Compliance testing of food contact materials     EU    FDA      

EU testing         Introduction    simulants&conditions    overall migration    specific migration    residual content    other testing  

Residual content testing

Restrictions for the residual amount of a component, instead of a specific migration limit, are set by the legislator in cases where specific migration of a component is difficult to obtain (for example because the component is very volatile) or impossible to determine directly (for example if the component is very reactive and would react with the food simulant). There are two ways to determine the residual content:

• by worst-case calculation

• by analytical determination

• calculation

If the amount of a component is already known to be so  small that the residual content limit is not exceeded, this is sufficient. This can be  calculated using already available information like ingredient specification, the amount of chemical added etc. One consequence  is that this worst-case calculation is not possible for monomers, but only for additives and processing aids. In real-life this approach could be used in rare cases only and an analytical determination is the method most commonly used.

Analytical determination of residual content

If a calculation is not possible or the value calculated is larger than the limit, the actual residual content has to be determined. Before the amount can be determined using suitable analytical equipment, the residual components have to be released from the food contact material. This can be done using several methods:

• Exhaustive extraction of the analyte using soxhlet or reflux. This method can be performed for non-volatile components. Thin samples like films can be extracted directly. Thicker materials need to be reduced in size using methods like cryogenic grinding of the material. The solvent used to extract samples can be analyzed using suitable analytical equipment.
• Dissolving the polymer using a good solvent and then precipitation of the polymer using a poor solvent (like methanol) for the polymer. Care should be taken that the analyte is not precipitated or included in the polymer. After removing of the polymer, the solvent can be analyzed using suitable analytical equipment.
• Dissolving the polymer in a good solvent, with a high boiling point, in a headspace vial. The analyte can be determined directly using GC with headspace sampling and injection. The main advantage is that no loss of volatiles can occur. However attention should be paid to matrix effects that can occur for presence of the polymer in the solvent, which may result in another equilibrium of the solvent/vapor distribution of the analyte.
• If the residual content of an element has to be determined the sample should be dissolved using a suitably aggressive solvent, followed by determination. using analytical equipment like ICP-MS or AAS .

Another source of analytical methods is on the website of JRC.

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