Microtitrations of organic bases in nonaqueous solvents

Gutterson, Milton; S., T.

doi:10.1007/bf01221828

Cited by 10 publications

(3 citation statements)

References 6 publications

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“…2. The present result was quite reasonable, because the pK a value of caffeinium ion was around 0.7 [2][3][4], and the neutral form was dominant in around pHs 4-10 region examined.…”

Section: Resultsmentioning

confidence: 64%

“…The electrode had a wide working pH range (5.5-9.5) and exhibited a Nernstian response in the range of 10 −6 to 10 −2 M caffeine with a slope of 59 mV per concentration decade. This result was very strange, because the pK a value of caffeinium ion was reported to be around 0.7 [2][3][4], and thus the neutral form was dominant in neutral pH region, according to an equilibrium equation between the protonated and the neutral form of caffeine shown in Fig. 1 Hassan et al [1], showing a response to the neutral form of caffeine, was questionable.…”

Section: Introductionmentioning

confidence: 66%

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A caffeine-sensitive membrane electrode: Previous misleading report and present approach

Katsu

Tsunamoto

Hanioka

et al. 2008

Analytica Chimica Acta

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Although a previous study [S.S.M. Hassan, M.A. Ahmed, M.M. Saoudi, Anal. Chem. 57 (1985) 1126] had shown that a caffeine-sensitive electrode made with picrylsulfonate and 1-octanol as a cation-exchanger and a solvent mediator, respectively, had a wide working pH range (5.5-9.5) and exhibited a Nernstian response, we could not find such response in this electrode. The present result was reasonable, because the pK(a) value of caffeinium ion was reported to be around 0.7 and the neutral form of caffeine was predominant in the pH range examined. Thus, we reinvestigated the response characteristics of a caffeine electrode, taking into consideration the pK(a) value, and constructed a new electrode with a combination of the lipophilic cation-exchanger, tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate (HFPB), and the solvent mediator with high degree of dielectric constant, 2-fluoro-2'-nitrodiphenyl ether (FNDPE). This electrode showed a pH-dependent response to caffeinium ion and gave a detection limit of 50muM with a slope of 55mV per concentration decade at pH 2. The use of other solvent mediators was less effective than that of FNDPE. The electrode was applied for the determination of caffeine in some central stimulants.

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