Standardization of the EGTA solution

EGTA working solution 0.01 mol/L (or 0.005 mol/L for samples with a salinity of 20). Take aliquots of the stock solution and dilute to 0.01 mol/L. The empirical titre is determined by standardization with the calcium standard solution. 

Borate buffer Dissolve 10 g of sodium tetraborate (analytical-reagent grade, a.g.), Na2B407 10 H2O and 30 g of sodium hydroxide (a.g.) in distilled water and dilute to 500 mL. 

GBAH indicator solution Glyoxal-bis(2-hydroxyanil), Q4H12N2O2,0.05 % in n-propanol. 

Standard calcium solution, 0.0103 mol/L Ca Dissolve exactly 1.0309 g of pure calcium carbonate (CaCOs, spectrographically standardized) in a few mL of dilute hydrochloric acid (HCl) and dilute to 1000 mL after addition of 13.670 g of magnesium nitrate, Mg(N03)2 6H2O (e.g., Suprapur , Merck), 0.0240 g of strontium chloride (a.g.), SrCl2 6H2O and 27.400 g of sodium chloride (eg., NaCl, Suprapur , Merck). The concentrations correspond to a salinity of about 35.0. 

Accurate burette For example Metrohm piston burette, calibrated, with subdivisions of 0.005 mL. 

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