A process for preparing a poly(aryl ether ketone) by a) obtaining i) 4,4'-difluorobenzophenone, and ii) one or more nucleophiles, wherein said nucleophiles are selected from the group consisting of p-hydroquinone, 4,4'-dihydroxybenzophenone, 4,4'-biphenol, 1,4-bis-(p-hydroxybenzoyl)benzene, 1,3-bis-(p-hydroxybenzoyl)benzene, and mixtures thereof, b) and reacting the obtained 4,4'-difluorobenzophenone and the one or more nucleophiles, to form the poly(aryl ether ketone), wherein the obtained 4,4'-difluorobenzophenone comprises a total concentration of one or more oxidizing species, as measurable by TiCl 3 back titration analysis of the obtained 4,4'-difluorobenzophenone, corresponding to between about 1.5 and about 80 μmol of TiCl 3 oxidized by the oxidizing species during the TiCl 3 back titration analysis per gram of obtained 4,4'-difluorobenzophenone, wherein said TiCl 3 back titration analysis comprising the steps of: c) preparing a 4,4'-difluorobenzophenone sample solution by contacting a measured quantity of 4,4'-difluorobenzophenone that may comprise one or more oxidizing species, one or more solvents, and a pH buffer, to form at least some of a sample solution within a measurement vessel, d) reducing the oxidizing species present in the sample solution with an excess initial quantity of at least one or moreTi 3+ compounds, e) measuring the quantity of excess Ti 3+ compounds remaining in the sample solution after the reduction of the oxidizing species, by back-titrating the sample solution after the reduction of the oxidizing species with an oxidant for the remaining Ti 3+ compounds, and f) calculating the quantity of Ti 3+ compounds used to reduce oxidizing species in the 4,4'-difluorobenzophenone, and g) relating the quantity of Ti 3+ compounds used to reduce oxidizing species in the 4,4'-difluorobenzophenone during the titration to the concentration of oxidizing species in the 4,4'-difluorobenzophenone by assuming that each mole of Ti 3+ compound provides one electron for the reduction of the one or more oxidizing species. a) obtaining i) 4,4'-difluorobenzophenone, and ii) one or more nucleophiles, wherein said nucleophiles are selected from the group consisting of p-hydroquinone, 4,4'-dihydroxybenzophenone, 4,4'-biphenol, 1,4-bis-(p-hydroxybenzoyl)benzene, 1,3-bis-(p-hydroxybenzoyl)benzene, and mixtures thereof, i) 4,4'-difluorobenzophenone, and ii) one or more nucleophiles, wherein said nucleophiles are selected from the group consisting of p-hydroquinone, 4,4'-dihydroxybenzophenone, 4,4'-biphenol, 1,4-bis-(p-hydroxybenzoyl)benzene, 1,3-bis-(p-hydroxybenzoyl)benzene, and mixtures thereof, b) and reacting the obtained 4,4'-difluorobenzophenone and the one or more nucleophiles, to form the poly(aryl ether ketone), c) preparing a 4,4'-difluorobenzophenone sample solution by contacting a measured quantity of 4,4'-difluorobenzophenone that may comprise one or more oxidizing species, one or more solvents, and a pH buffer, to form at least some of a sample solution within a measurement vessel, d) reducing the oxidizing species present in the sample solution with an excess initial quantity of at least one or moreTi 3+ compounds, e) measuring the quantity of excess Ti 3+ compounds remaining in the sample solution after the reduction of the oxidizing species, by back-titrating the sample solution after the reduction of the oxidizing species with an oxidant for the remaining Ti 3+ compounds, and f) calculating the quantity of Ti 3+ compounds used to reduce oxidizing species in the 4,4'-difluorobenzophenone, and g) relating the quantity of Ti 3+ compounds used to reduce oxidizing species in the 4,4'-difluorobenzophenone during the titration to the concentration of oxidizing species in the 4,4'-difluorobenzophenone by assuming that each mole of Ti 3+ compound provides one electron for the reduction of the one or more oxidizing species.