Validation of a Spectroscopic Quantification Method for Total Carbonyls and Small Organic Acids in Aerosols Relevant to Indoor and Outdoor Environments

Abstract

Carbonyls and small organic acids are ubiquitous in indoor and outdoor atmospheres; carbonyls also have significant health implications. In this study, we validate a rapid, simple, and cost-effective method for carbonyl and small organic acids quantification by ultraviolet–visible (UV–vis) spectroscopy detection after derivatizing the C═O moiety with 2,4-dinitrophenylhydrazine (DNPH). The spectroscopic method is benchmarked against accurate mass speciation by using high-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS). Complex natural mixtures relevant to indoor and outdoor air quality were examined: electronic (e-) cigarette aerosols from nicotine and cannabinoid sources, woodsmoke aerosols, and secondary organic aerosols from limonene ozonolysis. The spectroscopy method measured the UV–vis absorption of quinoidal ions, formed from DNPH hydrazones in alkaline solution, at 530 nm (A₅₃₀). A significant correlation was established between the two methods across a range of aerosol mass and chemical compositions tested, resulting in a recommended calibration factor (CF) of ∼5.16–5.34 × 10^–5 (M cm), where C_carbonyls (M) = A₅₃₀ × CF (M cm) × path length^–1 (cm^–1). The calibration factors, determined via two approaches─(1) by measuring the effective molar absorptivity of quinoidal ions produced from eight carbonyl-DNPH and acid-DNPH calibration standards, and (2) empirically from the correlation data without assumptions, were in good agreement with one another. The simple UV–vis spectroscopic method was a robust total carbonyl quantification method for multiple aerosol systems of environmental interest, which has utility in functional group apportionment, teaching laboratories, student projects, and preliminary screenings of carbonyl-related toxicity prior to more-detailed analyses.