Sample Preparation
Alkaline hydrolysis breaks down complex ester linkages in natural fats and synthetic wax additives prior to chromatographic analysis. Performing saponification clean up converts esterified lipids in paperboard extracts into water-soluble glycerol salts and fatty acid soaps. Potassium hydroxide dissolved in ethanol reacts with ester bonds at elevated temperatures under reflux conditions.
This chemical digestion step releases trapped non-saponifiable hydrocarbons for subsequent solvent extraction.
Lipid Removal
Paperboard substrates manufactured from primary wood pulp or recycled food packaging contain high levels of natural wood resins and synthetic waxes. Unmodified extracts foul chromatographic injection ports and co-elute with mineral oil saturated and aromatic hydrocarbons. Applying saponification clean up converts interfering triglycerides and resin acid esters into hydrophilic carboxylate salts that remain in the aqueous phase during liquid-liquid extraction.
Non-polar mineral oil hydrocarbons partition into the organic solvent phase, yielding a clean extract suitable for silica gel fractionation. Incomplete saponification leaves residual esters that damage high-performance liquid chromatography columns and distort aromatic hydrocarbon quantification. Reagent concentration and reaction time must be controlled to prevent breakdown of target mineral oil fractions.
Extract Purification
Phase separation following alkaline digestion isolates the non-saponifiable unsaponifiable fraction containing target hydrocarbons. Utilizing saponification clean up simplifies baseline integration by eliminating massive lipid interference peaks in gas chromatography. Clean extracts reduce instrument maintenance frequency and improve internal standard recovery rates.
Verification of complete ester digestion ensures accurate migration measurements for food packaging compliance.
