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Practical thermometric titrimetry 29 7.4.4. Titration of nickel Nickel can be titrated thermometrically using disodium dimethylglyoximate as titrant. The chemistry is analogous to the classic gravimetric procedure, but the time taken for a determination can be reduced from many hours to a few minutes. Potential interferences need to be considered. 7.4.5. Titration of anionic and cationic surfactants Anionic and cationic surfactants can be determined thermometrically by titrating one type against the other. For instance, benzalkonium chloride (a quaternary type cationic surfactant) may be determined in cleaners and algaecides for swimming pools and spas by titrating with a standard solution of sodium dodecyl sulfate (see Figure 21a). Alternatively, anionic surfactants such as sodium lauryl sulfate can be titrated with cetyl pyridinium chloride (see Figure 21b). . Fig. 21 a: Titration of benzalkonium chloride with sodium dodecyl sulfate Fig. 21 b: Titration of sodium lauryl sulfate in shampoo by titration with cetyl pyridinium chloride. Acetonitrile added to repress micellerelated phenomena. Note sudden rise in temperature immediately prior to the endpoint.
30 Practical thermometric titrimetry Thermometric titrimetry offers an opportunity to observe the influence of micelles on the conduct of the determination. To avoid the influence of micelle-related phenomena on the outcome of the titration, it is sometimes necessary to add a suitable solvent such as acetonitrile. 7.4.6. Titration of non-ionic surfactants When an excess of Ba 2+ is added to a non-ionic surfactant of the alkyl propylene oxide derivative type, a pseudo-cationic complex is formed. This may be titrated with standard sodium tetraphenylborate (see Figure 22). Two moles tetraphenylborate react with one mole of the Ba 2+ / non-ionic surfactant complex. Fig. 22: Thermometric titration of a non-ionic surfactant in a formulation containing an anionic surfactant. 7.5. Miscellaneous aqueous titrations 7.5.1. Titration of fluoride with boric acid Acidic solutions of fluoride (including hydrofluoric acid) can be determined by a simple thermometric titration with boric acid. B(OH) 3 + 3 F – + 3 H + BF 3 + 3 H 2 O The titration plot illustrated in Figure 23 shows that the endpoint is quite rounded, suggesting that the reaction might not proceed to stoichiometric equilibrium. However, since the regions of the temperature curve immediately before and after the endpoint are quite linear, the second derivative of this curve (representing the intersection of tangents) will accurately locate the endpoint. Indeed, excellent precision can be obtained with this titration, with a CV of less than 0.1.
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Monograph - Metrohm

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