Talasila Prasada Rao

Flow injection on-line preconcentration and flame atomic absorption spectrometric determination of iron, cobalt, nickel, manganese and zinc in sea-water

A rapid and sensitive flow injection analysis–atomic absorption spectrometric procedure is described for the determination of iron, cobalt, nickel, manganese and zinc based upon on-line preconcentration on a microcolumn packed with C18 material. These metals were complexed with 5,7-dichlorooxine from weakly acidic or neutral solutions in the flow system and adsorbed on the column. The preconcentrated elements were eluted with acidified methanol (pH ≥ 2) and injected directly into the nebulizer for atomization in an air–acetylene flame for measurement. The retention efficiency was better than 98%, resulting in sensitivity enhancement factors of 60, 80, 80, 80 and 60 for a 1 min preconcentration time for iron, cobalt, nickel, manganese and zinc, respectively. The respective detection limits were 4.0, 1.0, 1.0, 0.5 and 0.5 ppb, respectively. The throughput of samples was 30 h–1, with a loading time of 1 min. The method was applied to sea-water samples.

Differential pulse anodic stripping voltammetric determination of ziram (a dithiocarbamate fungicide).

A d.c. polarographic technique has been used previously for the determination of the pesticide, ziram, in aqueous samples, this paper reports differential pulse anodic stripping voltammetric determination of ziram zinc in rice samples using a static mercury drop electrode. The procedure developed distinguishes inorganic zinc and ziram zinc in sodium acetate-sodium chloride media. The procedure developed is suitable for the determination of concentrations as low as 10 ppb of ziram with a precision of 2.1% for five successive determinations of 150 ppb of ziram.

Ion-chromatographic determination of iodide in sea water with UV detection

A highly sensitive and selective ion-chromatographic procedure with UV detection at 227 nm was developed for the determination of trace amounts of iodide. The procedure utilizes 0.1M NaOH as eluent, which enables the determination of 1–100 μg I−1 I− with a precision of ca. 6%. 1000-fold amounts of other anions such as fluoride, chloride, phosphate, sulphate, bromide, nitrite and nitrate do not interfere. The method has been applied to determine iodide in sea water samples from the Indian coast.

Simultaneous determination of copper, mercury and lead by first-order derivative spectrophotometry using dithizone as reagent

A first-order derivative spectrophotometric method has been developed for the simultaneous determination of copper, mercury and lead at μg/L levels using dithizone as reagent. The procedure involves the simultaneous extraction of these elements by dithizone in chloroform from weakly alkaline solutions. Linear calibration curves were obtained in the ranges 0.5–10 (Cu), 1–10 (Hg) and 1–10 (Pb) μg present in 40 ml of aqueous phase with detection limits of 5 μg/L (Cu) and 20 μg/L (Hg and Pb). The R.S.D.s for 100 μg/L of copper, mercury and lead were 2.5, 2.6 and 3.1% respectively, for 5 determinations. The method is applicable for the determination of copper and lead in marine sediment samples with good precision and accuracy.

Mixed-ligand chelate extraction of trivalent lanthanides with 4,4,4-trifluoro-1-phenyl-1,3-butanedione and neutral oxo-donors

Mixed-ligand chelate extraction of trivalent lanthanides such as Nd(III), Eu(III) and Lu(III) into benzene with mixtures of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HBFA) and bis-2-ethylhexyl sulphoxide (B2EHSO) or triphenylphosphine oxide (TPhPO) from thiocyanate solutions was investigated. The results demonstrate that these metal ions are extracted as Ln(BFA)(3) with HBFA alone and in the presence of a neutral oxo-donor, B2EHSO or TPhPO(S), as Ln(BFA)(3).S and Ln(BFA)(3).2S. The equilibrium constants of the above species increase monotonically with decreasing ionic radii of these metals ions. The addition of a neutral donor to the metal chelate system not only enhances the extraction efficiency but also improves the selectivity among these trivalent lanthanides. Hence this mixed-ligand system may be useful for the extraction and separation of individual lanthanides and also for the separation of lanthanides as a group from other metal ions.

Determination of trace amounts of praseodymium by third-derivative molecular absorption spectrophotometry

A third-derivative molecular absorption spectrophotometric procedure is described for the determination of trace amounts of praseodymium (Pr). The procedure is based on the reaction of praseodymium with Bromopyrogallol Red (BPR) in acetate-buffered medium. The influence of various instrumental parameters and reaction conditions on the colour development of the BPR-Pr complex has been investigated. The proposed method is free of interference from up to 100-fold amounts of other rare earth elements (except yttrium, lanthanum and neodymium). In conjunction with ion-exchange separation, the proposed method has been applied to the determination of praseodymium in aluminium metal samples.

Spectrophotometric determination of traces of nitrite with rhodamine 6 G

A simple and highly selective spectrophotometric method is described for the determination of nitrite. The method is based on the measurement of decrease in absorbance at 525 nm of rhodamine 6 G in sulphuric acid medium. The decrease in absorbance is instantaneous on addition of nitrite and remains stable for 2 h. Linear calibration graph passing through the origin was obtained in the range 0.01–0.6 μg/ml nitrite. The method is free from interference of Cu2+, Fe3+ and SO32− which normally interfere in other procedures. The method was applied successfully to the determination of nitrite in well and sea water samples and in KNO3, NaNO3, table salt, sugar and milk powder samples.

Liquid-liquid extraction and spectrophotometric determination of cadmium with 1,10-phenanthroline and thymol blue

A simple and highly sensitive extraction spectrophotometric method was developed for the determination of traces of cadmium. The method is based on the preconcentrative extraction of ternary-ion-association complex of cadmium—1,10-phenanthroline-thymol blue into chloroform and subsequent determination by spectrophotometry. The ternary ion associate is stable for 20 h and cadmium content as low as 0.1 μg in 90 ml of sample can be determined. The method is precise and has been applied to the determination of cadmium in sea water, solder and high purity zinc and indium materials.