Answer 1:
As you know, Bisphenol A (BPA) is a colorless
small molecule and present in relatively low
concentrations in plastics and dyes. It can have
harmful effects on humans, particularly women and
young children, even at those low concentrations
because it mimics the hormone estrogen.
BPA can be detected directly from paper, plastics
BPA dissolves more easily in alcohol, which
is the primary component of hand sanitizers, than
in water. You can extract BPA by soaking the
thermal paper in alcohol. “Rubbing” (isopropyl)
alcohol from the drug store or vodka (an
ethanol/water solution) will work but ask your
parents/teacher before seeking these out. To get
BPA from your skin, you can swish your fingers in
the solution for about 10 seconds. (This procedure
was used in Biedermann, S., et al “Transfer of
bisphenol A from thermal printer paper to the
skin.” Anal Bioanal Chem 2010, 398, 571–576.
doi:10.1007/s00216-010-3936-9).
Detecting BPA in that solution effectively
and cheaply is a challenging problem and an area
of active research. It is detected
analytically using fluorescence – BPA absorbs
280nm light and emits strongly at 310nm. However,
both of these wavelengths are in the UV range
(invisible to the naked eye) and concentration
will hard to quantify without a UV-sensitive
spectrometer.
You may be able to detect BPA using
chromatography, a technique that detects how a
compound is drawn through a medium by a flow of
solvent. (See this page for more information:
orgchem ) This technique can be used to
separate and identify BPA, but you’d need a way to
see the BPA spot. If you use a fluorescent silica
sheets (available in some Chem labs), the BPA will
dampen the fluorescence of the sheet when present,
so a dark spot will appear under UV light.
However, many other organic compounds will appear
as a dark spot, so this isn’t a definitive test
for BPA. If you have pure BPA, you can compare how
far it travels up the sheet to your unknown for a
more confident identification.
To address this challenge, a research group at
the National University of Singapore has developed
a dye that complexes with BPA. When bound
specifically to BPA, the dye turns bright orange,
making it easier to detect BPA in the field. The
stronger the orange color, the more concentrated
the BPA in your sample. Unfortunately, this is dye
is not commercially available yet. (Zhang, L., et
al. “Orange alert: A fluorescent detector for
bisphenol A in water environments.” Analytica
Chimica Acta 2014, 815, 51–56.
doi:10.1016/j.aca.2014.01.038)
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