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Prothiofos ( O -(2,4-dichlorophenyl) O -ethyl S -propyl phosphorodithioate), an agricultural chemical, can be used as a membrane solvent to make a histamine-sensitive membrane electrode. An electrode constructed using prothiofos as membrane solvent and sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate as an ion-exchanger in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to histamine in the concentration range 5 × 10 −5 –1 × 10 −2 M with a slope of 56 mV per concentration decade in a physiologically balanced salt solution containing 154 mM NaCl, 2.7 mM KCl, 0.9 mM CaCl 2 , 5.6 mM glucose and 10 mM 4-(2-hydroxyethyl)-2-piperazineethanesulfonic acid (HEPES)–NaOH (pH 7.4). The limit of detection was 2 × 10 −5 M. This electrode is used to determine histamine release from mast cells. The histamine concentrations determined agreed well with those determined by an established fluorimetric assay. |
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