Physicochemical study of novel organoclays as heavy metal ion adsorbents for environmental remediation.

Four organic-modified clays based on a SWy-2 montmorillonite were prepared by embedding ammonium organic derivatives with different chelating functionalities (NH(2), COOH, SH or CS(2)) in the interlayer space of montmorillonite. Organic molecules such as (a) hexamethylenediamine, (b) 2-(dimethylamino)ethenethiol, (c) 5-aminovaleric acid and (d) hexamethylenediamine-dithiocarbamate were used for the clay modification in order to study the effect of the chelating functionality on heavy metal ions binding from aqueous solutions. The organoclays were characterized by powder X-ray diffraction (XRD), infrared (FTIR) and NMR spectroscopies. The experimental data showed that the organic molecules are intercalated into the interlamelar space with the long dimension parallel to the clay sheets. Their sorbing properties were evaluated for the removal of heavy metals, Pb, Cd and Zn, from aqueous solutions as a function of the pH. When compared with the unmodified SWy-2 montmorillonite, the modified clays show significant improvement in terms of sorbing selectivity as well as of metal loading capacity. The fit to adsorption data by a Surface Complexation Model shows that the intercalated molecules act as specific binding sites in the clay. These contribute additional sorption capacity which is additive to the variable charge edge-sites of the clay in competition with the permanent charge sites.

Determination of plasma, urine, and bovine serum albumin low-molecular-weight carbonyl levels by capillary gas chromatography with electron-capture and mass-selective detection.

Peroxidation of lipids produces low-molecular-weight carbonyl compounds, which are reactive with biological nucleophiles. The analysis of these compounds is often difficult. A multicomponent method for the determination of 11 of them in biological samples is reported. The samples are subjected to a pretreatment-derivatization procedure followed by gas chromatographic analysis with either electron-capture detection (ECD) or mass-selective detection (MSD) in the selected-ion monitoring mode. The procedure involves derivatization of the analyte with 2,4,6-trichlorophenylhydrazine, extraction with n-hexane, and separation of the derivatization products on a nonpolar gas chromatographic column. The concentration of the derivatization reagent, pH, reaction time, temperature, and presence of extraneous ions were investigated to determine the optimal derivatization conditions. Under these conditions, the method allows for the selective detection of low-molecular-weight carbonyl compounds at femtomole levels in several biological materials such as plasma, urine, and bovine serum albumin without interferences. The limits of detection were in the ranges 0.01-0.2 microM for ECD and 0.15-1.5 microM for MSD. The mean procedural recoveries obtained during the method validation were within the range 85-95% and the intra- and interassay standard deviations do not exceed 4.6 and 6.1%, respectively.