Quantitative analysis of polycyclic aromatic hydrocarbons using high‐performance liquid chromatography‐photodiode array‐high‐resolution mass spectrometric detection platform coupled to electrospray and atmospheric pressure photoionization sources

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants present in atmospheric aerosols and other environmental mixtures. They are of particular air quality and human health concerns as many of them are carcinogenic toxins. They also affect absorption of solar radiation by aerosols, therefore contributing to the radiative forcing of climate. For environmental chemistry studies, it is advantageous to quantify PAH components using the same analytical technics that are commonly applied to characterize a broad range of polar analytes present in the same environmental mixtures. Liquid chromatography coupled with photodiode array and high‐resolution mass spectrometric detection (LC‐PDA‐HRMS) is a method of choice for comprehensive characterization of chemical composition and quantification of light absorption properties of individual organic compounds present in the environmental samples. However, quantification of non‐polar PAHs by this method is poorly established because of their imperfect ionization in electrospray ionization (ESI) technique. This tutorial article provides a comprehensive evaluation of the quantitative analysis of 16 priority pollutant PAHs in a standard reference material using the LC–MS platform coupled with the ESI source. Results are further corroborated by the quantitation experiments using an atmospheric pressure photoionization (APPI) method, which is more sensitive for the PAH detection. The basic concepts and step‐by‐step practical guidance for the PAHs quantitative characterization are offered based on the systematic experiments, which include (1) Evaluation effects of different acidification levels by formic acid on the (+)ESI‐MS detection of PAHs. (2) Comparison of detection limits in ESI+ versus APPI+ experiments. (3) Investigation of the PAH fragmentation patterns in MS2 experiments at different collision energies. (4) Calculation of wavelength dependent mass absorption coefficient (MACλ) of the standard mixture and its individual PAHs using LC‐PDA data. (5) Assessment of the minimal injected mass required for accurate quantification of MACλ of the standard mixture and of a multi‐component environmental sample.

Molecular Analysis of Secondary Brown Carbon Produced from the Photooxidation of Naphthalene

“…The mass absorption coefficients (MAC OM , eq ) of the LC-separated BrC components were calculated according to the formula reported in Hettiyadura et al. , where i is the notation of a BrC component and A λ i is the area of the background subtracted LC-PDA chromatogram recorded at wavelength, λ, over the time of component appearance in the LC chromatogram, Δ t i . F is the solvent flow rate in mL/min, l is the path length of the PDA cell (1 cm), and m inj is the mass loading of naph -SOA [expressed as either OM or organic carbon (OC) to calculate MAC OM or MAC OC , respectively] injected into the HPLC in nanograms.…”

“…The calculations of molecular metrics such as DBE, modified aromaticity index (AI mod ), 50 carbon oxidation state (OSc), 51,52 and logarithmic saturation mass concentration (log 10 C 0 ) (μg m −3 ) 53 are described in Supporting Information (eqs S1−S4). The mass absorption coefficients (MAC OM , eq 1) of the LCseparated BrC components were calculated according to the formula reported in Hettiyadura et al 54,55 A F l m MAC (m g ) ( AU s) (mL min ) ln (10) (cm) (ng) 60 (s min ) 10…”

Atmospheric Brown Carbon on the Tibetan Plateau: Regional Differences in Chemical Composition and Light Absorption Properties

“…Calculation of the Mass Absorption Coefficient (MAC λ ) of BrC. The total MAC λ corresponding to BrC in each sample was calculated on the basis of HPLC-PDA data sets using the equation 27,38 (10) (cm) (ng) 60(s min ) 10 where A λ (μAU s) is the area of the HPLC-PDA chromatogram at wavelength λ from 0 to 60 min, F(mL min −1 ) is the flow rate of the HPLC system, l(cm) is the path length of the PDA optical cell (1 cm), m inj (ng) is the injected mass of a sample calculated by the concentration of water-soluble organic carbon (WSOC) and injected volume, ln(10) converts the absorption coefficient from base 10 to natural log, and 10 is the combined conversion factor between different units. The A λ (μAU s) of each sample was background subtracted using the light absorption by the LC mobile phase.…”

Optical Properties of Secondary Organic Aerosol Produced by Photooxidation of Naphthalene under NOx Condition

“…However, strong light-absorbing nitroaromatics (CHON, e.g., C 6 H 5 NO 4 , C 7 H 7 NO 4 , C 7 H 5 NO 5 , C 8 H 5 NO 5 , C 8 H 5 NO 6 , C 9 H 9 NO 6 , C 10 H 9 NO 4 ) are produced when NOx is involved in SOA formation ( Figure 3 b,c), and these species contribute significantly to the absorption of the SOA (∼ 45% of the MAC at 350–450 nm for the A49 experiment, Figure S6d ). Quantitative contributions of the identified BrC chromophores to the total MAC values of the solvent-extractable BrC were calculated using the method described by Hettiyadura et al 71 The major absorbing CHO species, which contain hydroxy, carbonyl, and carboxylic functional groups, elute faster than the CHON species, which contain additional nitro groups, probably due to the low polarity of the −NO 2 group, which reduces the overall polarity of CHON compounds.…”

“…3b,c), and these species contribute significantly to the absorption of the SOA (∼ 45% of the MAC at 350−450 nm for the A49 experiment, Figure S6d). Quantitative contributions of the identified BrC chromophores to the total MAC values of the solventextractable BrC were calculated using the method described by Hettiyadura et al 71 The major absorbing CHO species, which contain hydroxy, carbonyl, and carboxylic functional groups, elute faster than the CHON species, which contain additional nitro groups, probably due to the low polarity of the −NO 2 group, which reduces the overall polarity of CHON compounds. Xie et al detected eight nitroaromatic species in the SOA produced with an initial NOx/naphthalene ratio of 3.…”