Potential Matrix Effects in Iodometry Determination of Peroxides Induced by Olefins

Abstract

Peroxides (H 2 O 2 , ROOR, and ROOH) are an important reaction intermediate involved in a number of natural processes, including atmospheric autoxidation and lipid peroxidation in oils and animal tissues. Iodometry is an established spectroscopic technique that has been widely used to quantify total peroxide concentration in food, indoor, and outdoor samples. Iodometry provides selectivity toward peroxides through a quantitative reaction between I − and peroxides to form I 3 − via a molecular iodine (I 2 ) intermediate. However, equilibrium changes caused by a potential interaction between olefinic species and I 2 can suppress I 3 − formation, thereby underestimating peroxide concentration. For the first time in the current study, this unrecognized interference posed by olefins (OEs) is systematically investigated to gauge its effects on the accuracy of iodometry. A number of model molecules were investigated. The interference was observed to be unique to OEs, but universally affecting different peroxide species such as H 2 O 2 , tert-butyl hydroperoxide, and aerosol-bound peroxides. A simple kinetic box model was built to explain this chemistry. The measured rate constant for 3-octenoic acid was found to be 0.84 ± 0.02 M −1 s −1 . Overall, our results show matrix effects induced by OEs can underestimate peroxide concentration determined by iodometry for edible oils, indoor environments, and animal fat, but absent in most of the atmospheric samples. Nonetheless, our results point out the importance of this interfering chemistry in matrices enriched with OEs.

Organic Peroxides in Aerosol: Key Reactive Intermediates for Multiphase Processes in the Atmosphere

“…As indicated in Figure , most of the PO measurement assays (e.g., the KI, TPP, and DCFH methods) are suitable for bulk PO quantification only, with uncertainties arising from different sample preparation procedures across different laboratory studies. Recently, a potential matrix effect in the KI assay has been reported that underestimation of the peroxide content could occur with the interference from olefins (structurally dependent) in the system . Although the interference from alkenes is likely to be unimportant because of their low sensitivity and low typical concentrations in organic aerosol, such findings emphasize a careful interpretation of the KI-measured PO content in olefin-rich systems.…”

“…Recently, a potential matrix effect in the KI assay has been reported that underestimation of the peroxide content could occur with the interference from olefins (structurally dependent) in the system. 294 Although the interference from alkenes is likely to be unimportant because of their low sensitivity and low typical concentrations in organic aerosol, such findings emphasize a careful interpretation of the KI-measured PO content in olefin-rich systems. Additionally, some of the assays may be more sensitive to specific peroxides than to others, and therefore care must be taken in interpreting the PO quantification results.…”

“…Other factors apart from the SOA formation conditions might also contribute to the wide range of PO contents in SOA detected among different studies, such as different sample collection periods, extraction methods, matrix effects, and incubation durations. 197,294 A standardized protocol for bulk PO quantification is highly needed to minimize this uncertainty and facilitate comparison across different studies.…”

“…However, such an assumption has large uncertainties given that different SOA compounds may have different molecular weights and that some peroxides such as HOMs formed from autoxidation together with the ones formed from atmospheric aging processes may contain multiple peroxide functional groups, especially for more complex ambient samples. Other factors apart from the SOA formation conditions might also contribute to the wide range of PO contents in SOA detected among different studies, such as different sample collection periods, extraction methods, matrix effects, and incubation durations. , A standardized protocol for bulk PO quantification is highly needed to minimize this uncertainty and facilitate comparison across different studies.…”

Analytical methodologies for oxidized organic compounds in the atmosphere

“…Organic peroxides are strong oxidants which have been utilized in the analysis of peroxides. 158 The iodometric reactions have good specificity for peroxides, and the reactions are fast enough for quantitative analysis applications, although the substituents attached to the peroxide groups have an effect on the speed of the reaction. For example, a tert -butyl group in the molecule has been demonstrated to slow down the reaction as the group causes steric hindrance and possibly an inductive effect that stabilizes the peroxide group.…”