IL
CONFk&NTIAL -FILE NOTE
LABORATORY CIRCULATION ONLY FILE NM NO. OS35
CWA/VM/61 20th July, 1965.
REVIEW OF ANALYTICAL MEERMS POR THE JjXXW
OF -n qw'. @Q:D&
The Insecticides most counonly used on tobacco are DM, AldrIn, Dieldrin,
ErArin, Pamthion and Malathion A method
.@ with MR30 used an a growth reVjUtor
for the determination of MH30 bars been developed at R. & D.E. but no methods
are available for the determination of any insecticides.
A review has therefore been made of the methods available for the determination
of pesticide rridues *dch indicates that the most satisfactory methods
are those based on a GIC assay, an by this means the pesticides are identified
as well as quantitatively determined. Alternatively, Identification may
be carried out by paper chromtography or thin-layer chromtograpby followed
bV a suitable apectrophotometria method for quantitative assay. It Is proposed
to check which of the methods in the most satisfactory for the determination of
pesticide residues on tobacco. When satisfactory methods have been developed
R. & D.E. can monitor all tobaccos used by the CompwW with respect to
pesticide residues.
It la suggested that contact is made with the newly formed Pesticide
Residue Analysis Information Service (PRAIS) of the laboratory of the Goverment
Chemist as ]Knowledge of their experience in this field would be invaluable
particularly about the supply of pure Insecticides to be used as analytical
standards.
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Great Interest has developed recently - outside scientific circles
an well as within - In the possible presence of pesticide chemicals on foodstuffs.
Some pesticides are now in use for the control of tobacco insects and diseases
and as It my be necessary to monitor tobaccos for pesticide residues a
review has been made of possible analytical methods.
DMUSSION
Although there are several hundreds of chemicals which could be used
for the control of tobacco insects and diseases, there In no evidence to
show that more than a few are actually used. At the moment, MT, Aldrin,
Dieldrin, Ei4rin, Parathion and Malathion appear to be the most popular.
A list of all the pesticides which have been recommended as pesticides for
tobacco, Is given In the Appendix.
Any method for the determination of pesticide residues falls into three
sections, (1) extraction, (2) clean-up and (3) determination.
Extraction
Efficient extraction of the pesticide residue from plant material is
often difficult. Many solvents and mixtures of solvents have been studied.
Generally emphasis has been placed on using a system which will dissolve
cook
the peatioidal chemical whilat remaining miscible with the aqueous medium
of the tissue. Mixtures of hex&ne with Lao-propawl have been used extensive
(1-6) as-well as acetone (7-9) and acetonitrile (10-11),, In the cane of
manufactured tobacco the product In somewhat dehydrated and so solvents
such as hexam and dichloramethane would possibly be the most suitable (12-1k).
It has boon pointed out that care must be exercised not to judge the
efficiency of extraction merely on a high recovery of chemdoal added during
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an analytical procedure. Good recoveries of the chemical added my be achieved
,when really the degree of extraction of the actual weathered residue is
poor (15).
Clean-Up
After extracting the pesticide residue from a sample It La necessary
to carry out a clean-up procedure to remove substances present in the extract
which would interfere with the subsequent detection and determination,
The ideal clean-up procedure should be applicable to all types of Pesticides
and extracts. However, because of the complexity of the problem, there
is no such procedure and probably never will be., Nevertheless, several clean--
UP procedures are applicable to a number of different pesticides and these
have been reviewed recently (16). Clean-up methods used most frequently/
employ'partiticning between immiscible solvents and/or column chromatography
using alumina or carbon. Paper and thin layer chromatographic methods are
widely used for screening samples.
Undoubtedly, the clean-up stage Is the most laborious and time conwiming
stage of any analytical method for pesticide residues and so any technique
which can do away with this stage is a major advantage. At the moment Neutron
Activation Analyses (17) seem to be a possible answer although not a lot
of work ban been published in this field.
Determination
In the majority of "sea, which of the numeroua possible pesticides
has been used will not be known. A general procedure which can both Identify
and measure a large number of chemicals at me time Is therefore needed.
So far, the most useful methods for the determination stage have been chrowto-
graphic, -only 0. L. C. Paper or thln layer chromatography are particularly
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useful for Identification procedures - thin layer having to some extent
replaced paper because it in much quicker and has greater resolution and
Sensitivity,
Spectrophatowetrio methods, including infra-red# ultra-violet and visible,
are still used extensively for quantitative determinations when the identity
of the pesticide in known.
METHODS FOR PEMCIDES USM ON TOBACOO
Of the six pesticides most commonly used for the control of tobacco
insects and diseases, two are organo-phosphates - Pamthlon and Malathion
whereas the other four are chlorinated hydrocarbons - DDT, Endrin, Aldrin,
Dieldrin.
Prgmophosphate Pesticides
The most, satisfactory, methods for the determination of organophosphate
pesticide residues appear to be those based an the G.L.C. method employing
a sodium thermionio detector (SM) wM oh is highly sensitive to phosphorus
compounds (18). The response generated In a SM by compounds other than
phosphorus compounds la minimal. The hydrogen flame In the detector changes
to an intensely blue flame when a phosphorus compound La burned, indicating
the formation of a high energy stage, and this mechanism in apparently unique
In flame-ehemistry. In the presence of sodium, this energy can be measured
as electrical energy and in directly proportional to the amount of phosphorus
In the flape. As little as 0*1 p.p.m. of Parathion wd Malathion can be
determined b7 this method. Chlorinated hydrocarbons, the other group of
pesticides used on tobacco do not interfere unless present In fairly large
amountse
Provided that the identity of the pesticide has bom proved to be Parathlon
or Malathlon thee. substances may readily be determined colorimtrioally, CD
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although a different calorimetric method is needed for each of them.
