Thomas B. Coolidge

Determination of ionized calcium in serum with murexide

Abstract A simple method is described for the direct measurement of the calcium ion concentration in serum by the use of murexide.

Ionized Calcium in Saliva

The concentration of ionized calcium in the saliva is of interest in respect to (1) the initiation and propagation of the carious process and (2) the deposition of dental calculus. In the following, measurements of the ionized calcium concentration in saliva are reported. In general, the method consists in the addition of a dye-murexide-to the saliva and the measurement of the optical absorption, the principle of the method depending on the fact that murexide combines with calcium according to the mass law and the fact that murexide combined with calcium has a different optical absorption from murexide not so combined. The method was described by Raaflaubl and has been applied to the ultrafiltrates of serum by several investigators. Using brackets to denote molar concentrations, T.M. is total murexide, M is uncombined murexide, CaM is murexide complexed by calcium, [CaM] is a [T.M.], Ca is free calcium ions, T.C. is total calcium, Em is the molar absorption coefficient of uncombined murexide, Eca that of the calcium murexide complex, Et that of murexide at the isobestic point. The method is as follows. In preliminary experiments on solutions having a specific concentration of murexide, [T.M.], and a range of ionic strengths and pH values corresponding to those of saliva, the following are measured: (1) the absorption at 490 millimicrons and at 530 millimicrons in the presence of a relatively high concentration of calcium, Aca [T.M.] Eca; (2) the absorption at the same wave lengths in the absence of calcium, Am = [T.M.] Em; (3) the absorption at the same two wave lengths of calcium solutions of such concentration that [CaM] is of the same order of magnitude as [M], the absorption being Ax [M] Em + [CaM] Eca; (4) the wave length of the isobestic point and the absorption at the isobestic point, At [T.M.] Et. (As a result of these measurements Eca, Em, and Et are determined.) It can be shown that

A Method for the Chemical Measurement of Activity of Caries of the Enamel

The following experiments are believed to constitute chemical measurements of the rate of caries activity in enamel. The experimental procedure (fig. 1) is an outline as follows: the passage of material from the oral cavity (E) to the material (C) on the enamel surface is prevented by means of a barrier during an interval of approximately 10 minutes and the concentration of total phosphate in C is measured twice during this period. It is assumed: (1) that the line of separation (B) of enamel from the overlying debris (C) is experimentally definite because of the hardness of the enamel surface in the early stages of caries and the softness of the debris; (2) that if the migration of phosphate from E to C is prevented, a rise in the total phosphate concentration in C can be caused only by a migration of phosphate from the enamel (A) to C; (3) that the rate of migration of phosphate from A to C is the rate of caries activity, as the only considerable source of phosphate in A is the apatite of which the enamel is composed.