Bioluminescent flow-sensing device for the determination of magnesium (II)

Abstract

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 (Eupergit) placed inside a luminometer. The flow was air segmented and 10 µl samples were analysed. The sample assay rate was 20 h^–1 with no carryover. The optimum operational conditions were found to be 0.05 mmol l^–1 luciferin and 0.3 mmol l^–1 ATP (adenosine triphosphate) at a flow rate of 0.4 ml min^–1. The detection limit of the assay was 0.05 mmol l^–1 for an LUC—nylon coil and 0.01 mmol l^–1 for an LUC-Eupergit column or an r-LUC—nylon coil and the response was linear from 0.05 to 6.7 and from 0.01 to 6.7 mmol l^–1, respectively. Both the intra- and inter-assay 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 good agreement with those given by spectrophotometry with Xylidyl Blue II and by atomic absorption spectrometry.