HPLC: Continuing to Answer Challenges to Food and Drug Safety

Jan 01, 2010


Michael Swartz
Bisphenol A (2,2'-bis[4-hydroxyphenyl]propane), or BPA, is a key industrial chemical used to make polycarbonate plastic and epoxy resins and is used to prevent food contamination in canned goods and other food packaging. BPA can be released from these materials and can induce adverse effects in humans including hormonal responses, because it mimics estrogen. BPA is consistently in the news as mothers worry about it leaching from their baby bottles and hikers from their water bottles. Regulatory bodies like the FDA and county, state, and national legislatures are grappling with outright bans, or the existence of true causal relationships and effects and the BPA level at which the effects gain significance.

In early 2008, unusual reactions to heparin, a highly sulfated glycosaminoglycan widely used as an injectable anticoagulant, prompted a recall of the drug product later found to be adulterated. In another case of adulteration dating back to 2007, melamine added to food products to increase the apparent protein content was found to cause severe health issues.

In two of these three cases, high performance liquid chromatography (HPLC) played a significant role in discovery, and in all three cases, HPLC continues to play a role in subsequent monitoring and analysis. In this month's column, I'll discuss these three unique applications of HPLC, and how HPLC technology has helped to answer the challenges presented.

BPA: From Baby Bottles to Minestrone


Figure 1
BPA (Figure 1a) was first synthesized over 100 years ago and has been in commerce for more than 50 years (1). It is used in the synthesis of polyesters, polysulfones, and polyether ketones as an antioxidant in some plasticizers, and as a polymerization inhibitor in PVC. It is a key monomer in production of polycarbonate plastic and epoxy resins, and it is used in consumer products as diverse as baby and sport water bottles, sports equipment, medical and dental devices, bicycle helmets, lenses, household electronics, and CDs and DVDs. It is also used as a fungicide, in beverage and food can coatings, and is a precursor to the flame retardant tetra-bromo-bisphenol A. Plastic products and epoxy resins made from BPA monomers are classified as Type 7 (sometimes referred to as the catch-all "other" class) plastics, and BPA was approved by the FDA for use in food contact materials in the 1960s.


Figure 2
All good, right? Not so fast. In recent years, new concerns have been raised about BPAs safety. As long ago as 1938, BPA was discovered to be an artificial estrogen, and it has long been considered as an endocrine disruptor (2–4). In September 2008, the National Toxicology Program of NIH determined that BPA might pose risks to human development, raising concerns for early puberty, prostate effects, breast cancer, and behavioral impacts from early-life exposures (5). In the interim, conservative estimates of upwards of 100 peer-reviewed papers have been published studying the affects of BPA from a variety of sources, including both food-related and environmental (1,6–9). As a result, the EPA (10) and the FDA (11) have each weighed in on the topic, and the FDA, as a result of a recent assessment, released a draft report finding that BPA remains safe in food contact materials. This position is being re-assessed, however, as a subcommittee of FDA's science board recently raised questions about whether FDA's review had adequately considered the most recent scientific information available (12). That report is due out by the end of 2009, so by the time you read this, additional guidance on BPA exposure might be available from the FDA. Additional information about BPA is also available from the FDA website (13).


Table I: BPA sample preparation
Both HPLC and gas chromatography (GC) have been used for the analysis of BPA, with a variety of detectors including ultraviolet (UV), fluorescence, and mass spectrometry (MS). HPLC generally is preferred over GC for better accuracy and precision and faster run times (14). Reversed-phase HPLC using C18 columns and buffered (for example, 0.1% formic acid) or unbuffered aqueous–organic mobile phases containing either methanol or acetonitrile have been used. The choice of detector depends upon the desired level of detection (often into the low parts-per-billion [ppb] range), accuracy and precision, and the specificity needed given the sample matrix. For many analyses, UV or fluorescence detectors might suffice, particularly because sample preparation as outlined in Table I often results in a 1–2 orders of magnitude preconcentration (14,15). Assays with UV and fluorescence detectors typically provide the best accuracy and precision, however, MS or MS-MS detection using electrospray ionization (ESI) in negative ion mode provides the best specificity and sensitivity, albeit at a cost (16,17). An example MS-MS analysis of BPA from a commercially available water bottle using the sample preparation method outlined in Table I is illustrated in Figure 2. Recoveries are routinely above 90%, and repeatability is < 1% to a high of 7% for the method, depending upon the level.