&EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30605
EPA-600 4-80-008
January 1980
Research and Development
Polyurethane Foam as
Trapping Agent for
Airborne Pesticides
Analytical Method
Development
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-80-008
January 1980
POLYURETHANE FOAM AS TRAPPING AGENT
FOR AIRBORNE PESTICIDES
Analytical Method Development
by
James D. Adams and Joseph H. Caro
Soil Nitrogen and Environmental Chemistry Laboratory
Beltsville Agricultural Research Center
U.S. Department of Agriculture
Beltsville, Maryland 20705
Interagency Agreement No. 78-D-X0449
Project Officer
William R. Payne
Environmental Systems Branch
Environmental Research Laboratory
Athens, Georgia 30605
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30605
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory,
U.S. Environmental Protection Agency, Athens, Georgia, and approved for pub-
lication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
Environmental protection efforts are increasingly directed towards
preventing adverse health and ecological effects associated with specific
compounds of natural or human origin. As part of this Laboratory's research
on the occurrence, movement, transformation, impact, and control of environ-
mental contaminants, the Environmental Systems Branch studies complexes of
environmental processes that control the transport, transformation, degrada-
tion and impact of pollutants or other materials in soil and water; assesses
environmental factors that affect water quality; and develops new techniques
for measuring contaminants.
Pesticides transported in the air from application sites on forest and
agricultural lands are receiving increased attention because of their po-
tentially adverse health effects on humans and animals. A major problem in
efforts to measure ambient air concentrations of pesticides has been the lack
of an effective means of collecting samples for analysis. This report evalu-
ates the use of polyurethane foam as a trapping agent for selected airborne
pesticides.
David W. Duttweiler
Director
Environmental Research Laboratory
Athens, Georgia
iii
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ABSTRACT
This research program was initiated to develop and evaluate a method for
determining levels of organochlorine, organophosphorus and N-methylcarbamate
insecticides in air, using polyurethane foam as the trapping agent.
A multipesticide method was developed, using 4.4 cm-diameter plugs of
polyurethane foam as traps and a modified Sherma-Shafik multiresidue procedure
for analysis of foam extracts. With this method, the minimum detectable air
concentrations for vapors of 17 of the 18 organochlorine and organophosphorus
pesticides tested was 0.1 ng/m^ or less. Six carbamate pesticides did not
volatilize in sufficient amounts to allow analysis.
The experimental program consisted of measurements of efficiency of foams
for trapping vapors and aerosols, tests of foam compression during air samp-
ling, evaluations of techniques for extracting pesticide residues from the
foams, evaluations of extraction solvents, comparisons of the performance of
the ester and ether forms of polyurethane foam, evaluations of the steps in
the Sherma-Shafik analytical procedure, evaluations of GLC columns and instru-
mental parameters, and tests of derivatization procedures for electron-capture
gas chromatography of the N-methylcarbamates.
A 10-cm depth of foam was found to be an efficient trap for vaporized
pesticides. However, there were indications that the foam may be less
effective in trapping pesticides contained in airborne aerosols. Foams
compressed during air sampling, necessitating continuous monitoring of flow
rates for most accurate measurement of volume of air sampled.
Five-cycle Soxhlet extraction with 1:1 hexane-acetone was the best pro-
cedure for removal of pesticides from foam plugs. Excessive Soxhlet treatment
produced lower recoveries of organophosphorus insecticides. Other solvents
gave low recoveries or unacceptable levels of coextracted contaminants. The
ester form of polyurethane gave better results than the ether form. GLC
columns other than those recommended by Sherma and Shafik gave improved per-
formance in multiresidue analysis of extracts. Carbamates (in aerosols) were
best analyzed by derivatization with 0.1 ml pentafluoropropionic anhydride.
This report was submitted in fulfillment of Interagency agreement No.
D6-0136 (78-D-X0449) by the Soil Nitrogen and Environmental Chemistry Labora-
tory (formerly the Agricultural Chemicals Management Laboratory), SEA-AR,
U. S. Department of Agriculture, Beltsville, MD, under the sponsorship of the
U. S. Environmental Protection Agency. This report covers the period Septem-
ber 30, 1976, to January 15, 1979. Owing to the time required for recruitment
of personnel, work began on June 30, 1977. Work was terminated on Jan-
uary 15, 1979, because of the impending transfer of the principal investigator
to the U. S. Environmental Protection Agency.
iv
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CONTENTS
Foreword iii
Abstract iv
Acknowledgements vi
1. Introduction 1
2. Conclusions 2
3. Recommendations 4
4. Materials and Equipment 5
Pesticides 5
Solvents 5
Gas Chromatographs 5
Gas-Liquid Chromatography Columns 5
Polyurethane Foam Plugs 9
5. Experimental Program and Results 10
Investigation of PUF Trapping Efficiency 10
Evaluation of Pesticide Extraction Methods «; 27
Comparison of Ester and Ether Forms of PUF 43
Evaluation of GLC Columns and Procedures 49
Effect of Foam Structure on Air Flow Rates 66
Analysis of N-Methylcarbamate Insecticides 67
References 75
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ACKNOWLEDGEMENTS
We gratefully acknowledge the contributions of Mr. David P. T. Chen,
Mr. D. L. Brower and Mr. H. P. Freeman, who shared in the conduct of the
experiments. Mr. Chen is a National Urban League Fellow, assigned to the Soil
Nitrogen and Environmental Chemistry Laboratory on a temporary basis as a
research chemist; Mr. Brower is a soil scientist and Mr. Freeman is a chemist,
both on the permanent staff of the Laboratory. We also thank Dr. Henry F.
Enos, Deputy Director, Environmental Research Laboratory, U. S. Environmental
Protection Agency, Athens, GA, for advice and guidance during the formative
stages of the research program.
vi
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SECTION 1
INTRODUCTION
Every year in the United States, millions of pounds of pesticides are
applied to agricultural and forest lands, 65% by aerial application (1).
During application, a significant fraction remains in the air as vapor, as
particulate matter, or in aerosols. Also, some of the material that does
reach the ground can later be introduced into the air as vapor by
volatilization, or as adsorbate on fine particles by wind or by mechanical
agricultural operations. The movement of pesticides in air is a major mode of
their translocation over both short and long distances. These airborne
pesticides may have epidemiological consequences for both humans and animals.
As a result, the Congress has directed the EPA to establish a national system
to monitor ambient air for concentrations of pesticides.
A major obstacle to the implementation of a national system is that the
methods that have been used for trapping pesticides from air suffer from one
or more problems. Among these are poor trapping efficiency, limited air flow,
degradation of trapped pesticides, difficulty in recovery of trapped
pesticide, instability of the trapping medium, and difficulty with cleanup of
the recovered pesticide to permit its unambiguous quantitation.
Several of these effects do not occur with polyurethane foam (PUF). That
is, PUF is not hygroscopic; since it is semi-solid, it is not entrained in air
streams; it does not volatilize; and the polymer is relatively nonreactive and
therefore unlikely to degrade labile pesticides. Moreover, it has been
reported to perform efficiently as a trap for certain pesticides (2, 3).
The present study was designed to provide an in-depth evaluation of PUF as
a trapping agent for a broad spectrum of airborne pesticides, focusing on
efficiency of trapping, ease of recovery of trapped pesticides, relative
performance of the ether and ester forms of PUF, and compatibility of PUF with
the multipesticide analytical scheme of Sherma and Shafik (4). The latter had
shown promise for use in a national monitoring system, except that the
trapping procedure, air flow through a column of ethylene glycol, exhibited
unacceptable shortcomings.
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SECTION 2
CONCLUSIONS
The results of laboratory experiments using an airflow apparatus indicated
that PUF is an efficient trap for vapors of organochlorine and organophos-
phorus pesticides, even when substantial amounts of air are sampled. A 10-cm
depth of ester-form PUF was adequate for trapping vapors of the 18 volatile
compounds tested when as much as 55 m^ of air was passed through the
apparatus.
A finding having important implications for ambient monitoring was that
pesticides were not trapped as well by PUF when they were sampled as airborne
aerosols rather than as molecular vapors. The aerosol tests included a number
of carbamate insecticides that had not volatilized in earlier airflow
experiments.
During extended air sampling with plugs of PUF, the plugs compressed
somewhat and air flow rates decreased. In several 24-hour airflow tests, the
flow rate decrease ranged from 3 to 9%. Accurate measurement of volume of air
passing through PUF plugs in ambient air sampling will require monitoring of
flow rates.
Experiments showed that Soxhlet extraction was superior to both solvent
elution and immersed plug compression as a technique for removal of pesticides
from PUF plugs. However, excessive Soxhlet extraction should be avoided.
Tests showed that extractions carried beyond five Soxhlet cycles may cause
degradation and decreased recovery of the organophosphorus pesticides. The
best solvent for extraction was 1:1 hexane-acetone. Less polar solvents gave
low recoveries; more polar solvents coextracted interfering nonpesticidal
components.
Soxhlet extracts of PUF plugs were compatible with the Sherma-Shafik
multipesticide analytical procedure (4). Extracts could be analyzed, with low
background levels, at concentrations down to 0.1 ng/m^ Or lower for all
tested pesticides except for carbophenothion, which could be measured down to
0.3 ng/m3.
No significant differences between the ester and ether forms of PUF were
observed with respect to the trapping or extraction of pesticides.
In evaluations of GLC columns, improved performance was obtained by using
columns other than those recommended by Sherma and Shafik (4) for analysis of
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the three mixtures of pesticides resulting from their cleanup procedure.
Optimum results were obtained with use of these columns: (a) 1.5% OV-17 and
1.95% OV-210 on Chromosorb W HP; (b) 3% OV-1 on Chromosorb W; and (c) 3%
DC-200 on Gas Chrom Q.
Tests of the derivatization of the carbamate insecticides for analysis by
electron-capture gas chromatography showed that the pentafluoropropionic
anhydride (PFPA) procedure of Sherma and Shafik (4) gave the most satisfactory
results, except that response was enhanced by increasing the amount of PFPA
from the recommended 0.025 ml to 0.100 ml. Trifluoroacetic anhydride,
1-fluoro-2,4-dinitrobenzene and heptafluorobutyric anhydride were also tested
as derivatization reagents, the first two giving unacceptable results and the
last offering no improvement over PFPA.
Experiments with 2,4- and 2,6-diaminotoluene, which are products of PUF
degradation, showed that their PFPA derivatives were removed during extract
cleanup and, therefore, would not interfere with the quantitation of carbamate
insecticides.
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SECTION 3
RECOMMENDATIONS
The stability of pesticides trapped on polyurethane foam should be
confirmed with respect to humidity and photochemical oxidants to evaluate
suitability for use in areas of high or low humidity or high smog levels.
The recommended procedure should be field tested by sampling ambient air in
an urban, an industrial, and an agricultural environment.
If polyurethane foam is to be used in a multiple-site air monitoring
program for pesticides, it is recommended that, to trap pesticides in both
vapor and aerosol form, the column of foam be 25 cm deep and at least 4.4 cm
in diameter. All of the foam should be hydrophobic and from one manufacturing
lot. The foam should be thoroughly cleaned before use and be well protected
from contamination at all times. All GLC columns to be used for quantitation
should be from a single source to ensure uniformity in measurement of residue
levels in samples collected from different sites.
Further research is necessary to confirm the penetration of polyurethane
foams by aerosols and to determine the reasons and conditions for aerosol
penetration. If the mechanism for this penetration is understood, it may be
possible to modify the foam or sampling conditions to minimize the effect.
Previous reports on sampling pesticides in air have been concerned with vapors,
but aerosols may well be a major form in which pesticides occur in air. Accord-
ingly, it will be necessary to examine trapping efficiency for aerosols in
evaluations of pesticide adsorbants other than polyurethane foam, such as the
reticular porous polymers.
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SECTION 4
MATERIALS AND EQUIPMENT
PESTICIDES
Because one objective of the program was to evaluate the feasibility of
applying the Cherma-Shafik analytical procedure to PUF extracts, the
pesticides in the original paper by Sherma and Shafik (4) were selected for
use in this study. All pesticides used were analytical-grade standards,
obtained from commercial sources: a- and 3-BHC from Applied Science
Laboratories, Inc.; the remainder of the compounds from Supelco, Inc. The
list of pesticides, along with chemical names and equilibrium vapor pressures
as available, is shown in Table 1.
SOLVENTS
All solvents used were glass-distilled, pesticide grade, obtained from
Burdick and Jackson Co.
GAS CHROMATOGRAPHS
Four gas chromotographs were used in the program: (1) a Tracer Model 222,
equipped with a ^Hi electron-capture detector (ECD), for analysis of
organochlorine and carbamate insecticides; (2) a Tracer Model 560, with
ECD, also for organochlorine analysis; (3) a second Tracer Model 222, with a
flame photometric detector (FPD), for analysis of organophosphorus
insecticides; and (4) a Varian Model 2100, with an alkali flame ionization
detector (AFID), also for organophosphorus analysis.
GAS-LIQUID CHROMATOGRAPHY COLUMNS
Ten glass, packed GLC columns were used for pesticide analysis in the
various phases of the program. Four of these were obtained from commercial
sources, four were packed in our laboratory using packing material we had
prepared ourselves, and the remaining two were packed in our laboratory using
commercial packing material.
