Environmental Letters
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
Confirmation of Pesticide Residue Identity: Part IX Organophosphorus Pesticides John A. Coburn & A. S. Y. Chau To cite this article: John A. Coburn & A. S. Y. Chau (1975) Confirmation of Pesticide Residue Identity: Part IX Organophosphorus Pesticides, Environmental Letters, 10:3, 225-236, DOI: 10.1080/00139307509435824 To link to this article: http://dx.doi.org/10.1080/00139307509435824
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Date: 08 November 2015, At: 11:43
ENVIRONMENTAL LETTERS, lO(3). 225-236 (1975)
COSFI?JLATION OF PESTICIDE RESIDUE IDENTITY: PART IX 0RG.WOPHOSPHORUS PESTICI DES
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KEY KORDS: Confirmation, Organophosphorus, Pesticide, Hydrolysis, Pentafluorobenzyl bromide John A. Coburn and A . S . Y . Chau Water Quality Branch Canada Centre for Inland IJaters 867 Lakeshore Road P.O. Box 5050 Burlington, Ontario L7R 4A6 Canada
ABSTRACT This paper describes a confirmation procedure for residue levels of dyfonate, dichlorofenthion and cyanox. After extraction and quantitation.by flame photometric detector (FPD)
-
gas liquid chromato-
graphy (GLC), the organophosphorus pesticides are hydrolyzed in a 10% methanolic-potassium hydroxide solution. The phenolic hydrolysis products are then extracted from this solution and reacted with pentafluorobenzyl bromide to produce the pentafluorobenzyl (PFB) ether derivatives. These PFB ethers are subsequently cleaned-up and fractionated on a silica gel micro-column and analyzed by electron capture (EC)
-
GLC. 225
Copyright 0 1976 by hlarcel Dekker, Inc. All Rights Reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher.
COBURN AND CHAU
226
The chromatographic results of five other organophosphorus pesticides and five N-methyl carbamates, which are also analyzed by this method, are presented. As
low as 0.01 ug dyfonate and dichlorofenthion and 0.10 ug cyanox
from a one liter water sample can be confirmed. INTRODUCTION
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A
common feature of these three organophosphorus pesticides, as
illustrated in Figure I, is the production of a phenol o r thiophenol functional group during alkaline hydrolysis. Pentafluorobenzyl bromide, a novel reagent for derivatization of phenols and mercaptans has been reported by Ka~aharal-~.The resultant PFB ethers and thioethers exhibit excellent EC responses and good stability in solution, and are amenable to gas Chromatographic separations on liquid phases commonly used in pesticide residue analysis.
Dchiomfenlhion (VC-13@, 0-2.4-Dichbrophenyl phosphorolhioJte)
O.O-drethyl
cyanoxB ( 0 - p - C y a n o m n y l 0.0-dimethyl phosphomthioate)
Figure I Structures of Organophosphorus Pesticides
227
PESTICIDE RESIDUE IDENTITY. IX
Utilizing the hydrolysis of these three organophosphorus pesticides to produce the phenolic o r thiophenolic products and this reagent, a selective and sensitive confirmatory procedure has been developed. This reaction is illustrated in Figure 2. As low as 0.01 ug dyfonate and dichlorofenthion and 0.10 ug cyanox from a one liter water sample can be confirmed. EXPERIMENTAL
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Apparatus and Reagents la) Gas chromatographic equipment and operating conditions. A Tracor Nicro-Tek Model PIT 222 gas chromatograph equipped with two Ni-63 electron capture detectors and 1.87n x 3.5 mm ID U-shaped columns was used. The columns were packed with (i) 4.6% (w/w) OV-101 and 5.5% (w/w) OV-210 on Chromosorb I, 80-100 mesh, A.W.,
DMCS treated, (obtained from Chromato-
graphic Specialties Ltd., Brockville, Ontario) as described by Chau and Wilkinson4.
(ii) 3% (w/w) OV-225 on Chromosorb IV,H.P., 80-100 mesh
obtained from Chromatographic Specialties Ltd., Brockville, Ontario. Operating conditions; Temperatures )C'(
injection 205O, colum~ 190°,
detector 280°, carrier gas flow (10% methane-argon) 50 ml/min
+
20 ml/min
purge. The EC detectors were operated in the pulsed mode with the following electrometer settings: EC voltage, 5 5 volts; pulse rate, 90 usec; pulse width, 8 usec; and attenuations between 6.4-1.6 X lo-'
AFS.
