Refractometric determination of total solids and water of serum and urine.

Refractometric analysis of total solids in serum and urine is simple, accurate, and rapid. Adolph (1) demonstrated the high coefficient of correlation between refractive index and total solids of dog plasma and subsequently employed refractometry as an index of the total solids of human serum (2). Blohm (3), using a dipping refractometer, showed for human urine that the reading given by that fluid was proportional to its dissolved total solids, and he determined a refractometric coei&ient of proportionality. The application of refractometry is extended in the present paper with the determination of several new coefficients for total solids of serum and urine. The refractive index of serum has been used as a measure of total protein concentration (4, 5), but it has been supposed that high accuracy in this analysis can be obtained only when the albumin-globulin ratio is known (6) and when the lipide content is low (7). However, at least when refractometry is used as a measure of total solids, the albuminglobulin ratio is not vitiating, as we shall show, nor is there significant influence of the usual lipide content of serum on the determination. Refractometry is particularly advantageous for urine, since otherwise its total solids can be analyzed satisfactorily1 only by relatively elaborate procedures such as lyophilization. Estimates of urinary solids by means of specific gravity coefficients are considerably less accurate (3, 8).