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Formic acid. Liquid chromatography (2.2.29).
Test solution. Dissolve a quantity of the substance to be
examined equivalent to 2.0 g of the anhydrous substance in
water R and dilute to 100.0 mL with the same solvent (test
stock solution). Transfer a suspension of strongly acidic
ion-exchange resin R for column chromatography in water R
to a column of about 0.8 cm in internal diameter to give a
packing of about 20 mm in length and keep the strongly acidic
ion-exchange resin layer constantly immersed in water R. Pour
5 mL of water R and adjust the flow rate so that the water
drops at a rate of about 20 drops per minute. When the level
of the water comes down to near the top of the strongly acidic
ion-exchange resin layer, put the test stock solution into the column.
After dropping 2 mL of the solution, collect 1.5 mL of
the solution and use this solution as the test solution.
Reference solution. Dissolve 0.100 g of anhydrous formic
acid R in water R and dilute to 100.0mL with the same solvent.
Dilute 1.0 mL of the solution to 100.0 mL with water R.
Column:
— size : l = 0.25-0.30 m, Ø = 4-8 mm;
— stationary phase: strongly acidic ion-exchange resin R for
column chromatography (5-10 μm);
— temperature: 30 °C.
Mobile phase: dilute 5 mL of perchloric acid R to 1000 mL
with water R.
Flow rate: adjusted so that the retention time of formic acid is
about 11 min.
Detection: spectrophotometer at 210 nm.
Injection: 50 μL.
System suitability : reference solution:
— repeatability : maximum relative standard deviation of
2.0 per cent after 6 injections.
Limit:
— formic acid : not more than 10 times the area of the principal
peak in the chromatogram obtained with the reference
solution (0.5 per cent).
