Applications

This Bulletin describes the simultaneous determination of gold and copper by potentiometric titration using an Fe(II) solution as titrant. Fe(II) reduces Au(III) directly to the free metal, whereas Cu(II) does not react. By the addition of fluoride ions the Fe(III) is complexed and a shift of the redox potential is effected. Afterwards, potassium iodide is added, thus reducing the Cu(II) to Cu(I), and the free iodine is again titrated with the Fe(II) solution using a Pt Titrode.Chemical reactions:Au(III) + 3 Fe(II) → Au + 3 Fe(III)2 Cu(II) + 2 I- → 2 Cu(I) + I2I2 + 2 Fe(II) → 2 I- + 2 Fe(III)

Ag electrodes are used for the indication of the potentiometric endpoints in precipitation titrations between silver and halide or sulfide ions. A coating on the silver ring may increase the sensitivity of the electrode and can thus reduce the limit of detection. This is why a variety of coated Ag electrodes are commercially available. This bulletin describes how the silver ring of Ag electrodes can be coated with AgCl, AgBr, AgI or Ag2S by electrolysis.

If chloride and bromide are present in approximately equal molar concentrations they can be titrated directly with silver nitrate solution after addition of barium acetate. If, however, the molar ratio n(Br-) : n(Cl-) changes from 1 : 1 to 1 : 5, 1 : 10, 5 : 1 or 10 : 1 then greater relative errors must be expected with this method. The Bulletin describes an additional titration method that allows bromide to be determined in the presence of a large excess of chloride. The determination of small chloride concentrations in the presence of a large excess of bromide is not possible by titration.

In the following tables, the half-wave potentials or peak potentials of 90 metal ions are listed. The half-wave potentials (listed in volts) are measured at the dropping mercury electrode (DME) at 25 °C unless indicated otherwise.

Two methods are described for the determination of chromium: a biamperometric titration and a polarographic analysis.

A potentiometric, nonaqueous method is described for analyzing nitrating acid using cyclohexylamine as titrant. Both sulfuric and nitric acid can be determined quantitatively.

Two electrometric methods for determining the pH value of papers with homogeneous and heterogeneous pH cross-sections are described.

Carbonyl compounds (CC) occur in many products, such as bio-oils and fuels, cyclic and acyclic solvents, flavors and mineral oils. Carbonyl compounds can be responsible for the instability of these products during storage or processing. Especially pyrolysis bio-oils are known to cause issues during storage, handling and upgrading. This bulletin describes an aqueous and a non-aqueous analytical titration method for the determination of carbonyl compounds by potentiometric titration.

The determination of cyanide is very important not only in electroplating baths and when decontaminating wastewater but, due to its high toxicity, also in water samples in general. Concentrations of 0.05 mg/L CN- can already be lethal for fish.This Bulletin describes the determination of cyanide in samples of different concentrations by potentiometric titration.Chemical reactions:2 CN- + Ag+ → [Ag(CN)2]-[Ag(CN)2]- + Ag+ → 2 AgCN

It is essential to know before starting the sample analysis if the electrode is in a good state or not. A well workingelectrode will increase the quality of your results, as the accuracy and precision will be increased. Furthermore, tedious error tracking can be omitted and no sample is wasted due to a defect or old electrode. There exist several ways how to check metal electrodes, e.g., measurement of redox potentials, potentiometric titration or bivoltammetric titration. This bulletin describes the best methods for the various by Metrohm available metal electrodes.