A03037: LC-MS method development for the screening of non-volatile and polar compounds present in paper and board and plastic food contact materials.

Study Duration: April 2002 to August 2006

Contractor: Central Science Laboratory

The identification and measurement of non-volatile and polar substances is a relative weakness in the analytical chemist's armoury. Substances present in food packaging materials can originate from a number of sources:

• Known ingredients used to make the material, for example monomers and additives in plastics, or chemicals used in paper-making.
• Known or unknown isomers, impurities and transformation products of these known ingredients.
• Chemicals used to convert or fabricate the paper or plastic into its finished form; for example, inks and adhesives.
• Unknown contaminants, especially those in the feedstock if paper or plastics are recycled.

These substances may be important for consumer safety and improved methods for their analysis are needed. The development of analytical methods, for example within British Standards/Comit
de Europ
en Normalisation (BSi/CEN), has naturally concentrated on the first of these 4 sources.

It is important to have the means to identify and quantify as wide a range of potential migrants as possible. This facility has been provided for several years now for low molecular weight substances that are volatile, by using GC-MS (gas chromatography coupled to mass spectrometry) instruments that are found in most laboratories. However, GC-MS is poor for the analysis of substances, which are non-volatile due to their high molecular weight and/or polarity. Derivatisation techniques to improve volatility for GC-MS must make some assumptions on the functional groups that the 'unknown' may contain and so can be rather hit-or-miss. Advances in LC-MS (liquid chromatography coupled to mass spectrometry) techniques have led to a rapid increase in its use for non-volatile and polar compounds, but the transfer of established LC methods to LC-MS is not always straightforward in terms of mobile phase compatibility. The consequence is that, to date, LC-MS has provided relatively little information on the polar and non-volatile substances that may migrate from paper and plastics.

The capabilities of LC-MS methods have been explored for the analysis of polar and non-volatile substances that are present in food contact plastics, paper and coatings and may be possible chemical migrants to foodstuffs. Targeted compounds included: polyolefin additives; polyamide monomers and oligomers; polar substances: acids, glycols and diols; styrene monomer and oligomers; polyvinyl chloride additives; primary aromatic amines; inks and coatings chemicals; fluorescent whitening agents; melamine; biocides; and greaseproofing agents.

The approach adopted was two-fold:

• To develop LC-MS methods using atmospheric pressure ionisation techniques (LC-APcI-MS) for the determination of a suite of 'difficult' compounds at low detection levels. These methods were then modified to encompass the alternative ionisation technique of electrospray ionisation (LC-ESI-MS) and a selection of methods were also extended to include tandem MS (LC-MS/MS).
• To apply the methods to mixtures obtained as the total migrate or extracts from food contact paper and plastics. This would give information on the robustness of the methods in terms of potential interferences and their capability towards identifying uncharacterised, 'unknown' migrates.

Existing LC methods available from the literature and considered to be likely candidates for extension onto LC with an MS detector, were evaluated, modified and then transferred onto an LC-MS. Using flow injection analysis (i.e. with no chromatography) solutions of each substance were examined using a variety of ionisation modes and conditions, to identify the major ions that could be used for monitoring purposes. Both positive and negative ionisation modes were explored with different instrument settings. Having selected the best analytical conditions, performance characteristics of limit of detection, limit of quantitation and repeatability were established.

Packaging materials were subjected either to migration testing using food simulants or extraction testing using solvents. The total migrate (overall migration) or the total extractables were determined gravimetrically and then this residue was redissolved and analysed by LC-MS for the substances of interest.

For all the different types of packaging material, the targeted substances were detectable at only low levels relative to the total migrate/extractate and so there was a large fraction of chemicals that was not identified. Size exclusion chromatography was used on paper samples to isolate the fraction below molecular weight 1,000 Daltons, thought to be the toxicologically-relevant fraction. This proved limited in scope and needs further development using alternative solvent systems.

This work has shown that for targeted substances, LC-MS can be used successfully to test for migration from packaging materials. The technique is capable of good sensitivity and has the selectivity needed to ensure that the correct substance is monitored and confirmed. A suite of analytical methods and spectra has been established that deals directly with many important food packaging materials and substances. However, for low or medium-mass-resolution quadropole instruments, neither LC-MS nor LC MS/MS are particularly well suited for exploratory work and the identification of �unknowns�. This project has advanced understanding of the possibilities and limitations of LC-MS analysis and has produced several useful methods. These methods and the understanding obtained and reported should help inform LC-MS users in the future development of new methods for food packaging migrants.

The final report is available from the Agency's Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk