Bepaling van het zuur- of baseverbruik en van de alkaliniteit met Titrino 736

A 736ohm Metrohm titrator has been validated for determination of acidity in rainwater and alkalinity in groundwater. The performance characteristics have been determined in terms of reproducibilities and detection limits, and appeared to be comparable to those of the previously applied methods. The determination starts with reading of the pH and sample temperature. The determination of the acidity is carried out by gradually adding a 0.002 mol/l H2SO4 standard as titrant to the sample up to a fixed end-point of pH 4, and subsequently the sample is titrated back with 0.002 mol/l NaOH standard. The addition is stopped when a fixed end-point of pH 5.6.is reached. The reproducibility, in terms of the relative standard deviation, of the acidity determination is better than 4% at 100 mumol/l H3O-. The detection limit is 5 mumol/l for both hydroxide and hydronium. Acidity determination takes place in 8 minutes. The determination of the alkalinity (interpreted as the sum of the concentrations of bicarbonate, carbonate and hydroxide) is carried out by gradually adding a 0.05 mol/l HCl standard to the sample up to fixed end point of pH 8.3 (if the pH of the sample is higher than 8.3) and then up to end point of pH 4.5. The reproducibility, in terms of the relative standard deviation, of the alkalinity determination is 5% by 25 mmol/l (bi)carbonate. The detection limit for bicarbonate is 0.02 mmol/l. The applicable concentration range is 0.02 - 60 mmol/l. A typical alkalinity determination takes place in 10 minutes