4-[Bis(carboxymethyl)aminomethyl]-3-hydroxy-2-naphthoic acid as a fluorescent indicator for the complexometric titration of calcium plus magnesium

Successive determinations of calcium and magnesium in drinking water by complexometric, potentiometric digital titration to two equivalence points

“…The conditional sta-Flgure 4. Computed conditional stability constants for the Ca-EDTA complex and the Mg-EDTA complex as a function of pH: Pure solution (1, 2); 10-2 M 3,4-dihydroxybenzoic acid (3,4); 10~1 M 3,4-dihydroxybenzoic acid (5,6) Figure 5. Computed conditional stability constants for the Ca-EDTA complex and the Mg-EDTA complex as a function of pH: Pure solution (1, 2); 10-2 M acetylacetone (1, 3); 10~1 M acetylacetone (1,4) bility constant of the titrant ligand with respect to calcium ( Kca'L') must lie in the range 108-1010. The ratio between the conditional stability constants, •Kca'L'/íÍMg'L', must be approx.…”

“…Constant b (0.8) ensures maximum titrant increments of 380 counts when the slope of the curve is small. Constant c (5) ensures minimum titrant increments in the vicinity of the inflection points, which is desirable in order to obtain good resolution of the calculated, derived parameters and, hence, an accurate determination of the location of the equivalence points.…”

“…As the indicator system, a color indicator, viz., Murexide or Calcon (1), or potentiometric indication with a calcium-ion electrode (2), a silver electrode (3), or a mercury electrode (4) may be used. Calcium + magnesium can be titrated at pH 9-10 with EDTA or DCTA (1,5) as titrant. Here, too, the indicator system may be a color indicator, e.g., Eriochrome Black T (1), a fluorometric indicator DHNA (5) or potentiometric indication with a calcium-ion electrode or a cupric-ion electrode (6).…”

“…Calcium + magnesium can be titrated at pH 9-10 with EDTA or DCTA (1,5) as titrant. Here, too, the indicator system may be a color indicator, e.g., Eriochrome Black T (1), a fluorometric indicator DHNA (5) or potentiometric indication with a calcium-ion electrode or a cupric-ion electrode (6). Alternatively, calcium and magnesium can be determined successively by titrating calcium with EGTA and then titrating magnesium with DCTA, using Phthalein Complexon as a color indicator (7).…”