Philipp Weller, Martina Herrnreiter and Alfred Donaubauer NQAC Weiding/Nestlé Deutschland AG, Frankfurt Am Main, Germany.

Epoxidized soybean oil (ESBO) is widely used in the polymer industry, among other epoxidized vegetable and seed oils.¹ These epoxides of fatty acids are known to be highly effective costabilizers for polyvinyl chloride (PVC) and other polymers.^2,3 Such stabilizers are mandatory when using PVC because of its poor thermal stability. As a result of its epoxide moieties, ESBO can function as a scavenger for hydrochloric acid,⁴ which is released by PVC when thermal stress is applied and also as it ages.

ESBO is used as a plasticizer in gaskets in metal caps.³ Glass jars are often used to contain baby food and are usually sealed by metal caps coated with gaskets, consisting mainly of PVC with high amounts of plasticizers.⁴ Consequently, these gaskets come into direct contact with the food, particularly during sterilization and, afterwards, during storage. The stabilizers and plasticizers used here may constitute as much as 40% of the overall polymer's weight. Most of the additive formulations used for the production of plasticized PVC gaskets contain ESBO in various concentrations.³ Therefore, there is a potential for the migration of ESBO into foodstuffs (depending on the fat content).

Most commonly, ESBO is determined by GC after solvent extraction of the lipids. Since triacylglycerides themselves are not suitable for GC analysis, the next step is usually the derivatization to fatty acid methyl esters (FAMEs).^8–10 The fatty acids usually found in ESBO are composed of around 23% epoxidized oleic acid, 54% epoxidized linoleic acid and 8% epoxidized linolenic acid; the rest distributes mainly on palmitic and stearic acid.^2,5

In 1988, Castle et al. published a method, using GC–MS to determine the ESBO content of food.¹¹ The procedure is based on the transmethylation of the triacylglycerides by sodium methoxide and, subsequently, the derivatization of the resulting fatty acid methyl esters using boron trifluoride dietherate to form 1,3-dioxolanes. The target molecule is the diepoxy linoleic acid, which after the derivatization shows two well-separated peaks with almost identical mass spectra, which is believed to be the result of the formation of two stereoisomers. The exact structure of both isomers is actually not known. The internal standard (IS), cis,cis-11,14-diepoxyeicosanoate ethyl ester, shows the same behaviour. The structures and the corresponding mass spectra are shown in Figure 1. ESBO is quantified via the derivatives of the epoxidized linoleic acid by referring to the derivatives of the IS.

Figure 1

However, this method was not developed for the high sample numbers encountered in routine analysis. Because there is no further clean up of the extracts there is a heavy strain on the analytical equipment, which results in extensive downtimes caused by the need for cleaning. This is a critical issue in terms of cost and time in a routine laboratory.

Consequently, our focus was to develop a rugged, routine method with high selectivity and throughput that would also reduce the strain on the analytical equipment. This would be achieved by developing an appropriate clean-up step before analysis.

One common clean-up technique is gel permeation or size exclusion chromatography (GPC or SEC), which can easily be combined with GC–MS. Today, GPC is standard equipment in most routine laboratories and is highly automatable and simple to use, which are ideal prerequisites for the routine analysis of ESBO in baby food.