Microscale spectrophotometric methods for quantification of functional groups in oxidized organic aerosol

ABSTRACT

Spectrophotometric methods developed previously to quantify the major functional groups present in oxidized organic aerosol were modified for use with sample masses typical of those collected from ambient air. In these methods, carbonyl, hydroxyl, carboxyl, and ester groups are reacted with derivatizing agents that are specific to each functional group to form strongly light absorbing derivatives, a colored peroxide solution is formed through redox chemistry, and nitrates have an inherently strong absorbance. As described here, improved detection limits are made possible by measuring absorbance using a spectrophotometer that requires only a few microliters of solution for analysis, instead of the five milliliter volume required previously when using a standard cuvette. Use of this so-called NanoPhotometer allows comparable absorbances to be obtained with much less mass by concentrating samples by more than two orders of magnitude relative to previous methods. Detection limits are approximately 0.03, 0.02, 0.3, 1, 1, and 0.07 nmoles for carbonyl, hydroxyl, carboxyl, ester, peroxide, and nitrate groups, which correspond to approximately 0.8, 0.6, 10, 40, 50, and 5 ng of each functional group. In practice, depending on the composition of functional groups, the mass required for complete analysis of moderately oxidized organic aerosol is ∼10–100 µg. The new microscale methods were shown to provide good linearity, precision, and accuracy by comparing results from the analysis of standards and aerosol formed from reaction of α-pinene and O₃ with results obtained using the previously developed macroscale methods. The evaluation demonstrates that the microscale methods can be used to quantify these six functional groups at low organic aerosol mass concentrations.

Copyright © 2016 American Association for Aerosol Research

EDITOR:

• Mark Swihart

Acknowledgments

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation (NSF).

Funding

This material is based on work supported by the National Science Foundation under Grants AGS-1219508 and AGS-1420007.