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Parathlon contains a nitro-group and the calorimetric method (19) used
for its determination involves reduction of this nitro group with zinc dust
and hydrochloric &old. The resulting amino in diazatised and coupled with
N-1-naphthyletbylenediamine. Any other aromatic nitro compounds present
must be removed before this determination can be carried out, as must plant
pigments, fats and waxes, whl ah Interfere with the analyzes.
Malathlon cannot be determined by, the above method an It does not contain
a nitro-group* Malathion In decomposed by alkali in carbon tetrachloride-
ethanol solution into sodium I . phosphorodithloate and sodium fumarate.
The former compound In extracted Into water and converted into a copper complex
which is thek re-extraoted into carbon tetrachloride In which it forms an
intense yellow colour (19).
Chlorinated H=oarbon Pesticides
MT, Aldrin, Dieldrin and Endrin all are chlorinated hydrocarbons. An
vas the case for the orgamphosphates, the best method of analysis Lis based
on 0. L. C. as this will Identify and estimate the substances present. For
this G. L. C. assay, the electron capture ionisation detector In the most satisfactory
(20) as it exhibits an exceptionally sensitive and selective response to
halogen compound,, An little an nALnogram (ld":'j g) quantities can readily
be detectede
Alternatively a combined G.L.C.-combuation - micro-,ooulometric t1tratlon
procedure (21) can be applied to the analysis of chlorinated pesticidese
In this case the sensitivity is less than Is the case for the electron capture
detector.
Colorimetrio methods can be used for these chlorinated pesticides provided
a preliminary Identification has been carried out. In fact Aldrin, Diedrin
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and Wrin may all be determined br the same calorimetric method. 'The most
widely used In the phemyl azide method (19) although special precautions
are necessary due to the explosive nature of the phertyl. azide.
The most successful calorimetric method for DM Involves nitrat;lon of
MT to the tetranitra derivative (19) iftch produce* a coloured solution
In benzene when treated with nethanolic sodium methylate.
In conclusion It sho,ild be named that a Pe3tI*Id* Residue Analysis Information
Service (PPA13) has been established by the Laboratory of the Goverment
Mhemist (22) following the recommendation of the Report of the Research Committee
an Toxic Cheadcals. The main purpose of this service Is 'to assist laboratories
by reapplying Information on methods of analysis for pesticide residues and
on their principal degradation and metabolic products. They will also supply
information about the supply of analytical standards. As the Laboratory of
the Government Chemist has been actively engaged in the analyses of pesticides
for some times any Information which they are willing to provide will be
extremely ussfuls
ae
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RMCM
1.R,A. Baetzi J. of A.O.A.C. 1964, n 348.
2.LJ. Hudin " C,T* Sartent Old 1964, 1Z 353-
.3.J.Co Wtlen et als J. Agri Food Chem 1963, 11 416.
4.Jo?. Way" and E.R, Jacksons J.A.O.A.C. i963, 46 843.
5.M. Omn: Ibld 1963, 46 195.
6, Van Middeles et als J. Agri Food Chem 1963, 1.1 56.
7.W,H. Outermann and D.J. lAski J. Agri Pood Chem 1963, 11 301.
8.J. Kubistovat Pracovni Lekar 1963 1@ 108; C.A. 196,3a io&Q-2e.
9.A. \Taylor et &Is Analyst 1%,A, 2 49T.
10.D.E. Coffin and 0. SowaxT: J.Avo*A*Co 1964p 47 675*
II.R.C. Nelson: J.A*O.A*C. 1964. JZ 289.
12.T.E. Archer et &It Jo Agri Pood Chem 1963& 11- 58.
l3oMe Chiba and J.H, Morleyt j.A.o.A.c. i964 U 6S7.
14*J.C. Maltlen et ali J. Agri Food Chem 196.3. 11 410"
15,J.W. Cook and S. W1111amat Aml Chem 1965, JZ (5) 1,VR-
i6,W.F. McKinley et &It JOA.0-A.C. 19S4, U (5) 85,3-
17.R&A. Schmitt and Go Zwelgi J. Agri Food Chem 1952, 10 481.
18.L. Oluffrida and P. Xvest J.A.O.A.C. 1964o JZ .1112.
19.Analytical Methods tar Pesticides, Vol. II,, Zweig.
20.Burke and L. Gluffride- J.A.O.A.C. 1964# 47 .325-o
21.J. Burke PxA L. Johnsons Ibld 1952, la 348.
22.CoLeadstry in Britain 1965. 1 (7) 342.
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APFMIX
Common or trade names or pesticide compounds reccewnded for the amtrol
of tobacco insects and diseases are listed alphabeticaI4.
Aldrin
BHC
Mr
MVP
Demetan
Dleldrin
Dimethoate
Endrin
Outhian
Heptachlor
Malathion
Manet
Menazon
Metaseptex
Parathion
Sevin
Telodrin
Thiodan
7M
Penar
Dr. D.G. Feitop/his 6i
Dr. I.We Hughes
We Woods FAR*
Dr, CoWe Ayers
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