Meaning
Analytical chromatography challenges occur when low molecular weight polymers co-elute with target analytes, masking their presence or distorting quantitative results during extractable testing. Polyolefin wax interference is a common problem when analyzing polyethylene and polypropylene extracts for mineral oil hydrocarbons. These waxes are chemically similar to mineral oils and are extracted by the same solvents.
Analytical Extraction
Solvents used to extract contaminants from polyolefins also dissolve the wax fraction, which consists of oligomers with various chain lengths. These oligomers produce a large hump in the chromatogram that overlaps with the hydrocarbon peaks of interest. This overlap makes accurate integration and quantification impossible without additional cleanup steps.
Chemists must choose extraction temperatures carefully to minimize the dissolution of these high-molecular-weight waxes while still ensuring the complete recovery of the target contaminants.
Separation Technique
Pre-fractionation or specialized cleanup columns are used to remove the interfering waxes before gas chromatography analysis. This step selectively retains the low molecular weight polymer while allowing the target analytes to pass through. Implementing these techniques increases the runtime and cost of the analysis but is necessary for reliable data.
Processing Impact
Inaccurate testing results caused by this interference can lead to the false rejection of compliant recycled resin batches. Moulders rely on accurate data to ensure their materials meet regulatory food-contact limits. Correctly identifying and mitigating the interference ensures that only genuinely contaminated materials are diverted from the production line.
