Evaporate 100 mL to dryness in a tared dish on a hot plate at 60
: the weight of the residue does not exceed 25 mg (0.025%).
Limit of tannins
Mobile phase A
Adjust 1000 mL of water with phosphoric acid to a pH of 2.5 ± 0.1. Filter and degas.
Mobile phase B
Use filtered and degassed acetonitrile.
Dissolve an accurately weighed quantity of tannic acid in water to obtain a solution having a known concentration of about 0.03 mg of tannic acid per mL.
Use Witch Hazel.
(see Chromatography 621
)The liquid chromatograph is equipped with a 280-nm detector and a 5.0-mm × 15-cm column that contains packing L1 and is programmed to provide variable mixtures of Mobile phase A
and Mobile phase B.
Initially, the system is held at a mixture consisting of 90% Mobile phase A
and 10% Mobile phase B
for 5.0 minutes. The proportion of Solvent B
to Solvent A
is increased linearly to 100% over the next 15 minutes. The flow rate is about 1 mL per minute.
Separately inject equal volumes (about 25 µL) of the Standard solution
and the Test solution
into the chromatograph, record the chromatograms, and measure the responses for all peaks. If any peak corresponding to the retention time of tannic acid in the Standard solution
is present in the chromatogram of the Test solution
, its peak area is no more than that of the tannic acid in the Standard solution.