Table 1. UV–Vis Absorption and Analytical Parameters of 10^–5 M 1–5 in Water and Methyl Yellow in 1:3 (v/v) Methanol/Water.

	1a	2a	3b	4b	5b	methyl yellow
pKac	3.1	4.2	2.2	2.1	2.6	3.2
λmax. pH 7.0 (nm)	296	276	425	481	436	450
log ε pH 7.0d	3.20	3.41	4.23	4.12	4.07	4.20
λmax. pH 1.0 (nm)	296	276	529	530	515	514
log ε pH 1.0	3.41	3.55	4.62	4.35	3.87	4.40
DLpH 7.0 (nM)e			26	12	26
DLpH 1.0 (nM)e			6.9	3.3	18
log Pf	–1.89	–2.07	0.21	0.60	0.61	4.43

^aRef (42).

^bRef (31).

^cDetermined from the equation pH = pK_a + log [(A_max – A)/(A – A_min)].

^dMolar absorptivity ε in mol^–1 L cm^–1.

^eThe detection limit (DL) was determined using the equation DL = 3.3σ/S, where σ is the standard deviation of the blank absorbance at the λ_max at pHs 1 and 7 for 10 blank samples and S is the slope of the calibration curve based on plots of the absorbance at λ_max for seven concentrations between 10 and 100 μM at pHs 1 (dilute HCl) and 7 (N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer). Good linearity was observed with R² > 0.997.

^fLog P values determined using Chemsketch product version 12.01.