1986 Volume 35 Issue 4 Pages 368-372
In the spectrophotometric determination of beryllium with Chromazurol S (CAS, H4L) in the presence of cationic surfactant at pH 10.2, an increase in CAS concentration was required along with an increase in cationic surfactant concentration in order to obtain maximam and stable absorbance. From these results, the apparent equilibrium constant at pH 10.2 (Kapp) of the 1: 2 beryllium-CAS complex formation was investigated by varying the concentrations of cationic surfactant. The Kapp value decreased with an increase in cationic surfactant concentration. It was considered that possibly this was due to the effect of micellar volume on the partition of CAS between the water phase and the micellar pseudo phase. Partition ratio (DL) of CAS (HL3-) and the complex formation constant at pH 10.2 (k) could be determined from the Kapp value in the various concentrations of cationic surfactant. The DL value increased in the order of hexadecyltrimethylammonium chloride(HT)>hexadecyldimethyl-benzylammonium chloride(HD)>tetradecyldimethyl-benzylammonium chloride (TD)>hexadecylpyridinium chloride(HP)>dodecyltrimethylammonium chloride (DT)>dodecylpyridinium chloride (DP), according to the sum of carbon number of long chain alkyl and methyl radicals in the cationic surfactant. The k value decreased in the order of HP_??_DP>TD_??_HD>DT_??_HT, according to the number of methyl radical in the cationic surfactant. Molar absorptivity of the complex had the maximum value in the presence of HD and/or TD, and was 5.86×104 dm3 mol-1 cm-1 at 525 nm.
