o r k w i t h i m m o b i l e — m o b i l e p h a s e c h r o m a t o g r a p h y ( 9 ) d e m o n s t r a t e d that p e s t i c i d e separations c o u l d b e o b t a i n e d w i t h a w i d e d e g r e e of r e s o l u t i o n a n d

flexibility.

O n e of the first l a b o r a t o r y groups to a p p l y p a p e r

chromatography

as a n i d e n t i f i c a t i o n a n d e s t i m a t i o n t e c h n i q u e was t h a t of M i i l l e r et (10).

I n 1957, at the C o n t r o l L a b o r a t o r y i n B a s e l , his g r o u p

al.

developed

a n e x t r a c t i o n a n d c l e a n - u p p r o c e d u r e f o r a f e w o r g a n o c h l o r i n e a n d org a n o p h o s p h o r u s insecticides a n d t h e n d e t e r m i n e d the q u a n t i t y of r e s i d u e w i t h reverse phase p a p e r c h r o m a t o g r a p h y .

Similar procedures were f o l -

l o w e d b y M c K i n l e y a n d M a h o n i n C a n a d a (11) States (12).

a n d M i l l s i n the U n i t e d

T h i s first series of p a p e r s t r i g g e r e d w i d e a p p l i c a t i o n s of

p a p e r m e t h o d s for r e s i d u e d e t e r m i n a t i o n s (13, 14, 15, 16, 17, 18, 19, 21,

20,

22). T h i n - L a y e r Chromatography. A f e w years after the i n t r o d u c t i o n of

p a p e r c h r o m a t o g r a p h y , the p r i n c i p l e s of t h i n - l a y e r c h r o m a t o g r a p h y w e r e


8.

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Paper and Thin-Layer

121

Chromatography

demonstrated by M e i n h a r d and H a l l (23).

K i r c h e n e r et al. (24)

d u c e d t h e i n i t i a l t h i n - l a y e r c o a t i n g t e c h n i q u e s . S o l a et al. (25)

intro-

w e r e the

first g r o u p to s h o w t h a t insecticides c o u l d b e c h r o m a t o g r a p h e d b y this t e c h n i q u e , w i t h W a l k e r a n d B e r o z a (26)

presenting data obtained b y a

c o m p r e h e n s i v e c o v e r a g e of a l a r g e n u m b e r of solvents w i t h m a n y types of i n s e c t i c i d e s . T h e successful a p p l i c a t i o n of t h i n - l a y e r c h r o m a t o g r a p h y to determine multiple organochlorine

a n d organophosphorus

f o o d p r o d u c t s was a c c o m p l i s h e d b y K o v a c s (27,

residues i n

28).

E x c e l l e n t r e v i e w s of T L C t e c h n i q u e s as a p p l i e d to pesticides h a v e


been written by C o n k i n (29)

and by Abbot and Thomson

(30).

Personal Techniques C l e a n - u p . C h a r c o a l is the f a v o r i t e a d s o r b e n t f o r the first steps i n t h e author's c l e a n - u p p r o c e d u r e s

(31,

32).

I t is a n excellent d e c o l o r i z i n g

agent a n d removes m u c h of the l a r g e - m o l e c u l e interferences.

W h e n it

was i n i t i a l l y u s e d , there was a p r o b l e m of r e p r o d u c i b i l i t y . H e a v y m e t a l cations, e s p e c i a l l y i r o n , w e r e c h e l a t i n g w i t h or t y i n g u p the insecticides

Figure 1. Paper chromatogram of different concentrations of a mixture of methyl parathion (A), Methyl Trithion (B), and carbophenothion (C); also, 1-gram aliquots of cleaned-up samples of control squash and wax beans Paper: Whatman #1 20- X 20-cm Immobile phase: 20% dimethylformamide Mobile phase: 2,2,4-trimethylpentane Chromogenic reagent: p-nitrobenzylpyridine



122

PESTICIDES

Figure 2.

