Acetonitrile reference electrodes

Versus a Ag/AgN03 (0.01 M) + 0.1 M tetraethylammoniumperchlorate in acetonitrile reference electrode. The value refers to both the hexagonal and the (1x1) phase. 

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

Figure 3.45 (a) Spectral dependence of the optical response on pulsing a lead cathode in 0.4 M tetramethylammonium perchlorate in propylene carbonate saturated with C02 from + I.0V to +0.2 V at 30 Hz. The reference electrode was Li/0.5M Li +. (b) As in (a) except solvent changed to acetonitrile. From Aylmer-Kelly et at. (1973). 

Most common reference electrodes are silver-silver chloride (SSC), and saturated calomel electrode (SSC, which contains mercury). The reference electrode should be placed near the working electrode so that the W-potential is accurately referred to the reference electrode. These reference electrodes contain concentrated NaCl or KC1 solution as the inner electrolyte to maintain a constant composition. Errors in electrode potentials are due to the loss of electrolytes or the plugging of the porous junction at the tip of the reference electrode. Most problems in practical voltammetry arise from poor reference electrodes. To work with non-aqueous solvents such as acetonitrile, dimethylsulfoxide, propylene carbonate, etc., the half-cell, Ag (s)/AgC104 (0.1M) in solvent//, is used. There are situations where a conventional reference electrode is not usable, then a silver wire can be used as a pseudo-reference electrode. 

The reduction is usually made in a multi-compartment electrochemical cell, where the reference electrode is isolated from the reaction solution. The solvent can be water, alcohol or their mixture. As organic solvent A,A-dimethyl form amide or acetonitrile is used. Mercury is often used as a cathode, but graphite or low hydrogen overpotential electrically conducting catalysts (e.g. Raney nickel, platinum and palladium black on carbon rod, and Devarda copper) are also applicable. 

Cyclic voltammetry was conducted using a Powerlab ADI Potentiostat interfaced to a computer. A typical three electrode system was used for the analysis Ag/AgCl electrode (2.0 mm) as reference electrode Pt disc (2.0 mm) as working electrode and Pt rod (2.0 mm) as auxiliary electrode. The supporting electrolyte used was a TBAHP/acetonitrile electrolyte-solvent system. The instrument was preset using a Metrohm 693 VA Processor. Potential sweep rate was 200 mV/s using a scan range of-1,800 to 1,800 mV. 

Cyclic voltammetry experiments were controlled using a Powerlab 4/20 interface and PAR model 362 scanning potentiostat with EChem software (v 1.5.2, ADlnstruments) and were carried out using a 1 mm diameter vitreous carbon working electrode, platinum counter electrode, and 2 mm silver wire reference electrode. The potential of the reference electrode was determined using the ferrocenium/ ferrocene (Fc+/Fc) couple, and all potentials are quoted relative to the SCE reference electrode. Against this reference, the Fc /Fc couple occrus at 0.38 V in acetonitrile and 0.53 V in THF [30, 31]. 

Pavlishchuk and Addison [11] have discussed the foregoing discrepancies and made careful measurements of the reference electrodes commonly utilized by investigators in measuring potentials in acetonitrile. The correction to be applied for converting a potential measured against a reference electrode, ref to the ferrocene standard. Eye, can be expressed as ... 

All aqueous potential values are referenced to the standard hydrogen electrode. Nonaqueous potential values are referenced to ferrocene (Fc) if possible. Other references are indicated in parentheses where SCE represents the standard calomel electrode, A1 represents the Ag/Ag+ reference electrode ([Ag+] = 0.01 M unless otherwise indicated) and A2 represents the Ag/AgCl reference electrode. In acetonitrile, potential values referenced to SCE may be corrected to the ferrocene reference standard by subtracting 0.380 V, depending upon the anion present (a) Ref 11, (b) Ref 10c. c [Ag+] = 0.1 M. 

Silver-Silver Ion Electrode This is the most popular reference electrode used in non-aqueous solutions. Since Pleskov employed it in acetonitrile (AN) in 1948, it has been used in a variety of solvents. It has a structure as shown in Fig. 6.1(a) and is easy to construct. Its potential is usually reproducible within 5 mV, if it is prepared freshly using pure solvent and electrolyte. The stability of the potential, however, is not always good enough. The potential is stable in AN, because Ag+ is strongly solvated in it. In propylene carbonate (PC) and nitromethane (NM), however, Ag+ is solvated only weakly and the potential is easily influenced by the presence of trace water and other impurities. In dimethylformamide (DMF), on the other hand, Ag+ is slowly reduced to Ag°, causing a gradual potential shift to the negative direction.2) This shift can reach several tens of millivolts after a few days. 

