BS 1427:2009 pdf free download – Guide to on-site test methods for the analysis of waters.
4.1.3 Principle
Titration of test sample with standard acid to the visually determined end-point values of 8.3 pH units and 4.5 pH units. These end-points are the selected equivalence points for the alkalinity determinations of the three principal anions. Titration with acid against phenolphthalein to pH 8.3 represents titration of all hydroxide and conversion of carbonate to bicarbonate and is defined as the alkalinity to phenolphthalein (P). Titration with acid against methyl orange from pH 8.3 to pH 4.5 represents the titration of the bicarbonate to carbonic acid. An alternative to methyl orange is bromocresol green/methyl red indicator. The combined total titration with acid down to pH 4.5 is defined as the total alkalinity (T).
In chemically treated waters containing added ions, for example phosphate, silicate and borate, the alkalinity to phenolphthalein titration (P) can be affected by the added ions. Barium chloride (BaCI2) is added to suppress the effect of the added ions and both the alkalinity to phenolphthalein titration (P) and the modified alkalinity to phenolphthalein titration (PB) need to be measured. The latter is a measure of the caustic alkalinity only and, in conjunction with the measurement of alkalinity to phenolphthalein (P), allows the total alkalinity to be calculated. The alkalinity due to the presence of different anions can also be calculated (see Table 1).
NOTE 1 The total alkalinity end-point (T) is fixed atpH 4.5. The pH at which equivalence is reached is higher at low ionic strength and might not be at pH 4.5 for samples of low alkalinity (see 4.1.7).
NOTE 2 For the purposes of this method, alkalinity can be defined as the quantitative capacity of aqueous media to react with hydrogen ions.
4.1.4 Reagents
NOTE The standard volumetric solution (4.1.4.2) and test indicator solutions used for this test are commercially available and are recommended for designated room/area testing facility testing (see 2.3). A modified calculation formula is necessary where alternative titrant concentrations apply (see 27.3). Please also note that the reverse titration method does not use the concentrations of reagent specified in this subcla use on account of its different test methodology. In addition, the reverse titration test-kits for Total (T) Alkalinity may use bromocresol green/methyl red indicator in place of methyl orange indicator.
4.1.4.1 Distilled or de-ionized water. (See 2.7.1.)
4.1.4.2 Sulfuric acid standard volumetric solution, c (H2S04) = 0.01 mol/L, standardized by titration against a standard sodium carbonate solution, well stoppered and is stable for at least one month.
4.1.4.3 Phenolphthalein indicator, 1.0 g of phenolphthalein, dissolved in 100 mL of ethanol, diluted to 200 mL with water and mixed.
4.1.4.4 Mixed indicator, 0.200 g of bromocresol green and 0.015 g of methyl red, dissolved in 100 mL of ethanol and mixed. The indicator is stored in an amber bottle.
4.1.4.5 Methyl orange indicator, 0.05 g of methyl orange dissolved in 100 mL of water.