Paper chromatogram of 10 fig of carbophenothion its oxidative metabolites

IDENTIFICATION

(Trithion)

and

Paper: Whatman #3MM 20- X 20-cm Immobile phase: 10% soybean oil Mobile phase: 40% acetonitrile in distilled water Chromogenic reagent: silver nitrate-bromcresol green

so that n o n e or o n l y p a r t of t h e m w e r e b e i n g e l u t e d . A s i m p l e treatment w i t h h y d r o c h l o r i c a c i d t i e d u p the m e t a l ions a n d r e p r o d u c i b l e results w e r e o b t a i n e d t h e n f r o m the different w o o d charcoals.

Both column

e l u t i o n a n d b a t c h w i s e c l e a n - u p t e c h n i q u e s are u s e d . If there is a significant a m o u n t of o i l y m a t e r i a l left after the d e c o l o r i z i n g step, a second

t r e a t m e n t is necessary, i n v o l v i n g a s m a l l - v o l u m e

l i q u i d - l i q u i d partition (33).

T h i s a p p r o a c h has w o r k e d w e l l for o r g a n o -

chlorine and organophosphorus

insecticides.

S p o t t i n g . T h e present investigations of this l a b o r a t o r y are d i r e c t e d t o w a r d m a k i n g t h i n - l a y e r a n d p a p e r t e c h n i q u e s q u a n t i t a t i v e b y the use of o p t i c a l s c a n n i n g . I n p a r t i c u l a r , a p p l i c a t i o n s of the reflectance s c a n n i n g d e v i c e of B e r o z a et al. (34)

are b e i n g e x p l o r e d . V a r i a t i o n s i n the a p p l i -

c a t i o n of samples a n d standards to the c h r o m a t o g r a p h i c m e d i a h a v e a p r o n o u n c e d effect on the l i n e a r i t y of s t a n d a r d curves a n d d o not

give

good reproducibility. F o r q u a l i t a t i v e w o r k a n d the first q u a n t i t a t i v e s c a n n i n g t e c h n i q u e s , the s a m p l e w a s e v a p o r a t e d to dryness i n a c e n t r i f u g e t u b e a n d t h e n trans-


8.

GETZ


123

Chromatography

f e r r e d to the c h r o m a t o g r a m w i t h a s p o t t i n g p i p e t t e .

Several rinsings

w e r e p e r f o r m e d w i t h a v o l a t i l e solvent s u c h as ether or c h l o r o f o r m .

The

reference s t a n d a r d w a s u s u a l l y s p o t t e d w i t h a f e w fd of solvent. T h e

final

r e s u l t w a s a diffuse spot for the s a m p l e a n d a t i g h t spot for the s t a n d a r d . A f t e r d e v e l o p m e n t of t h e c h r o m a t o g r a m a n d v i s u a l i z a t i o n of the spots, i t w a s d i f f i c u l t to m a k e a n a c c u r a t e c o m p a r i s o n w i t h the s t a n d a r d . T h i s p r o b l e m is m i n i m i z e d b y the use of a n a u t o m a t i c spotter d e s i g n e d b y G e t z (35).

T h i s s p o t t i n g d e v i c e , a l l o w i n g c o m p l e t e c o n t r o l of

the i n i t i a l spot size of b o t h s a m p l e a n d s t a n d a r d b y the a p p r o p r i a t e c h o i c e of solvents a n d a i r flow, is a n i m p r o v e m e n t over a n e a r l i e r d e s i g n


b y B e r o z a et al.

(6).

C h r o m a t o g r a p h i c M e d i a a n d S o l v e n t Systems. # 3 M M 20- X

Whatman # 1

and

2 0 - c m papers are u s e d for p a p e r c h r o m a t o g r a p h y .

The

reverse phases of M i t c h e l l ( 9 )

g i v e excellent results for the o r g a n o c h l o -

rine and parent organophosphorus G e t z (36)

insecticides.

