Abstract: A test means for determining the presence of an ion in an aqueous test sample is disclosed, as well as a test device incorporating the test means, a method for preparing it and a method for using it. The test means is composed of a porous carrier matrix incorporated, substantially uniformly, with a homogeneous hydrophobic composition and with a buffering substance capable of providing a pH in the range of from about 5 to 10. The homogeneous hydrophobic composition contains an ionophore capable of forming a complex with the ion, a hydrophobic substance and a reporter substance capable of interacting with the complex of ionophore and ion to produce a detectable response. In a preferred embodiment, this invention provides a colorimetric test capable of measuring serum potassium.

Abstract: A test composition, device and method for determining a peroxidatively active substance in a test sample, as well as a method for preparing the device, are disclosed. The composition comprises an organic hydroperoxide and an indicator capable of providing a detectable response in the presence of the organic hydroperoxide and peroxidatively active substance, wherein the organic hydroperoxide is a substituted cumene hydroperoxide having the formula: ##STR1## in which any one of the X substituents is lower alkyl of from 1 to 6 carbon atoms, Cl, Br, I, NO.sub.2 or carboxyl; or any two of the X substituents, same or different, are lower alkyl of from 1 to 6 carbon atoms, Cl, Br, I, NO.sub.2 or carboxyl. The device comprises a carrier matrix incorporated with the composition, and the method comprises contacting a test sample with the device and observing a detectable response in the device.