Figure 2 Reaction Scheme for Derivatization of a Phenol Salt with Pentafluorobenzyl bromide.
COBURN AND CHAU
228
(bJ Reagents and solvents. All solvents were pesticide residue grade and used without purification. The pentafluorobenzyl bromide solution was prepared by dissolving one gram reagent (Aldrich Chemical CO. #lo, 105-2 (OC. -bromo-2,3,4,5,6- pentafluorotoluene
actinic flask.
(99'%))
in 100 ml acetone'in
(Caution: reagent is a strong lachrymator).
a low
A 10% (w/v)
potassiun hydroxide in methanol was prepared by dissolving 10 grams Fisher
Downloaded by [University of Cambridge] at 11:43 08 November 2015
ACS grade potassium hydroxide in 100 ml methanol in a low actinic flask. A 0.1 El potassium carbonate solution was prepared by dissolving 13.8 grams
Analar analytical reagent in 1.0 liter distilled water which was extracted twice with 100 ml portions of benzene. A 5% (w/v) potassium carbonate solutic was prepared.by dissolving 5 grams Analar analytical reagent in 100 ml distilled water. A 50% (v/v) sulphuric acid solution was prepared by carefully adding, with stirring, 100 ml concentrated reagent grade sulphuric acid to 100 ml distilled water. This solution was cooled and extracted twice with 100 ml volumes of benzene. The sodium sulfate was reagent grade (Fisher) and was heated for 12 hours at 60OoC. The silica gel was deactivated by adding 1% (w/w) distilled water to the silica gel, (grade 950, Davison Chemical, Baltimore, Maryland, 21226), mixed for two hours and stored in a sealed glass container. (c)
Standards. Dyfonate, dichlorofenthion and cyanox were analytical grade
and obtained from their respective manufacturers. Thiophenol (97%), 2,4dichlorophenol (99%) and p-cyanophenol (95%) were obtained from Aldrich Chemical
Co.
Procedure (See Figure 3 for complete schematic diagram) (a)
Extraction and hydrolysis.
-
The method of Ripley et a15 was
used for the extraction of organophosphorus pesticides, with no clean up before FPD-GLC analysis. Shake the benzene extract, which contains organophosphorus pesticide to be confirmed, with equal volume 0.1 El potassium carbonate. Discard aqueous solution and repeat alkaline
Downloaded by [University of Cambridge] at 11:43 08 November 2015
P E S T I C I D E RESIDUE IDENTITY. IX
229
- evaporate to lml + 5% K2C03 (25 ul) +
1% PFBBr (250 ul)
+
acetone ( 4nl)
-
3 0 min at 60°C or 4 hours at roo3 teqerature
- remove acetone,
replace with isooctane
/Fractionation
SI Benzene-Hexane Wash
1
-
25% Benzene-Hexane
75% Eenzene-Hexane
Fraction 1
Fraction 2
Figure 3 Schematic Diagram f o r Confirmation Procedure
wash o r c e more.
Evaporate o r g a n i c phase to 1.0 m l and add 2 m l 10%
methanolic KOH.
Allow mixture t o s t a n d a t room temperature (21OC)
overnight (16-18 hours) o r a t 6OoC f o r two hours i n l o o s e l y stoppered
COBURN AND CHAl
230 c e n t r i f u g e t u b e t o achieve complete h y d r o l y s i s .
Add 4 m l d i s t i l l e d
water t o h y d r o l y s i s s o l u t i o n and e x t r a c t twice with 5 m l p o r t i o n s o f benzene.
Discard t h e s e benzene washings.
with 0.2-0.4 benzene.
Acidify h y d r o l y s i s s o l u t i o n
m l 50% HZS04 t o pH 2-3. E x t r a c t twice with 3 ml p o r t i o n s o f
Wash t h e combined benzene e x t r a c t s with two 5 m l p o r t i o n s o f
d i s t i l l e d water and dry with 1 g sodium s u l f a t e .
Transfer d r i e d
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benzene with a few washings t o c l e a n c e n t r i f u g e tube and c o n c e n t r a t e t o 1.0 m l with g e n t l e stream of n i t r o g e n gas. (b)
D e r i v a t i z a t i o n and f r a c t i o n a t i o n .
-
Add 25 u l 5% KZC03 and
250 u l 1%(w/v) pentafluorobenzyl bromide reagent and make up t o 5 m l with acetone.
