Abstract: A method and composition for determining magnesium levels in a liquid. The composition contains a first enzyme reagent part having glycerol-kinase, adenosine 5'-triphosphate, 4-aminoantipyrene, .alpha.-glycerophosphate oxidase, peroxidase, glycerol kinase, water and a buffer capable of maintaining the solution at a pH between about 5.5 and about 9.2. The composition also contains a second trigger reagent part which has sodium 2-hydroxy-3,5-dichlorobenzene sulfonate, glycerol, water and a buffer capable of maintaining the solution pH between about 5.5 and about 9.2. In the method of the present invention, a liquid to be analyzed is contacted sequentially with the first enzyme reagent part and followed by the second trigger reagent and is measured to quantitatively detect the presence of a detectable species produced as a result of the reactions triggered by the mixture of the enzyme reagent part and the trigger reagent part.