What are anionic polar pesticides?
The presence of anionic polar pesticides in surface and drinking water, food and beverages has become a controversial issue in recent years. Glyphosate, for example, is one of the most widely used pesticides in the world — used as a crop desiccant and as herbicide to kill weeds. There are concerns about its potential adverse effects on human health. Current EU regulations establish maximum residue levels (MRLs) of glyphosate at 0.1 mg/kg in leeks. In wheat flour samples, higher MRLs typically apply, for instance in Japan and China are 5 mg/kg. Glyphosate metabolites, like AMPA, N-Acetyl glyphosate and N-Acetyl AMPA, that are not regulated in the current legislation might become part of future amendments, as regulatory body are looking to all possible glyphosate metabolites for a complete risk assessment.
In addition to glyphosate, perchlorate and chlorate have also been identified as controversial substances, mainly emerging as contaminations or by-products of fertilizers and disinfectants in drinking water systems respectively. They are highly soluble and persistent in nature, and therefore, also found in groundwater and, drinking water. As a result, it is difficult to grow or prepare fruits and vegetables not contaminated by these compounds. So the need to intensify the controls for these compounds in food is apparent.
What is ion chromatography coupled to mass spectrometry?
Triple quadrupole mass spectrometry coupled with liquid chromatography is used more and more for the determination of pesticides and veterinary drug residue in food matrices. However, when it comes to the analysis of the extremely polar compounds, there is still a barrier for their determination by LC-MS, since their polarity does not allow direct analysis by reversed-phase HPLC. Therefore, alternative methods and workflows are necessary for successful analysis and sensitive quantitation of polar pesticides. The coupling of ion chromatography with electrospray mass spectrometry opens new ways for the determination of these compounds in food matrix.
In my opinion, there are many advantages to using ion chromatography coupled with mass spectrometry. One major advantage is that we can analyze polar compounds, such as glyphosate directly. Also, we can carry out multi-class residue analysis from one extraction, without derivatization. Even if the analytical run times are longer than those for UHPLC-MS, the overall analysis efficiency is improved for multi-class analysis. And now newer IC systems are designed to handle the higher pressure, and are suitable for smaller particle size column which can reduce the run times. Other advantages of IC is good retention of ionic pesticides because of the higher column capacities and reproducible gradient elution with the use of the electrolytic eluent generation of the mobile phase in situ. For the analysis of anionic pesticides, KOH eluent is generated by the EGC 500 KOH, and the suppressor, which electrolyzes the KOH mobile phase to water at the exit of the column, and before the detector, is critical to enable the coupling to a mass spectrometer.
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There are many benefits to using the Thermo Fisher Scientific Altis triple quadrupole mass spectrometry system, including high sensitivity, selectivity , accuracy and precision in the negative ion mode as demonstrated in an application note titled Determination of Polar Pesticides in Grapes using a Compact Ion Chromatography System Coupled with Tandem Mass. Two or more precursor/product SRM ion transitions were monitored in the method for each target compound to achieve identification in compliance with the SANTE 11813/2017 Guidelines.
Development of a “Sample-to-Result” Workflow
This basic method has been further developed, validated and packaged into a workflow.
The workflow for the determination polar pesticides using IC-MS/MS contains everything required to set up the method rapidly in a laboratory, from sample preparation to final result. The workflow based on the modified QuPPe generic method which is applicable for extraction of a wide range of sample types. The IC-MS/MS system has complete methods for data acquisition, qualitative and quantitative processing for 16 anionic polar pesticides in a single run, and is easy to implement in the lab. The Integrion HPIC System offers increased uptime, robustness, while the TSQ Altis triple quadrupole mass spectrometer delivers best-in-class sensitivity and speed, as well as the robustness and reliability required for fast and accurate quantitation of analytes in a variety of matrices. Software is tailored for food safety applications and maximizes your lab’s productivity by enabling comprehensive reporting, and the development of expert methods regardless of user experience with the software.