Shake well and allow s o l u t i o n t o s t a n d minimum o f 4
hours a t room temperature (21Oc) f o r complete r e a c t i o n , o r 20 min. i n Add 2 m l i s o o c t a n e (2,2.4-trimethylpentane) t o
6OoC water b a t h .
acetone s o l u t i o n c o n t a i n i n g PFB e t h e r d e r i v a t i v e s and evaporate t o 1 m l with g e n t l e stream of n i t r o g e n gas. Add 2 m l i s o o c t a n e and r e p e a t evaporation t o 1 m l f i n a l volume.
Remove reagent and f r a c t i o n a t e
t h e d e r i v a t i v e s on a 1 g s i l i c a g e l micro-column p r e v i o u s l y Pre-wet t h e column with 5 m l hexane and p l a c e
d e s c r i b e d by
t h e i s o o c t a n e s o l u t i o n on t h e column.
E l u t e with 6 ml 5% benzene i n
hexane t o remove t h e excess r e a g e n t .
E l u t e w i t h 6 m l 25%benzene i n
hexane, c o l l e c t i n g t h e e l u a t e i n a c l e a n c e n t r i f u g e tube ( F r a c t i o n 1). E l u t e w i t h 8 m l 75% benzene i n hexane c o l l e c t i n g t h e e l u a t e i n another c l e a n c e n t r i f u g e tube ( F r a c t i o n 2).
The 2 f r a c t i o n s c o n t a i n i n g PFB
e t h e r d e r i v a t i v e s a r e t h e n analyzed by e l e c t r o n capture-GLC. RESULTS AND DISCUSSION I n t h e i n i t i a l development o f . t h i s technique t h e a u t h o r s r e p o r t e d t h e confirmation o f crufomate, fenchlorphos. p a r a t h i o n , methyl p a r a t h i o n 8
and f e n i t r o t h i o n
.
The simple e x t e n t i o n o f t h e p r e v i o u s l y r e p o r t e d
PESTICIDE RESIDUE IDENTITY. Lx
231
procedure was not possible and a few modifications were required in the column fractionation and clean up steps to incorporate dyfonate, dichlorofenthion and cyanox into the method. The derivatization conditions .(temperature and time) that had been successful for the first five organophosphorus pesticides worked equally as well for the compounds studied here. The best results (highest and
Downloaded by [University of Cambridge] at 11:43 08 November 2015
most consistant) were obtained from room temperature derivatization. The heated derivatization produced lower yields for dyfonate (average 5-10% lower) and less consistant results for both dyfonate and dichlorofenthion.
Four hours of room temperature derivatization was found to be sufficient for optimum yields of all three compounds, while in the heated derivatization procedure maximum yields were obtained in 20-30 minutes. The hydrolysis conditions reported previously were found to give satisfactory results for the three organophosphorus pesticides reported here. The data for the percent hydrolysis and extraction of the phenols' and thiophenol were obtained by comparing the results from the hydrolysis and derivatization of the parent compounds with the results of the derivatization of the respective phenols and thiophenol. These data are presented in Table I. The lower results for dyfonate can be attributed to the poorer extractability of thiophenol into benzene and not due t o incomplete hydrolysis since the first benzene extraction of the alkaline hydrolysis solution revealed no unhydrolyzed dyfonate. Ethyl acetate and ether were tested in the extraction of the hydrolysis products, however, no increase in recoveries was observed and at nanogram levels the reagent blanks were more pronounced with both solvents. Hydrolysis for two hours at
6OoC,
instead of at room temperature for 16-18 hours, resulted in significantly lower recoveries (15-20%) and greater variability in the results for dyfonate and dichlorofenthion. The method of hydrolysis showed no significant effect on the results for cyanox.
COBURN AND CHAU
232
TABLE I Combined Hydrolysis Yields of the Organophosphorus Pesticides and Extraction Recove
v
of Their Phenols
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Parent Compound
Yield (%)
Dyfonate
75%
Dichlorofenthion
85
Cyanox
88
In the fractionation of the PFB ether derivatives on the silica gel micro-column the derivatives of dichlorofenthion and cyanox were found to be quantitatively recovered in fraction 1 and fraction 2 respectively. It was found that approximately 10% of the dyfonate derivative was eluting in the wash fraction. This loss was eliminated by lowering the wash volume from 8 nl 5% benzene in hexane to 6 ml 5% benzene
in hexane.
This change did not affect the subsequent elution of any
of the other derivatives reportdhere or previously!