T h e reverse phases

of

successfully resolve the o x i d a t i v e m e t a b o l i t e s of the o r g a n o -

Figure 3. Thin-layer chromatogram of different concentrations of a mixture of methyl parathion (A), Methyl Trithion (B), and carbophenothion (C); also, 1-gram aliquots of cleaned-up samples of control squash and wax beans Plate: Brinkman prepared silica gel, 250 my Solvent: 70% 2,2,4-trimethylpentane, 25% acetone, 5% Chromogenic reagent: p-nitrobenzylpyridine

chloroform



124

PESTICIDES

Figure

4.

Thin-layer

IDENTIFICATION

chromatogram of actual organochlorine nursery soils

residues in

Plate: Eastman silica gel sheet Solvent: 90% 2,2,4-trimethylpentane, 10% methylene chloride Chromogenic reagent: silver nitrate-phenoxyethanol

p h o s p h o r u s i n s e c t i c i d e s . F i g u r e 1 represents some o r g a n o p h o s p h o r u s i n secticides c h r o m a t o g r a p h e d w i t h a n o n a q u e o u s m o b i l e phase, a n d F i g u r e 2 represents the o x i d a t i v e m e t a b o l i t e s of

carbophenothion

chromato-

g r a p h e d b y a n aqueous system. S i l i c a g e l , a l u m i n a , F l o r i s i l , cellulose, a n d p o r o u s glass are u s e d for p r e p a r i n g 20- X 2 0 - c m glass plates. C a l c i u m sulfate, c o l l o i d a l s i l i c a , a n d c o l l o i d a l a l u m i n a are u s e d as b i n d e r s . C o m m e r c i a l l y - p r e p a r e d plates also h a v e b e e n used. T h e solvent systems a n d adsorbents i n v e s t i g a t e d b y G e t z a n d W h e e l e r ( 3 7 ) are u s e d for i d e n t i f y i n g o r g a n o p h o s p h o r u s insecticides. T h e o r g a n o c h l o r i n e insecticides are r e s o l v e d b y a l u m i n a a n d s i l i c a g e l , u s i n g the solvent systems of K o v a c s ( 2 7 ) , W a l k e r a n d B e r o z a ( 2 6 ) , a n d B e r o z a et al

(38).

F i g u r e 3 shows s e p a r a t i o n of some o r g a n o p h o s p h o r u s insecticides b y t h i n - l a y e r c h r o m a t o g r a p h y , a n d F i g u r e 4 shows a c h r o m a t o g r a m of some o r g a n o c h l o r i n e insecticides i n s o i l extracts. D e v e l o p m e n t is c a r r i e d o u t i n tanks w i t h o u t liners, for

experience

has s h o w n t h a t the shape of the spot is m o r e s y m m e t r i c a l i f there is n o l i n e r present, e s p e c i a l l y w h e n b i n a r y or t e r n a r y solvent systems are used. Chromogenic Reagents.

I n o r d e r to d e t e r m i n e the R values of p u r e f

insecticides, a n y t y p e of reagent m a y b e u s e d to v i s u a l i z e the m i g r a t e d spot.

B u t w h e n this reagent is u s e d for a c t u a l r e s i d u e d e t e r m i n a t i o n s ,

t h e r e m a y b e n o n r e s i d u e spots f o r m e d b y extractives f r o m the substrate. T h e r e f o r e , i t is d e s i r a b l e t h a t the c h r o m o g e n i c reagents b e as selective as possible.


8.

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125

Chromatography

F o r d e t e c t i n g t h e p r e s e n c e o f o r g a n o c h l o r i n e c o m p o u n d s , a n acetone s o l u t i o n o f silver n i t r a t e is u s e d as a s p r a y reagent ( 8 ) . S i l v e r n i t r a t e also c a n b e i n c o r p o r a t e d into t h e t h i n - l a y e r m a t e r i a l (39)

a n d seems to

g i v e better results. H o w e v e r , t h e t h i n - l a y e r m e d i a m u s t h a v e a l o w c h l o r i n e c o n t e n t o r else t h e b a c k g r o u n d m a y t u r n b r o w n o r gray. T h e spots