Of the four commercial columns, three were 180-cm long, 2-mm I.D. coiled
columns for use in the Tracor 560 gas chromatograph. The packings in these
were: (a) 3% OV-210 on 80- to 100-mesh Supelcoport (Supelco, Inc.); (b) 5%
SE-30 on 80- to 100-mesh Supelcoport (Supelco, Inc.); and (c) 3% DC-200 on
100- to 120-mesh Gas Chrom Q (Applied Science Laboratories, Inc.). The fourth
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TABLE 1. TEST PESTICIDES
Common or trade name
Vapor pressure
mm Hg at T, C
Chemical designation
Aldrin
Aminocarb
a-BHC
3-BHC
Carbaryl
Carbofuran
Carbophenothion
p,p'-DDD
p,p»-DDE
o,p'-DDT
p,p'-DDT
Diazinon
Dieldrin
6 x 10
-6
<5 x 10
-3
3.05 x 10
-7
1.8 x 10
-7
25
26
20
3-D x 10*"''' 25
8.U x 10~5 20
25
1,2,3,^,10-10-hexachloro-l,k,ha.,5,8,8a-hexahydro-
U-endo,exo-5,8-dimethanonaphthalene
U-dimethylamino-m-tolyl N-methylcarbamate
a-isomer of 1,2,3,U,5»6-hexachlorocyclohexane
g-isomer of 1,2,3,U,5,6-hexachlorocyclohexane
1-naphthyl N-methylcarbamate
2,3-dihydro-2,2-dimethyl-7-benzofuranyl
N-methylcarbamate
0,0-diethyl-S-[[(p-chlorophenyl)thiojmethyl]
phosphorodithioate
1,1-di chloro-2,2-r-bi s (p^chlor ophenyl) ethane
1,l-dichloro^2,2-bis(p^ehlorophenyl)ethylene
1,1,l-trichloro^2-(o-chlorophenyl)-2~(p-chloro-
phenyl)ethane
1,1,l-trichloro-2,2-bis(p-chlorophenyl)ethane
0,0-diethylr-0- (2-isopropylr-l4.^methyl^6-pyrimidinyl)
phosphorothioate
1,2,3, ^, 10, lO^hexachloror-6,7-epoxy-l, U, Ua, 5,6,7,8,
8a-octahydro^-l, U-endo, exo^-5, 8i-dimethanonaph-
thalene
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TABLE 1. (continued)
Common or trade name
Vapor pressure
nm Hg
at
T, °C
Chemical designation
Endrin
Ethion
Heptachlor
Heptaehlor epoxide
2,3,5-iandrin.
Lindane
Malathion
Methiocart
Methoxychlor
Methyl parathion
Mexacarbate
1.5 x 10'
9.U x 10
1.25 x 10'
9.7 x 10
20
20
20
20
1 , 2 , 3 , k , 10 , 10-hexachloro-6 , 7-epoxy-l , h , ha , 5 , 6 , 7 ,
8 , 8a^oct ahydro^l , Wendo , endo^-5 , S^dimethanonaph-
thalene
0,0,0' ,0f»-tetraethyl S,S'r-methylene"bisphosphoro-
dithioate
1,^,5,6,7,8, 8-hept achloro-3a , h , 7 ,7a^tetrahydro-
U , 7-endo^-methanoindene
-3a , k , 7 , 7a-
1,^,5,6,7,8, 8^
tetrahydro-4 , 7-methanoindene
'2,3,5^tro,etju; ! jemu; H^methylcarbamate
Y-isomer of l,2,3,^,5»6-hexachlorocyclohexane
0 , 0-dimethyl S^ ( 1 , 2-dicarbethoxyethyl )
phosphorodithionate
li^methylthio-3 , 5-xylyl N-methylcarbamate
*
1 ,1 ,l*-trichloro-2 , 2-bis (.p-methoxyphenyl ) ethane
0 jO^dimethyl O^p-nitrophenyl phosphorothioate
U^dimethylamino-3 , 5-xylyl N-methylcarbamate
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TABLE 1 (continued)
Vapor pressure
Common or trade name
Parathion
oo
Propoxur
Ronnel
mm Hg at
-6
5-7 x 10
1.0 x 10~2
8 x 10~2
T, °C
20
20
25
Chemical designation
0,0-diethyl 0-p-nitrophenyl phosphorothioate
o-isopropoxyphenyl N-methylcarbamate
0,0-dimethyl 0-(2,U,5-trichlorophenyl) phosphoro-
thioate
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commercial column was a 180-cm long, 4-mn I.D. U-tube, packed with 3% OV-1 on
80- to 100-mesh Chromosorb W (Tracor, Inc.).
To prepare packings, we used 80- to 100-mesh Chromosorb W as support
material. The procedure was as follows, using SE-30 as an example: 0.50 g
SE-30 was dissolved in 35 ml chloroform in a 250-ml filter flask, and 9.50 g
of the support material was added. Vacuum was then applied until the solution
boiled briefly. The vacuum was released and the slurry was swirled gently.
Evacuation, release and swirling were repeated until all the free liquid had
evaporated. The remaining slurry, which had the consistency of damp sand, was
subjected to fluidized drying in a fluidizer ("HI-EFF", Applied Science^Labor-
atories, Inc.) with nitrogen flowing through. The fluidizer was placed on a
hot plate at about 100°C surface temperature until the material became free-
flowing.
Packings prepared by this procedure were: (a) 5% SE-30, as above; (b) 3%
OV-1, from 0.30 g OV-1, 35 ml chloroform and 9.70 g Chromosorb W; (c) 5%
OV-210, from 1.021 g OV-210, 70 ml chloroform and 19.40 g Chromosorb W; and
(d) another 5% OV-210, but treated with Carbowax 20M by the procedure of Ives
and Giuffrida (5).
To pack columns, we poured the dry, coated support material into one end
of a 180-cm long, 4-mm I.D. U-tube, while applying a vacuum to the other end
and simultaneously tapping the column. The column was then conditioned by
heating to 250°C for 18 hours in a flow of nitrogen. We packed columns with
the four self-prepared packings and with two commercial packings: (a) 3%
DC-200 on 100- to 120-mesh Gas-Chrom Q (Applied Science Laboratories, Inc.),
and (b) a mixture of 1.5% OV-17 and 1.95% OV-210 on Chromosorb W HP (Supelco,
Inc.) .
POLYURETHANE FOAM PLUGS
Polyurethane foam, in both ester (gray) and ether (white) forms, was pur-
chased in 5-cm-thick sheets from a commercial source, Read Plastics, Inc.,
Rockville, MD. Both of these foams were flexible, reticulated and hydrophobic
types. Cylindrical plugs, 45-mm diameter by 5 cm thick, were cut from the
sheets with a special tool mounted in a drill press. The tool was fabricated
to our specifications from thin-wall stainless steel tubing in our Instrument
Design Shop.
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SECTION 5
EXPERIMENTAL PROGRAM AND RESULTS
INVESTIGATION OF PUF TRAPPING EFFICIENCY
Laboratory evaluations of pesticide vapor trapping efficiency by various
media have generally involved the spiking of some type of source with small
quantities of the pesticides to be tested; passing a given volume of air
through the source and through the trapping medium in a suitable apparatus;
analyzing the source, trapping medium, and chamber washings for pesticide con-
tent; and calculating trapping efficiency by a material balance (6). The
factors that control the rate at which a given pesticide is volatilized in
these tests include the vapor pressure of the pesticide, air temperature,
airflow rate, energy of adsorption of the pesticide by the source material,
and surface area of the source.
The material balance approach is valid only if the pesticides are stable
during volatilization, trapping and analysis. Finding a suitable method for
introducing thermally unstable pesticides with very low vapor pressures into
air in such a system is a major experimental obstacle. Because of the latter
restriction, we conducted experiments on PUF trapping efficiency not only with
pesticides as molecular vapors, but also as components of aerosols.
First Vapor Trapping Experiment
One microgram of each of 16 pesticides was applied to a glass-fiber filter
mounted in an all-glass apparatus, and two ester-form PUF plugs, 5 cm deep and
45 mm in diameter, were placed in series in the apparatus as traps. Air was
drawn through the source and plugs for 22 hours at an average flow rate of
2.52 m /hr, a total volume of 55.4 m-*. At the end of that time, the plugs
were extracted individually by Soxhlet extraction with 1:1 hexane-acetone, and
the source was extracted by washing with acetone. The extracts were concen-
trated, separated into pesticide groups by silica-gel column chromatography
according to Sherma and Shafik (4), and quantitated by GLC. The analytical
results are listed in Table 2.
The results showed that the N-methylcarbamates (carbofuran, carbaryl,
methiocarb) did not volatilize from the source, that a 5-cm depth of PUF was
insufficient to trap the more volatile compounds quantitatively, and that some
degradative loss of parathion and methyl parathion apparently occurred. The
remainder of the compounds were quantitatively volatilized and trapped.
10
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Second Vapor Trapping Experiment
To aid pesticide volatilization and concurrently reduce chemical degrada-
tion, a trapping experiment was conducted at an elevated temperature and with
decreased volume of air flow. Glass wool (1.65 g) was placed in a 44-mm-I.D.
TABLE 2. PUFa TRAPPING EFFICIENCY FOR 1-yg
DOSES OF PESTICIDES IN 55 M3 OF AIR
Residues, % of applied pesticides
Compound
Aldrin
p,p'-DDE
p.p'-DDD
p,p'-DDT
Lindane
Heptachlor
Heptachlor epoxide
Dieldrin
Methoxychlor
Methyl parathion
Parathion
Diazinon
Ma lath ion
Carbofuran
Carbaryl
Methiocarb
Remaining
on source
0
0
0
3
0
0
0
0
42
0
0
4
29
100
100
91
On first
PUF plug
98
100
84
98
69
71
74
100
45
70
75
64
64
0
0
0
On second
PUF plug
23
0
0
17
3
33
0
0
0
0
0
24
0
0
0
0
Total
recovered
121
100
84
118
72
104
74
100
87
70
75
92
93
100
100
91
a Ester-form polyurethane
11
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glass tube and held in place with a brass screen. To this, 1 ml of hexane so-
lution containing 1 pg of each of 24 pesticides was applied slowly. After
evaporation of the hexane, two 5-cm, ester-form PUF plugs were placed in the
tube, and the tube was wrapped with heating tape. Air was drawn through the
apparatus for 2 hours at 4.3 m^/hr. The temperature in the chamber was
45°C during the experiment. The plugs (analyzed together) and the wool were
then subjected to 5-cycle Soxhlet extraction with 1:1 hexane-acetone. The ex-
tracts were concentrated, chromatographed on silica gel, and quantitated by
GLC. The analytical results are listed in Table 3.
Except for a-BHC, the organochlorine insecticides were quantitatively
trapped on the plugs. Certain of the organophosphorus compounds did not
volatilize completely, but the portions that did volatilize were
quantitatively trapped. The carbamates again did not volatilize from the
source to any appreciable extent. Attempts to detect the carbamates on the
plugs were confounded by GLC interference in the form of a large injection
peak. The low recovery of mexacarbate, a carbamate, may have been caused by
oxidation or thermal breakdown on the source.
TABLE 3. ESTER-FORM PUF TRAPPING EFFICIENCY AT 45°Ca
Residues, % ofapplied pesticides
Compound On source On plugs Total
a-BHC
Aldrin
p,p'-DDE
o.p'-DDT
p , p ' -DDD
p.p'-DDT
*
Lindane
3-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
0
0
0
0
0
0
0
0
0
0
0
0
76
98
100
110
92
86
93
102
88
101
95
113
76
98
100
110
92
86
93
102
88
101
95
113
12
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TABLE 3 (continued)
Compound
Residues, % of applied pesticides
On source
On plugs
Total
Ronnel
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
Propoxur
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
0 119
0 106
0 118
36 45
112 0
10 91
94
93
89
87
100
57
119
106
118
81
112
101
94
93
89
87
100
57
a 8.6 vr of air passed through system
Third Vapor Trapping Experiment
A further experiment on vapor trapping was conducted under intensified
conditions. Chamber temperature was increased again, to 52<>C, and air was
passed through the apparatus for 8 hours at 3.88 m^/hr, a total volume of
31 m3. The air was prefiltered through two ester-form PUF plugs before
entry into the sampling chamber. Two similar plugs were again used as traps.
The source and plugs were extracted, chromatographed and quantitated as
before, and the results are listed in Table 4.
Total recoveries of all organochlorine and organophosphorus pesticides
were quantitative or nearly so, showing that a 10-cm depth of PUF is an effic-
ient trap for these compounds. For the most part, the carbamates again re-
mained on the source. However, the small amounts of carbofuran and methiocarb
13
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TABLE 4. ESTER-FORM PUF TRAPPING EFFICIENCY AT 52°Ca
Compound
a-BHC
Aldrin
p , p ' -DDE
o,p'-DDT
p , p ' -ODD
p,p'-DDT
Lindane
g-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
Ronnel
Parathion
Ethion
C ar b oph eno th ion
Diazinon
Malathion
Propoxur
Carbaryl
TABLE 4 (continued)
Residues,
On source
0
0
0
0
0
2
0
5
0
0
3
0
5
0
0
0
5
3
82
78
% of applied pesticides
On plugs
92
106
99
101
88
104
95
98
88
83
98
95
102
88
96
82
90
90
10
0
Total
92
106
99
101
88
106
95
103
88
83
101
95
107
88
96
82
95
93
92
78
14
-------
TABLE 4 (continued)
Residues, % of applied pesticides
Compound On source On plugs Total
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
88
68
91
62
8
5
3
2
96
73
94
64
a 31.0 w? of air passed through system
that did evaporate were apparently trapped essentially quantitatively, sugges-
ting that PUF is also a suitable trapping agent for vapors of these carbamates.
Aerosol Generation
Since we had not been able to volatilize the carbamate insecticides in
amounts sufficient to allow .PUF evaluation, several experiments were performed
with pesticide solutions injected into air as aerosols. To do this, a test
chamber was fabricated from aluminum sheet. The chamber and associated equip-
ment are illustrated in Figure I/ and a closeup of the aerosol generating as-
sembly is shown in Figure 2. The pesticide solutions were contained in the
graduated glass chamber and the aerosols were generated by aspiration with a ,
stream of nitrogen through the vertical nozzle. The aerosol spray at the
bottom aperture of the test chamber moved upward, along with air flowing up
through the chamber and with PUF plugs mounted in a glass holder at
the top of the chamber to trap the flowing aerosols. A major shortcoming of
this apparatus was that the sample air could not be prefiltered to remove con-
taminants .
