Liquid-liquid extraction-chromogenic systems for vanadium(V) based on xylometazoline hydrochloride (XMZ) and azo derivatives of resorcinol (ADRs) were studied. The following ADRs were used: 4-(2-thiazolylazo)resorcinol (TAR), 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR), and 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR). Concentration of the reagents, pH of the aqueous medium and shaking time were subjects of optimization experiments. The chloroform-extracted ternary complexes were of composition 1:1:1. The molar absorptivity coefficients (ε λ), absorption maxima (λ), constants of extraction (Log K), and fractions extracted (E%) were found to be ε 553 = 2.50 × 10 4 dm 3 mol-1 cm-1 , Log K = 3.5, and E = 96% (ADR = TAR); ε 550 = 1.88 × 10 4 dm 3 mol-1 cm-1 , Log K = 3.4, and E = 98% (ADR = MTAR); and ε 554 = 2.62 × 10 4 dm 3 mol-1 cm-1 , Log K = 5.0, and E = 99.5% (ADR = HTAR). The Sandell's sensitivities and Beer's law limits were determined as well.

The interaction between CoII and 5-methyl-4-(2-thiazolylazo)-resorcinol (MTAR) was studied in a water-chloroform system, in the presence or absence of benzalkonium chloride (BZC) as a cationic ion-association reagent. The optimum pH, concentration of the reagents and extraction time for the extraction of Co were found. In the presence of BZC, the extracted ion-associate could be represented by the formula (BZ+)[CoIII(MTAR2–)2], where MTAR is in its deprotonated form. The following extraction-spectrophotometric characteristics were determined: absorption maximum, molar absorptivity, Sandell’s sensitivity, limit of detection, limit of quantification, constant of extraction, distribution ratio and fraction extracted. In the absence of BZC, the extraction is incomplete and occurs in a narrow pH range. The extracted chelate contains one deprotonated and one monoprotonated ligand: [CoIII(MTAR2–)(HMTAR–)].

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A water−isobutanol extraction-chromogenic system for Ni II , based on the azo dye 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR; H 2 L) and the ionic liquid Aliquat 336 (A336), was studied. Under the optimal conditions (c MTAR = 2.0 × 10-4 mol dm-3 , c A336 = 5.6 × 10-3 mol dm-3 , pH 8.5 and extraction time t = 1 min), Ni II is extracted as a ternary complex which can be represented by the formula (A336 +) 2 [Ni(L 2−) 2 ]. In the absence of A336, or in a slightly acidic medium, a binary complex, [Ni(HL −) 2 ], with an absorption maximum at λ = 548 nm and a shoulder at 590 nm is formed. The following extraction-spectrophotometric characteristics were determined at the above-mentioned optimal conditions: λ max (545 nm), molar absorptivity (5.0 × 10 4 dm 3 mol-1 cm-1), Sandell's sensitivity (1.2 × 10-3 μg cm-2), Beer's law limits (0.05-3.1 µg cm-3), constant of extraction (Log K = 6.1) and fraction extracted (99.2%). The effect of foreign ions was studied; the most serious interferences were caused by Co II , Cu II and Cr III .

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