A

Figure 5. Scan of five different concentrations of an organophosphorus insecticide mixture: (A) dimethoate, (B) mevinphos, (C) Dasanit, (D) malathion, (E) carbophenothion Plate: Quanta prepared silica gel, high abrasion resistance Solvent: 70% 2,2,4-trimethylpentane, 25% acetone, 5% chloroform Chromogenic reagent: p-nitrobenzylpyridine



126

PESTICIDES

10 Figure 6.

2.0

3.0

4.0

SO

6.0

IDENTIFICATION

70

AJ1

80

Standard curves obtained from (A) dimethoate, (B) mevinphos, (C) Dasanit in the concentration range of 0.5 to 8.0 fig

are d e v e l o p e d b y e x p o s i n g the c h r o m a t o g r a m to h i g h - i n t e n s i t y U V l i g h t . T h e colors v a r y f r o m b r o w n to p u r p l i s h - b l a c k . S e v e r a l reagents are u s e d for the o r g a n o p h o s p h o r u s insecticides. A n acetone s o l u t i o n of s i l v e r n i t r a t e a n d b r o m c r e s o l g r e e n ( o r b r o m p h e n o l b l u e ) (31, 3 2 ) is s p r a y e d onto the c h r o m a t o g r a m . T h e spots are v i s u a l i z e d b y s p r a y i n g w i t h a 0 . 0 1 % c i t r i c a c i d s o l u t i o n or a p H 4.0 citrate buffer s o l u t i o n . T h i s reagent reacts o n l y w i t h the t h i o p h o s p h o r y l c o n figurations

to g i v e b l u e or m a g e n t a spots.

Treatment w i t h p-nitrobenzylpyridine a n d tetraethylenepentamine visualizes a l l the o r g a n o p h o s p h o r u s insecticides as b l u e or m a g e n t a spots (40). S e r u m cholinesterase w i t h b r o m t h y m o l b l u e i n d i c a t o r a n d a c e t y l c h o l i n e as a substrate detects the c h o l i n e s t e r a s e - i n h i b i t i n g insecticides P o s s i b l e interferences w i t h the s i l v e r n i t r a t e c h r o m o g e n i c are s u l f u r c o m p o u n d s

(36).

reagent

w h i c h w o u l d g i v e a b r o w n spot a n d r e d u c i n g

g r o u p s o n m o l e c u l e s w h i c h m i g h t p r o d u c e a spot. T o date, no c o m p o u n d s other t h a n o r g a n o t h i o p h o s p h a t e s g i v e a b l u e or m a g e n t a spot w i t h the s i l v e r n i t r a t e - d y e reagent.

Sulfur

compounds

w i l l react w i t h the silver n i t r a t e to g i v e b r o w n spots, a n d artifacts w i t h a c i d characteristics h a v i n g R / s s i m i l a r to the insecticides w o u l d p r e v e n t the color f o r m a t i o n .


8.

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The

127

Chromatography

p - n i t r o b e n z y l p y r i d i n e w i l l react w i t h epoxides, lactones, o t h e r

a l k y l a t i n g - t y p e c o m p o u n d s , a n d h e r b i c i d e s s u c h as a t r a z i n e . I t w i l l also g i v e a c o l o r r e a c t i o n w i t h o r g a n o c h l o r i n e insecticides t h a t h a v e a n e p o x y group.

Quantitative Chromatography T h e r e h a v e b e e n m a n y attempts at q u a n t i t a t i n g p a p e r a n d t h i n - l a y e r c h r o m a t o g r a m s (41),

b u t the s i m p l e s t a p p r o a c h appears to b e o p t i c a l

d e n s i t y measurements of the m i g r a t e d spots.

M a n y excellent s c a n n i n g


devices are n o w o n the m a r k e t . T h e y are precise o p t i c a l i n s t r u m e n t s c a p a b l e of great a c c u r a c y w h e r e the o p t i c a l measurements are c o n c e r n e d . T h e one u s e d i n this l a b o r a t o r y is t h e reflectance scanner of B e r o z a et al. w h i c h uses d o u b l e - b e a m fiber optics.