Table 2 lists
TABLE 2 Retention Times of the PFB Ethers of the Organophosphorus Pesticide Phenols on OV-lOl/OV-210. PARENT CO?IPOUsD
RRT PARATHION (a)
Dyfonate
0.18
Dichlorofenthion
0.42
Crufomate
0.55
Fenchlorphos
0.63
Cyanox
0.90
Parathion or blethyl Parathion
1.11
Fenitrothion
1.18
(a)
Parathion retention tine was 9.9 minutes on this liquid phase.
PESTICIDE RESIDUE IDENTITY. IX
233
the retention times relative to parathion derivatives from all the organophosphorus pesticides analyzed. Figure 4 shows a
chroma-
togram of all these PFB derivatives after clean-up and fractionation on the silica gel column. During this study it was found that the elution pattern for the PFB derivatives varied significantly with dif-
Downloaded by [University of Cambridge] at 11:43 08 November 2015
ferent sources of silica gel while the between-batch variations were
1
2
dyfonate
1
2 dichlorofenthion 3 crufornate
4
fenchlorphos
4
5 cyanox 6 parathion or
methyl parathion 7 fenitrothion
r 0
FRACTION 1
L
L
I
I
I
4
8
12
1 16
RETENTION TIME (MINI
Figure
4
Chromatogram of Organophosphorus Pesticide Derivatives on OV-lOl/OV-210 Liquid Phase, After Fractionation on The Silica Gel Micro-column
234
COBURN AND CHAU
TABLE 3 Retention Times of Pentafluorobenzyl Ethers of Five Carbamate Phenols on OV-101/0V-210.
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PARENT CCNPOUND
RRT PARATHION(a)
Propoxur
0.24
Carbofuran
0.37
Metmercapturon
0.75
Sevin
0.77
Mobam
0.77
(a)
Parathion retention time was 9 . 9 minutes on this liquid phase.
minimal. It is expected that in other laboratories the eluting volumes may have to be altered from those reported here. The final step in this study was to determine if any of several N-methyl carbamates would interfer with the organophosphorus pesticides thereby causing erroneous confirmation. The retention times relative to parathion for the carbamate derivatives are listed in Table 3 and a chromatogram of all organophosphorus pesticide and carbamate derivatives after clean-up and fractionation is shown in Figure 5
.
235
PESTICIDE RESIDUE I D E N T I V . IX
n Downloaded by [University of Cambridge] at 11:43 08 November 2015
1 dyfonate 2 dichlorofenthion
3 crufomte 4 fenchlorphos 5 sevin 6 propoxur 7 carbofuran 8 mobam + metmercapturon 9 cyanox 10 parathion or methyl parathion 11 fenitrothion
I
0
1
4
8
12
16
RETENTION TIME (MINI
Figure 5 Chromatogram of Organophosphorus and Carbamate P e s t i c i d e D e r i v a t i v e s on OV-lOl/OV-210 Liquid Phase A f t e r F r a c t i o n a t i o n on a S i l i c a Gel blicro-column
236
COBURN AND
Cmu
AC KNOW LEDG EFlENT
The a u t h o r s are g r e a t f u l t o B.D.
R i p l e y o f t h e O n t a r i o M i n i s t r y of
A g r i c u l t u r e and W. Sans of t h e Dcpartmcnt of A g r i c u l t u r e f o r t h e i r v a l u a b l e c r i t i c i s m o f t h e manuscript. REFERENCES Kawahara, F.K.
(1968) Anal. Chem., 40, 2009-1010.
Kawahara, F.K.
(1968) Anal. Chem., 40, 2073-2075.
Kawahara, F.K.
(1971) Environ. Science and Technol., 5, 235-239.
Downloaded by [University of Cambridge] at 11:43 08 November 2015
I .
Chau, AS.Y. and Wilkinson, R . J . , 7, 93-104.
.
(1972) Bull.Environ. ContamToxicol.,
Ripley, B.D., 1033-1042.
Wilkinson, R . J . ,
Johnson, L.G.
(1971) Bull. Environ. Contam.Toxicol.,S,
Johnson, L.G.
and Chau, A.S.Y.,(1974)
JAOAC, 57,
542-545.
(1973) JAOAC, 56, 1503-1505.
Coburn, J . A . and Chau, A.S.Y.