First Aerosol Trapping Experiment
The first two tests of aerosol trapping were conducted with an
experimental aerosol bomb in lieu of the aerosol generator of Figure 2. In
the first test, the bomb was loaded with a hexane solution containing 5 yg of
each of 24 pesticides, plus about 100 ml of Freon 12, and was then screw-jack
mounted on its side for spraying upward into the test chamber. The assembly
was placed outdoors, at 24°C air temperature and 80% relative humidity. One
5-cm-thick ester-form PUF plug was installed as the trap. Five-second bursts
of aerosol were sprayed into the chamber every 15 seconds, for about 15
minutes. The Freon gas was vented for an additional 15 minutes without
15
-------
aerosol formation, then air was passed continuously through the system for one
hour. Total air flow (1.5 hours) was 8.5 w?. The chamber was washed down
with 300 ml acetone, the bomb residues were recovered by washing with acetone,
and the plug was Soxhlet-extracted as usual. Each of the three extract
solutions was concentrated, separated into three fractions on a silica gel
column, and quantitated by GLC. The results are listed in Table 5.
With the exception of certain of the carbamates, recoveries of pesticides
from the system were low, so that the effectiveness of the PUT trap could not
be adequately judged. Substantial amounts of material remained in the bomb,
and there were residues on the chamber walls for all but the most volatile
compounds. In general, recoveries were poorest for the organophosphorus
compounds, best for the carbamates. Results for the carbamates suggested that
ester-form PUF may be an effective trap for these pesticides when in airborne
aerosols. Volatilization and inefficient trapping of vapors of the most
volatile compounds may have contributed to the poor material balance in this
experiment, as suggested by the particularly low recovery for a-BHC. Loss of
a liquid chromatographic fraction (Fraction I) during analysis may also have
in.
Figure 1. Apparatus for aerosol trapping experiments
U
-------
contributed to this. Other factors that may have decreased pesticide recovery
include oxidation, hydrolysis, and degradative reactions catalyzed by the
aluminum surface of the test chamber. If there had been no volatilization nor
degradation during the experiment, all the pesticides should have had a
constant ratio of bomb:plug:chamber-wash residues. It is obvious that they
did not.
'
Figure 2. Closeup of aerosol generator
-------
TABLE 5. THE TRAPPING OF PESTICIDE AEROSOLS BY A
5-CM ESTER-FORM PUF PLUGa
Residues, % of applied pesticides
Compound
a-BHC
Aldrin
p.p'-DDE
o,p'-DDT
p,p'-DDD
p,p'-DDT
Lindane
B-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
Ronne 1
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
Propoxur
In
bomb
9.0
17.8
19.8
24.6
18.6
45-7
12.0
18.5
13.6
14.3
20.7
15.2
13.0
16.3
15.1
6.3
8.9
1.9
18.0
In chamber
washings
—
-
-
-
-
-
5.4
3.7
10.6
7.4
23.3
4.9
4.3
4.2
1.9
1.2
2.8
0.6
20.0
In PUF
trap
24.8
39.7
29.4
32.0
25.7
43.9
46.2
40.0
33.8
28.3
43.5
27.4
32.9
27.3
24.8
17.2
13.2
2.5
25.0
Total
133.8
157.5
149.2
156.6
144.3
189.6
63.6
62.2
58.0
50.0
87.5
47.5
50.2
47.8
41.8
24.7
24.9
5.0
63.0
TABLE 5 (continued)
18
-------
TABLE 5 (continued)
Residues, % of applied pesticides
Compound
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
In
bomb
17.0
27.0
-
14.5
34.5
In chamber
washings
2.4
19.6
21.2
4.4
8.0
In PUF
trap
25.0
57.0
87.0
22.0
76.0
Total
44.4
103.6
108.2
40.9
118.5
a 8.5 m-* of air passed through system
Second Aerosol Trapping Experiment
The preceding experiment was repeated, except that two ether-form (rather
than ester form) PUF plugs were placed in series as traps, flow rate was
4.82 m^/hr, temperature was 25°C, and relative humidity was 35%. The
analytical results are listed in Table 6.
Carbofuran and aminocarb could not be quantitated because of a large
interfering peak in the chromatograms, possibly a result of a contaminant
introduced during filling of the aerosol bomb. In general, total recoveries
of the remaining pesticides were low. Substantial amounts of all pesticides
were trapped on the second plug, strongly suggesting that at least part of the
poor recoveries was caused by passage of a portion of the aerosols through
both plugs. This is in contrast to the results with molecular vapors, which
were adequately trapped on two plugs (Tables 2, 3 and 4). The ratio of
residue levels on the second plug to those on the first was relatively
constant (last column, Table 6), suggesting that pesticide degradation was not
responsible for the low residue levels on the first plug. These levels were
generally somewhat lower than those found on the single plug of the previous
experiment (Table 5), which may be a result of the use of ether-form rather
than ester-form PUF, or may have been caused by the lower relative humidity in
the second experiment.
Third Aerosol Trapping Experiment
Following the experiment above, two additional tests were conducted on the
N-methylcarbamate insecticides alone, one outdoors and one with the apparatus
contained in a large environmental chamber. In these, the bomb used in the
19
-------
TABLE 6. THE TRAPPING OF PESTICIDE AEROSOLS BY TWO
5-CM ETHER-FORM PUF PLUGS*
Residues, % of applied pesticides
Compound
a-BHC
Aldrin
p,p'-DDE
o,p'-DDT
p.p'-DDD
p.p'-DDT
Lindane
3-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
Ronnel
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
In
bomb
10.5
17.0
15.2
19.3
16.0
23.6
20.6
11.1
13.0
10.2
14.8
15.2
13.0
16.2
15.1
6.3
7.0
15.3
In
chamber
washings
1.0
2.2
3.7
5.3
4.2
6.7
1.9
14.4
18.4
13.5
24.2
5.0
4.3
4.2
1.8
1.2
2.4
3.9
On
first
plug
17.1
26.8
21.3
24.1
21.7
27.8
36.5
34.6
34.5
30.4
47.5
27.5
33.0
27.4
24.8
17.2
9.8
23.8
On
second
plug
6.4
11.7
14.2
16.5
14.6
18.9
12.9
26.7
25.7
19.7
29.8
16.8
19.4
18.9
15.7
11.7
5.6
15.4
Total
35.0
57.7
54.4
65.2
56.5
77.0
71.9
86.8
91.6
73.8
116.3
64.5
69.7
66.7
57.4
36.4
24.8
58.4
Residue
ratio on
plugs:
2/1
0.37
0.44
0.67
0.68
0.67
0.68
0.35
0.77
0.74
0.65
0.63
0.61
0.59
0.69
0.63
0.68
0.57
0.65
TABLE 6 (continued)
20
-------
TABLE 6. (continued)
Residues, % of applied pesticides
Compound
Propoxur
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
In
bomb
15.7
12.8
-
-
12.0
10.0
In
chamber
washings
6.2
2.4
-
-
3.6
20.0
On
first
plug
28.0
24.0
-
-
18.5
26.5
On
second
plug Total
11.0 60.9
15.2 54.4
-
-
11.5 45.6
9.0 65.5
Residue
ratio on
plugs:
2/1
0.39
0.63
-
-
0.62
0.34
a 7.2 m3 of air passed through system
first two aerosol experiments was replaced with the aerosol generator
(Figure 2). Neither experiment yielded usable results, owing to contamination
of chromatograms that prevented quantitation of the carbamates.
A successful experiment was then performed, with the apparatus moved to a
second environmental chamber, using a mixture of organochlorine and organo-
phosphorus pesticides. Three high-flow ester-form PUF plugs were used in
series as traps. Ten ml of hexane containing 5 pg of each of the 18 compounds
was aspirated into the chamber by a stream of nitrogen, and washed into the
air stream in the chamber with 3 x 15 ml hexane. The conditions were:
29°C, 75% R.H., and 2.81 m3/hr flow rate. The pesticides were introduced
into the chamber in about 15 minutes and the air sampling was continued for 30
minutes, so that total air volume sampled was 2.1 m3. Extracts of the
various substrates were concentrated, separated by silica-gel liquid chromato-
graphy, and quantitated by GLC. Results are shown in Table 7.
Large losses of material occurred throughout this experiment. The first
PUF plug generally had the highest residue levels, but there were measurable
quantities of all the pesticides on the second and third plugs. The presence
of residues on the third plug after passage of only 2.1 nr of air contrasts
sharply with the quantitative trapping of molecular vapors by two ester-form
PUF plugs (10 cm) after passage of 55 m3 of air (Table 2). This again
implies that PUF, at least under certain conditions, may not trap aerosols as
readily as vapors.
21
-------
TABLE 7. THE TRAPPING OF PESTICIDE AEROSOLS BY THREE
5-CM ESTER-FORM PUF PLUGS*
Residues, % of applied
Compound
oe-BHC
Aldrin
p,p'-DDE
o,p'-DDT
p.p'-DDD
p,p'-DDT
Lindane
6-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
Ronnel
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
In
chamber
washings
0.8
1.4
10.4
13.7
10.0
13.7
3.0
7.3
10.0
17.4
14.3
7.1
5.5
10.8
9.6
30.2
15.4
16.2
On
first
plug
19.3
24.6
10.5
8.2
4.8
4.8
30.2
16.7
15.4
14.2
13.3
13.1
17.0
9.3
3.8
4.4
18.5
7.4
On
second
plug
0.5
1.0
2.0
2.7
2.4
3.3
1.5
1.2
2.5
2.1
1.7
22.1
12.2
1.3
2.3
2.2
20.8
1.7
pesticides
On
third
plug
0.6
0.7
2.5
2.9
2.9
3.4
2.0
2.3
3.4
5.6
2.7
2.4
18.5
3.1
3.9
4.4
2.2
3.9
Total
21.2
27.7
25.3
27.6
20.1
25.2
36.7
27.5
31.3
39.3
32.0
44.7
53.2
24.5
19.6
41.2
56.9
29.2
2.1 m3 of air passed through system
22
-------
Fourth Aerosol Trapping Experiment
To compare directly the performance of the two forms of PUF, a replicate
of the previous experiment was run, with the exception that ether-form, rather
than ester-form, plugs were used. The conditions were: 29°C, 75% R.H., and
2.88 m^/hr flow rate. The analytical results are listed in Table 8.
Poor recoveries again occurred. The degree of trapping of the organo-
chlorine insecticides agreed well with that of the previous experiment,
whereas trapping of some of the organophosphorus compounds was somewhat less
efficient. In general, the two forms of PUF apparently do not differ greatly
in their ability to trap pesticides in aerosols.
TABLE 8. THE TRAPPING OF PESTICIDE AEROSOLS BY THREE
5-CM ETHER-FORM PUF PLUGS3
Residues, % of applied
Compound
a-BHC
Aldrin
p,p'-DDE
o,p'-DDT
p,p'-DDD
p,p'-DDT
Lindane
e-BHC
Heptachlor epoxide
Dieldrin
Endrin
Methyl parathion
Table 8 (continued)
In
chamber
washings
0.4
1.5
13.8
16.7
13.7
13.9
4.7
8.7
18.2
24.8
23.4
11.4
On
first
plug
16.0
28.5
12.8
9.3
4.0
5.3 .
27.7
16.3
14.1
12.4
12.4
9.8
On
second
plug
n.d.
0.4
1.1
1.7
1.3
2.2
0.4
0.6
0.8
1.7
3.4
0.8
pesticides
On
third
plug
0.2
0.3
0.9
1.4
0.9
1.9
0.4
0.2
0.6
1.6
1.4
0.7
Total
16.6
30.7
28.6
29.1
19.9
23.3
33.2
25.8
33.7
40.5
40.6
22.7
23
-------
TABLE 8 (continued)
Residues, % of applied pesticides
Compound
In
chamber
washings
On
first
plug
On
second
plug
On
third
plug
Total
Ronne1
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
10.5
14.4
13.5
16.6
37.1
30.2
16.2
6.5
3.3
3.6
12.8
5.5
0.6
0.7
1.3
1.6
0.6
0.8
0.7
0.8
1.3
1.4
0.5
0.8
28.0
22.4
19.4
23.2
51.0
37.3
a 2.2 m-' of air passed through system
Fifth Aerosol Trapping Experiment
Because pesticide recoveries were consistently poor in the aerosol tests
conducted in the large aluminum test chamber, a smaller glass-chamber appar-
atus was fabricated in this Laboratory by Mr. H. P. Freeman. This was a modi-
fied Rappaport-Weinstock apparatus, consisting of a 44-mm ID glass tube with a
glass cup on the bottom, a stainless-steel 1.6-mm OD tube connecting an ex-
terior sample solution reservoir to a nitrogen-gas-driven aerosol generator
located above the cup, and space at the top of the tubular chamber for five
5-cm-thick PUF plugs. Dry nitrogen gas was introduced under slight pressure
through a tubulation in the center of the bottom cup and a vacuum pump was
used to equalize pressure in the chamber. This apparatus allowed the genera-
tion and trapping of aerosols without exposure to air, so that oxidation,
hydrolysis, or contamination from ambient vapors or aerosols could not occur.
In a three-hour experiment with this apparatus at a nitrogen flow rate of
3.43 m-Vhr, the trapping of eight organochlorine and five organophosphorus
insecticides by five ester-form plugs in series (25 cm of foam) was studied.
The plugs were extracted and analyzed individually and the results for the
organochlorines are listed in Table 9. Results for the organophosphorus com-
pounds are not tabulated because extracts for all but the first plugs were
lost.