(34)

H o w e v e r , there are other m a n i p u l a t i o n s p e r f o r m e d f o r c h r o m a t o g r a p h y t h a t affect the p r e c i s i o n a n d a c c u r a c y of the final result. A s m e n t i o n e d p r e v i o u s l y , the s p o t t i n g t e c h n i q u e v a r i a t i o n was m i n i m i z e d b y t h e use of a n a u t o m a t i c spotter (35)

w h i c h spots s a m p l e a n d s t a n d a r d u n d e r

s i m i l a r p a r a m e t e r s , a n d the size of the i n i t i a l spots are a d j u s t e d so t h a t the E i n s t e i n - S m o l u c h o w s k y effect is m i n i m i z e d (42),

allowing a range

of concentrations f r o m the m i n i m u m d e t e c t a b l e to 20 fig.

30 IS

20 IS 10

A43.

Figure 7.

10

2.0

30

4.0

SO

6.0

70

80

Standard curves obtained from (D) malathion and (E) carbophenothion in the concentration range of 0.5 to 8.0 /tg



128

PESTICIDES

IDENTIFICATION

Figure 8. A reflectance scan of 10-fig mixture of three organophosphorus insecticides resolved with paper chromatography Paper: Whatman #1 20- X 20-cm Immobile phase: 20% dimethylformamide Mobile phase: 2,2,4-trimethylpentane Chromogenic reagent: p-nitrobenzylpyridine

W i t h the s p o t t i n g t e c h n i q u e o p t i m i z e d , the r e p r o d u c i b i l i t y p r e c i s i o n w a s a l m o s t e n t i r e l y d e p e n d e n t u p o n the u n i f o r m i t y of the

chromato-

g r a p h i c l a y e r . M o s t plates h a d t h i c k edges so that samples or standards s p o t t e d n e a r the e d g e c o u l d not b e i n c l u d e d i n the q u a n t i t a t i v e c a l c u l a tions. O n e b r a n d of c o m m e r c i a l p l a t e p r e p a r e d b y s p r a y i n g t e c h n i q u e s gave the best u n i f o r m i t y f r o m e d g e to edge, a n d w h e n s t a n d a r d curves w e r e p r e p a r e d u s i n g the w h o l e p l a t e , v e r y s m o o t h curves w e r e o b t a i n e d . T h e other c o m m e r c i a l plates u s e d gave g o o d results w h e n the center w a s u s e d for f o u r samples or standards. T h e a b r a s i v e resistance of the plates h a v e to be better t h a n those u s e d for q u a l i t a t i v e w o r k , a n d the c h r o m o g e n i c reagents h a v e to b e a p p l i e d b y d i p p i n g or i n c o r p o r a t i n g i n t o the t h i n l a y e r to p r e v e n t d a m a g e to the surface a n d u n e v e n s p o t t i n g of the b a c k g r o u n d area. F i g u r e 5 shows the scans o b t a i n e d f r o m different concentrations of a m i x t u r e of five o r g a n o p h o s p h o r u s c o m p o u n d s :

dimethoate ( A ) , m e v i n -


8.

GETZ


129

Chromatography

phos ( B ) , Dasanit ( C ) , malathion ( D ) , a n d carbophenothion ( E ) . ures 6 a n d 7 s h o w the s t a n d a r d curves o b t a i n e d f r o m these scans

Figby

p l o t t i n g the areas of the curves vs. c o n c e n t r a t i o n . F i g u r e 8 is a scan of the 10-/*g m i x t u r e of m e t h y l p a r a t h i o n , M e t h y l T r i t h i o n , a n d c a r b o p h e n o t h i o n s h o w n i n F i g u r e 1. F i g u r e 9 c o m p a r e s the s t a n d a r d curves o b t a i n e d f r o m v a r i o u s c o n centrations of d i a z i n o n at t w o different a t t e n u a t i o n settings. T h e a t t e n u a t o r response is l i n e a r b u t the reflectance scan does n o t r e s p o n d l i n e a r l y (5).