(1974) JAOAC. 57 ( 6 ) , 1272-1278. Received June
9, 1975
Accepted J u l y 8, 1975
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
Confirmation of Pesticide Residue Identity: Part IX Organophosphorus Pesticides John A. Coburn & A. S. Y. Chau To cite this article: John A. Coburn & A. S. Y. Chau (1975) Confirmation of Pesticide Residue Identity: Part IX Organophosphorus Pesticides, Environmental Letters, 10:3, 225-236, DOI: 10.1080/00139307509435824 To link to this article: http://dx.doi.org/10.1080/00139307509435824
Published online: 02 Sep 2009.
Submit your article to this journal
Article views: 6
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=2esa20 Download by: [University of Cambridge]
Date: 08 November 2015, At: 11:43
ENVIRONMENTAL LETTERS, lO(3). 225-236 (1975)
COSFI?JLATION OF PESTICIDE RESIDUE IDENTITY: PART IX 0RG.WOPHOSPHORUS PESTICI DES
Downloaded by [University of Cambridge] at 11:43 08 November 2015
KEY KORDS: Confirmation, Organophosphorus, Pesticide, Hydrolysis, Pentafluorobenzyl bromide John A. Coburn and A . S . Y . Chau Water Quality Branch Canada Centre for Inland IJaters 867 Lakeshore Road P.O. Box 5050 Burlington, Ontario L7R 4A6 Canada
ABSTRACT This paper describes a confirmation procedure for residue levels of dyfonate, dichlorofenthion and cyanox. After extraction and quantitation.by flame photometric detector (FPD)
-
gas liquid chromato-
graphy (GLC), the organophosphorus pesticides are hydrolyzed in a 10% methanolic-potassium hydroxide solution. The phenolic hydrolysis products are then extracted from this solution and reacted with pentafluorobenzyl bromide to produce the pentafluorobenzyl (PFB) ether derivatives. These PFB ethers are subsequently cleaned-up and fractionated on a silica gel micro-column and analyzed by electron capture (EC)
-
GLC. 225
Copyright 0 1976 by hlarcel Dekker, Inc. All Rights Reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher.
COBURN AND CHAU
226
The chromatographic results of five other organophosphorus pesticides and five N-methyl carbamates, which are also analyzed by this method, are presented. As
low as 0.01 ug dyfonate and dichlorofenthion and 0.10 ug cyanox
from a one liter water sample can be confirmed. INTRODUCTION
Downloaded by [University of Cambridge] at 11:43 08 November 2015
A
common feature of these three organophosphorus pesticides, as
illustrated in Figure I, is the production of a phenol o r thiophenol functional group during alkaline hydrolysis. Pentafluorobenzyl bromide, a novel reagent for derivatization of phenols and mercaptans has been reported by Ka~aharal-~.The resultant PFB ethers and thioethers exhibit excellent EC responses and good stability in solution, and are amenable to gas Chromatographic separations on liquid phases commonly used in pesticide residue analysis.
Dchiomfenlhion (VC-13@, 0-2.4-Dichbrophenyl phosphorolhioJte)
O.O-drethyl
cyanoxB ( 0 - p - C y a n o m n y l 0.0-dimethyl phosphomthioate)
Figure I Structures of Organophosphorus Pesticides
227
PESTICIDE RESIDUE IDENTITY. IX
Utilizing the hydrolysis of these three organophosphorus pesticides to produce the phenolic o r thiophenolic products and this reagent, a selective and sensitive confirmatory procedure has been developed. This reaction is illustrated in Figure 2. As low as 0.01 ug dyfonate and dichlorofenthion and 0.10 ug cyanox from a one liter water sample can be confirmed. EXPERIMENTAL
Downloaded by [University of Cambridge] at 11:43 08 November 2015
Apparatus and Reagents la) Gas chromatographic equipment and operating conditions. A Tracor Nicro-Tek Model PIT 222 gas chromatograph equipped with two Ni-63 electron capture detectors and 1.87n x 3.5 mm ID U-shaped columns was used. The columns were packed with (i) 4.6% (w/w) OV-101 and 5.5% (w/w) OV-210 on Chromosorb I, 80-100 mesh, A.W.,
DMCS treated, (obtained from Chromato-
graphic Specialties Ltd., Brockville, Ontario) as described by Chau and Wilkinson4.
(ii) 3% (w/w) OV-225 on Chromosorb IV,H.P., 80-100 mesh
obtained from Chromatographic Specialties Ltd., Brockville, Ontario. Operating conditions; Temperatures )C'(
injection 205O, colum~ 190°,
detector 280°, carrier gas flow (10% methane-argon) 50 ml/min
+
20 ml/min
purge. The EC detectors were operated in the pulsed mode with the following electrometer settings: EC voltage, 5 5 volts; pulse rate, 90 usec; pulse width, 8 usec; and attenuations between 6.4-1.6 X lo-'
AFS.
