Premium
A flow‐injection/XPS investigation of the effect of redox equilibria on the selectivity of an iodide‐selective electrode
Author(s) -
Davey David E.,
Mulcahy Dennis E.,
O'Connell Gregory R.,
Smart Roger StC.
Publication year - 1995
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.1140070510
Subject(s) - chemistry , iodate , iodide , bromate , inorganic chemistry , selectivity , reagent , x ray photoelectron spectroscopy , thiosulfate , ascorbic acid , electrode , potentiometric titration , bromide , sulfur , catalysis , chemical engineering , organic chemistry , food science , engineering
Flow‐injection selectivity coefficients for a solid‐state iodide‐selective electrode were determined for three moderately interfering species—bromide, thiocyanate and thiosulfate–by injecting mixed iodide–interferent solutions into selected reagent streams. The use of neutral and acidified iodate and bromate oxidant streams was found to increase the selectivity of the iodide electrode towards the three interferents. The acidified streams also visibly modified the surface of the electrode membrane, although the resultant coating, ascribed to the formation of elemental sulfur and iodine, was easily removed by manual polishing with slurried alumina and a lint‐free cloth. X‐ray photoelectron spectroscopy (XPS) performed on pressed AgI/Ag 2 S pellets following immersion in the acidified iodate and bromate solutions revealed substantial surface modification, with the formation of AgIO 3 and AgBr, respectively. Use of ascorbic acid or metabisulfite reducing streams resulted in higher selectivity towards iodide than that obtained using either of the neutral oxidant streams, but less than that obtained in the presence of a simple nitrate reagent stream. In contrast, the use of a thiosulfate stream irreparably damaged the surface of the electrode to the point where subsequent flow‐injection experiments showed excessive peak broadening and very poor baseline recovery. XPS studies performed on the damaged membrane revealed a surface dominated by hydroxides and almost totally devoid of either AgI or Ag 2 S.