where Vb (inml) is the volume of hydrochloric acid solution used for the titration of the blank; V (in ml) is the volume of hydrochloric acid solution used for titration of the sample; CHCL (in mol ml−1) is the hydrochloric acid solution concentration and 4 is the ratio of the total solution volume (100 ml) and the volume taken for titration (25 ml).