Basic Concepts in Clinical Biochemistry-A Practical Guide.7z

21.3 Method

Calcium is estimated by O-Cresolphthalien Complexone method.

21.4 Principle........................................

Hydrochloric acid dissociates calcium from protein. Then total calcium reacts with
ortho-cresolphthalein complex to form a purple-colored complex in alkaline
medium. Diethylamine provides the alkaline pH, and 8-hydroxy quinoline prevents
the interference of magnesium ions. The color thus produced is compared with that
of calcium standard.

21.5 Reagents........................................

1.Cresolphthalein reagent: Dissolve 70 mg of ortho-cresolphthalein complexone
in 16.5 ml conc. HCl. Then add 2.5 g 8-hydroxy quinoline, mix and dilute to
1000 ml with distilled water.
2.Diethylamine buffer (3.75% v/v) in distilled water: Mix 3.75 ml diethylamine
in afinal volume of 100 ml distilled water.
3.Calcium Standard 4 mg %: Dissolve 10 mg of CaCO 3 in 0.1 N HCl and make
volume 100 ml with 0.1 N HCl solution.

23.6 Procedure

1. Take a set of 10 test tubes in duplicate and mark as blank, standard (S 1 – S 8 ), test
   for serum (Ts), and test for urine (TU) sample.

Calcium

Extracellular fluid

(9-11 mg/dl)

Intracellular

Cytoplasmic free

Protein bound

45-50% Diffusible &

Ultrafiltrable (50%)

Albumin bound (90%)

Globulin bound (10%)

Ionised

45-50%

Complexed

10%

Fig. 21.1 Distribution of calcium in bodyfluids

86 21 Estimation of Total Calcium in Serum and Urine