Figure 2 Reaction Scheme for Derivatization of a Phenol Salt with Pentafluorobenzyl bromide.
COBURN AND CHAU
228
(bJ Reagents and solvents. All solvents were pesticide residue grade and used without purification. The pentafluorobenzyl bromide solution was prepared by dissolving one gram reagent (Aldrich Chemical CO. #lo, 105-2 (OC. -bromo-2,3,4,5,6- pentafluorotoluene
actinic flask.
(99'%))
in 100 ml acetone'in
(Caution: reagent is a strong lachrymator).
a low
A 10% (w/v)
potassiun hydroxide in methanol was prepared by dissolving 10 grams Fisher
Downloaded by [University of Cambridge] at 11:43 08 November 2015
ACS grade potassium hydroxide in 100 ml methanol in a low actinic flask. A 0.1 El potassium carbonate solution was prepared by dissolving 13.8 grams
Analar analytical reagent in 1.0 liter distilled water which was extracted twice with 100 ml portions of benzene. A 5% (w/v) potassium carbonate solutic was prepared.by dissolving 5 grams Analar analytical reagent in 100 ml distilled water. A 50% (v/v) sulphuric acid solution was prepared by carefully adding, with stirring, 100 ml concentrated reagent grade sulphuric acid to 100 ml distilled water. This solution was cooled and extracted twice with 100 ml volumes of benzene. The sodium sulfate was reagent grade (Fisher) and was heated for 12 hours at 60OoC. The silica gel was deactivated by adding 1% (w/w) distilled water to the silica gel, (grade 950, Davison Chemical, Baltimore, Maryland, 21226), mixed for two hours and stored in a sealed glass container. (c)
Standards. Dyfonate, dichlorofenthion and cyanox were analytical grade
and obtained from their respective manufacturers. Thiophenol (97%), 2,4dichlorophenol (99%) and p-cyanophenol (95%) were obtained from Aldrich Chemical
Co.
Procedure (See Figure 3 for complete schematic diagram) (a)
Extraction and hydrolysis.
-
The method of Ripley et a15 was
used for the extraction of organophosphorus pesticides, with no clean up before FPD-GLC analysis. Shake the benzene extract, which contains organophosphorus pesticide to be confirmed, with equal volume 0.1 El potassium carbonate. Discard aqueous solution and repeat alkaline
Downloaded by [University of Cambridge] at 11:43 08 November 2015
P E S T I C I D E RESIDUE IDENTITY. IX
229
- evaporate to lml + 5% K2C03 (25 ul) +
1% PFBBr (250 ul)
+
acetone ( 4nl)
-
3 0 min at 60°C or 4 hours at roo3 teqerature
- remove acetone,
replace with isooctane
/Fractionation
SI Benzene-Hexane Wash
1
-
25% Benzene-Hexane
75% Eenzene-Hexane
Fraction 1
Fraction 2
Figure 3 Schematic Diagram f o r Confirmation Procedure
wash o r c e more.
Evaporate o r g a n i c phase to 1.0 m l and add 2 m l 10%
methanolic KOH.
Allow mixture t o s t a n d a t room temperature (21OC)
overnight (16-18 hours) o r a t 6OoC f o r two hours i n l o o s e l y stoppered
COBURN AND CHAl
230 c e n t r i f u g e t u b e t o achieve complete h y d r o l y s i s .
Add 4 m l d i s t i l l e d
water t o h y d r o l y s i s s o l u t i o n and e x t r a c t twice with 5 m l p o r t i o n s o f benzene.
Discard t h e s e benzene washings.
with 0.2-0.4 benzene.
Acidify h y d r o l y s i s s o l u t i o n
m l 50% HZS04 t o pH 2-3. E x t r a c t twice with 3 ml p o r t i o n s o f
Wash t h e combined benzene e x t r a c t s with two 5 m l p o r t i o n s o f
d i s t i l l e d water and dry with 1 g sodium s u l f a t e .
Transfer d r i e d
Downloaded by [University of Cambridge] at 11:43 08 November 2015
benzene with a few washings t o c l e a n c e n t r i f u g e tube and c o n c e n t r a t e t o 1.0 m l with g e n t l e stream of n i t r o g e n gas. (b)
D e r i v a t i z a t i o n and f r a c t i o n a t i o n .
