Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 202

hydrochloric acid between successive uses. A sulphanilamide reagent was prepared by
dissolving 5g of sulphanilamide in a mixture of 50ml of concentrated hydrochloric and
about 300ml of distilled water. This mixture is brought to the final volume of 500ml with
distilled water. The N -1-naphthyl)-ethylenediamine dihydrochloride reagent was prepared
by dissolving 5.05g of dihydrochloride in 500ml of distilled water.
If the sample pH was above 9 its pH was adjusted to between 8 and 9 using dilute
hydrochloric acid. 5 ml aliquots of sample were buffered by the addition of 0.1ml
20% /w/v) ammonium chloride and then added to the reaction tubes. The reaction tubes
were shaken vigorously in an upright position on an oscillatory shaker (about 150
oscillations min −1 ). After shaking for 25min, a 2.5ml aliquot was removed to another
tube into which was mixed 50 µL of sulphanilamide reagent. After at least 2min, but not
more than 5min, 50µL N -1-naphthyl)-ethylenediamine dihydrochloride reagent was
added and the mixture allowed to react for 10min. The absorbance was determined in
1cm glass cuvettes using a spectrometer.
Fig. 2.26 Absorption spectra of nitrate and nitrite standard solutions containing
1mg L −1 of nitrogen
Source: Reproduced with permission from the Royal Society of
Chemistry [405]