Reactions of o,o′-Dihydroxy Azo Dyes with the Third Group M(III) Ions: A Spectroscopic and Electrochemical Study

Table 3

Voltammetric characteristics of M(III)-azo dye system.

Azo dye	Metal	pH for investigation (pH^aoptimal)	New peaks	−𝐸𝑝^complex, V; (at pHoptimal)	Linear range, M
ERB	Sc	8.0–8.6	One peak P1	0.89	8⋅10^−7--2⋅10^−5
	Ga	3.3–4.6; 4.0–4.6	Two peaks P1, P2	0.50–0.61; 0.96–1.01	1⋅10^−7--1⋅10^−5 (P1)
		7.7–8.2	One peak P1	0.83
	In	9.5	One peak P1	0.84 [11]	4.0⋅10^−7--1.5⋅10^−5
	REE	10.0	One peak P1	0.96 [9]	4⋅10^−7--2⋅10^−5
EBT	Al	5.0	One peak P1	0.51	It was not studied
	Sc	5.5–6.5	One peak P1	0.64	1⋅10^−6--2⋅10^−5
	Ga	4.1–4.5; 4.4-4.5	Two peaks P1, P2	0.40–0.44; 0.95	1⋅10^−6--2⋅10^−5 (P1)
		8.3–8.7	One peak P1	0.66	It was not studied
	In	8.0–8.2	One peak P1	0.70	1⋅10^−6--1⋅10^−5
	REE	10.5	One peak P1	0.80 [10]	1⋅10^−6--2⋅10^−5
KLC	Al	5.1	One peak P1	0.52	8⋅10^−7--2⋅10^−5
	Sc	4.8; 8.2–9.0	One peak P1	0.59; 0.73–0.77	6⋅10^−7--1⋅10^−5; 1⋅10^−6--2⋅10^−5
	Ga	3.9–5.2; 4.4–5.5	Two peaks P1, P2	0.42–0.46; 0.98-0.99	2⋅10^−7--2⋅10^−5 (P1); 4⋅10^−7--1⋅10^−5 (P2)
	In	5.0–6.0	No new peaks observed, increasing of the current of In^3+→In^0 peak		1⋅10^−6--1⋅10^−4
	REE	9.0–9.5	One peak P1	0.89	1⋅10^−6--2⋅10^−5
Calc	Sc	3.5	One peak P1	0.53	2⋅10^−6--4⋅10^−5
	Ga	3.7–4.5; 4.3–5.3	Two peaks P1, P2	0.45–0.49; 0.98–1.04	1⋅10^−7--1⋅10^−5 (P1)
	In	4.0–5.5	No new peaks observed, increasing of the current of In^3+→In^0 peak		1⋅10^−6--1⋅10^−4
	REE		No new peaks observed		—
EBSE	Al	6.6–7.3	One peak P1	0.67–0.69	6⋅10^−7--1⋅10^−5
	Sc	6.4–7.0; 8.2–9.2	One peak P1	0.76-0.77; 0.77–0.79	1⋅10^−7--1⋅10^−5; 8⋅10^−7--1⋅10^−5
	Ga	5.4–7.0	Two peaks P1, P2; (the peak is not clear)	0.52–0.59	1⋅10^−6--2⋅10^−5
	In	4.9–5.6	No new peaks observed, increasing of the current of In^3+→In^0 peak	0.61	2⋅10^−6--2⋅10^−5
		6.7–8.9	One new peak; (not observed in the absence of EBSE)	0.63–0.67	6⋅10^−7--2⋅10^−5
	REE	7.5–8.5	One peak P1	0.80	1⋅10^−6--2⋅10^−5

aRange of pH at which current of complex peak is maximal or constant.