Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 467

Chapter 7
Anions in potable waters
7.1 Alkalinity
7.1.1 Single point titration method
Basson and Van Staden [1] have described a single point titration system for the
determination of total alkalinity in potable and domestic waters, based on flow injection
analysis. Water samples are injected automatically into the flow system using a flow
injection sampling unit. A sampling cycle of 30s allows 120 samples per h to be
analysed. The sample is reacted with an acid linear response buffer solution and the pH of
the resulting solution is measured with a glass electrode in a flow through assembly.
Details of the procedure are given below.
R eagents: Unless otherwise specified all reagents are of analytical grade quality.
The buffer solution is prepared by mixing 50ml of 6.01 g diethylmalonate in 7ml
concentrated hydrochloric acid diluted to 500ml, 59ml of 7.88g citric acid diluted to
500ml, 150ml of 5.22g p-nitrophenol diluted to 500ml, 3.87g diethylbarbituric acid
diluted to 500ml, 50ml of 2.32g boric acid diluted to 500ml and 50ml of 3.53g phenol
diluted to 500ml. The final solution is made 0.1mol L −1 with respect to sodium chloride.
Apparatus consisting of 30rpm flow injection sample, pH meter and micro blood
electrode consisting of a micro sensor assembly (Beckman Part No 580621) and a pH-
electrode (Beckman Part No. 39045), Hitachi model QPD 53 potentiometric recorder.
P rocedure: A schematic flow diagram for the system is shown in Fig. 7.1 Tygon
tubing of 0.50mm diameter was used and all connectors were made from Perspex. The
carrier stream consists of 0.1mol L −1 sodium chloride.
Water samples are automatically injected into the flow system by using a flow
injection sampling unit. Use a sampling cycle of 30s between successive samples giving a
capacity of 120 samples per h. Actuate the valve system on a time basis which is
correlated with the sampler unit.