Spectrophotometric method of analysis using barbituric acid-pyridine in the distillate

This method can be used after preliminary distillation to measure cyanide ion concentrations of between 0.005 and 0.05 mg CN /1 in surface water and sewage. In this range, which corresponds to a cyanide content of 2.5 to 25 pg in 10 ml absorption solution (assuming that 500 ml of the water sample was used), Lambert s and Beer s laws are borne out. 

Where the total cyanide concentration in the water sample is higher, it is necessary to dilute the sample or use smaller quantities of sample, or to use volumetric determination techniques. 

Hydrochloric acid, 1 m Sodium hydroxide, OA m Buffer solution, pH 5A see p. 503 Chloramine T solution  

Dissolve 1 g analytically pure chloramine T (sodium p-toluene-sulpho-chloramide) in 100 ml distilled water. The solution can be kept for approx. 1 week, but its effectiveness should be checked iodometrically. 

Put 3 g analytically pure barbituric acid into a 50 ml measuring flask. Swirl with a little distilled water and then add 15 ml freshly distilled pyridine (b.p. 115 - 118 °C). Dilute with distilled water, shaking the flask constantly, until the barbituric acid is almost completely dissolved and then add 2.5 ml analytically pure hydrochloric acid (1.19 g/ml). Allow to cool to 20 °C before topping up to the 50 ml mark with distilled water. The reagent can be kept in a brown glass flask for 1 day or for 1 week in the refrigerator. 

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Spectrophotometric method of analysis using barbituric acid-pyridine in the distillate... 

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