BIOLUMINESCENT FLOW-SENSING DEVICE FOR THE DETERMINATION OF MAGNESIUM(II)

A continuous-flow system was developed for the assay of magnesium(II) in serum, drugs and beverages, making use of firefly luciferase (LUC) (EC 1.13-12.7) or recombinant luciferase (r-LUC) from Escherichia coli immobilized on a nylon coil or a column of epoxy methacrylate (Euperg it) placed inside a luminometer. The flow was air segmented and 10 mul samples were analysed. The sample assay rate was 20 h-1 with no carry -over. The optimum operational conditions were found to be 0.05 mmol 1 -1 luciferin and 0.3 mmol 1-1 ATP (adenosine triphosphate) at a flow r ate of 0.4 ml min-1. The detection limit of the assay was 0.05 mmol 1- 1 for an LUC-nylon coil and 0.01 mmol 1-1 for an LUC-Eupergit column o r an r-LUC-nylon coil and the response was linear from 0.05 to 6.7 and from 0.01 to 6.7 mmol 1-1, respectively. Both the intra- and inter-as say relative standard deviations were lower than 7%. No interferences from ions present in the samples (Ca2+, Mn2+, Fe2+, Cu2+, Zn2+, Co2+) were found. Results obtained for serum by the present method were in g ood agreement with those given by spectrophotometry with Xylidyl Blue II and by atomic absorption spectrometry.