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.
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