Closed microwave digestion and a high-pressure asher have been evaluated for wet-oxidation and extraction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food products. 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 recoveries of spiked lead (median 92%), cadmium (median 92%), chromium (median 97%), and mercury (median 83%). All samples were spiked before digestion with 40 microg L(-1) Cd, Cr, and Pb and 8 microg 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) chloride as reducing agent resulted in considerably better accuracy than use of sodium borohydride reagent.

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Tin is considered to be a priority contaminant by the Codex Alimentarius Commission. Tin can enter foods either from natural sources, environmental pollution, packaging material or pesticides. Higher concentrations are found in processed food and canned foods. Dissolution of the tinplate depends on the of food matrix, acidity, presence of oxidising reagents (anthocyanin, nitrate, iron and copper) presence of air (oxygen) in the headspace, time and storage temperature. To reduce corrosion and dissolution of tin, nowadays cans are usually lacquered, which gives a marked reduction of tin migration into the food product. Due to the lack of modern validated published methods for food products, an ICP-AES (Inductively coupled plasma-atomic emission spectroscopy) method has been developed and evaluated. This technique is available in many laboratories in the food industry and is more sensitive than atomic absorption. Conditions of sample preparation and spectroscopic parameters for tin measurement by axial ICP-AES were investigated for their ruggedness. Two methods of preparation involving high-pressure ashing or microwave digestion in volumetric flasks were evaluated. They gave complete recovery of tin with similar accuracy and precision. Recoveries of tin from spiked products with two levels of tin were in the range 99+/-5%. Robust relative repeatabilities and intermediate reproducibilities were <5% for different food matrices containing >30 mg/kg of tin. Internal standard correction (indium or strontium) did not improve the method performance. Three emission lines for tin were tested (189.927, 283.998 and 235.485 nm) but only 189.927 nm was found to be robust enough with respect to interferences, especially at low tin concentrations. The LOQ (limit of quantification) was around 0.8 mg/kg at 189.927 nm. A survey of tin content in a range of canned foods is given.

An ED-XRF method for the rapid determination of a series of analytes (phosphorus, sulfur, chlorine, potassium, calcium, iron, zinc) in milk-based products has been developed and validated. The investigated samples were commercial products obtained from various parts of the world. Reference values measured by inductively-coupled plasma-optical emission spectroscopy and by potentiometry for chloride were used to calibrate the ED-XRF. Calibrations were established with 30 samples, and validation was made using a second set of 30 samples. An evaluation of this alternative method was done by comparison with data from the reference methods. Pellets of 4 g were prepared under 2 tons of pressure. For each sample, 3 pellets were prepared and analyzed. Limits of quantification and repeatabilities were evaluated for the described analytes.

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