The estimation of calcium in blood-serum / by John William Trevan and Henrietta Winifred Bainbridge.

  • Trevan, J. W. (John William)
Date:
[1926?]
Catalogue details

Licence: In copyright

Credit: The estimation of calcium in blood-serum / by John William Trevan and Henrietta Winifred Bainbridge. Source: Wellcome Collection.

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    Method. Apparatus. (1) Small centrifuge tubes of the dimensions shown in the hgure and made of resistance glass {e.g. Duroglass). We do not find that quartz tubes are necessary. The shape of the bottom of the tube is of importance; the sides of the conical end must be sufficiently steep for the oxalate precipitate to slide down to the apex of the cone during centrifuging. If any oxalate adheres to the sides of the tube there is a chance of losing some during decantation of supernatant liquid. The bottom of the tube inside should be just rounded off. (2) 1 cc. pipettes. (3) Glass stirring rods 10 cm. by T5 mm. made from drawn-out tubing. (4) Some form of micro-burette. The final titration for 1 cc. of serum con¬ sists of the addition of about 0-25 cc. of W/50 alkali. For this purpose we use the micrometer syringe described by one of us [Trevan, 1925]. A Rehberg burette would serve probably as well; or by using 2 cc. of serum as in the original Kramer and Tisdall method, together with A/100 alkali for the final titration, an ordinary 2 cc. burette could be used. In this case, however, the end-point error would be rather larger. (5) Centrifuge. (6) Wire holder for tube (see Fig. 1). Reagents. (1) Saturated ammonium oxalate (3-5 %). (2) A/50 sodium hydroxide. (3) A/100 acid. We have used both phosphoric acid, as recommended by Cahen and Hurtley [1916], and hydrochloric. We prefer the former. The acid should be titrated against A/50 NagCOg by a special method; excess of acid should be added to the standard carbonate and the amount un-neutralised titra¬ ted with the A/50 sodium hydroxide. The conditions of the calcium carbonate titration are thus more closely reproduced and the titration error diminished.