24
-------
TABLE 9. THE TRAPPING OF PESTICIDE AEROSOLS BY FIVE
5-CM ESTER-FORM PUF PLUGS*
Compound
Aldrin
p,p'-DDE
o,p'-DDT
p.p'-DDD
p,p'-DDT
Heptachlor ep oxide
Dieldrin
Endrin
Residues, % of applied pesticides
In
chamber On plug No.
washings 12345
nd 102.9 2.8 1.8 1.4 1.0
3.6 81.6 2.7 1.9 1.0 2.2
5.1 92.8 3.8 2.7 2.9 2.1
7.1 65.7 nd nd nd 2.2
9.7 70.6 5.6 4.2 3.6 3.9
nd 95.7 1.7 1.3 1.0 1.4
nd 87.3 4.9 3.6 2.0 4.2
nd 83.6 4.8 3.0 1.5 2.6
Total
109.9
93.0
109.4
75.0
97.6
101.1
102.0
95.5
a 10.3 m^ of air passed through system
Trapping of all the organochlorine pesticides was almost quantitative on
the first plug, but there were detectable residues on all the plugs. This
indicates that under these conditions small amounts of the pesticide aerosols
penetrated the first plug and were trapped on later plugs. In this experi-
ment, 25 cm of ester-form PUF was sufficient to trap organochlorine aerosols
essentially quantitatively. There were substantial but less than quantitative
amounts (60 - 75%) of the organophosphorus pesticides trapped on the first
plug; presumably, succeeding plugs would also have contained measurable
residues of these compounds.
Summary and Analysis of Pesticide Trapping Experiments
A number of conclusions may be drawn from the PUF trapping
(Tables 2-9). It is apparent that a 10-cm depth of foam is an
for vapors of organochlorine and organophosphorus pesticides.
the test pesticides from ca. 10 nP of air, and of many of them
as 55 m^ of air, was essentially quantitative. The ester form
somewhat, but not significantly, superior to the ether form in
efficiency. The N-methylcarbamate insecticides were extremely
experiments
efficient trap
Trapping of all
from as much
of PUF was
its trapping
difficult to
25
-------
vaporize, but the small amounts that did vaporize were apparently efficiently
trapped on PUF.
When the pesticides were injected into the air as aerosols, there were
indications that PUF trapping ability was substantially lower than with
molecular vapors. Although most of the residues were found on the first plug,
measurable amounts of all the test pesticides occurred on backup plugs, even
when as many as 5 plugs (25-cm total depth of PUF) were placed in series to
trap the aerosols. The pattern, high residue levels on first plug and much
lower levels on succeeding plugs, is consistant with three possible
interpretations, but the early termination of the experimental program did not
allow disclosure of which was operative. The possibilities are: (a) most of
the generated aerosols had vaporized by the time they reached the trapping
plugs, so that vapors were trapped on the first plug and aerosols, less
efficiently trapped, passed through; (b) hexane solvent carried into the
aerosols desorbed small amounts of the pesticides as it passed through the
plugs; or (c) plugs were contaminated before the experiments with low levels
of the pesticides not removed in earlier experiments with the same plugs, or
adsorbed from laboratory air.
One possible reason for poor trapping efficiency of aerosols by PUF is
electrostatic repulsion. Polymers such as PUF tend to have high dielectric
constants, thus can acquire significant electrostatic charges. Moreover,
droplets disrupted from an organic liquid such as hexane by atomization
acquire charges, and the charge to mass ratio increases as the solvent
evaporates (7). If the charges on the droplet and PUF surfaces were the same,
electrostatic repulsion would result and trapping efficiency would
consequently diminish. Humidity in air tends to dissipate electrostatic
charges, so that the charge effect would be accentuated under conditions of
low humidity.
The low recoveries of pesticides in the large-chamber aerosol experiments
and the differences in recoveries between compounds may have been caused by
any of a number of physical and chemical processes. Among the latter are
oxidation, hydrolysis, rearrangement, and catalytic degradation. These are
especially important for the organophosphorus pesticides. Hydrolysis would
cause a total loss from chromatograms obtained with the flame photometric
detector (FPD), since the hydrolysis products are nonvolatile phosphate
acids. Oxidation and rearrangement can give volatile products that would not
have the same GLC retention times as the parent organophosphorus molecules.
For example, it has been shown that the oxidation product and the
rearrangement product of parathion (paraoxon and S-ethyl parathion,
respectively) have shorter retention times than the parent molecule on 3%
OV-1, and that the three compounds are separable (8). Examination of the FPD
chromatograms in some of the experiments did in fact show a number of new,
small, short-retention-time GLC peaks. That these chemical transformations
were quite important to pesticide recovery was illustrated by the high
recoveries in the one experiment conducted under conditions in which they
could not occur (Table 9).
26
-------
Among the physical processes that may have contributed to losses are
imperfect injection of aerosol into the chamber, loss of droplets through
chamber apertures, imperfect washing of residues off chamber walls, and
aerosol passage through all the plugs because of poor adsorptivity, as
discussed above. The contribution of each of these processes to losses or
differences in recovery is unknown.
EVALUATION OF PESTICIDE EXTRACTION METHODS
Comparison of Three Extraction Techniques
Considerable exploratory work in analytical methodology was conducted
throughout our laboratory program, looking to development of the optimum
method for use of PUF as a trapping agent in a national airborne pesticide
monitoring program. An early phase of this involved a search for the best
technique for extracting a wide variety of pesticides from PUF plugs. Three
replicate experiments were performed, in which extractions of the 24 test
pesticides by Soxhlet treatment, mechanical squeezing, and simple elution were
compared. In each experiment, six ester-form PUF plugs were spiked directly
with all 24 compounds in hexane at 1 yg of each compound per plug. The hexane
was allowed to evaporate, then two of the plugs were Soxhlet-extracted with
250 ml of 1:1 hexane-acetone for five Soxhlet cycles; two were extracted by
squeezing each plug five times with a metal plunger in 50 ml 1:1
hexane-acetone and repeating this four times with fresh solvent, for a total
of 250 ml of extract solution; and the remaining two were extracted by passing
250 ml of .1:1 hexane-acetone through each plug at a rate of about 4 ml/min.
All extract solutions were concentrated, separated into fractions by liquid
chromatography according to Sherma and Shafik (4), and analyzed by GLC.
Results of the experiments are summarized in Table 10.
Several samples were lost during the many analytical manipulations
involved, but clear-cut findings were nevertheless obtained. For both the
organochlorine and organophosphorus insecticides, recoveries were little
different among the three techniques, but Soxhlet extraction gave the most
consistent results for classes of compounds and, at least for the
organochlorines, showed the least variation in replicate determinations of
individual compounds. Results by the squeezing and the elution techniques
were not appreciably different from each other with respect to both extent and
precision of pesticide recovery^ The very high and variable recovery of the
early-eluting a-BHC by all methods reflects the difficulty in quantitating on
a sharply sloped baseline. Results for the carbamates showed that recoveries
by the Soxhlet technique were not only distinctly higher than by the other
techniques, but were also the most consistent for the class. Variations in
recoveries of individual compounds, although large, were no greater than those
obtained by squeezing or elution.
Cumulative results for all 24 pesticides (last line, Table 10) indicated
that 5-cycle Soxhlet extraction with 1:1 hexane-acetone gave the highest and
most consistent recoveries, and it was consequently selected as the method of
choice in the other phases of the experimental program. The limitations to 5
27
-------
cycles and the selection of 1:1 hexane-acetone as the preferred solvent were
based on additional exploratory work described in detail in the following
sections.
TABLE 10. COMPARISON OF THREE TECHNIQUES FOR EXTRACTION
OF PESTICIDES FROM PUF PLUGS3
% Recovery by
Soxhlet
extraction
Compound
a-BHC
Aldrin
p.p'-DDE
o , p ' -DDT
p , p ' -ODD
p.p'-DDT
Lindane
g-BHC
Hept. epox.
Dieldrin
Endrin
Organochlorines
Me parathion
Ronne 1
Meanb
123.0
96. 3C
106. lc
95. 6C
96. 7C
93. 9C
82.0
85.0
89.4
99.2
94.6
96.5
85.3
90.3
Standard
deviation
35.1
8.1
9.9
10.6
4.2
8.5
5.7
18.9
10.2
7.1
15.3
11.0
24.2
6.2
Mechanical
squeezing
Meanb
128.3
108.5
104.9
100.2
131.5
107.9
86.3
76. 7e
85. 4e
94. Oe
84. 6e
101.4
84. 6C
73. 2C
Standard
deviation
23.3
10.1
14.2
12.9
23.4
17.8
10.2
14.1
22.7
11.7
9.6
17.2
9.6
2.8
Elution
Meanb
128.9
105.4
101.1
96.3
124.0
105.9
86.9
73. 4d
73. 5d
95. 2d
96. 5d
98.8
79.1
68.8
Standard
deviation
27.6
18.6
15.3
9.7
26.8
16.1
8.2
9.9
16.6
12.6
11.0
17.6
13.0
8.8
Table 10 (continued)
28
-------
TABLE 10 (continued)
% Recovery by
Soxhlet
extraction
Compound
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
Organophosphates
Propoxur
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
Car hamate s
All pesticides
Meanb
76.6
99.8
99.1
91. ld
95. 5d
91.1
91. 9d
97. 8d
81. 9d
85.3d
102. 5d
93. ld
92.1
93.8
Standard
deviation
18.9
8.7
5.3
6.9
5.0
8.2
13.0
20.5
26.3
10.5
3.3
25.1
7.6
9.4
Mechanical
squeezing
Meanb
89. 2C
91. Oc
99. 8C
89. 4d
79. 6d
86.7
80. 8d
56. 6d
73. 4d
53. 9d
88. 5d
36. 9d
65.0
88.0
Standard
deviation
5.0
4.2
7.2
4.6
2.6
8.6
19.4
11.8
11.9
19.4
10.3
16.0
19.3
21.3
Elution
Meanb
91.4
96.8
102.5
91. 9d
87. 6d
88.3
77.3d
66. 7d
70.3d
89. Od
73. 8d
63. ld
73.4
89.4
Standard
deviation
7.8
11.2
15.9
7.1
10.3
11.3
24.0
26.0
28.6
22.9
18.9
28.1
9.2
17.2
a Ester-form polyurethane
Six replicates, unless otherwise specified
c Five replicates
Four replicates
Three replicates
29
-------
Development of the Soxhlet Procedure
Because certain of the organophosphorus pesticides may degrade under
prolonged high-temperature conditions such as those encountered in Soxhlet
extraction, systematic study was made to determine the optimum number of
Soxhlet cycles for extraction of these compounds from PUF plugs. Twelve
ester-form plugs were precleaned by Soxhlet extraction with acetone for 850
cycles, then each plug was spiked with a hexane solution containing lyg of
each of the 7 test organophosphorus pesticides. The plugs were then dried and
placed individually in Soxhlet extractors. All plugs were extracted with
280 ml of 1:1 hexane-acetone, but the extractions were stopped after different
numbers of Soxhlet cycles ranging from 1 through 12. The extracts were
evaporated in Kuderna-Danish flasks with five drops of paraffin oil keeper
solution, dissolved in 1 ml acetone, and quantitated on a 3% OV-1 column with
flame photometric detector. Recoveries are listed in Table 11.
Extraction of all the test compounds proceeded very rapidly, reaching
quantitative level in only 2 cycles. At 3 cycles, recoveries were not only
quantitative, but also consistent for the class of compounds. Recoveries only
for the class remained essentially quantitative up to 9 cycles, but the
variability increased with increased cycling, a reflection of decreasing
recoveries of parathion and methyl parathion. The data were subjected to
least-squares regression analysis, with the postulation that change in
recovery is a first-order process with respect to time, and thus with respect
to number of extraction cycles. The operative relation is:
In y = a + b x
where y_ is the percent recovery, jc is the number of extraction cycles, b_ is
the slope of the regression line, and £ is the natural logarithm of the
intercept of the line. The coefficients of this equation are shown in Table
12, along with correlation coefficients, r. The regression analysis
statistically confirmed the observation that parathion and methyl parathion
were being lost with prolonged Soxhlet extration, as illustrated by the values
of the slopes of the regression lines. The negative values for parathion and
methyl parathion are significant at the 95% confidence level.
In view of these results, Soxhlet extraction for from 3 to 7 cycle.s
appeared to be the optimum range of duration of treatment, and 5 cycles was
consequently selected as the technique used in other phases of our
investigations. Five cycles would not produce significant loss of the labile
organophosphorus pesticides, while assuring quantitative recovery of other
organophosphorus compounds, carbamates, and organochlorine pesticide residues
on the PUF plugs.
Choice of Extraction Solvent
A large number of pure solvents and combinations of solvents can be used
for the extraction of pesticide residues from PUF. However, to keep the work
within practical bounds, it was necessary to choose a small number of likely
candidates for testing. The solvents had to be commercially available in
30
-------
TABLE 11. THE EFFECT OF NUMBER OF SOXHLET EXTRACTION
CYCLES ON RECOVERIES OF ORGANOPHOSPHORUS
PESTICIDES FROM POLYURETHANE FOAM PLUGS
% recovery
Compound
Diazinon
Me parathion
Ronnel
Malathion
Parathion
Ethion
Carbophenothion
Average
Std. deviation
1
90
83
90
89
86
90
88
88
2.6
2
105
95
102
105
95
108
103
102
5-0
3
98
100
99
99
95
100
100
99
1.8
1*
97
85
97
101
91
97
100
95
5.6
. 5
110
98
109
100
9^
100
102
102
5.8
at Soxhlet cycle No.
7
103
95
106
107
96
91
99
100
6.0
8
103
90
105
107
8U
99
98
98
8.5
9
109
95
10 U
105
95
97
102
101
5.H
10
91
75
97
99
77
101
100
91
11.0
11
108
86
105
10U
8U
100
99
98
9.U
12
97
78
101
101
^
97
103
9".
9.8
-------
TABLE 12. REGRESSION AND CORRELATION COEFFICIENTS
OF SOXHLET EXTRACTION DATA IN TABLE 11.
