Electrolyte solutions buffer selection

In practice isotachophoresis is usually performed in narrow tubes with electrodes at either end and is one form of capillary electrophoresis. For the separation of a particular type of ion, e.g. an anion, two buffered electrolyte solutions are selected that have different anions but a common cation with a buffering capacity. One of the anions (termed the leading electrolyte) should show a greater mobility than the other anion and occupies the anodic end of... 

Reference solutions In an ion-selective electrode assembly the internal reference solution (Figure 13-2) performs a dual function. It must contain one ionic species to provide a stable electrode potential for the internal reference half-cell and another to provide a stable membrane potential at the inner solution-membrane interface. In the usual pH glass electrode assembly the inner reference half-cell is Ag/AgCl the potential is stable because the internal reference solution is 0.1 M in chloride ion. The potential of the inner membrane surface also is stable because the internal filling solution is 0.1 ilf in hydrogen ion (or a buffered solution). The single-electrolyte solution 0.1 Af HCl serves admirably to provide a high and stable concentration of both ions. 

Once the system variables are set within reasonable ranges, the parameters that have most effect on migration times and selectivity are the composition, concentration and pH of the electrolyte solution, and the presence of additives, if used, to provide additional selectivity [100,101,404-406]. Four features are important for an acceptable separation (i) the analytes must have different mobilities (ii) the electrolyte solution must be homogeneous and the field strength uniform along the column (iii) neither analytes nor matrix components must interact with the column wall and (iv) the conductivity of the electrolyte solution must exceed the conductivity of the sample. Suitable buffers with their pKa and ion mobility values are given in Table 8.2. 

The CHEMFET is a special modification of the ion sensitive field effect transistor (ISFET) in which the gate oxide is covered with an ion selective membrane [2]. The ion selectivity is introduced by incorporation of ion-selective receptor molecules in a hydrophobic polymer membrane. Between the sensing membrane and the gate oxide of the ISFET a buffered hydrogel is introduced which serves as inner electrolyte solution and eliminates pH sensitivity and CO2 interference (Figure 1) [3],... 

---