AMPHOTERIC DOXYCYCLINE SENSITIVE ELECTRODES AND THEIR SELECTIVITIES

Electrodes sensitive to cationic or anionic doxycycline were constructed using doxycycline silicotungstate, tetraphenylborate and dipicrylaminate or cetyltrioctylammonium doxycyclinate as electro-active material. The doxyeycline sensitive electrode responds to the mono-protonated doxycycline over pH 1.5～3.5, while the doxycyclinate sensitive electrode responds to the mono-valency doxycyclinate anion with the enolic group of the B cycle being dissociated over the pH range of 8.0～10.5 with poor stability in potential. Microgram level of doxycycline hydrochloride in micro-volume samples can be determined using the inverted electrode of all-solid-state construction. Log K_ij values for symmetric quaternary ammoniums were found to be linearly related to the ionic potential and the induction effect index of the ammonium ion according to the equation log K_ij=12.46 I—38.24 Z/R+365.21. A general equation representing the log K_ij vs. carbon atom number of the alkyl group of the quaternary ammonium relation was given as log K_ij=26.5×(2.7)^-n-38.24×(1.26n+0.8)^-1+7.48. log K_ij for elements of ⅠA and ⅡA groups in the periodic system decreases with increasing Z/R.