31
HIGH RESOLUTION MS
The main advantage of this sophisticated MS technique is its very simple setup and tuning with all data being acquired only in full scan mode, without the need for specific parameters for each compound under investigation. This allows users to conduct an additional search for further possible contaminants after the sample run has been completed. The high resolving power of the system offers greatly enhanced detection capabilities, improving analytical accuracy and providing a high degree of confidence in the results. In addition, high resolution of 100,000 FWHM improves the chromatographic peak shape and facilitates its quantitation.
High resolution MS a simple sample preparation process which consists of the extraction of mycotoxins from raw materials without any specific clean up. As such, the method is capable of analysing a broad range of mycotoxins in a variety of matrices. Offering unique quantitation and target screening capabilities, ultra-high resolution MS enables analysts to monitor target compounds. Non-target screening is also possible eliminating the need to focus only on particular compounds and instead allowing scientists to search for unknowns in the material.
Positive and negative acquisition can be performed in a single run while also allowing for post acquisition data mining. Excellent stability and robustness are additional benefits of the method. Ultra-high resolution MS uses a narrow mass extraction window to improve the selectivity of chromatographic detection. The narrower the window is, the better the selectivity achieved, resulting in elimination of chemical background and chemical noise. A further significant advantage of the technique is its ability to achieve very good repeatability of injections. Repeatability is very important since, according to the European Commission Decision of C1 14 August 2002 [1], quantitation methods must offer repeatability below 20%.
Compared to TOF MS solutions, high-resolution MS systems provide lower detection limits and improved sensitivity. Additionally, the high resolving power of the systems minimises interferences. This cannot be achieved with the low- resolution capability offered by TOF MS instruments.
An experiment was developed to demonstrate the superiority of the method for monitoring the presence of priority fusarium mycotoxins as well as their masked forms in samples collected during beer production.
EXPERIMENTAL
A benchtop LC/MS system (Exactive™, Thermo Fisher Scientific, Bremen, Germany) was coupled to a U-HPLC chromatograph (Accela™, Thermo Fisher Scientific, San Jose, USA) to evaluate a mixture of mycotoxins, including masked mycotoxins in cereal extracts.
A 9 min gradient was applied to a 100mm x 2.1mm C18
column (2.1mm x 100mm x 1.8µm) with 5mM ammonium formate/methanol eluents. Mass measurements were performed at different mass resolving power settings ranging from 25,000 up to 100,000 FWHM.
NON TARGET SCREENING OF BEER USING SIMPLIFIED SAMPLE PREPARATION
The variability of analytes potentially present in the samples requires the simplification of the sample preparation step to avoid losses of analytes during sample extraction and clean up. In order to avoid missing mycotoxins and their metabolites, any sample adjustment (e.g. immuno-affinity or solid phase extraction clean-up) could not be used. The capabilities of single stage, high resolution MS for a non-targeted screening approach were tested on beer samples spiked with known amounts of mycotoxins and extracted using a simple sample preparation procedure based on the precipitation of beer with acetonitrile and centrifugation.
The Exactive MS system, using high mass resolving power of 100,000 FWHM and a narrow extraction window of 3 ppm, was employed for the analysis of prepared samples. Figure 1
Figure 3: Linearity of the calibration of zearalenone in the calibration range of 1-2500ng/mL.
Spotlight
Figure 2: The effect of mass resolution (A) and extraction window width (B) on the quality of chromatographic data and system selectivity. XICs of HT-2 toxin at concentration level 10ng/mL in beer matrix.
For routine use of the system in the mycotoxin analysis field, a wide linear dynamic range and the linearity of calibration for the analysed compounds should be maintained. During the experiments it was found that the system can maintain very good linearity of a several orders of magnitude. The calibration curve of zearalenone shown in Figure 3 demonstrates the excellent linearity and dynamic range achieved during analysis of a series of calibration standards.
presents example of extracted ion chromatograms of
deoxynivalenol at concentration level of 100µg/L. The results demonstrate the high selectivity and sensitivity of the technique compared to TOF mass spectrometry. In such a complex matrix, it would have been impossible to detect DON at low levels using a TOF instrument with resolving power below 12,000 FWHM.
CONCLUSION
The thorough screening of mycotoxins is required in the regulated environments of food and feed analysis since the presence of these toxins can result in serious adverse effects for humans and livestock. Single stage, full scan MS using Exactive demonstrates ultra high mass resolving power combined with good mass accuracy and selectivity for routine screening and quantitation of mycotoxins in food and feed samples.
Because of the mass selectivity, even in very complex matrices, the superior method results in a simplified sample preparation procedure and increases the number of detected compounds over a wide range of concentrations. In addition, ultra-high resolution MS surpasses conventional TOF MS technology, providing significantly lower detection limits and greatly improved sensitivity while also eliminating background matrix interferences. Further studies and research on this topic are being carried out and the results of the work will be published in a peer reviewed journal in the near future.
Figure 1: The comparison of the detection capability of TOF technology running with resolving power 12,000 FWHM (left) and Exactive system running at 100,000 FHWM resolving power (right).
Acknowledgements
Similarly, significant improvement of the identification and quantitation of HT-2 toxin in a beer sample was observed when a high mass resolving power of 100,000 FWHM was employed (Figure 2). The peak shape of HT-2 toxin has significantly improved using ultra-high resolving power (A). This was due to better separation of the mass peaks of HT-2 toxin and interfering species. Also, the high resolving power and excellent mass accuracy improved the selectivity of the system by using very narrow mass extraction windows down to 2 ppm (B)
The presented work and results have been undertaken under scientific collaboration with the Department of Food Chemistry and Analysis of the Institute of Chemical Technology in Prague, Czech Republic.
For the latest information about Thermo Scientific solutions and the wide range of applications for food safety, please call 800-532-4752, e-mail
analyze@thermofisher.com or visit
www.thermo.com/foodsafety.
[1] Rodriguez, I. and Wegleitner, K. (2008) Biomin Mycotoxin Survey 2007. Asian Pork Magazine June/July 2008.
[2] FAO Corporate Document Repository, Worldwide regulations for mycotoxins in food and feed in 2003,
http://www.fao.org/docrep/007/y5499e/y5499e07.htm
[3] Van der Heeft et al., J Am Soc Mass Spectrom 20 (2009), 451–463
[4] Kellman M. et al, in press
[5] Commission Decision of C1 14 August 2002 implementing Council Directive 96/23/EC concerning the performance of analytical methods and the interpretation of results;
http://www.bsmi.gov.tw/wSite/public/Attachment/f1224 039659469.pdf
Interested in publishing a Technical Article?
Contact Gwyneth Astles on +44 (0)1727 855574 or email:
gwyneth@intlabmate.com
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