Meaning
A continuous chemical modification step coupled directly to chromatographic separation to convert double bonds in unsaturated hydrocarbons into polar oxirane rings. Performing online epoxidation during mineral oil aromatic hydrocarbon analysis eliminates polyolefin oligomeric background that co-elutes with aromatic fractions. Peracetic acid or meta-chloroperoxybenzoic acid reacts rapidly with olefinic double bonds in the mobile phase, shifting their retention times away from target aromatic signals.
This automated pre-column reaction improves sample throughput and measurement reliability when testing polyolefin packaging materials.
Olefin Removal
Saturated and aromatic mineral hydrocarbons pass through the reaction coil unchanged, while synthetic polyolefin oligomers containing double bonds undergo rapid conversion into polar epoxides. Integrating online epoxidation into the chromatographic flow path prevents unreacted polyolefin molecules from entering the secondary column where they would otherwise overlap with toxic aromatic contaminants. Automated reagent dosing maintains consistent stoichiometric excess, ensuring complete conversion without manual sample preparation steps.
Reaction Kinetics
Temperature control and coil volume dictate the residence time required for complete conversion of mono-olefins and dienes. Insufficient reaction time leaves unreacted polyolefin background in the aromatic fraction, causing false positive quantification. Excess reaction time or aggressive acid concentrations can degrade sensitive aromatic target analytes.
Interference Reduction
Interference from recycled polyethylene and polypropylene oligomers presents a primary obstacle in food contact compliance testing. Converting these interfering species into highly polar compounds retains them on polar cleanup beds or shifts them to later retention windows, leaving clean aromatic hydrocarbon baselines.
