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[Detection/determination limit]
The detection limit is defined as 3 times, and the determination
limit as 10 times, the standard deviation of the entire
operation blank test results.
[Notes]
Bisphenol A (BPA), first synthesized in 1891, is widely used as
a starting material for polycarbonate and epoxy resins, and as a
stabilizer for PVC. About 130 thousand tons of BPA was produced
in Japan in 2001. The substance, a condensation product from two
phenol molecules and an acetone molecule, is white powder
readily soluble in acetone or methanol but hardly soluble in
water.
BPA has wide applications and has therefore raised concerns over
contamination by small amounts from various sources. While
animal experiments conducted so far are focused on the effects
of ingestion of small amounts of BPA only, it is indispensable
to investigate animals' exposure to BPA via the feeds, cages,
water bottles, litter, and ambient atmosphere actually used in
the experiment in order to improve the reliability of in vivo
experiments. An analytical procedure for BPA in animal feeds
with high sensitivity and precision is a prerequisite for this
purpose. The fact that soybean is one of major ingredients in
feeds has prompted several investigations on soybean isoflavones
in feeds, but studies on BPA in feeds have remained scanty.
1 The LC/MS analysis is simple in that it does not
involve derivatization of BPA, but is susceptible to
interference by foreign substances in certain samples.
2 The procedure can be applied to litter samples as well.
3 E.g. Waters' Sep-Pak alumina-A cartridge (1.7 g).
4 E.g. Waters' Oasis HLB cartridge (60 mg).
5
Since BPA is present in plastic and
rubber used in labware as well as in purified water, the blank value
must be kept as low as possible by the following in order to achieve a
sufficiently high sensitivity.
- Use Milli-Q water which contains a very low level of BPA.
- Clean glassware with acetone before use.
- Condition the cartridges with an appropriate amount of a solvent.
- Use glass microsyringes (instead of plastic tips) for transferring
small amounts of reagents.
- Clean the inside of the evaporator thoroughly by boiling acetone.
6 E.g, Agilent Technologies' Zombax XDB.
7 Use of 0.01% acetic acid-acetonitrile (55:45) as the
mobile phase is not impossible, but susceptible to interference
when analyzing feeds.
8 Feeds contain a considerable amount of lipids coming
from major ingredients such as fish flour or soybean. The
preparation method for serum or urine samples is not suitable in
this case. While Florisil and silica gel cannot remove lipids
completely, basic, neutral or acidic active alumina can do so.
Acidic active alumina is preferred here because of its BPA
recovery ratio of 60-80% in contrast to 30-40% for basic and
neutral active alumina.
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