14 Results and discussion


Each acquisition mode described above has a defined application role: an MS-only run is the method of choice for screening applications, while auto MS/MS is used in proteomics and other identification-based workflows, and targeted MS/MS is used for quantitation.


Waters MSE , with the ability to deconvolute fragments in the MS/MS domain and align with


one (or more) coeluting precursor ions from the MS domain, overcomes the limitations of a precursor selection-based approach, and the limitation of the duty cycle. However, the identification process is solely dependent upon the SW algorithm. With several thousand peaks per spectrum, the correct assignment of fragment ions to a molecular ion is challenging. SCIEX’s SWATH increases the selectivity by using multiple quadrupole precursor ion windows, producing significantly less complex fragment ion spectra. However, proteomics remains the key application.


Updates to European food safety guidelines (SANTE/11813/2017) [9] require analyte peaks from precursors and/or product ion(s) to fully overlap in the extracted ion chromatograms of HRAM spectrometry instruments. This is a substantial shift from previous MS-only screening, whereby the identification was traditionally done by mass accuracy, retention time (RT), and where applicable, isotope fidelity. Classic compound ID workflows using a single spectrum for identification were also not acceptable by the new guidelines. As quantitative experiments require at least 12 datapoints over the chromatographic peak, targeted MS/MS experiments are theoretically possible, but would require accurate RT knowledge of the compound. In contrast, for targeted quantitation, standards are needed to build a concentration curve from which the RT is apparent. This is not always the case for suspect screening or nontargeted screening, where the RTs are either totally unknown, based on a prediction, or merely suspected [10].


In such cases, depending on the size of the database that the suspect screening is performed against, too many targeted precursors may be coeluting, and the requirements of the 12 datapoints over the chromatographic peak are limited by the duty cycle. The only viable options for dealing with this are a DIA workflow, using either an MSE


/All Ions workflow, or a


SWATH-like quadrupole wideband selection. For the latter, the number of possible windows (and used collision energies) are limited again by the duty cycle. Even a moderate number of six windows and a fixed acquisition rate of 6 Hz in MS would require about 20 Hz in MS, and 10 windows, about 30 Hz. A TOF instrument under these fast acquisition rates would reveal a lower dynamic range compared to 3 Hz acquisition rates, and electrostatic trap instruments would exhibit lower resolution.


Conclusion


High resolution accurate mass spectrometry shows the fastest growth rate of all mass spectrometer techniques. This is due to substantial increase in both resolution and sensitivity, accompanied by acquisition modes and workflows suitable for nearly all applications in research and routine analysis. With all vendors competing in the space, no single specification can be used to determine suitability; rather, the whole performance spectrum needs to be considered.


Acknowledgement


Special thanks to Pat Perkins, David Weil, and George Stafford for providing critical insights to this publication and careful review.


References


1. Thompson, J.J. (1913). ‘Rays of Positive Electricity and Their Application to Chemical Analyses’. Longmans, Green and Company


2. Pramanik, B.N., Ganguly A.K., Gross, M.L. (2002) ‘Applied Electrospray Mass Spectrometry’ in Practical Spectroscopy Series Volume 32, 36-37


3. Gelpi, E. ‘From large analogical instruments to small digital black boxes: 40 years of progress in mass spectrometry and its role in proteomics. Part II 1985–2000’. J. Mass Spectrom. (2009) 44, 1137-1161


4. Noga, M., Sucharski, F., Suder, P., Silberring, J. ’A practical guide to nano-LC troubleshooting’ J. Sep. Sci. 2007, 30, 2179 – 2189


5. Eshraghi, J., Chowdhury, S.K. ‘Factors affecting electrospray ionization of effluents containing trifluoroacetic acid for high-performance liquid chromatography/mass spectrometry’. Anal. Chem. (1993) 65, 3528-3533


6. Mordehai, A., Fjelsted, J ‘Agilent Jet Stream Thermal Gradient Focusing Technology’ (2009) Agilent publication 5990-3494EN


7. Shaffer, S.A., Tang, K., Anderson, G.A., Prior, D.C., Udseth, H.R., and Smith, R.D. (1997). ‘A Novel Ion Funnel for Focusing Ions at Elevated Pressure using Electrospray Ionization Mass Spectrometry’. Rapid Communications in Mass Spectrometry. 11 (16): 1813–1817


