Microanalytical Determination of Formaldehyde by Direct Titration with Hydroxylamine Using Interdigitated Microelectrode Array Biamperometric End-Point Indicator

摘要

An interdigitated microelectrode array (IDA) biamperometric titration is presented for the microdetermination of formaldehyde. It is based on a direct titration of formaldehyde with hydroxylamine under the formation of formaldoxime. The released hydrogen cations react with hydroxyl anions in 0.1 M NaOH. The interdigitated pair of two individually polarizable microelectrodes serves as a biamperometric end-point indicator. Hydroxylamine together with dissolved free oxygen behave as a quasi reversible mixed redox system, therefore a significant increase of current flowing between the IDA segments polarized by 100 mV is observed when the first excess of titrant appears in the titrated solution. Because of the small dimension of the IDA sensor this principle can be extended for a microanalytical variant of this method. Formaldehyde contents down to 10−3 M in small volume waste water samples could be determined by this technique. These samples usually contain carboxylic acids which interfere in iodimetric determinations, but do not influence the titration of formaldehyde with hydroxylamine.