BS EN 973:2009 pdf free download – Chemicals used for treatment of water intended for human consumption一 Sodium chloride for regeneration of ion exchangers.
B.2.2 Principle
Dissolution of the sample with a mixture of water, sodium chlorate and hydrochloric acid.
Oxidation with the nascent chlorine, converting all forms of mercury to ionic mercury (II).
Reduction of the excess of oxidant by hydroxylamine hydrochloride and of mercury (II) to atomic mercury by tin (II) chloride.
Entrainment of the mercury in a stream of gas and measurement of the absorbance at a wavelength of 253,7 nm.
B.2.3 Reagents
All reagents shall be of recognized analytical grade having the lowest possible mercury content and the water used shall conform to grade 3 in accordance with EN ISO 3696.
Store all reagents in glass bottles.
B.2.3.1 Sodium chloride with a mercury content less than 20 jig/kg.
B.2.3.2 Hydrochloric acid, c(HCI) 6 mol/l (azeotropic mixture).
Purify this solution as follows.
Add 500 ml of water and 5 ml of sulfuric acid density p 1,84 g/ml, mass fraction 96 % solution to 500 ml of hydrochloric acid density p 1,19 g/ml, mass fraction 37 % solution. Distill the azeotropic mixture.
B.2.3.3 Sodium chlorate (NaCIO3), approximately 100 gIl solution.
B.2.3.4 Potassium dichromate (K2Cr2O7), approximately 4 gIl solution.
Dissolve 4 g of potassium dichromate with 500 ml of water. Add 500 ml of nitric acid p 1,40 g/ml, mass fraction 65 % solution and mix.
B.2.3.5 Tin(II) chloride (SnCI2.2H20), approximately 100 g/l solution.
Dissolve 25 g of tin (II) chloride dihydrate with 50 ml of warm hydrochloric acid p 1,19 g/ml, mass fraction 37 % solution. Allow to cool and add 1 g to 2 g of metallic tin. Dilute to 250 ml with water and mix. Prepare this solution just before use and slowly pass nitrogen through during 30 mm to remove the mercury.
Ensure that oxidation of solid tin (II) chloride by air is prevented.
B.2.3.6 Hydroxylamine hydrochloride (NH2OH.HCI), approximately 100 g/l solution.
B.2.3.7 Mercury, stock standard solution (I), C(Hg) = 1 000 mg/I, commercial standard solution or to be
prepared as follows:
— dissolve 1,354 g of mercury (II) chloride (HgCl) with 50 ml of hydrochloric acid solution (B.2.3.2) and add 50 ml of potassium dichromate solution (B.2.3.4). Transfer to a 1 000 ml volumetric flask, dilute to the mark with water and mix;
— store this solution in a cool, dark place and renew after two months.
B.2.3.8 Mercury, standard solution (II), C(Hg) = 1 mg/I.
Prepare this solution just before use by successive dilutions of the stock standard solution (I) (B.2.3.7). Add 50 ml of potassium dichromate solution (B.2.3.4) for preparing 1 000 ml of final solution.
B.2.3.9 Air or nitrogen
Use a gas containing no mercury or other components capable to provide absorbing radiations at a wavelength of 253,7 nm.
NOTE Any mercury present should be removed by a charcoal filter.
B.2.4 Apparatus
Ordinary laboratory apparatus and glassware.
NOTE All new glassware used for this determination, including flasks used for reagents or samples should be washed as follows and thoroughly rinsed with water after each operation:
with a brush and detergent if the walls are greasy;
with dilute nitric acid c(HNO3) 7 mol/l.
The glassware should be checked by carrying out several blank tests until satisfactory results are obtained before using it for actual determinations. Thereafter such glassware should be used for mercury determination only.
B.2.4.1 Apparatus allowing the determination of mercury
An example of suitable apparatus is shown in the Figure B.1. This applies to an open-circuit measuring system and comprises principally the following:
B.2.4.1.1 Atomic absorption spectrometer
B.2.4.1.2 Mercury hollow cathode lamp
B.2.4.1.3 Low-pressure mercury vapour lamp
B.2.4.1.4 Measuring cell, minimum path length 10 cm with windows transparent to radiation of 253,7 nm.