Applications of high-resolution electrospray ionization mass spectrometry to
measurements of average oxygen to carbon ratios in secondary organic
Adam P. Bateman,
a Julia Laskin,
b and Alexander Laskin,
c Sergey A. Nizkorodov
a Department of Chemistry, University of California, Irvine, Irvine, California 92617, USA.
b Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland,
c Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,
* Corresponding author: Sergey Nizkorodov Tel: +1-949-824-1262
Number of ESI mass spectra collected for each sample for each ESI mode. The same number
of ESI mass spectra were collected at each dilution for Mixtures A – F.
Adjusted parameters used for the determination of O/C ratio in the Analytical Procedure for
Elemental Separation (APES) from HR-AMS-ToF datThe ratios of ions were obtained from single
runs, rather than an average over the entire sampling time, and verified at various times throughout the
reaction period. A relative ionization efficiency (R.I.E.) for the HR-AMS-ToF data of 1.0 was used for
water and R.I.E. of 1.4 was used for organics.
(H2O+)org:(CO2 )org (H2O+)org:(OH+)org:(O+)org
The relative ESI sensitivity of each standard for each dilution averaged across all mixtures for
each ionization mode. Each compound’s ESI sensitivity has been scaled relative to (+) mode cis-
pinonic acid. The ratios of (+) mode sensitivities to (-) mode sensitivities are also listed. Table S1
provides evidence for significant matrix effects. For example, in the (+) mode, succinic acid and DL-
malic acid are only observed at the lowest concentration level, while citric acid only appears in the mass
spectra corresponding to the highest concentration. All compounds are detectable in the (-) mode at all
Compounds used in analysis of solution O/C using ESI-MS are tabulated with corresponding
structures, molecular formulas, o/c ratios, and calculated log P values, experimental log P values are listed
in parentheses were available. Prediction of log P was performed using ACD/ChemSketch Freeware
version 12.01 (Advanced Chemical Development Inc., Toronto, Canada). Experimentally measured
values of log P where used if they were available, and they agreed well with the predicted values.
Previously identified compounds in limonene SOA using GC-are tabulated with
corresponding structures, molecular formulas, o/c ratios, and calculated log P values. Limononaldehyde
(C10H16O2) was not detected in the negative ion mode, therefore it was not included in Figure 3.
Compounds with the same elemental formulae (C9H14O3, C10H16O3, and C9H14O4) could not be
distinguished in the HR ESI-MS, therefore the average log P value was used in Figure 4.
O/C values estimated for HR ESI-MS dataset obtained from the dark ozonolysis of limonene
The error has been calculated based on multiple samples and ES ionization efficiencies and propagated
O/C values estimated for HR ESI-MS dataset obtained from the dark ozonolysis of isoprene
Also listed are O/C values measured from online ToF-AMS of the chamber aerosol.
Average relative ionization efficiency factors scaled to (+) mode pinonic acid plotted against
each compound’s o/c ratio for (+) and (-) mode. As this figure demonstrates, there is no obvious
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