Enzyme Immunoassayand EnzymeInhibitionAssayof Methotrexate,with Use of the CentrifugalAnalyzer

Methotrexate was determined by the homogeneous en-zyme immunoassay (EMIT#{174})with the Multistat and Centri-fiChem centrifugal analyzers and by the enzyme inhibition assay with use of the Multistat centrifugal analyzer. With both methods, the standard curve extends from 0.2 to 2.0 mol/L and there is no Interference from bilirubin in concentrations up to 100 mg/L. Moderately lipemic sam-ples do not interfere with the EMIT method, but lower the values obtained with the enzyme inhibition assay. Hemo-globin concentrations as great as 1 g/Ldo not affect results for methotrexate obtained by the enzyme inhibition assay. With the EMIT assay, methotrexate values are lowered in samples containing hemoglobin in concentrations ex-ceeding 750 mg/L. With the EMIT assay, the following compounds in concentrations of 1 mmol/L do not interfere