What does mass spectrometry have in common with fishing? My first thought was “not much,” until I attended a recent pesticide symposium. The truth is there are some interesting analogies between fishing and the use of mass spectrometry in the determination of pesticide residues.
Fishing with a rod and line is targeted and analogous to triple quadrupole mass spectrometry: you select your line weight and bait in an attempt to catch one type of fish (or ion), selectively discarding different species of similar size and weight. Fishing with a net is even more analogous to HRAM, as it captures all of the fish (or ions). The fish are then sorted after the catch event, similar to post-acquisition data processing of ion masses by software. You can view a video of Fernández-Alba’s presentation, titled Evaluation of Q Exactive LC-MS for Pesticide Residues in Fruits and Vegetables (link to symposium) along with a video sound byte explaining the need for the development of screening approaches to detect more residues.
Why Fish For More Pesticide Residues?
Despite their widespread use and excellent quantification and identification properties, triple quadrupole MS systems are limited by the need to optimize acquisition parameters based on a pre-selected list of pesticides. If a pesticide present in the sample is not included in the predefined list, it will not be detected. Such ‘false-negative’ results raise concern that the misuse of pesticides, or contamination during storage and transportation, may go undetected in the global network of food production and trade. In recent years, there have been a number of high-profile cases, such as the misuse of isofenphos methyl (link to news article) and contamination with nitrofen (link to news article). Hence the interest in the use of HRAM mass spectrometers that can be operated in full scan mode (no pre-defined list required) to screen for a higher number of pesticides in a single analysis, including non-targeted pesticides, to better protect consumers.
What Kind of Nets Are Available?
There are nets to catch all species. More non-polar pesticides require analysis using gas chromatography (GC) (link to product page), while more polar pesticides require analysis by liquid chromatography (LC) (product page), each coupled to HRAM. Dr. Hans Mol described the new gas chromatography-mass spectrometry (GC-MS) (link to product page) system as a highly promising technique to complement the LC-Orbitrap to enable new comprehensive catch-all workflows for quantitative analysis of targeted compounds, as well as qualitative screening of non-targeted compounds for both GC- and LC-amenable pesticides. Prof. A Hajslova showed how different species’ pesticides, mycotoxins and pyrrolizidine alkaloids (link to ScienceDirect article), in this case, can be successfully captured, quantified and identified using the LC-Orbitrap.
In a recent Analytical Scientist article titled Food (Analysis) for Thought (link to article), Amadeo Fernández-Alba discussed some of the possibilities and benefits of screening by LC- HRAM (link to product page). He concluded with the following words:
“The switch to full-scan HRAM instruments is not going to happen overnight, but I do believe that we’ve reached a tipping point in pesticide analysis. Comparable performance and price to triple quadrupole MS instruments coupled with the advantages of full scan mode and accurate mass for identification make more widespread adoption almost inevitable.”
Visit these additional resources if you’re interested in broad scope screening of pesticide residues in food:
If increasing the scope of methods by the simultaneous screening, detection, quantification and identification of pesticide residues in food is an issue in your laboratory, I’d like to hear your thoughts and experiences.