The calculation of calcium: the calculation formula of calcium, the determination of serum calcium how to determine the blood routine?

In GB/T6436-2002 "determination of calcium in Feed" (EDTA complexation method), it is mentioned to do a blank test, but the blank value is not subtracted from the calculation formula. I don't know why?

The formula for calculating calcium:

Xerov × C × 40.08 × 1000/Vw

Vmurt-titration consumes EDTA standard solution volume, ml

Concentration of CEDTA-- standard solution, mole / liter

Vw-- water sample volume, ml

40.08 mole mass of Ca ~ (2 +), g / mol.

Determination of serum calcium (methyl thymol blue colorimetry) 1. Principle: calcium ions in serum combine with methyl thymol blue (MTB) in alkaline solution to form a blue complex. By comparing the colorimetric standard with the calcium standard of the same treatment, the content of calcium can be calculated. 2. Reagent composition and preparation: 1. Reagent 1: MTB reagent: 40ml × 1 bottle, 4 ℃ preservation. 2, reagent 2: alkaline solution: 100ml × 1 bottle 3, reagent 3: protein clarifier: 5ml × 1 bottle, it will solidify when the weather is cold, and it can be used only after the water bath is heated to transparent. 4. 2.5mmol/L calcium standard solution: lml × 2, 4 ℃ away from light. 3. Procedure: blank tube standard tube determination tube reagent 1:MTB reagent (ml) 1.01.0 reagent 2: alkaline solution (ml) 2.0 2.0 deionized water 10u l 2.5mmol/L calcium standard solution 10u l serum 10u l, after standing for 5 minutes, the wavelength was 610mn, the light diameter was 1cm, the distilled water was adjusted to zero, and the absorbance of each tube was measured. Calculation: 1. Calculation formula: calcium content in serum (mmol/L) = (A determination-A blank) / (A standard-A blank) × 2.5