TY - JOUR
T1 - A caffeine-sensitive membrane electrode
T2 - Previous misleading report and present approach
AU - Katsu, Takashi
AU - Tsunamoto, Yumi
AU - Hanioka, Nobumitsu
AU - Komagoe, Keiko
AU - Masuda, Kazufumi
AU - Narimatsu, Shizuo
N1 - Funding Information:
This work was supported by a Grant-in-Aid for Scientific Research (KAKENHI 19590039) from the Japan Society for the Promotion of Science. We are grateful to Ms. Yuko Mitani of this faculty for technical assistance.
PY - 2008/7/14
Y1 - 2008/7/14
N2 - 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 pKa 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 pKa 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 50 μM with a slope of 55 mV 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.
AB - 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 pKa 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 pKa 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 50 μM with a slope of 55 mV 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.
KW - 2-Fluoro-2′-nitrodiphenyl ether
KW - Caffeine determination
KW - Caffeinium ion
KW - Ion-selective electrode
KW - Solvent mediator
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U2 - 10.1016/j.aca.2008.05.027
DO - 10.1016/j.aca.2008.05.027
M3 - Article
C2 - 18558123
AN - SCOPUS:46549088801
SN - 0003-2670
VL - 620
SP - 50
EP - 54
JO - Analytica Chimica Acta
JF - Analytica Chimica Acta
IS - 1-2
ER -