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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 40 minutes. Tributyl phosphate and triph-
enyl phosphate are recommended surrogates for
GC/FPD (EPA Method 8141B).
To meet the challenges of OPPs analysis, Restek
chemists use an Rtx®-CLPesticides column. Rtx®-
CLPesticides columns have a 330ºC maximum oper-
ating temperature, superior inertness, and low bleed.
Figure 1 shows excellent resolution of the European
OPP Mix, obtained in less than 25 minutes. 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 in OPP-
containing extracts. The ability to clean an Rtx ®-
CLPesticides column at high temperatures enables us
to make more 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, an Rtx®-CLPesticides column, and our new
European OPP Mix, are important parts of attaining
this goal.
• 11 •
2003 Volume 2
800-356-1688
Resolve Complex Mixtures of
Organophosphorus Pesticides,
Using an Rtx®-CLPesticides GC Column and a
New Restek Reference Mix
✔ Fast, efficient analyses, using an Rtx®-CLPesticides column and flame
photometric detection.
✔ New OPP reference mix corresponds to strict European criteria.
✔ Concentrations of mix components vary according to FPD response.
By Katia May, Ph.D., R&D Chemist, and Lydia Nolan, Environmental Innovations Chemist
Organophosphorus pesticides (OPP) are widely used
to protect fruits and vegetables from insects.
Unfortunately, these toxic materials 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 in milk, eggs, meat, or poultry is stated in
the Code of Federal Regulations.2 Multi-residue meth-
ods in AOAC Official Methods of Analyses3 and the
FDA Pesticide Analytical Manual4 are used to deter-
mine OPPs and organochlorine pesticides. Analytical
procedures for OPPs usually involve GC with 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 phosphorous mode minimizes interfer-
ence by materials that do not contain phosphorus.
Recently, our European customers asked us to dev-
elop a stable reference mix of target OPPs, with con-
centrations appropriate for analysis by GC/FPD. The
components in our new European OPP Mix 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 the OPPs, demeton, is a mix-
ture of O- and S- isomers. We include demeton-S in
the mix, and follow US EPA Method 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 and Human Services, Food and
Drug Administration.
acephate 200µg/mL
azinphos methyl(guthion) 400
chlorpyrifos 100
demeton-s-methyl 200
dichlorvos (DDVP) 500
dimethoate 200
ethion 200
malathion 200
methamidophos 500
methidathion 200
omethoate 1000
pirimiphos methyl 100
profenfos 200
pyrazophos 500
tokuthion (prothiofos) 200
tolclofos-methyl 100
Organophosphorous Pesticide
Mix, European Formulation
(16 components)
In methylene 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: European OPP Mix (cat.# 32418)
100–1000µg/mL in acetone
Inj.: 0.5µL direct, open-top Siltek™ Drilled Uniliner® 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 1 min.) to 150°C @ 7°C/min. to 280°C @ 15°C/min.
(hold 10 min.)
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. pirimiphos methyl 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 Pesticides Mix, European Formulation on an
Rtx®-CLPesticides column.
GC_EV00676