Coefficients
'Compound a b
Diazinon 4.6377(103.3)a -0.0019 -0.107
Methyl parathion 4.6240(101.9) -0.0185 -0.661*
Ronnel 4.6220(101.7) +0.0010 +0.095
Malathion 4.6269(102.3) +0.0007 +0.084
Parathion 4.6022(99.7) -0.0157 -0.701*
Ethion 4.6250(102.0) ' -0.0040 -0.353
Carbophenothion 4.6151(101.0) -0.0006 -0.120
a Numbers in parentheses are antilogs of a, and are intercepts expressed
as % pesticide recovery
adequate purity for pesticide residue analysis, not be unduly hazardous, be
inert to the pesticides, be readily distilled and evaporated, and be
reasonably priced. Alcohols, ethers and aromatic solvents were rejected
because they could not meet one or more of these criteria. Hexane and
acetone, by contrast, were selected for study because they not only met the
criteria, but also had a history of use as pesticide extractants. Moreover,
they differed greatly with respect to polarity, so that they provided needed
contrast in dissolving power. Hexane, being relatively nonpolar, is a less
powerful solvent than the more polar acetone. Tests were conducted with
pesticide-grade" hexane, pesticide-grade acetone, and a 1:1 mixture of the
two. In the interests of time, experiments were limited to extractions of the
seven test organophosphorus insecticides from ester-form PUF plugs,
circumventing the need for the liquid chromatographic separation step of the '
Sherma-Shafik procedure.
In the first experiment, six ester-form PUF plugs were precleaned by
individual Soxhlet extraction with hexane for 17 hours at about 5 cycles per
hour, then were dried by drawing PUF-filtered air through for about an hour.
Three of the plugs were each spiked with 1 ml of hexane containing 0.1 yg of
each of the seven OP pesticides, and the other three were spiked with 1 ml of
hexane containing 1.0 yg of each pesticide. The plugs were placed
individually in size E Soxhlet extractors (Kontes Glass Co.) and left open for
15 min. to evaporate the hexane. The extractors were then fitted to 300-ml
boiling flasks and 250 ml of hexane, acetone, or 1:1 hexane-acetone was poured
through the plugs. Temperatures of the Soxhlet heaters were adjusted to give
32
-------
solvent distillation rates of about 20 minutes per extraction cycle. After
five cycles, each solvent was cooled to about 35°C and poured into a
Kuderna-Danish (K-D) flask fitted with a 15-ml receiver tube. A boiling chip
and 5 drops of a 1% paraffin oil-in-hexane keeper solution were added to each
flask, Snyder columns were fitted to the flasks, and the flasks were heated
gently in a steam bath until solvent loss through the Snyder columns stopped.
The flasks were removed from the steam bath and, after cooling, about 5 ml of
residual solution remained in each receiver. This was evaporated with gentle
heating in a stream of nitrogen to 1 ml. The solutions were quantitated with
the alkali-flame ionization detector, using a 3% OV-1, 180-cm column at
200°C. The elution times for the organophosphorus compounds, as determined
with individual standards, were: diazinon, 2.4; methyl parathion, 3.1;
ronnel, 3.5; malathion, 3.85; parathion,4.15; ethion, 9.8; and
carbophenothion, 11.1 minutes.
The final concentrates obtained from the acetone and 1:1 hexane-acetone
extractions were yellow oils that yielded chromatograms so contaminated that
quantitation of the early peaks of interest was not possible. By contrast,
the hexane extracts were colorless and yielded acceptable chromatograms.
Results with hexane are shown in Table 13. Recoveries of 1 yg of the test
compounds were generally high and consistent, whereas those at the 0.1 pg
level were considerably lower and more variable. Above-quantitative
recoveries of 0.1 ug of malathion and ethion were produced by background
interferences.
The contaminated extracts obtained with acetone and hexane-acetone in the
above experiment were evidence that hexane-precleaning of the PUF plugs was
not adequate except for further extraction with hexane. Consequently, the
experiment was repeated with plugs that had been subjected to more intensive
pretreatment. Six ester-form PUF plugs were individually Soxhlet-extracted
with acetone for 170 hours at about 5 cycles per hour. During this treatment,
the foam plugs swelled somewhat, showing that the more polar acetone
penetrated the polyurethane matrix as well as passing through the open
channels of the PUF. This swelling did not interfere with the subsequent
analytical process. The cleaned plugs were dried by drawing PUF-prefiltered
air through the plugs for 1 hour, during which time the plugs shrank to their
original dimensions. The procedure of the previous experiment was repeated,
and yielded colorless extracts and usable chromatograms. Thus, initial plug
cleaning by Soxhlet extraction with acetone for 850 cycles was adequate,
whereas Soxhlet extraction with hexane for 85 cycles was not. The results of
the repeat experiment are tabulated in Table 14.
The superiority of 1:1 hexane-acetone as a pesticide extractant for PUF
was apparent in this experiment. At the 1-jJg spike level, recoveries of all
the test compounds were essentially quantitative with the mixed solvent,
whereas those with acetone were somewhat more variable and those with hexane
were not only more variable, but also substantially less than quantitative.
At the 0.1-yg level, recoveries with all the solvents were lower and quite
variable, but the mixed solvent again was best. These results led us to use
1:1 hexane-acetone as the solvent of choice in the other phases of our
experimental program.
33
-------
TABLE 13. RECOVERY OF ORGANOPHOSPHORUS INSECTICIDES FROM
SPIKED PUF PLUGS BY SOXHLET EXTRACTION WITH HEXANE
Percent recovery at
Compound 1 vg per plug 0.1 yg per plug
Diazinon
Methyl parathion
Ronne 1
Malathion
Parathion
Ethion
Carbophenothion
115
85
102
99
88
92
91
86
60
66
155
57
120
101
Average 96.0 92.1
Standard deviation 10.3 36.0
Performance of the Developed Method With PUF Extract Blanks
Having identified the most suitable extraction technique, duration of
extraction, and solvent, we conducted a systematic study of the method of
choice, 5-cycle Soxhlet extraction with 1:1 hexane-acetone, to determine
whether the procedure would yield coextractives from PUF that would interfere
with analysis of any of the 24 test pesticides. Each of the three fractions
resulting from the silica-gel liquid-chromatographic cleanup step of the
Shenna-Shafik analytical method (4) was examined. Of the 24 compounds, 6
organochlorines occur in Fraction I, 5 organochlorines and 5 organophosphates
in Fraction II, and 2 organophosphates and the 6 carbamates in Fraction III.
Specific compounds are indicated in the chromatograms that follow. The
chromatograms of PUF blank extracts and of extracts spiked with appropriate
pesticide standard solutions can be used not only to illustrate the presence
or absence of coextracted interferences to pesticide detection and
quantitation, but also to evaluate the minimum detectability of each pesticide.
Six ester-form PUF plugs were Soxhlet-extracted with acetone for 98 hours
at about 5 cycles per hour (490 cycles). To remove acetone, the solvent was
decanted while the plugs were squeezed with a metal plunger. Then, clean
34
-------
TABLE 14. RECOVERY OF ORGANOPHOSPHORUS INSECTICIDES FROM
SPIKED PUF PLUGS BY SOXHLET EXTRACTION WITH THREE SOLVENTS
Percent recovery at
Compound
Diazinon
Me parathion
Ronne 1
Malathion
Parathion
Ethion
Carbophenothion
Hexane
98
76
82
80
79
83
68
1 ug per
Hex-Acet
103
95
98
101
96
100
97
plug
Acetone
110
93
102
95
94
98
101
Hexane
105
51
72
90
38
82
55
0.1 jig per
Hex-Acet
91
82
65
121
73
111
95
plug
Acetone
128
37
85
105
65
81
89
Average
Std deviation
80.9
9-1
98.6
2.9
99.0
5.9
70.4
23.7
91.1
20.0
84.3
28.8
300-ml receiver flasks containing 280 ml 1:1 hexane-acetone were fitted to the
Soxhlets without removing the plugs, and extraction was conducted for 5
cycles. The extract solutions were evaporated to dryness with 5 drops of
keeper solution, taken up in 0.5 ml hexane, and chromatographed on silica
gel. The resulting fractions were analyzed by GLC, spiked with appropriate
pesticide standard solutions, and analyzed again by GLC under the same
conditions.
The chromatograms for Fraction I, both blank and with spike, are presented
in Figure 3. Analysis was by 63flli electron-capture gas chromatography
(ECGC) on a 1.5% OV-17/1.95% OV-210 column. The spike solution contained
0.1 yg of each of the 6 organochlorine insecticides normally found in Fraction
I, plus 0.1 jig of lindane. The latter was included because it was
occasionally found in Fraction I as well as in Fraction II, its normal
location. Comparison of the two chromatograms in Figure 3 shows that Soxhlet
extraction of these plugs with acetone for about 490 cycles constituted
adequate treatment for precleaning the plugs. No significant interferences to
the quantitation of the organochlorine compounds appear in Fraction I. Each
of the peaks in Figure 3B represents 4 x 10~H grams of the appropriate
pesticide.
35
-------
B
1. a-BHC
2. Lindane
3. Aldrin
k. p,p'-DDE
5. o.p'-DDT
6. p,p'-DDD
7. p,p'-DDT
Figure 3. Fraction I chromatograms. A. PUF blank; B. Spiked blank
36
-------
Because both, organochlorine and organopbosphorus pesticides occur in
Fraction II, PUF blanks were chromatograpbed by both electron-capture and
flame-photometric GLC. Chromatograms typical of the six samples of each that
were run are presented in Figure 4. In Figure 4A, the column was 1.5%
OV-17/1.95% OV-210, and temperatures of inlet, column, and 63Ni-detector
were 250°, 205°, and 325°C, respectively. Injection volume was 4 pi
from 15 ml of final extract. The three small peaks that are shown at.
retention times of 1.3, 1.8, and 3.7 minutes appeared in the chromatograms of
all six samples at about the same level. There was also a large peak, not
illustrated, at about 23 minutes. This peak did not occur in solvent blanks,
but did appear in all plug extracts, with some variation in peak height. In
figure 4B, the column was 3% OV-1 and 5 yl of a 1-ml extract was injected.
There were no detectable peaks after the injection peak.
Two representative blank extracts were spiked with standard solutions
containing the five organochlorine and five organophosphorus pesticides that
elute in liquid-chromatography Fraction II. Spiked-blank solution volumes
were adjusted to the original volumes of the blank extracts, then one solution
was analyzed by ECGC and the other by FPD-GC. The electron-capture chromato-
gram is reproduced in Figure 5 and the flame-photometric chromatogram in
Figure 6.
In Figure 5, each peak represents 0.27 ng of a pesticide. The first of
the small peaks in the blank (Figure 4A) appears as a small shoulder at the
leading-edge base of the lindane peak, the second occurs between the peaks
for $-BHC and ronnel, and the third is seen between the peaks for ronnel and
methyl parathion. The large late peak, designated peak A, is illustrated in
this chromatogram. Although none of the background peaks interfere with the
peaks of interest, the large late peak does make it necessary to delay further
injections on the column until the peak has cleared the detector. In
Figure 6, each of the peaks represents about 5 ng of the designated organo-
phosphorus pesticide. No interferences with quantitation are evident.
A fraction III PUF blank eluate off the silica-gel column was evaporated
to 0.5 ml, and 10 yl of this solution was analyzed by flame-photometric GLC.
In the chromatogram, reproduced in Figure 7A, there are two small, early
peaks. A standard solution containing diazinon and malathion, which would
normally appear in Fraction III, was added to the blank solution, the volume
was adjusted, and 10 yl of this solution was injected into the GC, with the
result depicted in Figure 7B. The first large peak represents 5 ng of
diazinon and the second, 10 ng of malathion. Neither of the background peaks
interfered with the pesticide peaks.
The remaining five Fraction III blanks were evaporated with keeper solu-
tion and derivatized with pentafluoropropionic anhydride (PFPA) according to
the method developed for the carbamate insecticides, as described in a later
section of this report. Electron-capture GC of the derivatized blanks gener-
ally showed a relatively broad injection peak and three small, early peaks.
One of the chromatograms, representing injection of 0.6 yl out of 5 ml of so-
lution onto a 3% DC-200 column, is shown in Figure 8. This sample, as may be
seen, produced several somewhat larger peaks as well as a large, late peak,
37
-------
Figure h. Fraction II FUF blanks. A. Electron-capture chromatogram.
B. Flame photometric chromatogram
38
-------
1. Lindane
2. g-BHC
3. Ronnel
k. Methyl parathion
5. Heptachlor epoxide
6. Parathion
7. Dieldrin
8. Endrin
9 - Ethion
10. Carbophenothion
Figure 5. Fraction II spiked blank—electron-capture
39
-------
1. Methyl parathion
2. Ronnel
3. Parathion
h. Ethion
5. Carbophenothion
Figure 6. Fraction II spiked blank—flame photometer
40
-------
f
r^^J
B
1. Diazinon
2. Malathion
Figure 7« Fraction III ehromatograms.
B. OP-spiked blank
A. PUF "blank;
41
-------
Figure 8. Electron-capture chromatogram of PUF blank extract
derivatized with PFPA
42
-------
and may be considered as a worst case. A standard solution containing the 8
compounds normally found in Fraction III - 6 carbamates and 2 organophos-
phates - was also derivatized with PFPA and subjected to ECGC on a 3% DC-200
column. The chromatogram, representing an injection of 120 pg of each carba-
mate, is shown in Figure 9. The two organophosphorus compounds produced only
one peak, sufficiently removed that it did not interfere with the carbamate
peaks. To estimate the possible extent of interference arising from the PUF
background, the derivatized standard of Figure 9 and the derivatized blank of
Figure 8 were simultaneously applied to the column at the same injection
volumes as before. The chromatogram produced is shown in Figure 10. The
large, late peak does not interfere with any of the carbamate peaks, but at
least two of the small peaks do interfere. Comparison of peak heights for the
standard and spiked blank shows that the peak sizes of aminocarb and
mexacarbate were affected by the PUF blank. The aminocarb peak height was
increased about 48%, and that of mexacarbate about 63%, relative to the peak
heights in the standard. Such interferences, though random, do occur, and
would have greatest effect at very low carbamate levels. Consequently, false
positive results could be obtained unless identities of the peaks were
confirmed by independent means.
