Scientists have been challenged by the capability limits of gas chromatography high- resolution mass spectroscopy (GC-HRMS) systems for years. There has been interest in a high-resolution accurate mass (HRAM) system with applications in food safety, and a new GC-HRMS technology for pesticide analysis indicates a step forward in GC-MS analysis.

Mass Accuracy Benefits

At the recent 1st International Symposium on Recent Developments in Pesticides Analysis in Prague, Hans Mol, Ph.D., of the RIKILT Research Institute and Jana Hajslova, Ph.D., a professor at the Institute of Chemical Technology, Prague, presented new data obtained using a technology called the Q Exactive GC system  based on GC separation, electron ionization (EI) and detection using a hybrid quadrupole-Orbitrap mass spectrometer. Mol described the system as a promising and complementary method to LC-Orbitrap that together enable new comprehensive workflows for quantitative analysis of targeted compounds and qualitative screening of non-targeted compounds for both GC and LC amenable pesticides. He also discussed the advantages of excellent mass accuracy (<1 ppm) for each scan across a peak in a complex matrix, at a resolving power (RP) of 60,000, and the simplicity of one acquisition event to obtain multiple accurate mass ions that can make use of existing EI-MS libraries.View videos of the symposium

Resolving Power

As sample types increase in complexity, the resolving power of the mass spectrometer becomes a key factor in reliable pesticide detection. A study that examines high-efficiency broad scope screening of pesticides using GC-HRAM details the mass accuracy, acquisition rate, linearity, detectability, accuracy, precision and identification capability observed at high resolving power. The experiment revealed that 60K RP (m/z 200, full width half maxima, FWHM) was needed to discriminate analytes of interest from matrix components and thus achieve reliable results for pesticides spiked into animal feed. The results indicate that the new system, when used with specific screening software, is an effective tool for routine screening of pesticides in food and feed samples.

Similar experiments for the analysis of pesticides in baby food again demonstrated that full scan acquisition at high resolving power (60,000 FWHM at m/z 200) provided a sufficient number of scans across individual chromatographic peaks to obtain excellent measurement precision over a wide linear dynamic range. Based on retention time (±0.1 min window), accurate mass information (±2 ppm window), ion ratios, isotopic pattern similarity (measured versus theoretical), and library search hit (NIST14 all 132 pesticides spiked at 10 ng/g were detected and identified in acetonitrile extracts of baby food.  Overall the Q Exactive GC system provided selectivity at least if not better than, and quantitative performance comparable to, GC triple quadrupole MS.

Different Pesticides Screening Methods

Hajslova also discussed the use of the Orbitrap technology in two different pesticide screening methods. The first approach focused on the targeted screen for pesticides from a customized HRAM database and a review of data using software. The second method involved non-targeted screening using deconvolution of accurate mass data and spectral library matching with identification using accurate mass fragments. When analyzing pesticides in whiskey samples, Hajslova commented that she was surprised that many compounds where automatically identified.  Since a non-targeted method involves full scan data, it allows the identification of compounds that would go undetected in a targeted method.

Screening using high-resolution mass spectrometry is an effective way to increase the scope of analysis. Routine resolving power of 60,000 FWHM eliminates matrix interferences, increasing confidence in results when screening pesticides in complex matrices. Consistent sub-ppm mass accuracy ensures confident compound identification.