Junction potential drift

Drift Liquid junction potential at the reference not constant/Change the reference electrode. Loose contact/Rectify the fault. Electrode not plugged in properly/Rectify the fault. 

Using KOH or NaOH with pH in the range 13 to 14 as the inner electrolyte gives rise to a change in the liquid junction potential error of about 30 to 35 mV for one pH unit change in the outer test solution. Consequently, when pH in a high pH test solution gradually decreases due to carbonation, a reference electrode of this kind will drift . 

Choice of electrolyte for salt bridges and reference electrodes. Many of the difficulties encountered in potentiometric measurements can be attributed to erratic or drifting junction potentials caused by clogged junctions. Certain elementary rules should be observed in choosing the filling solution for a salt bridge or reference electrode, particularly when they will be used in organic solvents or solutions that are only partially aqueous. 

However, most of the time, the corrective term to E° is unfortunately unknown and beyond the error associated with potential measurements on an absolute (NHE) scale, mainly because of junction potential and reference electrode potential drifts. Thus in actual experiments Ej/2 and E° (or E°) are generally considered identical [94]. 

Baseline drift [Fig. 6.10(7)]. In optical detectors this is due to deposition of material on the windows of the flow cell. Such depositions may often be removed by injecting a reagent that dissolves the material, or by washing the system with a suitable wash liquid or detergent. In potentiometric detector systems, the drift may be caused by a change in the standard cell potential (either drift in the value of the indicator electrode or the reference electrode or both) or by a change in junction potentials. 

EOG Lower frequencies, small signal DC and low drift Electrode-skin junction potential, artifact reduction... 

In potentiometry with ISEs, there are two significant causes of potential drift (other than variation in the analyte activity) variations in the liquid junction... 

The most common reference electrode systems used in aqueous solutions are Ag/AgCl and the calomel electrode. If aqueous-based references are used in nonaqueous solution, however, large liquid junction is produced and often more serious, aqueous contamination of the nonaqueous cell occurs. Thus this combination is not recommended. The use of an Ag/Ag non-aqueous-based reference is suggested for nonaqueous electrochemistry. To avoid large junction potentials, the RE solvent should be as close in nature as possible to the cell solvent system. Often potentials are calibrated with a standard, such as ferrocene or cobaltocene. Suggested standards are listed in Table 2-2, along with reduction potentials and other properties. Construction of an Ag/Ag reference for nonaqueous use is shown in Figure 2-6. Reference electrodes can drift with time and must be carefully maintained. 

Stability of System (Drift, Reference Electrode, Junction Potential, Error)... 

Difficulties encountered with electrode measurements are most often traced directly to the reference electrode junction. Since this portion of the electrode is of such great importance to the measurement, its selection should be considered carefully. A pH meter with readability of at least 0.01 pH is usually employed for application when a high degree of accuracy is required. If the wrong reference electrode is used, an error or drift may occur that is of such magnitude that it could be observed even on a meter which has a readability of 0.1 pH. Some examples of typical problems arising from liquid junction potentials are shown in Figure 3.8. 

If a reference junction has a high resistance value or is exhibiting the typical problem of liquid junction potentials, such as readings which are drifting or require a long stabilization time, it may require clearing. There are a number of steps which can be implemented to lower the junction resistance and liquid junction potential ... 

It is difficult to measure accurately the hydrogen ion activity of high purity water having a low conductivity such as less than 10 micromhos. The problem arises from the high resistance and unbuffered nature of high purity water and from the liquid junction potential that is developed that is, the measurement is likely to be noisy because of the high sample resistance, it is likely to drift because of carbon dioxide adsorption, and it is likely to require considerable stabilization time or be in error because of a large liquid junction potential. 

A novel thin-film Ag AgCl structure was used. A pinhole or a combination of a pinhole and a cellulose acetate plug was used for the liquid junction [80]. Although the electrode with the pinhole junction showed potential drift to the positive side due to KCl effusion, the electrode with the combinatory junction could give a stable electrode potential within 1 mV for several hours. No dependence on KCl concentration or pH of the external electrolyte solution was observed in the latter type of electrode. The behavior of such miniature electrode was comparable to that of the commercial liquid-junction electrodes. 

A large variety of quasi-reference electrodes have been used based on metal wires such as silver [40], platinum [41], aluminium [42], tungsten [43], magnesium [44], etc. Typically electrodes are placed directly into the IL solution or separated from the main solution inside a fritted glass tube/compart-ment. In order to minimise liquid junction potentials in the latter case, the same ionic liquids as per the measurements is used as electrolyte. It is the authors experience that separation of the quasi-reference electrode allows for a reduction in potential drift when compared to direct insertion into the electrochemical cell. 

High ionic strength streams can also cause a slow drift in liquid junction potential of the reference electrode. For certain types of electrodes and process conditions, it can take hours for the reference electrode to reach an equilibrium state. In cases of contamination of the internals of the reference, the drift does not stop but continues. The best method of reducing junction potential errors and contamination is a flowing junction reference, but the flow rate of electrolyte must be small enough not to contaminate the sample. 

The short immersion time of laboratory electrodes reduces the errors from the chemical attack and dehydration of the glass of the measurement electrode and the drift of the liquid junction potential of the reference electrode. 

The most popular reference electrode has a silver-silver chloride inner electrode and a potassium chloride electrolyte. Hie potassium and chloride ions have about the same mobility, which minimizes the junction potential from a difference in diffusion rates. However, the potassium chloride solution is saturated and tends to crystallize especially at low temperatures, which reduces the diffusion rate and causes a drift in the associated potential at the junction. Also, silver from the silver-silver chloride internal element gets into the potassium chloride fill, reacts with sulfides and nitrates, and clogs the junction. 

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