A new method provides determination of organochlorine pesticides and polychlorinated
biphenyls using GC/MS/MS operated in MRM mode.
PCBs with Modern
» by Brahm Prakash, William Lipps, Shimadzu Scientific Instruments
The determination of chlorinated pesticides (OCPs) and polychlorinated biphenyls (PCBs) in environmental matrices is a common analysis in most environmental aboratories. These compounds are typically analyzed by
employing solid phase or liquid-liquid extraction with methylene chloride, concentration, solvent exchange into hexane, and
interference removal using acid, copper, or column chromatography. Analysis is done using gas chromatography (GC) with
electron capture detection (ECD) and requires confirmation of
every detected component on another dissimilar GC column.
However, GC-ECD techniques are prone to positive and negative bias in complex matrices, resulting in unnecessary cleanup
costs and/or violations of NPDES permits. Clearly, a new method for pesticides and PCBs based on modern GCMS technology
This article describes use of a triple quadrupole GC/MS/MS
method using multiple reaction monitoring (MRM) mode for sensitive and selective detection and quantitation of organochlorine
pesticides and PCBs. A database with optimized MRM transitions
for all of the OCPs and PCBs, including relative retention times for
all components, makes method setup possible within minutes. The
use of GC/MS/MS MRM mode provides enhanced selectivity, spec-ificity and sensitivity in complex matrices with potential co-eluting
This article also presents all instrument operating conditions
and instrument method performance statistics, including method
linearity, accuracy, precision and instrument detection limits for
Chlorinated pesticides (OCP) and polychlorinated biphenyl
(PCB) congeners (known collectively as Aroclor) are among the
environmental organic compounds most difficult to measure.
The difficulty is primarily due to the fact that they are found at
very low concentrations. The EPA-approved method for OCPs
and PCBs in wastewater is EPA Method 608.2. Method 608
relies upon gas chromatography with electron capture detection
(GC-ECD) to measure a targeted list.
GC-ECD is one of the few techniques available capable of
detecting halogenated compounds at very low concentrations.
GC-ECD is a non-specific detection technique that can produce a signal for non-target compounds. As a result, when
using GC-ECD for pesticides and PCBs in environmental
samples, other components in the sample can be detected
and interfere with both identification and quantitation.
Target compounds are identified by retention time. Aroclors
are a mixture of hundreds of different congeners requiring
identification by the analyst visually comparing the chromatography of the unknown with the chromatography of the
GC-ECD Suffers from Matrix Interferences
The matrix itself can have a profound impact on the chromatography and on the response of the ECD. High levels of
non-target components in the matrix can co-elute. False positives result if the co-eluting compound responds to the detector, whereas false negatives result if the co-eluting compound
quenches the ECD signal.
The EPA requires that any detected compound be analyzed
again on a different chromatography column to “confirm” the
identity of every detected component. This second column confirmation means that every sample is either analyzed twice, or
that the laboratory instrument is equipped with two columns
and two detectors. The second column confirmation may help
to recognize interferences, but cannot guarantee interferences
Second column confirmation for all positive GC-ECD peaks
does not guarantee positive identification or quantitation of
the pesticides. Just as there may be co-elution on the primary
column, there can be co-elution on the second column as well.
Hydrocarbons and the presence of other components (such as
PCBs) can interfere.