Study on solid phase extraction and spectrophotometric determination of vanadium with 2,3-dichloro-6-(2,7-dihydroxy-1-naphthylazo)quinoxaline.

A sensitive, selective and rapid method has been developed for the determination micrograms per liter level of vanadium ion based on the rapid reaction of vanadium(V) with 2,3-dichloro-6-(2,7-dihydroxy-1-naphthylazo)quinoxaline (DCDHNAQ) and the solid phase extraction of the colored complex with C18 cartridge. The DCDHNAQ reacts with V(V) in the presence of citric acid-sodium hydroxide buffer solution (pH 3.3) and benzyldimethyl tetradecylammonium chloride (zephiramine) medium to form a violet complex of a molar ratio 1:2 [V(V) to DCDHNAQ]. This complex was enriched by solid phase extraction with C18 cartridge and the enrichment factor of 100 was obtained by elution of the complex from the cartridge with acetonitrile. The molar absorptivity and Sandell sensitivity of the complex are 2.45x10(5) L mol(-1) cm(-1) and 0.0208 ng cm(-2) at 573 nm in the measured solution. Beer's law is obeyed in the range of 0.01-0.45 microg mL(-1), whereas Ringbom optimum concentration ranges found to be 0.025-0.425 microg mL(-1). The detection and quantification limits are 3.2 and 9.9 microg L(-1), respectively in the original samples. This method was applied to the determination of vanadium(V) in steel, soil, water and biological samples with good results.

Spectrophotometric studies and applications for the determination of yttrium in pure and in nickel base alloys.

Yttrium reacts with 5-(4'-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (I), 5-(2'-bromophenylazo)-6-hydroxypyrimidine-2,4-dione (II), 5-(2',4'-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (III), 5-(4'-nitro-2',6'-dichlorophenylazo)-6-hydroxypyrimidine-2,4-dione (IV), 5-(2'-methyl-4'-hydroxyphenylazo)-6-hydroxypyrimidine-2,4-dione (V) to form a dark pink complexes, having an absorption maximum at 610, 577, 596, 567 and 585 nm, respectively. The complex formation was completed spontaneously in theil buffer solution and the resulting complex was stable for at least 3 h after dilution. Under the optimum conditions employed, the molar absorptivities were found to be 1.60 x 10(4), 1.29 x 10(4), 1.96 x 10(4), 1.45 x 10(4) and 1.21 x 10(4) l mol(-1) cm(-1) and the molar ratios were (1:1) and (1:2) (M:L). The linear ranges were found within 95 microg of yttrium in 25 ml solution. One of the characteristics of the complex was its high tolerance for calcium and hence a method of separation and enrichment of microamounts of yttrium by using calcium oxalate precipitate was developed and applied to measure yttrium in nickel-base alloys. Interfering species and their elimination have been studied. The precision and recovery are both satisfactory.

Simultaneous spectrophotometric determination of thorium and rare earth metals with pyrimidine azo dyes and cetylpyridinium chloride.

Thorium and rare earth elements (REE) react with 5-(2',4'-dimethylphenylazo)6-hydroxypyrimidine-2,4-dione (I) and 5-(4'-nitro-2',6'-dichlorophenylazo)6-hydroxypyrimidine-2,4-dione (II) in the absence of cetylpyridinium chloride (CPC) to form red complexes. The molar absorptivity and Sandell sensitivity were calculated in absence of CPC. In its presence, REE - complexes are not formed due to miceller masking, whereas Th(4+) has a sensitive reaction with the studied reagents I and II, with enhancement of the color intensity of the complex. Most of the foreign ions are tolerated in considerable amounts; 150-2400-fold amounts of rare earth do not interfere with the determination of thorium. The optimum experimental conditions of the complex formation reactions and the compositions of thorium complexes are described. A simple method is proposed for simultaneous determination of thorium and rare earth element without previous separation.