Evaluation of different SIA sample–buffer configurations using a fluoride-selective membrane electrode as detector

The peak profiles of four different buffer–sample SIA configurations, e.g. buffer–sample; sample–buffer; buffer–sample–buffer and sample–buffer–sample with the last two in the sandwich mode were evaluated with a fluoride-selective membrane electrode as detector. The best response characteristics and peak shapes as well as recovery and precision values were obtained for the buffer–sample configuration. For low concentration levels, sandwich SIA configurations are more suitable, when optimum buffer and pH are used. The utilisation of a cheap electrolyte with a minimum consumption of buffer and a cheap, robust instrumentation made the SIA system suitable for on-line determination of fluoride.