Aqueous Extraction Method
Standardized extraction of water-soluble components from paper and board materials intended for contact with foodstuffs occurs under prolonged exposure to boiling water. The en 647 hot water extract protocol prescribes preparing five grams of paper cut into small pieces, immersing the test specimens in two hundred and fifty millilitres of boiling distilled or deionised water, and holding the mixture in a reflux flask at boiling point for two hours. The procedure targets food contact applications where packaging encounters aqueous liquids at elevated temperatures, such as filter papers, bake-in trays, hot beverage cups and cooking pouches.
The protocol terminates at the production of the aqueous filtrate, serving as a sample preparation standard rather than an analytical determination of specific chemical entities.
Filtrate Preparation Procedure
Uniform disintegration of dry paper ensures that hot solvent reaches interior cellulose fibrils and chemical additives distributed throughout the sheet. The en 647 hot water extract method requires pure grade water with an electrical conductivity below zero point five millisiemens per metre to avoid baseline contamination of analytical equipment. Heating under reflux maintains a constant extraction volume, preventing the concentration of non-volatile substances during the thermal cycle.
Once the two-hour reflux cycle concludes, filtration through a clean glass fritted filter or ashless paper filter separates the fibrous residue from the leachate. The resulting aqueous solution holds extracted starch residues, sizing agents, wet-strength resin derivatives and water-soluble mineral salts.
Analytical Boundary Conditions
Cold liquid contact testing relies on room temperature extraction protocols such as EN 645, making this boiling water method inapplicable for refrigerated dry-pack cartons. High temperatures promote the hydrolysis of bound retention aids and cross-linked resins that remain inert during ambient testing, yielding higher concentrations of extractable matter. The method does not apply to non-porous barrier films or metal foils unless they form part of a composite paperboard structure where paper edges or faces remain exposed to water.
Analytical detection limits are governed by the instrument methods applied downstream to the filtrate, which include spectrophotometry, liquid chromatography and mass spectrometry. Quantitative yields depend directly on the basis weight, porosity and fibre preparation of the original test specimen.
