Optimization of parameters for differential pulse voltammetry at the hanging mercury drop electrode

Abstract

The detection limit o f differential pulse voltammetry at a hanging mercury drop electrode is investigated. The most important result of this study is that very small pulse amplitudes considerably improve the signal-to-background ratio and lead to lower detection limits. Due to the fact that (in practice) the background current does not originate only from capacitive properties of the electrode, an optimal pulse duration also exists, which guarantees the highest signal-to-background ratio. It is shown that the background current consists of the capacitive current and a very noisy but, on average, constant component, presumably of a faradaic nature that originates from impurities. The effects of the prepulse time, the pulse amplitude, the pulse duration, the step height of the staircase ramp, and the duration of the current sampling time on the signal and background intensity and noise are described, LNTRODUCTIONDifferential pulse voltammetry (DW) has become the most widely used voltammetric method because of its high sensitivity and general applicability [I]. For an analytical chemist there are two main features of any analytical method, that is, the detection limit and the selectivity. Both properties of DPV have been studied, but not always rigorously.Optimal parameters for DPV and differential pulse polarography (DI'P) were established long ago. Most authors [2-81 recommend a pulse amplitude of mV with a 20-40 ms time delay after the pulse is applied and before sampling the current. The current measurement is made during a time interval o f 20-40 ms. Pulse amplitudes between 10 and 100 mV are often viewed as a good compromise between large values of peak current and an adequate resolution [l, 6, 81, but the detection limit depends on the ratio of faradaic-to-background current, on the sensitivity (faradaic current/concentration), and on the noise level of the background current. Hence, we studied the influence of several parameters of DPV on the detection limit.' To whom correspi)ndence should be addressed. THEORETICAL CONSIDERATIONSThe charging current (at the dropping mercury electrode) in differential pulse polarography is given by the following relationship [9]: where 4[E2] and q [E1 ] are the charge densities at potentials E2 and E l , respectively, t is the time of current measurement before the pulse is applied, and tp is the time of measurement after the pulse is applied. According to Equation 1, the charging current will be smaller at higher tlt, ratios, as will the pulse amplitudes [E2 -El] = E,. The charge density, q, depends on the nature and concentration of the electrolyte and on the dc potential. At a stationary electrode the charging current decays according to. 5 --flRc,, I, = e R where R is the resistance in ohms and c,) is the double layer capacity.The faradaic peak current, if,,, will increase with increasing pulse amplitude [ 101: Tt, u + 1 ( 3 ) 0 1989 VCH Puhlihrrs. Inc

Analysis of water in room temperature ionic liquids by linear sweep, differential pulse and square wave cathodic stripping voltammetries

“…Fig. 4B shows a typical record when DPV is used as the stripping technique, with a potential program optimized for that purpose according to literature recommendations [64]. In Fig.…”