8. May, J.C., Goodwin, C.R., Lareau, N.M., Leaptrot, K.L., Morris, C.B., Kurulugama, R.T., Mordehai, A., Klein, C., Barry, W., Darland, E., Overney, G., Imatani, K., Stafford, G.C., Fjeldsted, J.C., and McLean, J.A. (2014). ‘Conformational Ordering of Biomolecules in the Gas-Phase: Nitrogen Collision Cross Sections Measured on a Prototype High Resolution Drift Tube Ion Mobility-Mass Spectrometer’. Analytical Chemistry 86(4), 2107–2116.


9. https://ec.europa.eu/food/sites/food/files/plant/docs/pesticides_mrl_guidelines_ wrkdoc_2017-11813.pdf


10. Schymanski, E.L.1, Singer, H.P., Slobodnik, J., Ipolyi, I.M., Oswald, P., Krauss, M., Schulze, T., Haglund, P., Letzel, T., Grosse, S., Thomaidis, N.S., Bletsou, A., Zwiener, C., Ibáñez, M., Portolés, T., de Boer, R., Reid, M.J., Onghena, M., Kunkel, U., Schulz, W., Guillon, A., Noyon, N., Leroy, G., Bados, P., Bogialli, S., Stipaniev, D., Rostkowski, P., and Hollender, J. (2015). ‘Non-target Screening with High-Resolution Mass Spectrometry: Critical Review using a Collaborative Trial on Water Analysis’. Anal Bioanal Chem. Aug; 407(21):6237–55.


Read, Share and Comment on this Article, visit: www.labmate-online.com/article Passive Sampling of Mercury in Ambient Air with Superior Detection Performance


Mercury is an air pollutant of global concern because of its high toxicity and ability to bio-accumulate in the food chain. Currently the monitoring of mercury in ambient air is not as extensive as it should be due to the limited number of monitoring sites around the globe.


Cost effective monitoring solutions are, therefore required for widespread and unique deployment in order for a better understanding of the Hg distribution and occurrence.


The employment of Atomic Fluorescence Spectroscopy (AFS) with either cold vapour generation for the ultra-sensitive detection of Hg has been PS Analytical’ s core competency for over 30 years.


PS Analytical introduce the use of passive samplers (based on gold amalgamation Amasil traps) in conjunction with the highly sensitive and selective lab based AFS


When deployed in the field for several months the traps pre-concentrate a sufficient mass of mercury to be analytically measured. These traps are then collected and returned to the lab for analysis by dual-amalgamation AFS. The mercury that is collected on these traps is thermally desorbed and carried to the analyser for quantification. The reusable traps may then be redeployed again for further air monitoring.


PSA works with many industries, organisations and markets to deliver industry leading analysers. The systems are used to analyse; waters, soils, sediments, air, stack gas, blood, urine, food and beverage, petrochemicals, polymers, minerals and many other sample types.


More information online: ilmt.co/PL/LDoP 51196pr@reply-direct.com


New Portable Quadrupole Analyser Introduced


The Hiden pQA portable gas analyser from Hiden Analytical is a versatile mass spectrometer and offered with a range of interchangeable sampling inlets to suit a broad application range. MIMS inlets are offered for analysis of dissolved species in ground water, fermentation cultures, soil samples, and general applications where analysis of dissolved species in liquid sample is required. The system is suited to gas analysis applications, where sample volume is small, and for environmental applications where detection of low concentration levels is required. The pQA system has a mass range of 200 amu and sub ppb detection levels. Extended mass range to 300amu is optional.


The system is supplied in a Pelican® case and can be powered by a 12 V supply for field use, battery and/or solar powered, or a 220 V supply for laboratory use.


The new pQA system is designed to be compact, lightweight and portable extending the applications of high sensitivity, high dynamic range multi gas analysis by mass spectrometry for use in the field, on riverbanks, at sea, or in the laboratory.


More information online: ilmt.co/PL/e0Vj 51079pr@reply-direct.com


INTERNATIONAL LABMATE - FEBRUARY 2020


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88