A new approach for measuring the carbon and oxygen content of atmospherically relevant compounds and mixtures

Abstract

Abstract. Due to its complexity, gas- and particle-phase organic carbon in the atmosphere is often classified by its bulk physicochemical properties. However, there is a dearth of robust, moderate-cost approaches to measure the bulk chemical composition of organic carbon in the atmosphere. This is particularly true for the degree of oxygenation, which critically affects the properties and impacts of organic carbon but for which routine measurement approaches are lacking. This gap has limited the understanding of a wide range of atmospheric components, including particulate matter, the mass of which is monitored worldwide due to its health and environmental effects but the chemical characterization of which requires relatively high capital costs and complex operation by highly trained technical personnel. In this work, we demonstrate a new approach to estimate the mass of carbon and oxygen in analytes and mixtures that relies only on robust, moderate-cost detectors designed for use with gas chromatography. Organic compounds entering a flame ionization detector were found to be converted with approximately complete efficiency to CO2, which was analyzed downstream using an infrared detector to measure the mass of carbon analyzed. The ratio of the flame ionization detector (FID) signal generated to CO2 formed (FID∕CO2) was shown to be strongly correlated (R2=0.89) to the oxygen-to-carbon ratio (O∕C) of the analyte. Furthermore, simple mixtures of analytes behaved as the weighted average of their components, indicating that this correlation extends to mixtures. These properties were also observed to correlate well with the sensitivity of the FID estimated by structure activity relationships (quantified as the relative effective carbon number). The relationships between measured FID∕CO2, analyte O∕C, and FID sensitivity allow the estimation of one property from another with <15 % error for mixtures and <20 % error for most individual analytes. The approach opens the possibility of field-deployable, autonomous measurement of the carbon and oxygen content of particulate matter using time-tested, low-maintenance detectors, though such an application would require some additional testing on complex mixtures. With some instrumental modifications, similar measurements on gas-phase species may be feasible. Moreover, the potential expansion to additional gas chromatography detectors may provide concurrent measurement of other elements (e.g., sulfur, nitrogen).

Quantification of Isomer-Resolved Iodide CIMS Sensitivity and Uncertainty Using a Voltage Scanning Approach

“…Analytes are quantified by integrating chromatographic peaks detected by the FID. Sensitivity of the FID to an oxygenated organic compound is estimated based on its elemental formula, identified by the CIMS, as described by Hurley et al (2020). In brief, FID detection of hydrocarbons provides a near-universal response per unit carbon mass, which is easily obtained by a multi-point calibration to a hydrocarbon.…”

Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

“…In brief, aerosols are collected with a sampling flow rate of 9 slpm through a nine-jet impactor with a 50 % collection cut-off point of 0.085 µm (Williams et al, 2006). The collection cell is equipped with a liquid injection port where chemical standards can be quantitatively added through an automatic liquid injection system (Isaacman et al, 2011). After a 5-15 min sample collection period, which is equivalent to 0.045-0.135 m 3 of air sampled, samples are thermally desorbed in helium to the head of the GC column by heating the cell to 300 • C at a rate of 50 • C min −1 while the GC column is held at 50 • C with ∼ 3 sccm of helium carrier gas flow.…”

“…For example, analyte 1 with a retention time of 2000 s has the most abundant sig- nals in FID while analyte 2 with a retention time of 2380 s is the largest peak in CIMS. Since FID sensitivity differs between compounds by less than a factor of two (Hurley et al, 2020), the peak area of FID approximates the relative mass of a compound in a sample matrix. However, comparing to the near-universal response of FID signals, the signals of iodide CIMS per unit mole of analytes may vary up to 5 orders of magnitude and highly depend on their enthalpies of binding with iodide (Iyer et al, 2016;Lopez-Hilfiker et al, 2016a).…”

“…While implementation of this calibration approach is complex, here we provide a proof-of-concept quantitative anal-3900 C. Bi et al: Coupled TAG-CIMS/FID for isomer-resolved chemical analysis ysis. Hurley et al (2020) demonstrated that the number of moles of an analyte can be calculated from its FID peak area based on a calibration response factor to hydrocarbons, with a correction for oxygenation based on the chemical formula identified by CIMS (specifically, the FID response per carbon atom relative to maximum = −0.54 O / C + 0.99, where O / C is the oxygen-to-carbon ratio in the target analyte; Hurley et al, 2020). By applying the calibration approach for the two analytes in the example, analyte 1 (i.e., C 10 H 14 O 3 ) is found to be roughly 4 times more abundant than analyte 2 (i.e., C 9 H 14 O 3 ) on a per mole basis, but appear substantially lower in its CIMS signal due to a 10 times lower sensitivity.…”

Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

“…For example, Analyte 1 (C10H14IO3 -) with a retention time of 2000 seconds has the most abundant signals in FID while Analyte 2 (C8H10IO4 -) with a retention time of 2380 seconds is the largest peak in CIMS. Since FID sensitivity differs between compounds by less than a factor of two (Hurley et al, 2020), the peak area of FID approximates the relative mass of a compound in a sample matrix. However, comparing to the near-universal response of FID signals, the signals of iodide CIMS per unit mole of analytes may vary up to five orders of magnitudes and highly depend on their enthalpies of binding with iodide (Iyer et al, 2016;Lopez-Hilfiker et al, 2016a).…”