[Coupling of 1-naphthol with fast-red-TR. Studies on the optimization of a continuous determination of acid phosphatase, I. (author's transl)].

In the course of studies on the optimization of a method for the continuous determination of acid phosphatase, the coupling of 1-naphthol with fast-red-TR was investigated: 1. In the presence of detergents or protein, the detection reaction gives a linear response for spectral absorption in the range 0-1 against concentration. 2. The reaction between naphthol and fast-red-TR salt is first order with respect to 1-naphthol. 3. The half life time for the coupling must be less than 0.5 min, in order to keep the lag phase of the reaction below 2 min. 4. Shortening of the coupling half life time (increase in the rate of the indicator reaction) was achieved by increasing the fast-red concentration and pH-value, and by alterations, within certain limits, of ionic strength and the concentration of protein and/or detergents. 5. Development of the chromophore depends on time and the presence of proteins and/or detergents. Reliable measurements are only possible at the isosbestic point of the chromophore. In the presence of albumin, these are 460 nm and 390 nm. 6. Reproducible formation of the chromophore requires the presence of protein (albumin); replacement by detergents is possible to a limited extent. 7. In order to avoid a time-dependent bathochromic effect, buffer materials should be present in the lowest possible concentration: citrate buffer 0.2 mol/l; acetate buffer 0l.4 mmol/l. 8. By coupling with fast-red-TR salts, serum proteins result in increased positive values (apparent enzyme activity) up to 2.6 U/l, depending on the measurement wavelength for the chromophore. 9. Molar absorption coefficients for wavelengths 390, 405 and 460 nm were determined. 10. Recommendations are given for the optimization of the indicator reaction in the determination of acid phosphatase by hydrolysis of naphthyl phosphate.