A new procedure for rapid determination of nitrate and a study of the preparation of the phenol‐sulphonic acid reagent

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Abstract
A rapid procedure for the determination of nitrate in dilute aqueous solution is described and the chelated structure of the nitrophenolsulphonic acid formed in the reaction is discussed. Reproducible results are obtained when nitrate solution is added to the phenolsulphonic acid reagent but not if the order of addition is reversed.A critical examination of the different methods used by various workers in preparing the phenolsulphonic acid reagent has been made. It is concluded that fuming sulphuric acid may safely be omitted, that considerable latitude is permissible in the proportion of sulphuric acid to phenol, and that heating for more than two hours is not significant.Phenoldisulphonic acid may therefore be conveniently replaced by p‐phenolsulphonic acid which is easier to prepare; the latter reagent is sensitive to 2.5 p.p.m. of nitrate‐nitrogen in solution.