Photometric, colorimetric, and acid-base characteristics of nitroso-R-salt

Optical and colorimetric characteristics of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt) are studied in aqueous solutions at pH 4–10. Equations of calibration plots are obtained as the colorimetric functions of the concentration, and the molar coefficients of the colorimetric functions are calculated. The dissociation constants of nitroso-R-salt are determined by colorimetry at an ionic strength of 0.1–0.5, reduced to zero ionic strength, and compared with the literature data. Advantages of colorimetry over spectrophotometry in the determination of the dissociation constants of colored reagents are demonstrated.