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Kaufmann A.,Official Food Control Authority | Kaufmann A.,Kantonales Labor Zurich
Analytical and Bioanalytical Chemistry | Year: 2012

High-resolution mass spectrometry (HRMS), which is used for residue analysis in food, has gained wider acceptance in the last few years. This development is due to the availability of more rugged, sensitive, and selective instrumentation. The benefits provided by HRMS over classical unit-mass-resolution tandem mass spectrometry are considerable. These benefits include the collection of full-scan spectra, which provides greater insight into the composition of a sample. Consequently, the analyst has the freedom to measure compounds without previous compound-specific tuning, the possibility of retrospective data analysis, and the capability of performing structural elucidations of unknown or suspected compounds. HRMS strongly competes with classical tandem mass spectrometry in the field of quantitative multiresidue methods (e.g., pesticides and veterinary drugs). It is one of the most promising tools when moving towards nontargeted approaches. Certain hardware and software issues still have to be addressed by the instrument manufacturers for it to dislodge tandem mass spectrometry from its position as the standard trace analysis tool. © Springer-Verlag 2012. Source


Kaufmann A.,Official Food Control Authority | Kaufmann A.,Kantonales Labor Zurich | Butcher P.,Official Food Control Authority | Maden K.,Official Food Control Authority | And 2 more authors.
Rapid Communications in Mass Spectrometry | Year: 2011

The quantitative and confirmative performance of two different mass spectrometry (MS) techniques (high-resolution MS and tandem MS) was critically compared. Evaluated was a new extraction and clean-up protocol which was developed to cover more than 100 different veterinary drugs at trace levels in a number of animal tissues and honey matrices. Both detection techniques, high-resolution mass spectrometry (HRMS) (single-stage Orbitrap instrument operated at 50 000 full width at half maximum) and tandem mass spectrometry (MS/MS) (quadrupole technology) were used to validate the method according to the EU Commission Decision 2002/657/EEC. Equal or even a slightly better quantitative performance was observed for the HRMS-based approach. Sensitivity is higher for unit mass resolution MS/MS if only a subset of the 100 compounds has to be monitored. Confirmation of suspected positive findings can be done by evaluating the intensity ratio between different MS/MS transitions, or by accurate mass based product ion traces (no precursor selection applied). MS/MS relies on compound-specific optimized transitions; hence the second, confirmatory transition generally shows relatively high ion abundance (fragmentation efficacy). This is often not the case in single-stage HRMS, since a generic (not compound-optimized) collision energy is applied. Hence, confirmation of analytes present at low levels is superior when performed by MS/MS. Slightly better precision, but poorer accuracy (fortified matrix extracts versus pure standard solution) of ion ratios were observed when comparing data obtained by HRMS versus MS/MS. Copyright © 2011 John Wiley & Sons, Ltd. Source


Kaufmann A.,Official Food Control Authority | Kaufmann A.,Kantonales Labor Zurich | Butcher P.,Official Food Control Authority | Maden K.,Official Food Control Authority | And 2 more authors.
Analyst | Year: 2011

Some twenty cultured fish samples were analyzed for possible residues of veterinary drugs with high resolution mass spectrometry (single stage Orbitrap) coupled to ultra performance liquid chromatography. Quantitative analysis based on external standards covered 110 analytes. Some 116 additional compounds were monitored without having access to reference materials. Detection was based on calculated exact masses and narrow mass windows. Furthermore, a number of semi-targeted techniques were evaluated and compared to corresponding triple quadrupole precursor scan experiments. Single stage high resolution mass spectrometry was used to monitor compound specific product ions (without relying on a previous precursor selection). The capabilities of neutral loss searches based on exact masses were shown by detecting small concentrations of incurred oxytetracycline residues. High resolution mass spectrometry provided more sensitivity and selectivity than corresponding tandem quadrupole precursor and neutral loss scans. The currently limiting factor is the not adequate performance of the available software used for data mining. The high number of false positives that were produced, when searching for chlorine isotopic patterns, was clearly linked to the fact that the utilized software does not perform a peak deconvolution, but simply investigates one individual spectrum after another. © 2011 The Royal Society of Chemistry. Source


Kaufmann A.,Kantonales Labor Zurich | Walker S.,Kantonales Labor Zurich
Rapid Communications in Mass Spectrometry | Year: 2016

Rationale The Q Orbitrap permits multiplexed targeted selected ion monitoring (SIM) or tandem mass spectrometry (MS/MS) scans. Such scans provide a significantly higher sensitivity than conventional full scan acquisition. However, due to the multiplexing, a monitored product ion extracted from a MS/MS scan can no longer be linked to the precursor ion from which it was derived. Furthermore, due to the automatic gain control, quantification based on targeted product ions acquired in the multiplexed MS/MS mode can become questionable. Methods The application programming interface (API) of the Q Exactive has been used to program a multiplexed targeted MS/MS mode that permits the establishment of a link (based on digital coding) between the product ion and the responsible precursor ion. Furthermore, switching off the automatic gain control feature and the definition of appropriate C-trap settings were tested to improve the quantification performance. Results The use of dedicated decoding scans permitted the clear assignment of all monitored product ions to the responsible precursor ion. Furthermore, the customized multiplexed targeted scan used for quantification showed good sensitivity and linearity for a maximum number of eight co-eluting analytes. Conclusions Multiplexed targeted MS/MS scans can be optimized to provide better selectivity (correct linking of an observed product ion to the responsible precursor ion) as well as improved quantitative performance (enforcement of an identical ion injection time for all targeted precursor ions). These two improvements are relevant for quantitative residue analysis. Copyright © 2016 John Wiley & Sons, Ltd. Source


Kaufmann A.,Kantonales Labor Zurich | Walker S.,Kantonales Labor Zurich
Rapid Communications in Mass Spectrometry | Year: 2012

Orbitrap technology offers a combination of different technical specifications which have not yet been achieved by other high-resolution mass spectrometry instrumentation. This refers to the combination of sensitivity, dynamic range, mass accuracy, resolution and speed. The high stability of the mass axis and the general ease of use made the orbitrap instrumentation attractive for routine laboratories. However, there are circumstances where significantly deviating relative isotopic abundance (RIA) and shifting accurate masses can be observed. RIA becomes biased at low ion counts. Furthermore, two adjacent, only partially resolved near-isobaric ions are detected with a deviating RIA. The presence of a very intensive mass peak does not only induce Fourier transformation related artefacts (side-lobes) but can cause mass shifts of small adjacent near-isobaric mass peaks. These effects are not as drastic as known for Fourier transform ion cyclotron resonance instruments. Still, users trying to identify or quantify trace level compounds should be aware about such limitations in order to avoid possible pitfalls. © 2012 John Wiley & Sons, Ltd. Source

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