Abstract Closed microwave digestion and a high-pres- sure asher have been evaluated for wet-oxidation and ex- traction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food prod- ucts. For the high-pressure asher a combination of nitric and sulfuric acids was efficient for destruction of a range of packaging materials; for polystyrene, however, nitric acid alone was more efficient. For microwave digestion, a reagent containing nitric acid, sulfuric acid, and hydrogen peroxide was used for all materials except polystyrene. Use of the high-pressure asher resulted in the highest recover- ies of spiked lead (median 92%), cadmium (median 92%), chromium (median 97%), and mercury (median 83%). All samples were spiked before digestion with 40 μg L –1 Cd, Cr, and Pb and 8 μg L –1 Hg in solution. The use of indium as internal standard improved the accuracy of results from both ICP–MS and ICP–AES. Average recovery of the four elements from spiked packaging materials was 92 ± 14% by ICP–MS and 87 ± 15% (except for mercury) by ICP– AES. For mercury analysis by CVAAS, use of tin(II) chlo- ride as reducing agent resulted in considerably better ac- curacy than use of sodium borohydride reagent. Introduction Trace metal contamination of packaging material is a po- tential problem because the metals might migrate into the food product during storage or they might be a disposal hazard. Analytical procedures for monitoring concentra- tions of such elements in packaging materials [1, 2] are usually based on tests involving migration of elements from the material into a contact solution then analysis of the ex- tracted metals. CEN methods for paper and paper board, intended to come in contact with foodstuffs, are based on aqueous extraction followed by electrothermal atomic-ab- sorption spectrophotometry (ETAAS) for determination of Pb, Cd, and Cr and cold vapour atomic-absorption spec- trophotometry (CVAAS) for the determination of Hg. The ISO method for coatings of paints, lacquers, inks, textiles, polymers, paper, and paper board used for toys [3] is based on extraction of soluble elements under conditions which simulate the material remaining in contact with stomach acid for the period of time after swallowing (e.g. extrac- tion at 37 °C in HCl 0.07 mol L –1 for 2 h). Other publica- tions [4–9] describe the analysis of Pb, Cd, Cr, and Hg in paper packaging, paperboards, and wall-coverings after a migration test or leaching of the respective chemical species. Determination of these metals is usually performed by ETAAS and CVAAS. Another approach is to determine the total concentrations of the various elements in the pack- aging material. This usually involves acid digestion to de- stroy the matrix, and thus to liberate the elements before their analysis. A variety of procedures have been pub- lished for the analysis of plastics, papers, and paper board [10–18]. A non-destructive method, total reflection X-ray fluorescence spectroscopy [19] has also been reported re- cently for measurement of the heavy metal content of plas- tics. The aim of this work was to develop routine proce- dures suitable analysis of total lead, cadmium, chromium, and mercury in a range of packaging materials used within the food industry. The efficiency of wet-oxidation by mi- crowave digestion (MW) and use of the high-pressure asher (HPA) was compared. Results obtained by inductively coupled plasma–mass spectrometry (ICP–MS) and axial inductively coupled plasma–atomic emission spectrome- try (ICP–AES) for lead, cadmium, and chromium have been compared, as have those from ICP–MS and CVAAS for mercury. Precision, accuracy, and limits of quantifica- tion and detection data are presented for each technique. Loïc Perring · Marie-Isabelle Alonso · Daniel Andrey · Bernard Bourqui · Pascal Zbinden An evaluation of analytical techniques for determination of lead, cadmium, chromium, and mercury in food-packaging materials Fresenius J Anal Chem (2001) 370 : 76–81 © Springer-Verlag 2001 Received: 16 November 2000 / Revised: 27 December 2000 / Accepted: 3 January 2001 ORIGINAL PAPER L. Perring () · M.-I. Alonso · D. Andrey · B. Bourqui · P. Zbinden Quality and Safety Assurance Department, Nestlé Research Centre, Vers Chez les Blanc, 1000 Lausanne 26, Switzerland e-mail: loic.perring@rdls.nestle.com