Future Prospects A s w e c o m p a r e p a p e r w i t h t h i n - l a y e r c h r o m a t o g r a p h y , w e c a n see t h a t p a p e r sheets as s u c h p r o b a b l y w i l l b e s u p p l a n t e d b y t h i n - l a y e r c e l l u l o s e m e d i a . T h i s means that the same i m m o b i l e - m o b i l e systems t h a t are a p p l i e d to p a p e r c a n also b e u s e d for c e l l u l o s e t h i n l a y e r . T h e i n o r g a n i c adsorbents d o n o t a p p e a r to b e v e r y efficient f o r r e s o l v i n g h i g h l y polar compounds.

W h e n t h e y are i m p r e g n a t e d w i t h i m m o b i l e phases,

ascension times are i n c r e a s e d g r e a t l y because the c a p i l l a r i e s are b e i n g

I CM

b IAll NO N

SO

40-

30-

20 V5/2

/0MS.

2.0

Figure 9.

4 T

A comparison

60

80

10

12

14

of standard curves obtained from diazinon at two different attenuation levels


130 filled

PESTICIDES

IDENTIFICATION

w i t h a l i q u i d , a n d l i q u i d - l i q u i d p a r t i t i o n i n g is also t a k i n g p l a c e .

I n some instances, t h e ascension times are too l o n g f o r p r a c t i c a l purposes. W i t h t h i n - l a y e r cellulose, w e c a n u t i l i z e t h e separations p r o d u c e d b y i m m o b i l e - m o b i l e phases w i t h better r e s o l u t i o n because

t h e spots p r o -

d u c e d a r e m o r e c o m p a c t t h a n that o b t a i n a b l e f r o m p a p e r . A n y m a t e r i a l w i t h a c a p i l l a r y s t r u c t u r e that c a n b e m a d e to a d h e r e as a l a y e r c a n b e u s e d f o r t h i n - l a y e r c h r o m a t o g r a p h y .

Quantitative de-

t e r m i n a t i o n s b y this t e c h n i q u e are b o u n d to increase as m o r e a n d m o r e laboratories o b t a i n s c a n n i n g e q u i p m e n t . companies

T h i s w i l l g i v e i m p e t u s to t h e

w h o m a k e c o m m e r c i a l l y - p r e p a r e d plates to p r o d u c e

them


w i t h m o r e care a n d u n i f o r m i t y .

Literature Cited (1) Mrak, E . M., U . S. Department of Health, Education and Welfare, "Report on the Secretary's Commission on Pesticides and their Relationship to Environmental Health," Parts I and I I , 1969. (2) Morley, H . V., Residue Rev. (1966) 16, 1. (3) Samuel, B. L . , Hodges, H . K., Residue Rev. (1967) 17, 45. (4) Thornburg, W . W . , "Analytical Methods for Pesticides, Plant Growth Regulators and Food Additives," Vol. I, p. 87-108, Academic, New York, 1963. (5) Biros, F . , Burke, J. A . , Gaul, J. A . , Corneliussen, P. E., "Pesticide Analytical Manual, Vol. I, Ch. 4, 5, 6, U . S. Department of Health, Education and Welfare, Food and Drug Administration. (6) Duggan, R. E., Barry, H . C., Johnson, L . Y., Williams, S., "Pesticide Analytical Manual, Vol. I I , U . S. Department of Health, Education and Welfare, Food and Drug Administration. (7) Consden, R., Gordon, A. H . , Martin, J. P., Biochem. J. (1944) 38, 224. (8) Mitchell, L . C., J. Assoc. Offic. Agr. Chemists (1957) 40, 999. (9) Mitchell, L . C., J. Assoc. Offic. Agr. Chemists (1958) 41, 781. (10) Müller, R., Ernst, G., Schock, H . , Mitt. Gebiete Lebensm. Hyg. (1957) 48, 152. (11) McKinley, W . P., Mahon, J. H . , J. Assoc. Offic. Agr. Chemists (1959) 42, 725. (12) Mills, P., J. Assoc. Offic. Agr. Chemists (1959) 42, 734. (13) Bates, J. A., Jr., Analyst (1965) 90, 453. (14) Evans, W . H . , Analyst (1962) 87, 569. (15) Getz, M . E., Residue Rev. (1963) 2, 9. (16) Major, A., Jr., Barry, H . C., J. Assoc. Offic. Agr. Chemists (1961) 44, 202. (17) Major, A., Jr.,J.Assoc. Offic. Agr. Chemists (1962) 45, 387. (18) Rusiecki, W . , Henneberg, M . , Turkowska, T., Biul. Inst. Ochrony Roslin (1965) 32, 23. (19) Storherr, R. W., Tighe, J. F . , Sykes, J. F . ,J.Assoc. Offic. Agr. Chemists (1960) 43, 731. (20) Storherr, R. W., Onley, J.,J.Assoc. Offic. Agr. Chemists (1962) 45, 382. (21) Yip,G.,J.Assoc. Offic. Agr. Chemists (1962) 45, 367. (22) Zweig, G., Archer, T . E., J. Agr. Food Chem. (1958) 6, 910. (23) Meinhard, J. E., Hall, N . J., Anal. Chem. (1949) 21, 185. (24) Kirchener, J. G., Heller, G. J., Anal. Chem. (1951) 23, 420. (25) Sola, T . , Salimenen, K., Fiskari, K., Z. Lebensm. Untersuch. Forsch. (1962) 117, 369.


