Optical sensor for the determination of ions

A composition comprising

• (a) a plasticizer-free, hydrophobic polymer having a glass transition temperature Tg of from -150 to 50.degree. C., and
• (b) a compound of the formula I or II as fluorophore ##STR13## in which R.sub.1 and R.sub.3, and R.sub.4 and R.sub.6 are C.sub.1 -C.sub.30 alkyl or C.sub.1 -C.sub.30 alkyl-CO--, and R.sub.2 and R.sub.5 are H or C.sub.1 -C.sub.30 alkyl, with the proviso that the total number of carbon atoms in the alkyl groups is at least 5, or a salt thereof with an inorganic or organic acid,
• (c) an ionophore which forms a complex with the ion to be determined, and
• (d) counterions in the form of lipophilic salts,
• wherein components (a) to (d) are not covalently bonded to one another.

An optical sensor for the determination of ions in aqueous measurement samples, in particular by means of fluorescence spectrometry, which comprises

• (a) a transparent support
• (b) which is coated on at least one side with a transparent coating which comprises
• (b1) a plasticizer-free, hydrophobic polymer having a glass transition temperature T.sub.g of from -150 to 50.degree. C.,
• (b2) the salt of a lipophilic anion,
• (b3) an ionophore which forms a complex with the ion to be determined, and
• (b4) a compound of the formula I or II as fluorophore ##STR14## in which R.sub.1 and R.sub.3, and R.sub.4 and R.sub.6 are C.sub.1 -C.sub.30 alkyl or C.sub.1 -C.sub.30 alkyl-CO--, and R.sub.2 and R.sub.5 are H or C.sub.1 -C.sub.30 alkyl, with the proviso that the total number of carbon atoms in the alkyl groups is at least 5, or a salt thereof with an inorganic or organic acid,
• wherein components (b1) to (b4) are not covalently bonded to one another.