Abstract: Tetrazolium salt compounds represented by the following general formula (1): ##STR1## wherein R.sup.1 and R.sup.2 independently represent hydrogen atom, nitro group, cyano group, carboxyl group or a halogen atom, preferably nitro group; R.sup.3 represents an alkyl group or an alkoxyl group, preferably methyl group or methoxy group; and M represents an alkali metal or an ammonium. The compounds are useful for quantitative measurement of a dehydrogenase, and characterized to have high water-solubility and excellent storage stability in the state of an aqueous solution.

Abstract: A method for detecting and determining a volatile or volatilizable substance in an aqueous solution or liquid and an apparatus employed for this method are disclosed. The volatile component, vaporized from the solution through a water repellent and gas permeable membrane, is brought into contact with a dried or partially dried transparent film-like color developing carrier which is provided adjacent to the membrane, and the determination is carried out by the degree of color-change of the carrier. The apparatus comprises a cover plate with sample holes, a membrane, a color developing carrier, and a cover plate with observation windows. The members are fitted tightly together to form a single composite layer.