On-line distillation systems

In these configurations, the vapour or residue containing the analyte(s) Is Introduced continuously Into the instrument or analyser. A distinction should be made depending on whether the analyte of interest Is volatile or not. 

When it is the vapour phase which is to be collected, the system uses a reagent to generate or release the volatile species, which are led directly to the analyser. Below are described two examples differing in the need for heating, compulsory in one and dispensable in the other. 

Pihlar and Kosta [3] have developed a continuous distillation system for the amperometric determination of cyanide In water with the aim of avoiding interference from other electroactive species. The configuration is depicted in Fig. 4.7. A peristaltic pump sets the flow of sample, which Is continuously aspirated, and that of the different reagents, in addition to regulating the two outgoing streams of the system. The sample, acidulated with a phosphoric acid stream, is introduced Into the distillation unit, also shown in Fig. 4.7. Its 

7 On-line distillation system for the amperometric determination of cyanide in water, (a) Diagram of the continuous system for establishment of the different streams, (b) Details of the distillation and absorption units. (Reproduced from [3] with permission of Elsevier). 

There are several commercial accessories available with different degrees of automation for hydride generation as an on-line preliminary stage in the determination of species by non-flame atomic absorption spectroscopy. An interesting alternative on account of its simplicity involves generating the hy- 

---