In sum, our experiments show that, when the best analytical methodology is
used, pblyurethane foam does not interfere with the quantitation of even very
low levels of airborne organochlorine and organophosphorus insecticides, but
that some interference with certain of the N-methylcarbamates may possibly
occur.
COMPARISON OF ESTER AND ETHER FORMS OF PUF
Experiments were conducted to ascertain whether the extractability of the
test pesticides from the two types of PUF differed significantly. In tests of
recoveries from pesticide aerosols, the ester form had yielded slightly, but
not significantly, superior results (Tables 7 and 8), which may have reflected
differences in extractability.
Four ether-form PUF plugs were spiked with all 24 pesticides, two at
1.0 pg of each compound per plug, and two at 0.1 pg per plug. In addition,
two ester-form plugs were spiked at the 0.1-yg level. The six plugs were
extracted with 1:1 hexane-acetone for five Soxhlet cycles and the extracts
were evaporated with five drops of keeper solution, put through liquid
chromatography on silica gel, and quantitated by GLC. The results for the
0.1-pg spikes are recorded in Table 15 and those for the 1.0- yg spikes in
Table 16. In the latter table, the results obtained earlier with ester-form
plugs are shown for comparison.
Although average recoveries of all pesticides showed no significant
differences between the two forms of PUF at both spike levels, close
examination of the data reveals clear trends that indicate that extractability
of pesticides from ester-form PUF is superior to that from ether-form
material. For example, in Table 15, recoveries of 10 of the 24 compounds from
ester-form PUF were in the optimum range between 90 and 100%, whereas
recoveries of only 3 compounds were in that range with ether-form PUF.
43
-------
1. Propoxur
2. Carbofuran
3. Aminocarb
k. Mexacarbate
5. Carbaryl
6. Methiocarb
OP. Organophosphorus peak
Figure 9- ECGC chromatogram of Fraction III standard solution
derivatized vith PFPA
44
-------
1. Propoxur
2. Carbofuran
3- Aminocarb
h. Mexacarbate
5. Carbaryl
. £•_ Methipc_arb
A. Background peaks
OP. Organophosphorus peak
Figure 10. ECGC chromatogram of combined PUF blank and Fraction III
standard, PFPA-derivatized
45
-------
TABLE 15. RECOVERIES OF PESTICIDE SPIKES (0.1 yG PER COMPOUND)
FROM ESTER- AND ETHER-FORM PUF PLUGS BY SOXHLET EXTRACTIONS
Pesticide recoveries, %
Ester- form PUF
Compound
a-BHC
Aldrin
p , p ' -DDE
o.p'-DDT
p,p'-DDD
p,p'-DDT
Lindane
3-BHC
Hept. epox.
Dieldrin
Endrin
Me parathion
Ronnel
Parathion
Ethion
Carbophenothion
Diazinon
Ma lath ion
Propoxur
Repl. 1
84.0
86.9
93.0
100.0
87.4
109.7
97.3
87.8
82.4
86.0
57.9
88.2
94.9
97.2
94.8
77.3
94.4
104.8
80.0
Repl. 2
104.4
99.1
105.4
116.3
99.8
130.5
68.3
89.3
77.6
86.6
79.7
74.6
87.1
83.3
96.8
80.0
63.6
91.9
110.0
Avg.
94.2
93.0
99.2
108.2
93.6
120.1
82.8
88.6
80.0
86.3
68.8
81.4
91.0
90.3
95.8
78.7
79.0
98.4
95.0
Ether- form PUF
Repl. 1
145.1
163.4
187.7
190.0
187.5
201.0
88.5
84.6
76.2
83.5
70.1
87.5
100.0
86.6
88.9
88.9
-
-
187.5
Repl.
76.5
86.6
94.3
102.3
86.9
118.4
84.7
87.7
79.1
83.3
82.0
78.8
96.2
74.7
105.6
105.3
83.7
85.5
165.0
2 Avg
110.8
125.0
141.0
146.2
137.2
159.7
86.6
86.2
77.7
83.4
76.1
83.2
98.1
80.7
97.3
97.1
83.7
85.5
176.3
TABLE 15 (continued)
46
-------
TABLE 15 (continued)
Pesticide recoveries, %
Compound
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
Average
Std. deviation
Ester-form PUF
Repl. 1 Repl. 2 Avg.
175.0 177.0 176.0
20.0 150.0 85.0
432.0 680.0 556.0
135.0 247.0 191.0
210.0 151.0 180.5
121.4
98.2
Ether-form PUF
Repl. 1 Repl. 2 Avg
32.5 125.0 78.8
80.0 45.0 62.5
350.0 412.0 381.0
73.0 175.0 124.0
233.0 262.0 247.5
121.9
69.1
a 5 cycles, with 1:1 hexane-acetone
TABLE 16. RECOVERIES OF PESTICIDE SPIKES (1.0 yG PER COMPOUND)
FROM ESTER- AND ETHER-FORM PUF PLUGS BY SOXHLET EXTRACTION3
Pesticide recoveries, %
Ester-formEther-form PUF
Compound PUF Repl. 1 Repl. 2 Avg
a-BHC 123.0 176.6 160.6 168.6
Aldrin 96.3 91.5 77.8 84.7
p,p'-DDE 106.1 92.0 76.0 84.0
o,p'-DDT 95.6 93.3 78.6 86.0
p,p'-DDD 96.7 84.7 75.0 79.9
TABLE 16 (continued)
47
-------
TABLE 16 (continued)
Pesticide recoveries, %
Compound
p.p'-DDT
Lindane
3-BHC
Kept. epox.
Dieldrin
Endrin
Me parathion
Ronne 1
Parathion
Ethion
Carbophenothion
Diazinon
Malathion
Propoxur
Carbaryl
Carbofuran
Aminocarb
Methiocarb
Mexacarbate
Average
Std. deviation
Ester-form
PUFb
93.9
82.0
85.0
89.4
99.2
94.6
85.3
90.3
76.6
99.8
99.1
91.1
95.5
91.9
97.8
81.9
85.3
102.5
93.1
93.8
9.4
Ether-form
Repl. 1
94.3
67.8
99.8
76.4
101.1
83.5
77.8
78.0
80.7
97.1
86.2
80.3
90.9
97.5
101.0
97.0
88.0
100.0
100.0
Repl. 2
79.8
69.8
93.9
71.6
89.6
86.4
72.9
71.8
74.9
88.9
80.1
80.4
89.5
81.6
88.3
94.0
136.0
85.0
128.0
PUF
Avg
87.1
68.8
96.9
74.0
95.4
85.0
75.4
74.9
77.8
93.0
83.2
80.4
90.2
89.6
94.7
95.5
112.0
92.5
114.0
91.0
19.8
a 5 cycles, with 1:1 hexane-acetone
k Averages, from Table 10
48
-------
Similarly, of the 24 compounds in Table 16, 20 gave recoveries closer to 100%
with ester- than with ether-form material, and 14 of the 24 were closer in
Table 15. If the data for aminocarb and mexacarbate, which were shown in the
previous section to be interfered with by underlying background peaks, are
deleted, the average deviations from 100% recovery at the 1.0-yg level are
8.6 +_ 1.5 and 17.3 _+ 3.0% for the ester and ether forms, respectively. We
therefore judge ester-form PUF to be the superior material for an air
monitoring program.
EVALUATION OF GLC COLUMNS AND PROCEDURES
One of the most important factors in the quantitation of pesticides by
gas-liquid chromatography is the performance of the columns used. The coating
of the liquid on the support material and the packing of the coated solid into
the columns are critical factors and are subject to considerable variability.
The quality of a column is manifest in the chromatograms obtained with it as
to its ability to separate the compounds to be analyzed, the sharpness of the
peaks, and the relation of peak height to quantity of compound. On a poorly
prepared column, closely eluting peaks will be poorly separated and will
exhibit tailing. On a properly prepared column, the calibration curve, the
graph of peak height vs. quantity of injected material, will be a straight
line that ends at the origin. When reactive compounds such as the
organophosphorus and carbamate pesticides are chromatographed on a poorly
prepared column, the calibration graphs curve upward and may not pass through
the origin. The usual cause for this phenomenon is retention and degradation
of the compounds on uncoated support material.
We examined the quality of the columns that had been purchased or prepared
for use in this study, particularly seeking comparable or even improved per-
formance in comparison to that reported by Sherma and Shafik in the original
publication of the general analytical method (4). These authors used a 5%
OV-210 column for the organochlorine insecticides in liquid-chromatography
Fractions I and II (except that a 5% SE.-30 column was used for dieldrin), a 5%
OV-210 Carbowax-treated column for the organophosphates in Fractions II and
III, and a 5% SE-30 column for the carbamates in Fraction III.
A 5% OV-210 column prepared in this laboratory was tested with the six
organochlorine pesticides found in Fraction I plus lindane, which is also
sometimes found in Fraction I. The conditions were 180<>C column temperature
and 60 ml/min carrier gas flow rate, as specified by Sherma and Shafik. In
the chromatogram, the seven peaks were completely resolved except for slight
overlap between p,p'-DDD and p,p'-DDT. The chromatogram was very similar to
that of Figure 2 in the Sherma-Shafik paper, and will not be repeated here.
For comparison, a mixed column, 1.5% OV-17/1.95% OV-210, was also tested with
the same mixture of pesticides, but at 200OC column temperature and
36 ml/min carrier gas flow rate. The chromatogram is presented in Figure 11.
The retention times of the compounds relative to aldrin are: a-BHC, 0.48;
lindane, 0.63; aldrin, 1.00; p,p'-DDE, 2.29; o,p'-DDT, 3.24; p.p'-DDD, 3.52;
and p,p'-DDT, 4.28. As may be seen, the o.p'-DDT and p.p'-DDD peaks do
overlap somewhat, but the peaks are adequately separated for quantitation of
all seven compounds, and the overlap is no greater than the p,p'-DDD and
49
-------
1. a-BHC
2. Lindane
3. Aldrin
U. p,p'-DDE
5. o,p'-DDT
6. p,p'-DDD
7. p,p'-DDT
7
0
Figure 11.
8
Mi nutes
12
16
ECGC chromatogram of 0.2 ng each of Fraction I
organochlorine insecticides, obtained with a
1.5* OV-17/1.95* OV-210 column.
50
-------
p.p'-DDT overlap on the 5% OV-210 column reported by Sherma and Shafik. The
most significant difference in the chromatograms for the two columns is the
shift of the p,p'-DDD peak away from the p,p'-DDT peak and toward the o,p'-DDT
peak. Figure 11 indicates that a mixed 1.5% OV-17/1.95% OV-210 column can be
a suitable alternative to a 5% OV-210 column for the analysis of
liquid-chromatography Fraction I.
A major advantage of the mixed OV-17/OV-210 column over a 5% OV-210 is
that the former can separate all 10 compounds found in Fraction II, whereas
the latter does not adequately separate dieldrin and methyl parathion, as
illustrated in Table III of Sherma and Shafik. Figure 12 is an
electron-capture chromatogram for all five organochlorine and five
organophosphorus compounds that occur in Fraction II. The retention times of
the compounds relative to that of aldrin are: lindane, 0.63; 3-BHC, 0.72;
ronnel, 0.99; methyl parathion, 1.29; heptachlor epoxide, 1.53; parathion,
1.71; dieldrin, 2.37; endrin, 2.91; ethion, 4.35; and carbophenothion, 4.68.
This chromatogram suggests that, at relatively high concentrations, it may be
possible to quantitate the organophosphorus compounds by electron-capture
detection at the same time that the organochlorine compounds are analyzed.
The 5% OV-210 column treated with Carbowax 20M, recommended by Sherma and
Shafikj was tested for ability to separate the five organophosphorus
pesticides in Fraction II and the two in Fraction III. All pesticides within
a fraction were adequately separated and the peak shapes were reasonably
symmetrical. However, if all seven pesticides are applied to this column,
malathion and methyl parathion overlap, as shown in Figure 13. To obtain this
chromatogram, all seven pesticides at 5 ng per compound were injected
simultaneously, column temperature was 180°C, and flame photometric
detection was used. In a comparative test of a 3% OV-1 column with the seven
organophosphorus pesticides at 5 ng per compound, it was found that the peaks
were all separated. A typical chromatogram with this column, showing
differences in order of elution as well as improved resolution, is illustrated
in Figure 14. Calibration graphs were linear and the line passed through the
origin. Figure 15 is a calibration graph for diazinon and is typical of the
graphs for the organophosphorus compounds, although the others all had lower
slopes. The 3% OV-1 column was used almost exclusively for the quantitation
of organophosphorus compounds in the other phases of our experimental program
because tests could be run with all seven compounds without the necessity for
prior separation by liquid chromatography.
The SE-30 column prepared in this laboratory did not perform as well as
that used by Sherma and Shafik for analysis of the N-methylcarbamates
(4, Fig. 7). As an illustration of our results, Figure 16 is a chromatogram
of the seven test carbamates, at 600 pg per compound, derivatized with PFPA
and using the Sherma-Shafik GLC conditions, 195°C column temperature and
70 ml/min carrier gas flow rate. As may be seen, carbofuran and aminocarb
were not well separated. Separation was improved slightly by decreasing the
column temperature to 165°C, as illustrated in Figure 17. By temperature
programming from 165°C to 195°C at 10°C/min. after a 5-minute hold at
165QC, the peak heights for carbaryl and methiocarb were improved, as
illustrated in Figure 18. However, the separation of carbofuran and aminocarb
was no better under these conditions.
