Overview of AMS Mass Spectrometry Analysis: Low vs. High Mass Resolution Qi Zhang Department of Environmental Toxicology University of California at Davis Aerodyne/Nanjing University Chinese AMS/ACSM Clinic Nanjing, China April -22, 18 1 Raw MS (Low Mass Resolution) 1
Ensemble MS Analysis Mass Conc. of Species Ensemble spectrum of gas and NR-PM materials. MS analysis Partial spectra for chemical species based on known relationships between peaks: Fragmentation pattern of inorganic & gas species Isotopic ratios of elements Ensemble ms ensemble = c air ms air + c SO4 ms SO4 + c NO3 ms NO3 + + c org ms org Summing signals in the partial mass spectrum of a species its mass concentration e.g., C org ( g m -3 ) = m/z i org Ion rate (Hz) 600 400 0 0 2x10 3 1 10 0 Ion rate (Hz) 40 60 m/z NO 3 80 NH 4 100 Use fragmentation table Qi Chen s talk 0x10 3 8 6 4 2 0 Ion rate (Hz) 40 40 60 m/z 60 m/z 80 SO 4 80 100 100 Allan et al. J. Aerosol Sci., 04 3 AMS Organic Mass Spectrum m/z 43: tracer ion for less oxidized species (e.g., carbonyls) f43: indicator for average oxidation degree m/z 44: tracer ion for highly oxygenated species (e.g., acids) f44: indicator for average oxidation degree m/z = 7: tracer ion for long chain HCs (HOA) Obtain information on individual organic species / classes MS deconvolution based on fragmentation table (works with 1 mass spectrum) This approach is not suitable for identifying organic components b/c thousands or more organic compounds in atmospheric aerosols Not able to definitively describe the relationships between peaks Can use multivariate analysis (e.g., PMF, ME2) b/c the quantitative and additive nature of AMS/ACSM data Zhang et al. ES&T, 0 2
A Simplified View of OA Oxidation 0.30 0.2 0. f 44 0.1 OOA LV-OOA SV-OOA Mexico City (flight) LV-OOA Mexico City (flight) SV-OOA Mexico City (flight) T0 Mexico City (flight) T1 Mexico City (flight) T2 Mexico City (ground T0) OOA HULIS Fulvic acid Component wtih biogenic influence 1.1 0.9 0.7 O/C Ratio 0.10 0. 0.0 0.3 0.00 0.1 Ng et al., ACP, 10 0.00 0.0 0.10 f 43 0.1 0. Raw MS (High Mass Resolution) 3
Exact Mass and Mass Defect/Excess Mass Excess or Defect 0.1 Mass number of elements: 0.08 H = 1.0078 0.06 C = 12.0000 0.04 O = 16 1.9949 0.02 N = 14.0031 0 S = 32 31.9721-0.02-0.04-0.06-0.08-0.1 0 40 60 80 100 Atomic Number Due to setting 12 C = 12.0000 and the mass lost to binding energy, the mass of every other element is NOT a whole number. The most common isotopes of H and N both weigh more than their assigned whole number atomic mass. The most common isotopes of O and S weighs less than their assigned whole number atomic mass. 7 What Can High Mass Resolution Do for Us? Signal (Arbitrary units) 0.1 0.10 0.0 Increase in resolution typically means a decrease in signal 0.00 42.9 CHNO DeCarlo, Kimmel et al., Analytical Chemistry, 06. 43.0 43.1 43.2 C 2 H 3 O C CH 3 N 2 H N C 3 H 7 2 8 4
Mass Analyzer: Resolving Power Mass accuracy 4 Mass peak width ( Δm 0% ) Full width of mass spectral peak at half-maximum peak height Mass resolution / Resolving Power (m / Δm 0% ) Quantifies ability to isolated single mass spectral peak Mass accuracy is the ability to measure or calibrate the instrument response against a known entity. Difference between measured and actual mass 9 Exercise: Calculate R & A Argon Atomic Weight (Da): 39.948 39.9622 Atomic mass (m a /u) Abundance 3.967 0.33% 37.9627 0.06% 0.019 39. 9624 99.6% R 39.96 0.019 213 A 0.0002 39.9624 10 6 ppm
