Ion chromatographic determination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode.
The determination of free sulfide and cyanide by pulsed amperometric detection (PAD) at a silver-working electrode was improved through a deep de-oxygenation (at least 10 min) of both standard and real solutions containing the two analytes and adopting a two-potential waveform able to eliminate Ag working electrode fouling. The waveform stepped around the oxidation of Ag in the presence of 0.1-0.4 M hydroxyl ion, from -0.1 to 0.1 V versus saturated calomel electrode (SCE). The eluent composition (0.4 M NaOH plus 7.5 mM oxalate solution) allowed a very good column efficiency and selectivity. The presence of a polysulfide species was hypothesized in sulfide solutions that had not been de-oxygenated and aged. The polysulfide eluted just before sulfide and was confirmed by a chemical test with SO3(2-) producing the elimination of the polysulfide peak. Detection limits, according to the Hubaux-Vos method, were 1.0 and 2.0 microg/l for S2- and CN , respectively. We demonstrated good performance of the optimized method by repeatedly injecting standard solutions and by analyzing different real matrices. The method exhibited very good accuracy and repeatability (10 microg/l and a 500 microl injection loop, had a repeatability better than 3% for sulfide and 100 microg/l had a repeatability better than 1% for cyanide). The two-potential waveform ensured long-term stability of the electrode surface that required no manual polishing procedure for at least 1 month (20 analysis per day).
Giuriati
Caterina
C
Ambiente s.p.a., Centro Igiene e Protezione Ambiente, Piazzale Donegani 12, 44100 Ferrara, Italy.
Cavalli
Silvano
S
Gorni
Alfredo
A
Badocco
Denis
D
Pastore
Paolo
P
D002853:Chromatography, Liquid / Q000379:methods*; D003486:Cyanides / Q000032:analysis*; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D012834:Silver; D013440:Sulfides / Q000032:analysis*
D003486:Cyanides; D013440:Sulfides; D012834:Silver