51
-------
1. Lindane
2. g-BHC
3. Ronnel
k. Methyl parathion
5. Heptachlor epoxide
6. Parathion
7. Dieldrin
8. Endrin
9. Ethion
10. Carbophenothion
1
0
1
4
i
8
i t
12 16
Minutes
i
20
Figure 12. ECGC chromatogram of O.U ng each of Fraction II
insecticides, obtained with a 1.5$ OV-17/1.95$
OV-210 column.
52
-------
1. Diazinon
2. Ronnel
3. Malathion plus
Methyl parathion
k. Parathion
5. Carbophenothion
6. Ethion
Figure 13. Flame-photometric chromatogram of 5 ng each of the test
organophosphorus insecticides, obtained with a 5% OV-210/
Carbowax column
53
-------
1. Diazinon
2. Methyl parathion
3. Ronnel
k. Malathion
5. Parathion
6. Ethion
7. Carbophenothion
Figure lU. Flame-photometric chromatogram of 5 ng each of the test
organophosphorus insecticides, obtained with a 3% OV-1
coliomn
54
-------
20
16
£
u
12
O)
-------
1. Propoxur
2. 2,3,5-Landrin
3. Carbofuran
U. Aminocarb
5. Mexacarbate
6. Carbaryl
T. Methiocarb
Figure l6. Electron-capture chromatogram of N-methylcarbamate
insecticides, obtained with a 5$ SE-30 column at
195°C
56
-------
1. Propoxur
2. 2,3,5-Landrin
3. Carbofuran
k. Aminocarb
5. Mexacarbate
6. Carbaryl
T. Methiocarb
Figure IT. Electron-capture chromatogram of N-methylcarbamate
insecticides, obtained with a 5% SE-30 column at
165°C
57
-------
1. Propoxur
2. 2,3,5-Landrin
3. Carbofuran
H.- Aminocarb
5. Mexacarbate
6. Carbaryl
7. Methiocarb
Figure 18. Electron-capture chromatogram of N-methylcarbamate
insecticides, obtained by temperature programming
as described in text
58
-------
In surveying the columns available in this laboratory, we found that a 3%
DC-200 column gave excellent response with the pentafluoropropionate
derivatives of the carbamates. This is illustrated in Figure 19, which
represents an injection of 400 pg of each compound. The peak height for
propoxur was about double that found for PFP-propoxur at 600 pg with SE-30
column (Figure 16). However, the peaks for 2,3,5-Landrin and carbofuran were
not separated. In a later experiment, 20 pg of each of the compounds in
liquid-chromatography Fraction III except 2,3,5-Landrin (that is, diazinon,
malathion and the remaining six carbamates) were treated with PFPA and applied
to the 3% DC-200 column. The chromatogram is reproduced in Figure 20. Both
of the organophosphorus compounds elute after the PFP-carbamates and the
latter are well separated, with excellent sensitivity with respect to noise
level. Calibration graphs for the six carbamates are presented in Figure 21.
All six graphs are linear and pass through the origin, indicating that
compound degradation on the DC-200 column is not a problem.
In the Sherma-Shafik procedure, diazinon and carbaryl elute together from
the SE-30 column, and at some levels of diazinon this compound must be removed
by an acid wash before carbaryl can be quantitated. By contrast, diazinon
does not interfere on the DC-200 column. Since 2,3,5-Landrin is a minor
constituent of Landrin and, moreover, production of the latter has been
discontinued by the manufacturer, 2,3,5-Landrin was omitted in the other
phases of our studies so that the superior DC-200 column could be used for the
quantitation of the carbamates.
To summarize, we have found GLC columns that exhibit advantages in
performance over those recommended by Sherma and Shafik for quantitation of
each of the classes of test pesticides. Our selections include a 1.5%
OV-17/1.95% OV-210 mixed column for organochlorine insecticide analyses, a 3%
OV-1 column for the organophosphorus compounds, and a 3% DC-200 column for the
N-methylcarbamates. The use of alternate columns is also beneficial in that
retention times on more than one column can provide evidence with respect to
confirmation of identity of individual pesticides.
EFFECT OF FOAM STRUCTURE ON AIR FLOW RATES
In the vapor trapping experiments described earlier, the PUF plugs
appeared to compress somewhat during air sampling and the flow rate seemed to
diminish with time. Six experiments were performed to confirm this effect, to
determine the relationship of flow rate* to sampling time, and to determine if
the change in flow rate was directly related to the porosity of the foam.
High-flow (low pressure drop), 45-mm PUF plugs were tested in three of the
experiments, medium-flow plugs in the other three.
For each experiment, a single plug was placed in a glass sampling holder
and air was drawn through the plug by vacuum pump. The pressure across the
plug was measured with a diaphragm vacuum gauge, and the flow rate was
measured with a rotameter. Readings were taken periodically over a 24-hour
period.
59
-------
1. Propoxur
2. 2,3,5-Landrin and Carbofuran
3. Aminocarb
U. Mexacarbate
5. Carbaryl
6. Methiocarb
Figure 19- Electron-capture chromatogram of UOO pg each of
N-methylcarbamates, obtained on a 3% DC-200 column
60
-------
1. Propoxur
2. Carbofuran
3. Aminocarb
k. Mexacarbate
5. Carbaryl
6. Methiocarb
7. Diazinon
8. Malathion
Figure 20. Electron-capture chromatogram of 20 pg each of
Fraction III pesticides, obtained on a 3% DC-200
column
61
-------
12
8
1. Propoxur
2. Carbofuran
3. Methiocarb
h. Mexacarbat e
5- Aminocarb
6. Carbaryl
0.5
1.0
1-5
2.0
2.5
Figure 21. Calibration graphs of N-methylcarbamate insecticides, obtained on
a 3% DC-200 column
62
-------
With all plugs, flow rates decreased with time and the pressure across the
plugs increased slightly with time. The flow rates decreased relatively
rapidly at the start of the experiments and asymptotically approached the
final flow rates. The decrease in flow rate ranged from 3.2 to 9.0% of the
initial value, and no relationship was apparent between porosity of the plug
and degree of decrease in the flow rate. The change in flow rate with time
for a typical experiment is presented in Table 17. The plug in this
experiment was rated as high-flow, and the total decrease in flow rate was
8.6%,of the initial value.
Quantitation of the pesticide residue levels in air depends on the
accuracy of the flow rate measurement as well as on the analytical
procedures. These experiments indicate that, for maximum accuracy in
quantitation of pesticides in air with PUF foam, the flow rate should be
monitored continuously during the sampling.
TABLE 17. CHANGE IN AIR FLOW RATE WITH TIME OF AIR
PASSAGE THROUGH A PUF PLUG
Hours of
air flow
0
0.1
0.5
1.5
2.5
3.5
4.5
6.5
23.5
24.5
Air flow rate,
m3/hr
5.22
5.18
5.04
4.99
4.92
4.88
4.88
4.84
4.77
4.77
ANALYSIS OF N-METHYLCARBAMATE INSECTICIDES
Evaluation of Carbamate Derivatization Procedures
Several problems exist in the GLC determinations of N-methylcarbamates.
These compounds generally have low vapor pressures, so that GLC retention
63
-------
times are long; they are thermally unstable and decompose in the GLC column
under common gas chromatographic conditions; and their sensitivities to
detection by electron-capture and other detectors is not high. The
Sherma-Shafik procedure (4) attempts to solve all these problems by
derivatization of the N-methylcarbamates with pentafluoropropionic anhydride
(PFPA) according to the method of Shafik et al. (9). In this procedure, the
nitrogen-bound proton of the carbamate is replaced by a pentafluoropropionyl
(PFP) moiety. The resulting PFP-carbamate compounds are more volatile and
more stable than the parent carbamates and also have five fluorine atoms to
enhance electron-capture detection. Several other derivatization procedures
have also been used to facilitate quantitation of carbamates. For example,
the phenolic moieties liberated from the carbamates have been derivatized by
l-fluoro-2,4-dinitrobenzene (FDNB) (10). This method has been used on soil
residues in this laboratory with excellent results (11). Parent N-methyl-
carbamates can also be derivatized with trifluoroacetic anhydride (TFAA) and
heptafluorobutyric anhydride (HFBA) in reactions similar to that for PFPA. We
performed a number of experiments to determine which method was best for
analysis of the seven test N-methylcarbamate insecticides, and to optimize the
analytical conditions.
Effect of PFPA Concentrations on GLC Peak Heights—
The procedure of Shafik et al. (9) specifies that the carbamates in 2 ml
isooctane should be reacted with 0.025 ml PFPA, with one drop of pyridine as
catalyst. After one hour at room temperature, the reaction is stopped by
addition of 3 ml phosphate buffer. Three ml isooctane and 0.05 ml
acetonitrile are added and the aqueous layer is aspirated with a pipet. The
organic layer is washed three times with 2 ml water, with the wash removed
each time by aspiration, and is then dried by addition of 0.5 g sodium
sulfate. An experiment was conducted using this procedure, partly for
familiarization but also to examine the effect of increasing the amount of
PFPA reagent. Pyridine was redistilled (12, p. 175), and phosphate buffer was
prepared as specified by Sherma and Shafik (4). A standard solution of the
seven carbamates and the two organophosphorus insecticides that elute in
liquid-chromatography Fraction III was prepared in hexane at 1 Ug/ml per
compound. One drop of keeper solution and 1.00 ml of this standard were
placed into each of seven 15-ml Kuderna-Danish receiver tubes. The contents
of each tube were evaporated at 50oc in a water bath by a stream of nitrogen
gas. The Shafik et al. procedure was -then followed, except that 0.025, 0.05,
0-10, 0.15, 0.20, 0.25 or 0.30 ml PFPA was added to a tube. The derivatized
carbamates were analyzed by electron-capture GLC on a 5% SE-30 column (the
superiority of the 3% DC-200 column had not yet been discovered). Figure 22
shows the chromatogram, representative of the seven chromatograms, for the
standard treated with 0.10 ml PFPA. The relatively poor resolution of peaks,
previously shown for the 5% SE-30 column (Figure 16), was apparent. However,
the organophosphorus components of the standard solution did not interfere
with the carbamate peaks.
The height of each peak in each of the seven chromatograms was measured
and is recorded in Table 18. Changes in the amount of PFPA used in the
reaction did not affect the peak heights of the individual carbamates
equally. Peak heights increased for all the compounds as the quantity of PFPA
64
-------
1. Propoxur
2. 2,3,5-Landrin
3. Carbofuran
h. Aminocarb
5. Mexacarbate
.6. Carbaryl
7. Methiocarb
0
8 12
M i n.
16
20
Figure 22. Electron-capture chromatoeram of kOO pg each, of the
N-methylcarbamates, reacted with 0.1 ml PFPA
65
-------
TABLE 18. THE EFFECT OF CONCENTRATION OF PFPA REAGENT
ON GLC PEAK HEIGHTS OF CARBAMATE INSECTICIDES
Peak heights, mm
PFPA volume added, ml
Compound 0.025 0.05 0.10 0.15 0.20 0.25 0.30
Propoxur 46 52 80 91 88 95 92
2,3,5-Landrin 46 50 74 77 78 80 74
Carbofuran 30 33 46 49 52 54 50
Aminocarb 48 36 54 36 36 31
Mexacarbate 33 38 43 35 27 27 26
Carbaryl 3 3 8 8 18 20 20
Methiocarb 6 9 15 19 22 23 19
was increased up to about 0.10 ml, but the increase was much more modest for
aminocarb and mexacarbate than for the other compounds. Moreover, the
aminocarb and mexacarbate peaks decreased in size as the amount of PFPA
exceeded 0.1 ml, whereas the other peaks leveled off or continued to
increase. At the highest levels of PFPA, the carbofuran peak tended to
obscure the aminocarb peak. The data indicated that an increase of the PFPA
from 0.025 ml up to 0.10 ml in the Shafik et al. procedure would be beneficial.
Evaluation of a TFAA-derivative Procedure—
Seiber (13) demonstrated that temperature and solvent polarity strongly
affect rates of N-methylcarbamate derivatization by peffluoroacyl anhydrides.
When the reaction is performed in polar solvents, shorter reaction times
and/or lower temperatures may be used to effect complete derivatization.
Greenhalgh et al. (14) reported that methiocarb could be trifluoroacetylated
in 15 minutes at 100°c in ethyl acetate. We therefore performed an
experiment to compare results from the Greenhalgh et al. procedure with those
from the Shafik et al. meth6d.
A 1-ml aliquot of each 1-ppm carbamate standard solution was placed into a
screw-cap vial, one drop of keeper solution was added, and the solvent was
evaporated at 50°C in a stream of nitrogen. Ethyl acetate (2 ml) and
0.20 ml TFAA were added and the vial was capped. After two hours, the vial
was opened, excess reagent and solvent were evaporated in a stream of
66
-------
nitrogen, and 1 ml ethyl acetate was added. This solution was analyzed by GLC
as in the Sherma-Shafik procedure.
The injection peak was very large and tailed badly. Moreover, the
derivative peaks were relatively small, had short retention times, and were
not well separated. TFAA, and perhaps ethyl-TFA (if formed from ethyl acetate
by transesterification), may not be totally removed in the evaporation step;
if not, they would produce a large injection peak such as that observed.
Greenhalgh et al. used flame-photometric detection in the sulfur mode for
analysis of methiocarb. In that system, neither TFAA nor ethyl-TFA would
interfere. The Greenhalgh et al. procedure did not give acceptable results
with electron-capture detection and was consequently abandoned.
Comparison of PFPA With HFBA for N-Methylcarbamate Derivatization—
Seiber (13) reported that TFA, PFP and HFB derivatives of several
N-methylcarbamates had similar stabilities and rates of formation. However,
the electron-capture response increased two-fold for carbaryl and five-fold
for carbofuran from the TFA to HFB derivatives. We conducted an experiment to
determine if the HFB derivatives would offer higher electron-capture response
and/or better separation of GLC peaks than the PFP derivatives.
