Am. Tan et Cl. Xiao, DIRECT DETERMINATION OF CAUSTIC HYDROXIDE BY A MICRO-TITRATION METHODWITH DUAL-WAVELENGTH PHOTOMETRIC END-POINT DETECTION, Analytica chimica acta, 341(2-3), 1997, pp. 297-301
An automatic micro-titration method for the direct determination of ca
ustic hydroxide in aluminate solution is proposed, which is based on a
cid-base titration with sulfosalicylic acid and phenolphthalein as the
titrant and the indicator, respectively. Sulfosalicylic acid is also
the complexing agent for aluminum to prevent the formation of aluminum
hydroxide precipitate. Since only 30 mu l of sample is injected into
the titration cell, direct titration without dilution is possible; tit
rant's consumption is reduced to less than 7.5 ml even for the most co
ncentrated samples. Furthermore, the end-point is detected by a light
emitting diode (LED)-based dual-wavelength photometer, with one of the
wavelengths as a reference for correcting the interference of barium
carbonate precipitate. Samples containing 50-300 g l(-1) (expressed as
Na2O) of caustic hydroxide can be analyzed with a sampling frequency
of 45 samples per hour. A relative standard deviation of 0.27% is obta
ined for 13 determinations of a typical sample containing 170.4 g l(-1
) of sodium oxide.