-
Add 25 u l 5% KZC03 and
250 u l 1%(w/v) pentafluorobenzyl bromide reagent and make up t o 5 m l with acetone.
Shake well and allow s o l u t i o n t o s t a n d minimum o f 4
hours a t room temperature (21Oc) f o r complete r e a c t i o n , o r 20 min. i n Add 2 m l i s o o c t a n e (2,2.4-trimethylpentane) t o
6OoC water b a t h .
acetone s o l u t i o n c o n t a i n i n g PFB e t h e r d e r i v a t i v e s and evaporate t o 1 m l with g e n t l e stream of n i t r o g e n gas. Add 2 m l i s o o c t a n e and r e p e a t evaporation t o 1 m l f i n a l volume.
Remove reagent and f r a c t i o n a t e
t h e d e r i v a t i v e s on a 1 g s i l i c a g e l micro-column p r e v i o u s l y Pre-wet t h e column with 5 m l hexane and p l a c e
d e s c r i b e d by
t h e i s o o c t a n e s o l u t i o n on t h e column.
E l u t e with 6 ml 5% benzene i n
hexane t o remove t h e excess r e a g e n t .
E l u t e w i t h 6 m l 25%benzene i n
hexane, c o l l e c t i n g t h e e l u a t e i n a c l e a n c e n t r i f u g e tube ( F r a c t i o n 1). E l u t e w i t h 8 m l 75% benzene i n hexane c o l l e c t i n g t h e e l u a t e i n another c l e a n c e n t r i f u g e tube ( F r a c t i o n 2).
The 2 f r a c t i o n s c o n t a i n i n g PFB
e t h e r d e r i v a t i v e s a r e t h e n analyzed by e l e c t r o n capture-GLC. RESULTS AND DISCUSSION I n t h e i n i t i a l development o f . t h i s technique t h e a u t h o r s r e p o r t e d t h e confirmation o f crufomate, fenchlorphos. p a r a t h i o n , methyl p a r a t h i o n 8
and f e n i t r o t h i o n
.
The simple e x t e n t i o n o f t h e p r e v i o u s l y r e p o r t e d
PESTICIDE RESIDUE IDENTITY. Lx
231
procedure was not possible and a few modifications were required in the column fractionation and clean up steps to incorporate dyfonate, dichlorofenthion and cyanox into the method. The derivatization conditions .(temperature and time) that had been successful for the first five organophosphorus pesticides worked equally as well for the compounds studied here. The best results (highest and
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most consistant) were obtained from room temperature derivatization. The heated derivatization produced lower yields for dyfonate (average 5-10% lower) and less consistant results for both dyfonate and dichlorofenthion.
Four hours of room temperature derivatization was found to be sufficient for optimum yields of all three compounds, while in the heated derivatization procedure maximum yields were obtained in 20-30 minutes. The hydrolysis conditions reported previously were found to give satisfactory results for the three organophosphorus pesticides reported here. The data for the percent hydrolysis and extraction of the phenols' and thiophenol were obtained by comparing the results from the hydrolysis and derivatization of the parent compounds with the results of the derivatization of the respective phenols and thiophenol. These data are presented in Table I. The lower results for dyfonate can be attributed to the poorer extractability of thiophenol into benzene and not due t o incomplete hydrolysis since the first benzene extraction of the alkaline hydrolysis solution revealed no unhydrolyzed dyfonate. Ethyl acetate and ether were tested in the extraction of the hydrolysis products, however, no increase in recoveries was observed and at nanogram levels the reagent blanks were more pronounced with both solvents. Hydrolysis for two hours at
6OoC,
instead of at room temperature for 16-18 hours, resulted in significantly lower recoveries (15-20%) and greater variability in the results for dyfonate and dichlorofenthion. The method of hydrolysis showed no significant effect on the results for cyanox.
COBURN AND CHAU
232
TABLE I Combined Hydrolysis Yields of the Organophosphorus Pesticides and Extraction Recove
v
of Their Phenols
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Parent Compound
Yield (%)
Dyfonate
75%
Dichlorofenthion
85
Cyanox
88
In the fractionation of the PFB ether derivatives on the silica gel micro-column the derivatives of dichlorofenthion and cyanox were found to be quantitatively recovered in fraction 1 and fraction 2 respectively. It was found that approximately 10% of the dyfonate derivative was eluting in the wash fraction. This loss was eliminated by lowering the wash volume from 8 nl 5% benzene in hexane to 6 ml 5% benzene
in hexane.
