Method of test and survey of caprolactam migration into foods packaged in nylon-6

Abstract

An analytical method for the determination of the nylon-6 monomer caprolactam in foods is described. The foodstuff was extracted with ethanol : water (1:2) containing capryllactam as internal standard and the extract was defatted using hexane. The extract was analysed by liquid chromatography coupled with mass spectrometry. The test method was calibrated down to 0.7 mg kg⁻¹. The repeatability of the method was good, with a relative standard deviation of 9% at the 15 mg kg⁻¹ level. The method was demonstrated to be accurate in an independent external check sample exercise. The new method was applied to the analysis of 50 retail foodstuffs packaged in nylon-6. Caprolactam was detected and confirmed in nine of the 50 food samples, in the range 2.8–13 mg kg⁻¹. The presence of caprolactam was indicated in a further 15 samples, in the range 0.8–11 mg kg⁻¹, but these samples did not meet all of the five confirmation criteria applied. All migration levels (both confirmed and unconfirmed) were below the European specific migration limit for caprolactam, which is 15 mg kg⁻¹. The average migration for all 50 samples, setting non-detectables at half the limit of detection, was 2.6 mg kg⁻¹ with a standard deviation of 3.1 mg kg⁻¹ (n = 50). All samples found to contain detectable levels of caprolactam migration were for applications involving heating the food in the packaging. They were packs of, for example, sausage meat for which the food would have been heat processed in the nylon casing, or they were nylon pouches for heating foods by boiling, microwaving or roasting.

Keywords:

• caprolactam
• liquid chromatography-mass spectrometry (LC-MS)
• analysis
• migration
• nylon-6
• food
• packaging
• monomer

Acknowledgements

The authors thank Pilar Gonzalez, Department of Chemistry, University of Leeds, for supplying the check samples for blind analysis. They gratefully acknowledge support from the UK Food Standards Agency (FSA) for funding the work. The statements and conclusions are the responsibility of the authors alone and should not be taken to represent the opinion of the FSA.