A potentiometric study of the coordination of the fluorophore, 2-methyl-8-(4-toluenesulfonamido)6-quinolyloxyacetic acid, ¹LH[sub 2] (the intracellular Zn[sup 2+] probe, Zinquin A) in its deprotonated form, ¹L[sup 2-], in Zn[sup 2+] ternary complexes, [Zn[sup n]L¹L][sup n] (where n is the charge of [sup n]L) at 298.2 K in 50% aqueous ethanol (v/v) and I = 0.10 (NaClO[sub 4]), shows that the formation of [Zn[sup n]L¹L][sup n] from [Zn[sup n]L][sup (2+n)+] is characterized by log(K[sub 5]/ dm³ mol[sup -1]) = 8.23 ± 0.05, 4.36 ± 0.18, 8.45 ± 0.10, 10.00 ± 0.06, 11.53 ± 0.06 and 5.92 ± 0.15, respectively, where [sup n]L = ²L - [sup 6]L and [sup 7]L[sup 3-] are 1,4,7,10-tetraazacyclododecane, 1,4,8,11-tetraazacyclotetradecane, 1,4,7-triazacyclononane, 1,5,9-triazacyclododecane, tris(2-aminoethyl)amine and nitrilotriacetate, respectively, and K[sub 5] is the stepwise complexation constant. Dissociation of a hydroxo proton from triethanolamine, [sup 8]L, occurs in the formation of [Zn[sup 8]LH[sub -1]][sup +] that subsequently forms [Zn[sub 8]LH[sub -1]L][sup -] for which log(K[sub 5]/dm³ mol[sup -1]) = 9.87 ± 0.08. The variation of K[sub 5] and the 5-fold variation of quantum yield of ¹L[sup 2-] as its coordination environment changes in Zn[sup 2+] ternary complexes are discussed with reference to the use of ¹L[sup 2-] in the detection of intracellular Zn[sup 2+]. [ABSTRACT FROM AUTHOR]