Magnesium is an important biological element, which is mainly found in bone, muscle cells, soft tissues, serum and red blood cells. It is involved in the synthesis of nucleic acid and protein, and is a cofactor of various enzymes and transporters. It plays an important role in regulating cardiac excitability, neuromuscular conduction, vasomotor contraction, blood pressure and energy metabolism.

The magnesium in the serum reacts with the complexometric indicator (Calmagite) to form the Calmagite-Mg compound. The absorbance of this compound at 540 nm is proportional to the concentration of magnesium in the sample. 

1. The assay temperature of this method is not required strictly. But it should be kept constant, because the color is sensitive to the temperature.

2. The color of reaction solution can be stable for 1 hour.

1. Blank tube: Add 1000 μL of working solution to 2 mL EP tube.

    Standard tube: Add 1000 μL of working solution to 2 mL EP tube.

    Sample tube: Add 1000 μL of working solution to 2 mL EP tube.

2.  Incubate the tubes at 37℃ for 5 min.

3. Blank tube: Add 10 μL of double distilled water to blank tube.

    Standard tube: Add 10 μL of 1 mmol/L Magnesium Standard to standard tube.

    Sample tube: Add 10 μL of sample to sample tube.

4.  Mix fully with vortex mixer and incubate the tubes at 37℃ for 2 min.

5.  Set the spectrophotometer to zero with double-distilled water and measure the OD value of each tube at 540 nm with 0.5 cm optical path quartz cuvette.