Abstract: An improved multilayer element for detecting glucose in samples of biological fluid which may contain with fluoride ion as a contaminant or preservative is described. The improved element comprises a buffered Trinder's reagent, which reagent comprises glucose oxidase, peroxidase, 4-aminoantipyrine and a phenolic or naphtholic coupler, which is buffered to a pH between about 4.5 and about 6.0. Such a buffering reduces any interference which may be due to fluoride ion present in the sample under analysis.

Abstract: A colorimetric assay method for the detection of bilirubin in various liquid samples, particularly biological liquids. A multi-zone analytical element based on this assay method is also disclosed. The assay method employs an interactive mordant composition for bilirubin having one or more binding sites for bilirubin, such composition comprising a hydrophobic organic matrix and at least one charge-bearing cationic group. Upon mordanting of bilirubin by the interactive mordant composition, the mordanted bilirubin exhibits an absorption peak shift of at least 10 nm. and at least a 50% increase in molar extinction coefficient.