Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 238

Fig. 2.33 Working curve for the nitrite analysis in the presence of large nitrate
excess. Cary spectrophotometer mod. 15, with 50Å/div., optical path
10cm
Source: Reproduced with permission from Marcel Dekker Inc. [540]
addition technique outlined below. In this technique, all solutions are made with the same
concentration of nitrate; then, a known and accurately measured amount of nitrite is
added to all solutions except to the reference blank.
All solutions, including the blank, are prepared to contain the same concentration of
nitrate. To all solutions, except the blank, a known and exactly measured amount of
nitrite is introduced to bring its concentration to the 2×10 −3 mol L −1 range; this
concentration was calculated from the known molar absorptivity of nitrite (E 355 =24.0) in
order to raise the absorbance of the sample into the region of minimum photometric error.
Therefore, the solutions to be analysed for nitrite contain the same added background
concentration of nitrate and nitrite.
The excellent results obtained under these conditions for a range of nitrite standards are
shown in Fig. 2.33.
2.63.9 Ion chromatography
The application of this technique is discussed under multianion analysis in sections
12.2.1, 12.2.4 and 12.2.5.