<P> Typical titrations require titrant and analyte to be in a liquid (solution) form . Though solids are usually dissolved into an aqueous solution, other solvents such as glacial acetic acid or ethanol are used for special purposes (as in petrochemistry). Concentrated analytes are often diluted to improve accuracy . </P> <P> Many non-acid--base titrations require a constant pH throughout the reaction . Therefore, a buffer solution may be added to the titration chamber to maintain the pH . </P> <P> In instances where two reactants in a sample may react with the titrant and only one is the desired analyte, a separate masking solution may be added to the reaction chamber which masks the unwanted ion . </P> <P> Some redox reactions may require heating the sample solution and titrating while the solution is still hot to increase the reaction rate . For instance, the oxidation of some oxalate solutions requires heating to 60 ° C (140 ° F) to maintain a reasonable rate of reaction . </P>

Which of the following methods can be used to determine the end point in a titration