One ml of the Fraction III standard solution and one drop of keeper
solution were placed in a 4-dram screw-cap vial and evaporated in a stream of
nitrogen at 50°C. Benzene (4 ml) was added and the vial was sonicated for 2
minutes to dissolve the pesticides. After addition of 0.10 ml HFBA, the vial
was sealed with a teflon-lined cap and heated at 100°C for 2 hr. The
solution was diluted with 4 ml hexane and washed three times with 5-ml
portions of water. It was then dried with sodium sulfate and concentrated to
5.0 ml with a stream of nitrogen. This solution was analyzed by GLC on a 3%
SE-30 column, resulting in the chromatogram shown in Figure 23. In the
figure, each peak represents approximately 200 pg of the designated
carbamate. Although the retention times here were longer and the residue
levels lower by half, a comparison of Figure 23 with Figure 22 shows that the'
response with this HFBA procedure was no better than that with the Shafik PFPA
procedure. There was also no advantage in terms of effort or analysis time.
The same Fraction III standard was also derivatized with 0.10 ml HFBA by
the Shafik et'al. procedure detailed above. The derivatized solution was
analyzed on the 3% DC-200 column at 165oc column temperature. At the 200-pg
residue level, six sharp and well-separated peaks were obtained for the seven
carbamates. Derivatization of each carbamate individually with HFBA showed
that 2,3,5-Landrin and carbofuran had such close retention times that they
would appear as one peak when both compounds were present. The six-peak
chromatogram of the HFB-carbamates was therefore essentially identical to that
obtained with the PFP-carbamates on the same column (Figure 19).
A standard solution containing only the six test carbamates, without
2,3,5-Landrin, was prepared at 1 ug/ml per compound. One ml of this solution
was derivatized with 0.10 ml HFBA by the Shafik et al. procedure and analyzed
on a 3% DC-200 column. The chromatogram is presented in Figure 24. A
comparison of this figure with the corresponding chromatogram for the
67
-------
1. Propoxur
2. 2,3,5-Landrin
3. Carbofuran
k. Amiriocarb
5. Mexacarbate
6. Carbaryl
7. Methiocarb
Figure 23. Electron-capture chromatogram of 200 pg each of the
W-methylcarbamates, reacted with 0.1 ml HFBA
68
-------
1. Propoxur
2. Carbofuran
3. Aminocarb
k. Mexacarb ate
5. Carbaryl
6. Methiocarb
Figiire 2k. Electron-capture chromatogram of six HFB-carbamate
derivatives, obtained on a 3% DC-200 column
69
-------
PFP-carbamates (not shown) demonstrates that there is little difference in
retention times or peak heights between HFB-carbamates and PFP-carbamates.
Our experiments have shown that HFBA can be regarded as a substitute for, but
apparently not an improvement on, PFPA in the Shafik et al. procedure.
Evaluation of l-Fluoro-2,4-dinitrobenzene for Derivatization of Carbamates—
Holden (10) reported a procedure for the GLC determination of several of
the carbamates used in this study. Reaction of l-fluoro-2,4-dinitrobenzene
(FDNB) with carbamates yielded ether derivatives of the phenolic moieties
liberated from the carbamates. These derivatives were well-separated and
readily quantitated on a DC-200 GLC column. We conducted an experiment to
determine if the Holden procedure could be applied to extracts from
polyurethane foam, and if it offered any advantage over the PFPA
derivatization.
A blank was prepared by Soxhlet-extracting a PUF plug with 280 ml 1:1
hexane-acetone for five cycles. The solution was evaporated and 5 ml 5%
aqueous borax solution and 0.5 ml FDNB reagent (1.5 ml FDNB in 25 ml acetone)
were added. The contents were agitated in an ultrasonic bath, heated at
70°C for one hour in a water bath, and then extracted with 5 ml hexane. The
extract was analyzed by GLC on a 3% DC-200 column, resulting in the
chromatogram reproduced in Figure 25. If a carbamate were present in the
extract at the 1-ug level, this chromatogram would represent an injection of
40 pg of the carbamate. This high background level was shown, by
derivatization of the carbamates by the same procedure and addition to the
blank, to be prohibitive for quantitation of the carbamates. Consequently,
the method was abandoned.
Effect of Diaminotoluenes on Quantitation of N-Methy1carbamates
When PUF degrades, two of the products are 2,4- and 2,6-diaminotoluene
(15). These compounds would be detected by an electron-capture detector if
they were present in the final extracts of the Sherma-Shafik procedure and
thus might interfere with GLC analysis of organochlorine or carbamate
pesticides. In the case of the carbamates, any diaminotoluenes occurring in
liquid-chromatogrpahy Fraction III would have to be derivatized by PFPA to
interfere with pesticide quantitation. Each of the diaminotoluenes has four
reactive amino protons. If all four possible substitutions were accomplished
by PFPA, the diaminotoluenes would be detectable at very low concentrations by
electron-capture detection. We conducted tests to determine the likelihood
and possible extent of the interference.
For the following tests, 2,4- and 2,6-diaminotoluene were purchased from a
commercial source (Aldrich Chemical Co.) and recrystallized three times from
absolute ethanol to remove impurities. Individual 1000-ppm standard solutions
of both compounds were prepared by weighing 50 mg of the recrystallized
material into a 50-ml volumetric flask and adding acetone. These standards
were serially diluted to the 1 ug/ml level in hexane. One ml of each of the
diluted standards was evaporated, with five drops of paraffin oil keeper
solution, and derivatized with PFPA. GLC analysis of the derivatives on a 3%
DC-200 column showed that the two peaks were slightly separated and that the
70
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\
Figure 25. Electron-capture chromatogram of a PUF-plug
blank extract derivatized with FDNB
71
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retention times were very close to that of PFP-propoxur. To check this, a
solution containing 1 yg of propoxur was added to 1-ml aliquots of the 1-ppm
diaminotoluene standards. These solutions were evaporated, derivatized and
analyzed on a 3% DC-200 column. The chromatograms are presented in Figure
26. The propoxur peak was slightly removed from that of 2,6-diaminotoluene,
but was not separated from the 2,4-diaminotoluene peak. Electron-capture
response of the PFP-diaminotoluenes was very high. Each peak in Figure 26
represents an injection of 40 pg of material; the peak heights of the
diaminotoluenes were almost four times that of propoxur. The diaminotoluenes
have been reported to occur in concentrations as high as 400 ppm in PUF, and
this test shows that they could interfere with quantitation of propoxur on 3%
DC-200 if they are present in Fraction III.
A further test was conducted to determine if the PFP-diaminotoluenes would
interfere with quantitation of carbamates on an SE-30 column. One ml of a
standard solution containing 1 yg of each of the pesticides that occur in
Fraction III was added to 1 ml each of the 1-ppm diaminotoluene standards.
This was evaporated with 5 drops of keeper solution, derivatized with PFPA,
and quantitated by GLC on a 5% SE-30 column. The chromatogram is presented in
Figure 27. The two PFP-diaminotoluenes appear as one peak that is adequately
separated from PFP-propoxur.
After these tests, it remained to be determined whether the
diaminotoluenes would appear in any of the three liquid-chromatography eluate
fractions. One-mi aliquots of the 1-ppm diaminotoluene solutions, evaporated
and resuspended in 0.5 ml hexane, were chromatographed on a silica-gel column
as required by the Sherma-Shafik procedure. Each fraction was analyzed by
ECGC, Fraction III being derivatized with PFPA before analysis. There were no
unusual peaks in the chromatograms, so the diaminotoluenes apparently do not
elute from the liquid-chromatography column.
72
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1. 2,6-Diaminotoluene
2. 2,^-Diaminotoluene
3. Propoxur
Figure 26. Electron-capture chromatograms of diaminotoluenes and
propoxur, obtained on a 3% DC-200 column
73
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2.
3.
U.
5.
6.
7.
8.
2,U-Diaminotoluene
plus 2,6-Diaminotoluene
Propoxur
2,3,5-Landrin
Carbofuran
Aminocarb
Mexacarbate
Carbaryl
Methiocarb
Figure 27- Electron-capture chromatogram of Fraction III pesticides plus
diaminotoluenes, obtained on a 5$ SE-30 column
74
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REFERENCES
1. Fowler, D. L., and J. N. Mahan. The Pesticide Review, 1977. Agricultural
Stabilization and Conservation Service, U. S. Department of Agriculture,
Washington, D. C., 1978. 44 pp.
2. Turner, B. C., and D. E. Glotfelty. Field Air Sampling of Pesticide
Vapors With Polyurethane Foam. Anal. Chem., 49 (1):7-10, 1977.
3. Lewis, R. G., A. R. Brown and M. D. Jackson. Evaluation of Polyurethane
Foam for Sampling of Pesticides, Polychlorinated Biphenyls and
Polychlorinated Naphthalenes in Ambient Air. Anal. Chem. 49
(12):1668-1672.
4. ,Sherma, J., and T. M. Shafik. A Multiclass, Multiresidue Analytical
Method for Determining Pesticide Residues in Air. Arch. Environ. Contain.
Toxicol. 3(1):55-71, 1975.
5. Ives, N. F., and L. Giuffrida. Gas-Liquid Chromatographic Column
Preparation for Adsorptive Compounds. J. Assoc. Offie. Anal. Chemists
53(5):973-977, 1970.
6. Rhoades, J. W., and D. E. Johnson. Evaluation of Collection Media for Low
Levels of Airborne Pesticides. National Technical Information Service
PB-275,668, 140 p, 1977.
7. Mercer, T. T. Aerosol Technology in Hazard Evaluation. Academic Press,
New York, 1973.
8. Spencer, W. F., J. D. Adams, R. E. Hess, T. D. Shoup and R. C. Spear.
Conversion of parathion to paraoxon on soil dusts and clay minerals as
affected by ozone and UV light. Submitted to J. Agric. Food Chem., 1979.
9- Shafik, T. M., D. Bradway and P. F. Mongan. Electron Capture Gas
Chromatography of Picogram Levels of Aromatic N-methyl Carbamate
Insecticides. Presented at 163rd ACS National Meeting, Boston,
Massachusetts, April, 1972.
10. Holden, E. R. Gas Chromatographic Determination of Residues of
Methylcarbamate Insecticides in Crops as Their 2,4-Dinitrophenyl Ether
Derivatives. J. Assoc. Offic. Anal. Chemists 56(3):713-717, 1973.
11. Caro, J. H., D. E. Glotfelty, H. P. Freeman and A. W. Taylor. Acid
Ammonium Acetate Extraction and Electron Capture Gas Chromatographic
Determination of Carbofuran in Soils. J. Assoc. Offic. Anal. Chemists
56(6):1319-1323, 1973.
75
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12. Vogel, A. I. A Text-book of Practical Organic Chemistry. John Wiley and
Sons, New York, 1962.
13. Seiber, J. N. N-Perfluoroacyl Derivatives for Methylcarbamate Analysis
by Gas Chromatography. J. Agric. Food Chem. 20(2):443-446, 1972.
14. Greenhalgh, R., W. D. Marshall and R. R. King. Trifluoroacetylation of
Mesurol (4-Methylthio-3,5-xylyl-N-methylcarbamate), its Sulfoxide,
Sulfone, and Phenol Analogs for Analysis by Gas Chromatography. J.
Agric. Food Chem. 24(2):266-270, 1976.
15. Guthrie, J. L., and R. W. McKinney. Determination of 2,4- and
2,6-Diaminotoluene in Flexible Urethane Foams. Anal. Chem.
49(12):1676-1680, 1977.
76
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/4-80-008
2.
3. RECIPIENT'S ACCESSIONING.
.TITLE AND SUBTITLE
Polyurethane Foam as Trapping Agent for Airborne
Pesticides: Analytical Method Development
5. REPORT DATE
January 1980 issuing date
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
James D. Adams and Joseph H. Caro
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
Soil Nitrogen and Environmental Chemistry Laboratory
Beltsville Agricultural Research Center
U.S. Department of Agriculture
Beltsville, Maryland 20705
10. PROGRAM ELEMENT NO.
A1VL1A
11. CONTRACT/GRANT NO.
Interagency Agreement
78-D-X0449
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory—Athens GA
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30605
13. TYPE OF REPORT AND PERIOD COVERED
Final, 9/76-1/79
14. SPONSORING AGENCY CODE
EPA/600/01
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A method for determining levels of organochlorine, or'ganophospjiorus, and N-methy
carbamate insecticides in air was developed using 4.4 cm-dimeter plugs of polyure-
thane foam as traps and a modified Sherma-Shafik multiresidue procedure for analysis
of foam extracts. With this method, the minimum detectable air concentrations for
vapors of 17 of the 18 organochlorine and organophosphorus pesticides tested was 0.1
nanogram per cubic meter or less. Six carbamate pesticides did not volatilize in
sufficient amounts to allow analysis.
The experimental program consisted of measurements of efficiency of foams for
trapping vapors and aerosols, tests of foam compression during air sampling, evalua-
tions of extraction solvents, evaluations of techniques for extracting pesticide resi-
dues from the foams, comparisons of the performance of the ester and ether forms of
polyurethane foam, evaluations of the steps in the Sherma-Shafik analytical procedure,
evaluations of GLC columns and instrumental parameters, and tests of derivatization
procedures for electron-capture gas chromatography of the N-methylcarbamates,
A 10-cm depth of foam was found to be an efficient trap for vaporized pesticides
Five-cycle Soxhlet extraction with 1:1 hexane-acetone was the best procedure for re-
moval of pesticides from foam plugs.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Air Pollution
Chemical analysis
Gas chromatography
Monitors
Pesticides
07C
14B
68A
99A
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report}
21. NO. OF PAGES
83
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE 77
4 U.S GOVERNMENT PRINTING OFFICE 1960-657-146/5568
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