Studies on measurement of plasma magnesium: application of the Magon dye method to the "Monarch" centrifugal analyzer.

The "Magnesium Liquid Stable Reagent Set" from Medical Analysis Systems, Inc., is evaluated. The method, which involves Magon dye binding and bichromatic absorbance measurements, was used in a Monarch centrifugal analyzer. Results were compared with those by atomic absorption spectrometry. The calibration curve for the Magon method is linear to 2.5 mmol/L, with a 2-microL sample volume. Analytical recovery of magnesium added to human plasma ranged from 95 to 102%. The working reagent is stable for at least five days at 15 degrees C. At concentrations of 0.54 and 1.20 mmol/L, the respective CVs were 2.15 and 3.60% within batch, and 3.13 and 3.24% between batch. We analyzed 150 clinical samples for magnesium by both methods. Absorbance readings at 520/600 nm rather than 520/690 nm improved the correlation (r = 0.9777 and r = 0.9428, respectively). Calcium, albumin, phosphate, or bilirubin did not significantly interfere.