SPME for the analysis of bisphenol A

Bisphenol A (BPA) is commonly used for food packaging applications such as polycarbonate bottles and the linings of metal cans used for soups, juices, etc. It is a suspected endocrine disruptor an therefore, low-level, long-term exposure as a result of migration into food from packaging materials is a concern. The use of BPA in food contact applications is regulated by the Food and Drug Administration (FDA), and in 2013 was prohibited for use in the packaging materials of infant formula. For other food contact applications, margins of safety were published by FDA as “NOAEL”, which stands for “no observed adverse effect level”. This NOAEL was set at 5 mg/kg body weight per day, which is well above the estimated dietary intake. Similarly, tolerable daily intake or “TDI” was set by the European Union (EU) at 4 μg/kg body weight per day. While exposure to BPA through diet is thought to be low, testing continues in order to assess its migration into food from can and lid linings, plastic containers, etc. In the case of the EU, the specific migration limit (SML) for BPA from packaging into food has been amended in Sept 2018 to 0.05 mg/kg (formerly 0.6 mg/kg) food. In case of contact materials for food products with intended use for infants or young children, no BPA migration from coatings or varnishes is permitted at all.

Extraction methods for determination of BPA in food include both solvent extraction (SE) and solid phase extraction (SPE), with the latter more commonly used with liquid samples and the former for solid samples. Analysis can be done by either LC or GC, and both have been used throughout the literature. Solid phase microextraction (SPME) has been used for the determination of BPA in water, but has not been widely used for this application in food matrices due to sensitivity and fiber ruggedness issues associated with exposure to matrix components such as fats and proteins.

Merck KGaA has published an application that revisits the use of SPME to develop a quick, easy, and sensitive method for analysis of BPA in a variety of food products. The issues mentioned previously related to food matrices and SPME were addressed through the use of an overcoated (OC) divinylbenzene (DVB) fiber. The overcoating, which consists of polydimethylsiloxane (PDMS), protects the DVB layer from contamination and increases the physical robustness of the fiber.

The article describes an immersion SPME-GC-MS/MS method using an overcoated PDMS/DVB fiber was developed for the low level analysis of BPA from various food products. Method linearity from different matrices - a fruit flavored beverage, canned pumpkin, pureed carrot baby food, and cream of chicken soup - was in the range of 0.9871 (carrots) to 0.9995 (beverage). Method accuracy and reproducibility at a 10 ppb spiking level was between 80-110%, with RSD/RPD values of <15%. Durability testing showed the OC fiber to be more physically robust, with more consistent response compared to a standard fiber; the SPME method had only a few steps and was easy to automate. In addition, it was highly sensitive, and when combined with GC-MS/MS, provided the selectivity necessary to be used with different matrices.