Abstract: Hemiacetals are disclosed which correspond to the following formula II ##STR1## in which R' is an aliphatic or cycloaliphatic residue,Ar is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic residue andX.sup.1, X.sup.2 and X.sup.3 are selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, fluoro, chloro, bromo and nitro, wherein however at least one of said substituents has to be selected from the stated halo atoms or nitro. The hemiacetals are formed reversibly from an alcohol and a corresponding keto compound and the hemiacetals of formula II differ from the corresponding keto compounds as to their light absorption in the ultraviolet, visible or infrared range, or a fluorescence or luminescence is created or quenched when the keto compound is converted into the hemiacetal of formula II. Said reaction can be performed in sensors which are used for the optical determination of alcohols.

Abstract: Hemiacetals are disclosed which correspond to the following formula II ##STR1## in which R' is an aliphatic or cycloaliphatic residue,Ar is an unsubstituted or substituted monocyclic or polycyclic aromatic or heteroaromatic residue andX.sup.1, X.sup.2 and X.sup.3 are selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, fluoro, chloro, bromo and nitro, wherein however at least one of said substituents has to be selected from the stated halo atoms or nitro. The hemiacetals are formed reversibly from an alcohol and a corresponding keto compound and the hemiacetals of formula II differ from the corresponding keto compounds as to their light absorption in the ultraviolet, visible or infrared range, or a fluorescence or luminescence is created or quenched when the keto compound is converted into the hemiacetal of formula II. Said reaction can be performed in sensors which are used for the optical determination of alcohols.

Abstract: Hexacarboxylic acid hexa-amides are described which form new lipophilic magnesium complexes with magnesium ions. The hexa-amides are preferably novel compounds comprising three dicarboxylic acid diamide moieties interconnected to form a non-cyclic, monocyclic, bicyclic, tricyclic or polycyclic structure. Test devices such as test trips or ion-selective members are provided which contain hexacarboxylic acid hexa-amides as the ion-selective component. The test devices have a high selectivity for magnesium ions over alkali metal ions and other alkaline earth metal ions. Selectivity for magnesium ions over sodium and calcium ions permits determination of magnesium concentration in biological materials, including body fluids such as blood serum or whole blood. Magnesium concentration and activity can also be determined in sample solutions having a neutral or slightly acidic pH.

Abstract: Ion selective parts are described which comprise a polymeric material, an ion selective component and optionally furthermore a plasticizer and which ion sensitive parts are suited for the determination of the concentration or activity of ions in liquid media. The polymeric material of said ion sensitive parts is a copolymer in which 5-25 mol-% of the monomeric units of said copolymer are substituted with one or more hydrophilic substituents which are selected from the group comprising hydroxy groups, carboxylic acid groups, sulphonic acid groups and phosphonic acid groups. The inventive ion selective parts have, compared with corresponding ion selective parts in which the polymeric material is free of the stated hydrophilic groups or has a lower content of said hydrophilic groups, a better stability of the standard potential E.sub.o and a lower asymmetry potential or no asymmetry potential at all.