Minimizing Contamination from Plastic Labware in the Quantification of C16 and C18 Fatty Acids in Filter Samples of Atmospheric Particulate Matter and Their Utility in Apportioning Cooking Source Contribution to Urban PM2.5

Abstract

Palmitic acid (C16:0) and stearic acid (C18:0) are among the most abundant products in cooking emission, and thus could serve as potential molecular tracers in estimating the contributions of cooking emission to particulate matter (PM2.5) pollution in the atmosphere. Organic tracer analysis in filter-based samples generally involves extraction by organic solvents, followed by filtration. In these procedures, disposable plastic labware is commonly used due to convenience and as a precaution against sample-to-sample cross contamination. However, we observed contamination for both C16:0 and C18:0 fatty acids, their levels reaching 6–8 ppm in method blanks and leading to their detection in 9% and 42% of PM2.5 samples from Hong Kong, indistinguishable from the blank. We present in this work the identification of plastic syringe and plastic syringe filter disc as the contamination sources. We further demonstrated that a new method procedure using glass syringe and stainless-steel syringe filter holder offers a successful solution. The new method has reduced the contamination level from 6.6 ± 1.2 to 2.6 ± 0.9 ppm for C16:0 and from 8.9 ± 2.1 to 1.9 ± 0.8 ppm for C18:0 fatty acid. Consequently, the limit of detection (LOD) for C16:0 has decreased by 57% from 1.8 to 0.8 ppm and 56% for C18:0 fatty acid from 3.2 to 1.4 ppm. Reductions in both LOD and blank variability has allowed the increase in quantification rate of the two fatty acids in ambient samples and thereby retrieving more data for estimating the contribution of cooking emission to ambient PM2.5. With the assistance of three cooking related tracers, palmitic acid (C16:0), stearic acid (C18:0) and cholesterol, positive matrix factorization analysis of a dataset of PM2.5 samples collected from urban Hong Kong resolved a cooking emission source. The results indicate that cooking was a significant local PM2.5 source, contributing to an average of 2.2 µgC/m3 (19%) to organic carbon at a busy downtown roadside location and 1.8 µgC/m3 (15%) at a general urban site.

Studies of Labware Contamination during Lipid Extraction in Mass Spectrometry-Based Lipidome Analysis

“…Eppendorf polypropylene extracts introduced 13 primary amide contaminants and 8 fatty acid contaminants. Plastic-related contamination of palmitic acid (FA 16:0), stearic acid (FA 18:0), − oleic acid (FA 18:1), oleamide (NAH 18:1), and erucamide (NAH 22:1) ,, had been previously reported in literature. However, polypropylene or plastic-related contamination of NAH 22:2, NAH 22:0, NAH 24:1, NAH 20:1, NAH 20:0, NAH 24:0, NAH 22:3, NAH 21:1, NAH 23:1, NAH 23:0, NAH 21:0, FA 20:0, FA 18:2, FA 14:0, FA 22:1, and FA 22:0 has not been published yet, to the best of our knowledge.…”

“…Among the previously identified contaminants, 21 surfactants structurally identical with biological lipids have been discerned. These surfactants are deliberately integrated into polymers during the manufacturing process for their role as lubricants or slip agents. − They encompass primary amide lipids (also recognized as primary fatty amides) and fatty acid lipids (shorthand notation: FA). Primary amides [subclass ID: FA0801] do not have a species shorthand in the LIPID MAPS classification, nomenclature, and shorthand notation system as of September 2023 .…”

“…Plastic additives, such as antioxidants, antistatic agents, and other plasticizers, can be released into contacting fluids . Lubricants and slip additives, such as oleamide, erucamide, stearamide, myristamide, palmitamide, linoleamide, elaidamide, palmitate, and stearate, , can originate from plastics as they are necessary during the plastic manufacturing process.…”

Hourly organic tracers-based source apportionment of PM2.5 before and during the Covid-19 lockdown in suburban Shanghai, China: Insights into regional transport influences and response to urban emission reductions

“…The fifth factor (F5) shows high abundance of unsaturated and saturated fatty acids. The long straight chain unsaturated and saturated fatty acids are released or formed during the cooking process, serving as reliable markers to trace cooking emissions ( Wang et al, 2020b ; Cheng and Yu, 2020 ). The PAHs-rich factor (F6) is characterized by high abundance of two lumped PAH species (i.e., PAHs252 and PAHs276).…”

Assessing diatom-mediated fatty acids in intertidal biofilm: a new conservation concern

“…Application of direct LC analysis without derivatization can avoid the time-consuming preparative steps that risk contamination from ubiquitous fatty acids in the lab. Palmitic acid and stearic acid are fatty acids that have been found to be common laboratory contaminants in disposable plasticware used to avoid cross contamination between samples (Cheng and Yu 2020). Using glass, rather than plastic, helped to reduce the contamination and decrease the limit of Table 3 Comparison between fatty acids and naphthenic acids (Shang et al 2013) detection when studying these fatty acids.…”