in the chromatography system, so it is important that
the injector be free of surface contaminants. The
analysis usually requires high temperatures, and
often causes bleed problems. Analysis time typically
exceeds 40minutes. Tributyl phosphate and triph-
enyl phosphate are recommended surrogates for
GC/FPD (EPAMethod 8141B).
Tomeet the challenges of OPPs analysis, Restek
chemists use anRtx
®
-CLPesticides column. Rtx
®
-
CLPesticides columns have a 330ºCmaximum oper-
ating temperature, superior inertness, and low bleed.
Figure 1 shows excellent resolution of the European
OPPMix, obtained in less than 25minutes. The 30m,
0.32mm ID, 0.50µm column is well suited to the
split/splitless injection and FPD detection: all com-
pounds, including the surrogates, are resolved. The
high temperature stability of Rtx
®
-CLPesticide
columns enables us to program the column to
330°C following each analysis, to bake out high
molecular weight contaminants common inOPP-
containing extracts. The ability to clean anRtx
®
-
CLPesticides column at high temperatures enables us
tomakemore injections before replacing the col-
umn, compared to commonly used cyano phase
columns.
Fast, efficient separations are an important goal in
any analysis. In analyses of organophosphate pesti-
cides, anRtx
®
-CLPesticides column, and our new
EuropeanOPPMix, are important parts of attaining
this goal.
• 11 •
2003
Volume 2
800-356-1688
Resolve ComplexMixtures of
Organophosphorus Pesticides,
Using anRtx
®
-CLPesticidesGCColumn and a
NewRestekReferenceMix
✔
Fast, efficient analyses, using anRtx
®
-CLPesticides column and flame
photometric detection.
✔
NewOPP referencemix corresponds to strict European criteria.
✔
Concentrations ofmix components vary according to FPD response.
By KatiaMay, Ph.D., R&DChemist, and Lydia Nolan, Environmental Innovations Chemist
Organophosphorus pesticides (OPP) arewidely used
to protect fruits and vegetables from insects.
Unfortunately, these toxicmaterials can accumulate
in human fat tissue, potentially leading to death by
respiratory depression.
1
In Europe, OPPs are consid-
ered a very serious risk to human health, and analy-
sis of food products for these pesticides is important
in quality control. OPPs also are strictly regulated in
the United States. Policy in regard to pesticide
residues inmilk, eggs, meat, or poultry is stated in
the Code of Federal Regulations.
2
Multi-residuemeth-
ods in AOACOfficial Methods of Analyses
3
and the
FDA Pesticide Analytical Manual
4
are used to deter-
mineOPPs and organochlorine pesticides. Analytical
procedures for OPPs usually involve GCwith a selec-
tive detector, such as a flame photometric detector
(FPD) or a nitrogen-phosphorous detector (NPD), to
detect low ppb levels of target compounds. Use of an
FPD in the phosphorousmodeminimizes interfer-
ence bymaterials that do not contain phosphorus.
Recently, our European customers asked us to dev-
elop a stable referencemix of target OPPs, with con-
centrations appropriate for analysis by GC/FPD. The
components in our new EuropeanOPPMix are espe-
cially important in quality control of milk, infant for-
mulas, and baby foods. We include these in varied
concentrations, according to the responses they elicit
from an FPD. One of theOPPs, demeton, is amix-
ture of O- and S- isomers. We include demeton-S in
themix, and followUS EPAMethod 8141B for quan-
tifying this isomer. OPP compounds are photosensi-
tive and are easily degraded during handling, stor-
age, or analysis. When preparing and storing the new
mix, we follow stringent measures to ensure pro-
longed stability.
Analyses of OPPs are challenging and time-consum-
ing. Individual OPPs are difficult to identify because
of coelutions and shifting retention times on different
capillary phases. OPPs can degrade on reactive sites
References:
1.
Monitoring exposure of organophosphorus and/or
carbamate insecticides
Saskatchewan Labor, Canada.
2. Code of Federal Regulations, 40 CFR sec. 180.6. Office of the
Federal Register Archives and Records Administration.
3. Official Methods of Analysis 5th Ed., 1990, Section 970.52.
Association of Official Analytical Chemists, AOAC International,
Arlington, VA.
4. Pesticide Analytical Manual Vol.1, 3rd Ed., 1994, Section 304-
11. U.S. Department of Health andHuman Services, Food and
Drug Administration.
acephate
200µg/mL
azinphosmethyl(guthion)
400
chlorpyrifos
100
demeton-s-methyl
200
dichlorvos (DDVP)
500
dimethoate
200
ethion
200
malathion
200
methamidophos
500
methidathion
200
omethoate
1000
pirimiphosmethyl
100
profenfos
200
pyrazophos
500
tokuthion (prothiofos)
200
tolclofos-methyl
100
Organophosphorous Pesticide
Mix, European Formulation
(16 components)
Inmethylene chloride, 1mL/ampul
Each
5-pk.
10-pk.
32418
32418-510
—
w/data pack
32418-500
32418-520
32518
Rtx
®
-CLPesticides 30m, 0.32mm ID, 0.50µm (cat.# 11139)
Sample:
EuropeanOPPMix (cat.# 32418)
100–1000µg/mL in acetone
Inj.:
0.5µL direct, open-top Siltek
™
DrilledUniliner
®
inlet liner (cat.# 21055-214.5)
Inj. temp.:
250°C
Carrier gas:
helium, constant pressure
Linear velocity: 35cm/sec. @80°C
Oven temp.:
80°C (hold 1min.) to 150°C@7°C/min. to 280°C@15°C/min.
(hold 10min.)
Det.:
FPD@280°C
Concentration
on-column
(ng)
1.methamidophos
1.25
2.dichlorvos
1.25
3.acephate
0.50
4.demeton-s-methyl
0.50
5. tributylphosphate (IS) 1.25
6.omethoate
2.50
7.dimethoate
0.50
8. tolclofos-methyl
0.25
9.pirimiphosmethyl
0.25
10.chlorpyriphos
0.25
11.malathion
0.50
12. tokuthion
0.50
13.methidathion
0.50
14.profenfos
0.50
15.ethion
0.50
16. triphenylphosphate
(surrog.)
1.25
17.azinphos-methyl
1.00
18.pyrazophos
1.25
Figure 1
—Organophosphorus PesticidesMix, European Formulation on an
Rtx
®
-CLPesticides column.
GC_EV00676
