Electrode interference

Hua et al. [595] have described an automated flow system for the constant-current reduction of uranium (VI) onto a mercury film-coated fibre electrode. Interference from iron (III) was eliminated by addition of sulfite. The results obtained for uranium (VI) in two reference seawater samples, NASS-1 and CASS-1, were 2.90 and 2.68 g/1, with standard deviations of 0.57 and 0.75 g/1, respectively. 

Table 17-1 shows that an overpotential of 1 V is required for 02 formation at the Pt anode. Overpotential is the main reason why not much happens in Figure 17-6 until —2 V is applied. Beyond —2 V, the rate of reaction (the current) increases steadily. Around —4.6 V, the current increases more rapidly with the onset of reduction of H30+ to H2. Gas bubbles at the electrode interfere with deposition of solids. 

Sources of Error. Several common causes nl measurement problems are electrode interferences and/or fouling of the pH sensor, sample matrix effects, reference electrode instability, and improper calibration of the measurement system. 

In measurements with ion-selective electrodes, interference by other ions is expressed by selectivity coefficients as in Eq. (17). If the nature of the ion-selective membrane is known, these interferences may easily be estimated. For example, in the determination of chloride with a Cl -selective electrode containing AgCl as the electroactive component in its membrane, concentrations of bromides or iodides (generally X ) must be controlled because they form less soluble silver salts than AgCl the solubility products of corresponding silver halides are used in Eq. (20) to estimate the selectivity coefficient ... 

Detailed analysis of these data, and data collected at the same wells on different dates, will be published elsewhere. Data are presented here only to illustrate the kind of electrode response which can be expected in more complicated redox environments. The use of the two types of redox electrodes again illustrates the utility of a dual electrode approach to ORP measurements. Substantial differences between Pt and WIG electrodes indicate electrode interferences which may obviate calculations based on the Nernst equation. 

Interferences. Broadly speaking, interferences may be classed into two general categories chemical interferences in solution, such as complexation, and electrode interferences due to less than perfect electrode specificity. An ion-selective electrode will respond, more or less strongly, to ions other than the one for which it is nominally designed. 

Electrogravimetric analysis would be simple if there were only a single analyte in an otherwise inert solution. In practice, there may be other electroactive species that interfere. Water decomposes to H2 at the cathode and to O2 at the anode at sufficiently high voltage. Gas bubbles at an electrode interfere with deposition of solid. Because of these complications, control of electrode potential is important for successful analysis. 

Table 2. Typical selectivity coefficients of nitrate electrode interferants...

Two nuiin types of interferences are encountered by ion selective electrodes. Thqr are (0 method interference, and fit) electrode interference. 

One primary difference must be understood in characterizing supercapacitors using the three- and two-electrode cells. The information obtained using the former technique comes solely from the target electrode process without interference from the other electrode. With the latter technique, the information obtained is the sum of contributions from both electrodes. Interference from the second electrode must be subtracted to determine the sole contribution of the target electrode. The information obtained from the threecell technique is ex situ and does not necessarily reflect the real situation. However, it is commonly used for fast screening because it does not require an entire supercapacitor assembly The information obtained from the twocell method is considered in situ or close to the real operating conditions. 

Light from the counter-electrode interferes with the light reflected from the membrane, giving an interference ring each time the optical path length changes by half a wavelength ... 

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