Abstract: A process for rapidly and conveniently measuring the magnesium concentration of a biological fluid, such as blood or urine, is carried out by fixing amounts of a chelatometric dye, metal cation masking agents, a chelating agent, an alkaline buffer, and a stabilizer on a bibulous material covered with a semipermeable membrane, adding the test specimen, and measuring the amount of color change of the dye at a selected wavelength. The amount of color change is proportional to the quantity of magnesium in the original specimen and can be measured by visual comparison to a standard color chart or with a dedicated reflectance photometer. Furthermore, a method is given for expanding the range of linearity. The method for making the dry indicator includes coating bibulous material with a reaction solution which is dried thereon, followed by coating this material with an organic solution which is dried thereon.

Abstract: A process for measuring the calcium concentration of a biological fluid is carried out by fixing the amounts of phospholipase A2 (PLA) and phosphatidylcholine (PC), in the presence of a buffer and a detergent such as sodium deoxycholate, in enzymatic Reaction I, ##STR1## and measuring the rate of appearance of the products so that the rate of reaction of PLA can be determined. The reaction rate of this enzyme is directly proportional to the level of calcium present. The calcium concentration of the biological fluid being tested is quantitatively determined by comparing the reaction rate of pohospholipase A2 to a standard of known calcium concentration. Preferably, the reaction rate of porcine pancreas phospholipase A2 is measured by determining the amount of lysolecithin produced in Reaction I by comparison of the optical density of the resultant color of coupled Reactions II and III,lysolecithin+erythrocytes.fwdarw.hemoglobin IIhemoglobin+peroxide+In.fwdarw.