Multiresidue Pesticide
Analysis in Food and
Agricultural Samples
The analysis of pesticide residues in food samples is increasingly be- coming an important technique. Most pesticides are designed to kill pests. However, many pesticides can also pose risks to people. The
health effects of pesticides depend on the type of pesticide. Some, such as
organophosphates and carbamates, affect the nervous system. Others can
irritate the skin or eyes. Some pesticides may be carcino-
genic.
Many food samples contain a range of pesticides. This
number can sometimes be in the hundreds. As a result,
most analytical techniques are not geared towards measuring a single pesticide. Most analytical laboratories will be
performing multi-residue methods to detect a large number of pesticides in a single sample. These pesticides can
be acidic, basic and neutral, and the sample matrix may
contain components such as lipids, sterols, etc.
As the sample matrix can contain interferences, sample
preparation is needed prior to injection into the chro-
matography system. Due to increasing throughput require-
ments and cost pressures, a multi-residue method should
meet the following criteria:
• Fast to perform — Use as few process steps as possible
• Easy to execute — Avoid laborious process steps such as evapora-tion/reconstitution
• Use a minimum amount of solvents and sorbents — Reduce costs and
environmental impact
Many multi-residue methods involve lengthy steps, such as multiple
separations. This can lead to the likelihood of greater error in the final
analysis. By minimizing the number of steps, greater accuracy in results
and a greater throughput of samples can be achieved.
In 2003, Anastassiades and Lehotay developed a way to simplify multi-residue pesticide analysis, leading to a technique that is simple, quick to
perform and inexpensive, but still gives excellent results. This technique
was named QuEChERS, an acronym for Quick, Easy, Cheap, Effective,
Rugged and Safe. This technique is increasingly becoming the method of
choice for multi-residue pesticide analysis in food samples. The QuEChERS technique is:
• Quick – Sample throughput is high and it can detect a range of pesticides in a single extraction
• Easy – No need for automation during the process and laborious
process steps are eliminated
• Cheap – It uses less sorbent and solvent than other multi-residue methods
• Effective – It gives high recoveries and accurate results for a range of
pesticide types
• Rugged – It can detect a range of pesticide types, such as polar compounds and pH-dependent compounds
• Safe – The technique does not use chlorinated solvents; extraction is
typically carried out using acetonitrile (this is LC- and GC-amenable)
www.thermo.com/columns
This method is a sample preparation
technique using solvent extraction of high-moisture samples with acetonitrile, ethyl
acetate or acetone and partitioning with
magnesium sulfate alone or in combination with other salts, followed by sample
clean-up using a dispersive solid-phase
extraction (SPE) technique.
The first step (sample extraction) involves adding a homogenized food sample to a 50-ml centrifuge tube containing
magnesium sulfate and a salt such as
sodium chloride or sodium acetate. Upon
addition of acetonitrile and extensive
shaking and centrifugation of the tube, the
MgSO4 induces a phase separation between the acetonitrile and water layers.
The compounds of interest transfer into
the acetonitrile layer.
A portion of this acetonitrile layer is
next transferred to a clean-up tube. This
tube is typically 2 or 15 ml in volume and
contains a combination of sorbent materials in different amounts. Magnesium sulfate is present to remove any excess
water from the sample. Primary/secondary
amine (PSA) is used for the removal of organic acids and polar pigments, while
endcapped C18 is used for lipid and sterol
removal. Graphatized carbon block is
used if substances such as chlorophyll are
present and may break down during
analysis.
Selection of the most appropriate
product is determined by the following parameters:
• Starting sample matrix
• Sample volume
• AOAC/EPA method followed (if applicable)
Following sample extraction and clean-up, a portion of the sample can then be injected directly onto an LC or GC system
without any need for evaporation, reconstitution or derivatization.
This technique was initially developed
for analysis of fruit and vegetable products. However, research has shown that it
can be successfully utilized with other matrices such as milk, honey and rice. The
technique has also been used to investigate non-pesticide food toxins, such as
acrylamide in various food matrices. It is
increasingly being utilized in food safety
laboratories around the world and is anticipated to grow in popularity over the coming years. In addition, Thermo Scientific
HyperSep Dispersive SPE products contain the proper sorbents for optimum extraction, clean-up and separation of
analytes from complex matrices such as
food products.
