Measurement of the precursor accurate mass and retention time alone can lead to a high number of false positive results, particularly with complex matrices such as QuEChERS extractions. However by including 'diagnostic' qualifier ion (QI) information as a mandatory requirement in the confirmation criteria, false positive detections are practically eliminated, delivering maximum confidence in your screening result.
The Bruker PesticideScreener continuously generates fragment ions using broadband Collision Induced Dissociation (bbCID). During the complete screening process, the QTOF mass spectrometer rapidly and continuously cycles between low collision energy (TOF-MS) and elevated collision energy (bbCID) MS/MS, resulting in the seamless collection of accurate mass precursor and fragment ion data in a single analysis.
The ability of the PesticideScreener to detect 'all of the ions, all of the time' in full scan MS and MS/MS modes without compromising sensitivity or resolution, results in a dataset that is complete and unrestricted. The diagnostic Qualifier Ions (QI's) can then be used as a part of an enhanced pesticide confirmation criterion to eliminate false positive findings as well as delivering unambiguous ID's for closely eluting similar pesticides.
At the heart of the PesticideScreener solution lies the exact mass pesticide database. In addition to monoisotopic precursor ion masses and retention time data, the database also contains diagnostic QI information, comprising of accurate mass bbCID fragments and 'in source' fragment ions as well as adduct and isomer information.
The detection of diagnostic QI's can be specified as a mandatory requirement as part of the confirmation criteria. Figure 4 shows how unique mandatory QI's enable two closely eluting isomeric pesticides (terbutryn and prometryn) to be clearly distinguished from each other.
Data processing for screening and quantitation is powered by TASQ (Target Analysis for Screening and Quantitation) software. TASQ intelligently uses the diagnostic qualifier ions s to reduce false positive detections, bringing a new level of confidence to screening workflows.
For total confidence in the results, four dimensions of confirmation are used in the PesticideScreener 2.1 workflow
- Parent ion or adduct accurate mass
- Retention time
- Isotopic pattern fidelity
- Fragment qualifier ions
Color coded screening results are easily reviewed in either a sample centric or analyte centric fashion as desired by the analyst. Once reviewed, qualitative and quantitative sample reports are then easily generated.
TASQ enables the analyst to specify multiple QI's in the PesticideScreener data processing step. Figure 6 shows the clear and unambiguous positive ID of prometryn and terbutryn pesticides summarized by the color coded MRSQ column of the results table.
If calibration standards are incorporated into the experiment, then a combined screening and quantitation experiment is realised without the need for a second sample injection.