8. (26) (27) (28) (29) (30) (31) (32) (33)


(34) (35) (36) (37) (38) (39) (40) (41) (42)

GETZ


Chromatography

131

W a l k e r , K . C., Beroza, M., J. Assoc. Offic. Agr. Chemists (1963) 46, 250. Kovacs, M. J., Jr., J. Assoc. Offic. Agr. Chemists (1963) 46, 884. Kovacs, M. J., Jr., J. Assoc. Offic. Agr. Chemists (1964) 47, 1097. C o n k i n , R., Residue Rev. (1964) 6, 136. Abbot, D . C., Thomson, J., Residue Rev. (1965) 11, 1. Getz, M. E., J. Assoc. Offic. Agr. Chemists (1962) 4 5 , 393. Storherr, R. W . , Getz, M. E., Watts, R. R., F r i e d m a n , S. J., E r w i n , F . , Giuffrida, L., Ives, F . , J. Assoc. Offic. Agr. Chemists (1964) 47, 1087. Beck, E . W . , Johnson, J . C., J r . , Getz, M. E., Skinner, F. B . , Dawsey, L . H., W o o d h a m , D . W . , Derbyshire, J. C., J. Econ. Entomol. (1968) 6 1 , 605. Beroza, M., Hill, K . R., Norris, K . , Anal. Chem. (1968) 40, 1608. Getz, M. E., "An Automatic Spotter for Quantitative TLC Analysis by Optical Scanning," Meeting of the Association of Official Analytical Chemists, Washington, D . C., October 1970. Getz, M. E., Friedman, S. J., J. Assoc. Offic. Agr. Chemists (1963) 46, 707. Getz, M. E., Wheeler, H . G., J. Assoc. Offic. Anal. Chemists (1968) 5 1 , 1101. Beroza, M., Getz, M. E., Collier, C . W . , Bull. Environ. Contam. Toxicol. (1968) 3, 18. Adams, H. R., Schechter, M. S., Meeting of the Association of Official Agricultural Chemists, 77th, Washington, D . C., October 14-17, 1963. Watts, R. R., J. Assoc. Offic. Agr. Chemists (1963) 46, 707. Shellard, E . J., Ed., "Quantitative Paper and T h i n L a y e r Chromatography," p. 1-133, Academic, N e w York, 1968. Giddings, J. C., J. Chromatog. (1959) 2, 48.

RECEIVED July 6, 1970. Mention of proprietary products is for identification only and does not i m p l y endorsement of these products by the U. S. Department of Agriculture.


Past, Present, and Future Application of Paper and Thin-Layer

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