I. Svancara et al., VOLTAMMETRIC DETERMINATION OF SILVER AT ULTRATRACE LEVELS USING A CARBON-PASTE ELECTRODE WITH IMPROVED SURFACE CHARACTERISTICS, Electroanalysis, 8(4), 1996, pp. 336-342
A differential pulse anodic stripping voltammetric method for the dete
rmination of silver is described. A new type of electrodeposition for
preconcentrating the analyte, Ag+, was investigated, enhancing the ele
ctrolytic accumulation efficiency onto a carbon paste electrode by ion
pair formation. A carbon paste electrode containing tricresyl phospha
te as a pasting liquid was modified in situ with heptylsulfonic acid (
sodium salt). The modifier gave rise to an additional accumulative eff
ect towards the target ions based on ion pairing which resulted in an
enhanced sensitivity of the electrode. Additional activation of the el
ectrode surface at -1.0 V (vs. SCE) for 60 a improved the detection li
mit significantly. The detection limit was found to be 2.5 x 10(-12) M
Ag+ (accumulation time 15 min), and could be even lowered by increasi
ng the period of preelectrolysis. The current response was linearly de
pendent on the concentration up to 2 x 10(-5) M Ag under optimized con
ditions. The effects of paste composition, voltammetric parameters, co
mposition of the supporting electrolyte as well as the influence of al
kylsulfonic acids and of cathodic activation upon the determination of
Ag were studied. Interferences from about 20 elements were investigat
ed with particular attention to Cu, Hg, and Au. By masking with ethyle
nediaminetetraacetate (EDTA), Cu and Hg did not affect the response of
Ag up to a 10 000-fold and 500-fold molar excess in concentration, re
spectively. Au did not interfere with the determination of Ag up to a
100-fold molar excess if its absolute concentration was lower than 5 x
10(-7) M. For higher concentration levels, [AuCl4](-) could be separa
ted by passing the analyte solution through an anion-exchanger column
(Dowex-1) prior to stripping analysis. Due to the extremely low detect
ion limit and high selectivity, the method could be applied to determi
ne Ag at its ubiquitous level in tap water. With this method, the corr
osion of silver cutlery in tap water could be monitored. The results a
greed well with those obtained by using inductively coupled plasma mas
s spectrometry (ICP-MS).