The Synermed® magnesium is detected in the infrared region of the spectrum thus avoiding the absorbance of hemoglobin and minimizing the absorbance of lipemia. Except in geriatric populations, most pathologic magnesium values are below normal. Consequently, signal levels [absorbance changes] are very low. Low levels of serum background noise is very important to avoid chromatic interference, especially in the important pathologic low levels.
Magnesium reacts with Xylidyl Blue I to produce a Magnesium-xylidyl blue complex which is red in color at the alkaline pH of the reagent. The disappearance of the near-infrared absorbing blue color is proportional to the amount of magnesium present in the serum.
Xylidyl Blue I + Mg+2 -> Xylidyl Blue-Mg+2 complex
The disappearance of the initial blue color as the xylidyl-Mg complex is formed can be measured between 630 nm and 670 nm and is proportional to the magnesium concentration. Calcium is prevented from forming a complex with the xylidyl blue by the inclusion of EGTA in the reaction mixture.