http://cires1.colorado.edu/jimenez-group/usrmtgs/usersmtg7/amscomparisons.pdf Multiple Peaks at Integer m/z (isobaric ions) Are Commonly Seen in the HR-ToF-AMS Data http://cires1.colorado.edu/jimenez-group/usrmtgs/usersmtg8/pikatutorial.pdf Distinguish different classes of organics and inorganic species Resolution of 000 allows for unambiguous identification of isobaric ions at m/z < 100. Provides a powerful check for values in the frag list 6
HR-ToF-AMS Data Analysis Goal: apportion signal to all contributing ions, be as quantitative as possible, for as many m/z s as possible in HR-ToF-AMS mass spectra. m/z cal, peak width, peak shape are all critical for HR-MS analysis to work properly. (wiki page and Donna s tutorials) Mass Calibration Needs to be as accurate as possible Peak Width Sigma parameter from Gaussian Peak Shape Needs to be consistent Modified Gaussian http://cires1.colorado.edu/jimenez-group/usrmtgs/usersmtg8/pikatutorial.pdf HR-ToF-AMS Data Analysis Software: SQUIRREL and PIKA http://cires1.colorado.edu/jimenez-group/wiki/index.php/tof-ams_analysis_software Donna Sueper s HR-ToF- AMS Data Analysis Tutorial Videos http://cires1.colorado.edu/jimenez- group/wiki/index.php/tof- AMS_Analysis_Software#Are_tutoria ls_available.3f 7
m/z cal, peak width, peak shape are all critical for HR- MS analysis to work properly. Extra efforts are needed to do these correctly. Peak width and shape need high signal, C x H y+ and C x H y O z+ ions are usually easier to determine well, but be extra cautious if you want N-containing ions. Don t over-fit! Sometimes you have to just accept that your data is not good enough for HR analysis in PIKA Separation of Organic Ion Classes thousands of compounds C 2 H 3 O + (m/z = 43): tracer ion for less oxygenated species (e.g., carbonyls) % of total 12 10 8 6 4 O/C = 0.7, H/C = 1.38, N/C = 0.002, OM/OC = 1.88 CO 2 + (m/z = 44): tracer ion for highly oxygenated species (e.g., acids) f44: indicator for average oxidation degree C 2 H 4 O 2 + (m/z = 60): tracer ion for levoglucosan f60: indicator for BB influence 2 C x H y C x H y O 1 C x H y O 2 H y O 1 C x H y N p C x H y O z N p 0 10 30 40 0 60 70 m/z (amu) 80 90 100 110 1 UMR instrument would only resolve peak height 8
References Allan, J.D., Delia, A.E., Coe, H., Bower, K.N., Alfarra, M.R., Jimenez, J.L., Middlebrook, A.M., Drewnick, F., Onasch, T.B., Canagaratna, M.R., Jayne, J.T., Worsnop, D.R., 04. A generalised method for the extraction of chemically resolved mass spectra from Aerodyne aerosol mass spectrometer data. Journal of Aerosol Science 3, 909-922. Ng, N.L., Canagaratna, M.R., Zhang, Q., Jimenez, J.L., Tian, J., Ulbrich, I.M., Kroll, J.H., Docherty, K.S., Chhabra, P.S., Bahreini, R., Murphy, S.M., Seinfeld, J.H., Hildebrandt, L., DeCarlo, P.F., Lanz, V.A., Prevot, A.S.H., Dinar, E., Rudich, Y., Worsnop, D.R., 10. Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry. Atmos. Chem. Phys. 10, 462-4641. Zhang, Q., Alfarra, M.R., Worsnop, D.R., Allan, J.D., Coe, H., Canagaratna, M.R., Jimenez, J.L., 0. Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry. Environmental Science & Technology 39, 4938-492. DeCarlo, P.F., Kimmel, J.R., Trimborn, A., Jayne, J., Aiken, A.C., Gonin, M., Fuhrer, K., Horvath, T., Worsnop, D.R., Jimenez, J.L., 06. A Field-Deployable High-Resolution Time-of- Flight Aerosol Mass Spectrometer. Analytical Chemistry. 9