Selective Spectrophotometric Determination of Trace Amounts of Cadmium in Soil and Sediment Samples Using a Green Aqueous Biphasic Extraction.

A green extraction spectrophotometric method was presented for the determination of trace amounts of cadmium in soil and sediment samples. This method is based on the selective extraction of cadmium as its iodide complex by aqueous biphasic extraction composed of polyethylene glycol (PEG) and sodium sulfate, and a subsequent sensitive determination by spectrophotometry using 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol. This extraction method is simple and environmentally benign, since the organic solvents used for the traditional liquid-liquid extractions are replaced by the non-toxic polymer and inorganic salt.

On-line redox derivatization liquid chromatography for selective separation of Fe(II) and Fe(III) cyanide complexes using porous graphitic carbon.

On-line redox derivatization HPLC was applied for the analysis of Fe(II) and Fe(III) cyanide complexes. The HPLC system used consisted of two C18 silica columns treated with trimethylstearylammonium chloride and a small column packed with porous graphitic carbon (PGC) placed between them. The PGC column treated with sodium sulfite completely reduced the Fe(III) cyanide complex to the Fe(II) complex, while the Fe(II) cyanide complex was converted to the Fe(III) complex by the PGC column treated with hydrogen peroxide.

Multistep pH-peak-focusing countercurrent chromatography with a polyethylene glycol-Na2SO4 aqueous two phase system for separation and enrichment of rare earth elements.

Multistep pH-peak-focusing countercurrent chromatography was developed for separation and enrichment of rare earth metal ions using a polyethylene glycol-Na(2)SO(4) aqueous two phase system (ATPS) and pH stepwise gradient elution. Metal ions in a sample solution are chromatographically extracted in a basic stationary phase (polymer-rich phase of the ATPS) containing a complexation ligand such as acetylacetone at the top of the countercurrent chromatography (CCC) column. After the sample solution is introduced, the mobile phases of which the pH values have been adjusted with buffer reagents are delivered into the column by stepwise gradient elution in order of decreasing pH.

Evaluation of the thermal effect on separation selectivity in anion-exchange processes using superheated water ion-exchange chromatography.

The thermal effect on retention and separation selectivity of inorganic anions and aromatic sulfonate ions in anion-exchange chromatography is studied on a quaternized styrene-divinylbenzene copolymer anion-exchange column in the temperature range of 40-120 °C using superheated water chromatography. The selectivity coefficient for a pair of identically charged anions approaches unity as temperature increases provided the ions have the same effective size, such that the retention of an analyte ion decreases with an increase in temperature when the analyte ion has stronger affinity for the ion-exchanger than that of the eluent counterion, whereas it increases when it has weaker affinity. The change in anion-exchange selectivity with temperature observed with superheated water chromatography has been discussed on the basis of the effect of temperature on hydration of the ions.

Reversed-phase ion-pair liquid chromatographic method for determination of reaction equilibria involving ionic species: exemplification of the method using ligand substitution reactions of ethylenediaminetetraacetatochromium(III) ion with acetate and phosphate ions.

A reversed-phase ion-pair liquid chromatographic method is presented for the determination of reaction equilibria involving ionic species of the same charge sign as reactant and product compounds. It has been demonstrated that ion-exchange chromatography or reversed-phase ion-pair chromatography is a useful tool for the determination of equilibrium constants of chemical reactions involving ionic species such as metal complexation reactions. Previous work with these methods has been based on the assumption that the limiting retention factors of the reactant and product species are constant independent of concentration of the chemical species (X) in the mobile phase, which reacts with the analyte compound.

On-column electrochemical redox derivatization for enhancement of separation selectivity of liquid chromatography use of redox reaction as secondary chemical equilibrium.

An on-column electrochemical redox derivatization for enhancement of high-performance liquid chromatography (HPLC) separation selectivity is presented using electrochemically modulated liquid chromatography (EMLC) and porous graphitic carbon (PGC) as the packing material. PGC therefore serves two purposes: it acts both as a chromatographic stationary phase and as a working electrode. The capability of on-column electrochemical redox derivatization was evaluated using hydroquinone and catechol as model compounds.

Measurement of mobile-phase volume in reversed-phase liquid chromatography and evaluation of the composition of liquid layer formed by solvation of packing materials.

The mobile-phase volumes (Vm) in reversed-phase liquid chromatography (RPLC) with alkyl-bonded silica, defined as the difference between the total volume of eluent in the column (V0) and the volume of the eluent solvent layer formed by solvation of the bonded phase (VL), are determined by the method derived from the eluent electrolyte effect on the retention of ionic analytes. The validity of the Vm values obtained is evaluated by comparing them with the retention volumes of various organic compounds and inorganic ions, which have been suggested as unretained markers, and those obtained from a linear dependence of the logarithmic retention factor on the carbon numbers of homologous series. From the results obtained, it has been concluded that the solvated liquid phase on a column packing material should be assigned to a part of the stationary phase and the method developed for determination of the Vm value based on the ion partition model gives the most reasonable value as the mobile-phase volume in RPLC.

Preconcentration and determination of cadmium by GFAAS after solid-phase extraction with synthetic zeolite.

The solid-phase extraction (SPE) method for the preconcentration of trace amounts of cadmium using synthetic zeolite A-4 and its determination by graphite furnace atomic absorption spectrometry (GFAAS) was investigated. The preconcentration conditions, such as the optimum pH range of the sample solution for the adsorption of cadmium and the kind of acid solution for dissolving the cadmium-adsorbed synthetic zeolite A-4, as well as the measurement conditions for the determination of cadmium by GFAAS, e.g.

On-line redox derivatization liquid chromatography using double separation columns and one derivatization unit.

A new on-line redox derivatization technique using double separation columns and one redox derivatization unit was presented for enhancement of separation selectivity of HPLC. This on-line redox derivatization HPLC system consisted of two separation columns and one redox derivatization unit placed between them. The redox reaction proceeds in the derivatization unit so that an analyte compound migrates as its original form in the first column, while as its oxidized or reduced form in the second column.

Evaluation of the surface charge properties of porous graphitic carbon stationary phases treated with redox agents.

The effect of treatment of porous graphitic carbon (PGC) stationary phases with hydrogen peroxide and with sodium sulfite on the retention behavior of analyte compounds has been investigated using benzene, aromatic sulfonate ions, and benzyltrialkylammonium ions as model compounds. It is shown that the retention times of the cationic analytes are increased by treating the PGC column with the reducing agent, while decreased by treating it with the oxidizing agent. On the other hand, the retention times of the anionic analytes are decreased by treating the column with the reducing agent, while increased by treating it with the oxidizing agent.