Two analytical methods for priority pollutants specified by the USEPA (38) use HPLC separation and fluorescence or electrochemical detection. Method 605, 40 CFR Part 136, determines benzidine and 3,3-dichlorobenzidine by amperometric detection at +0.80 V, versus a silver/silver chloride reference electrode, at a glassy carbon electrode. Separation is achieved with a 1 1 (v/v) mixture of acetonitrile and a pH 4.7 acetate buffer (1 M) under isocratic conditions on an ethyl-bonded reversed-phase column. Lower limits of detection are reported to be 0.05 /xg/L for benzidine and 0.1 /xg/L for 3,3-dichlorobenzidine. Method 610, 40 CFR Part 136, determines 16 PAHs by either GC or HPLC. The HPLC method is required when all 16 PAHs need to be individually determined. The GC method, which uses a packed column, cannot adequately individually resolve all 16 PAHs. The method specifies gradient elution of the PAHs from a reversed-phase analytical column and fluorescence detection with an excitation wavelength of 280 nm and an emission wavelength of 389 nm for all but three PAHs naphthalene, acenaphthylene, and acenaphthene. As a result of weak fluorescence, these three PAHs are detected with greater sensitivity by UV-absorption detection at 254 nm. Thus, the method requires that fluores-... 

Acetonitrile interacts with the d10 metal ions Cu1 and Ag1 to form solvated species of marked stability. This stability has been used in potentiometry where the Ag, 0.01 M AgN03 couple in acetonitrile has been recommended as a reversible reference electrode.154... 

This would be accomplished by immersing the chemically modified electrode, a reference electrode, and an auxiliary electrode into an appropriate electrolyte solution (e.g., 0.1 M NaC104 in acetonitrile). The potential difference between the modified electrode (the working electrode) and the reference would then be adjusted to a value appropriate to drive this reaction, using a commercially available potentiostat, and the resulting anodic current would be measured. 

Reference Electrode Acetonitrile Propylene Carbonate Dimethyl Formamide Dimethyl Sulfoxide... 

Quasireference electrode (QRE) — (-> reference electrode, pseudoreference electrode). An electrode that maintains a given, but generally not well-defined, potential during the course of a series of electrochemical experiments. It has the advantage of not contaminating the test solution by solvent or ions that a conventional reference electrode might contain and transfer. Thus in studies in aprotic solvents, like acetonitrile, a silver wire can behave as a QRE. It must be calibrated with respect to a true reference electrode or reference redox couple that is added at the end of the experiments to obtain meaningful potential values. 

Fig. 20. Cyclic voltammogram of 38 in acetonitrile 0.1 M n-Bu4NPF6 as electrolyte Ag/AgN03 reference electrode (ref 43)...

The substrates and products just noted were separated on an Ultrasphere I.P. CI8 column (4.6 mm x 250 mm, 5 /tm). The mobile phase contained 75 mAf sodium phosphate (pH 2.75), 1 mM sodium octylsulfate, 500 fiM EDTA, and 13% (v/v) acetonitrile. Quantitation was by electrochemical detection of the products using 0.75 V versus an Ag/AgCl reference electrode. 

Other careful electrochemical measurements of the oxidation potentials of 2,4,6-tri-t-butylphenol and 2,6-di-t-butyl-4-methylphenol in acetate buffered ethanol or acetonitrile have been measured by Mauser et al.184). They determined the static potentials using a boron carbide indicator and a mercury/mercury-acetate reference-electrode. Since in this case the oxidation of the phenols and not the phenolates to the phenoxyls has been determined the oxidation potentials cannot be compared with those in Table 12. For other electrochemical oxidations of phenols in buffered aqueous solutions using a graphite electrode see Ref. 185 186>. 

Parker and Bethell, 1980. Measurements made at a platinum electrode at 23°C with a supporting electrolyte (BU4NBF4) concentration of 0.1 M. Measurement precision was better than 0.2 mV in the peak potentials. The E" values are the mean of 15 determinations and are referred to a bias setting of —1.50 V vs an Ag/Ag+ reference electrode in acetonitrile... 

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