Determination of tin using the AAS hydride technique

3 Determination of tin using the AAS hydride technique General remarks 

Tin ions are reduced to tin hydride from a boric-acid-buffered medium by means of sodium borohydride, transferred to a heated quartz cuvette by a current of inert gas, decomposed thermally, and the absorption of the atoms is measured in the beam of an atomic-absorption spectrometer. In the hydride technique, the element which is to be determined is volatilized as a gaseous hydride and in this way separated off from the matrix. Interference may occur if there is a considerable excess of elements such as antimony, arsenic, bismuth, mercury, selenium or tellurium which can also be volatilized with this technique. Above all, heavy metals such as copper and nickel in the solution have a disturbing effect during hydride formation itself. Interference due to phosphoric acid and hydrochloric acid may also be observed. It is therefore vital to check the method by the addition technique. 

Atomic absorption spectrometer with hydride attachment 

Dissolve 3 g sodium borohydride (NaBHz ) and 1 g sodium hydroxide (NaOH) in water and make up to 100 ml. 

Transfer 20 ml of the sample solution to the hydride system and adjust to a pH of 0.6 to 1 by adding sodium hydroxide solution or hydrochloric acid. Then add 600 mg of solid, crystalline boric acid as a buffer. Allow a constant current of inert gas (argon) to flow through the system at a rate of 60 1/h in order to expel the air. Following this, continuously add the 3 % sodium borohydride solution using a peristaltic pump. Tin ions are reduced to tin hydride and directed by the inert gas current into a quartz cuvette heated to 8 0 where they are thermally decomposed. Measure the absorption. 

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