This shows one advantage of using an alkaline eluent for the analysis of procainamide in serum such as procainamide. Procainamide cannot be separated from other serum components at pH 3 or 7. However, since procainamide, which is one of a tertiary amine, dissociates a little at pH11, in consequence, it is strongly retained by the packing material of Asahipak ODP-50 4D ( a column for reversed phase chromatography ) and can be separated from other serum components.
As explained above, for the analysis of basic drugs which have tertiary amino groups, an alkaline eluent at pH11 is effective.

1) Dissolve procainamide in CH ₃ CN (1.0 mg/mL).
2) Put 10 μL of the above in the centrifuge tube and blow dry it.
3) Add 1,000 μL of the serum and stir.
4) Add 3,000 μL of CH ₃ CN and stir.
5) Centrifuge (3,500 rpm , 20 min) skim and filtrate by using a 0.45 μm filter to make a sample.
6) Inject 20 μL of the sample.

Sample : Procainamide in serum

Column       : Shodex Asahipak ODP-50 4D (4.6 mm I.D. x 150 mm)
Eluent       : 25 mM Phosphate buffer/CH3CN=75/25
Flow rate    : 0.6 mL/min
Detector     : UV (254 nm)
Column temp. : 30 °C