A titrimetric method for determining organic acids and bases in urine.

HE RECENT EMPHASIS on disorders of acid-base metabolism has necessitated a reappraisal of those urinary constituents which represent elimination of acid or base. The conventional expression for urinary acid excretion (“net acid excretion”) is titratable acid bicarbonate + ammonia (T.A. CO2 + NH4 ) (1). It has been the contention of this laboratory that acid excretion is more inclusively represented by the expression T.A. CO2 + NH4 O.A. + O.B., where O.A. indicates organic acid and O.B. indicates organic base, respectively (2). According to this concept, the excretion of citrate, the anion of an organic acid, may be considered equivalent to the loss of bicarbonate. Likewise, the excretion of lysine 11+, a hydrogen ion conjugate of an organic base, may be considered equivalent to the excretion of NH4+, also the hydrogen ion conjugate of an organic base (NH3). Methods have been previously described for determination of both organic acids and organic bases. The standard method for organic acid is that of Van Slyke and Palmer (3), who precipitated the phosphates and carbonates with Ca(OH)2 and then titrated from pH 2.7 to 8.0 using phenolphthalein as an indicator. Dawson et al. (4) applied a similar technic to the determination of organic bases by first adjusting the urine plus Ca(OH)9 to pH 8.0 with 0.1 N. HC1, using phenolphthalein as an indicator, and then back-titrating to pH 10.0, using a Beckman pH meter. Ammonia was determined separately and subtracted from the total organic base.