This change did not affect the subsequent elution of any
of the other derivatives reportdhere or previously!
Table 2 lists
TABLE 2 Retention Times of the PFB Ethers of the Organophosphorus Pesticide Phenols on OV-lOl/OV-210. PARENT CO?IPOUsD
RRT PARATHION (a)
Dyfonate
0.18
Dichlorofenthion
0.42
Crufomate
0.55
Fenchlorphos
0.63
Cyanox
0.90
Parathion or blethyl Parathion
1.11
Fenitrothion
1.18
(a)
Parathion retention tine was 9.9 minutes on this liquid phase.
PESTICIDE RESIDUE IDENTITY. IX
233
the retention times relative to parathion derivatives from all the organophosphorus pesticides analyzed. Figure 4 shows a
chroma-
togram of all these PFB derivatives after clean-up and fractionation on the silica gel column. During this study it was found that the elution pattern for the PFB derivatives varied significantly with dif-
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ferent sources of silica gel while the between-batch variations were
1
2
dyfonate
1
2 dichlorofenthion 3 crufornate
4
fenchlorphos
4
5 cyanox 6 parathion or
methyl parathion 7 fenitrothion
r 0
FRACTION 1
L
L
I
I
I
4
8
12
1 16
RETENTION TIME (MINI
Figure
4
Chromatogram of Organophosphorus Pesticide Derivatives on OV-lOl/OV-210 Liquid Phase, After Fractionation on The Silica Gel Micro-column
234
COBURN AND CHAU
TABLE 3 Retention Times of Pentafluorobenzyl Ethers of Five Carbamate Phenols on OV-101/0V-210.
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PARENT CCNPOUND
RRT PARATHION(a)
Propoxur
0.24
Carbofuran
0.37
Metmercapturon
0.75
Sevin
0.77
Mobam
0.77
(a)
Parathion retention time was 9 . 9 minutes on this liquid phase.
minimal. It is expected that in other laboratories the eluting volumes may have to be altered from those reported here. The final step in this study was to determine if any of several N-methyl carbamates would interfer with the organophosphorus pesticides thereby causing erroneous confirmation. The retention times relative to parathion for the carbamate derivatives are listed in Table 3 and a chromatogram of all organophosphorus pesticide and carbamate derivatives after clean-up and fractionation is shown in Figure 5
.
235
PESTICIDE RESIDUE I D E N T I V . IX
n Downloaded by [University of Cambridge] at 11:43 08 November 2015
1 dyfonate 2 dichlorofenthion
3 crufomte 4 fenchlorphos 5 sevin 6 propoxur 7 carbofuran 8 mobam + metmercapturon 9 cyanox 10 parathion or methyl parathion 11 fenitrothion
I
0
1
4
8
12
16
RETENTION TIME (MINI
Figure 5 Chromatogram of Organophosphorus and Carbamate P e s t i c i d e D e r i v a t i v e s on OV-lOl/OV-210 Liquid Phase A f t e r F r a c t i o n a t i o n on a S i l i c a Gel blicro-column
236
COBURN AND
Cmu
AC KNOW LEDG EFlENT
The a u t h o r s are g r e a t f u l t o B.D.
R i p l e y o f t h e O n t a r i o M i n i s t r y of
A g r i c u l t u r e and W. Sans of t h e Dcpartmcnt of A g r i c u l t u r e f o r t h e i r v a l u a b l e c r i t i c i s m o f t h e manuscript. REFERENCES Kawahara, F.K.
(1968) Anal. Chem., 40, 2009-1010.
Kawahara, F.K.
(1968) Anal. Chem., 40, 2073-2075.
Kawahara, F.K.
(1971) Environ. Science and Technol., 5, 235-239.
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I .
Chau, AS.Y. and Wilkinson, R . J . , 7, 93-104.
.
(1972) Bull.Environ. ContamToxicol.,
Ripley, B.D., 1033-1042.
Wilkinson, R . J . ,
Johnson, L.G.
(1971) Bull. Environ. Contam.Toxicol.,S,
Johnson, L.G.
and Chau, A.S.Y.,(1974)
JAOAC, 57,
542-545.
(1973) JAOAC, 56, 1503-1505.
Coburn, J . A . and Chau, A.S.Y.
(1974) JAOAC. 57 ( 6 ) , 1272-1278. Received June
9, 1975
Accepted J u l y 8, 1975
