Pervaporation in chemical analysis

Unlike thermal processes such as distillation, pervaporation relies on the relative rates of solute permeation through a membrane and is a combination of evaporation and gas diffusion. The analytical pervaporation systems consist of a membrane module suitable for liquid sample introduction and a vacuum (or a sweeping gas) on the permeate side. It has been used in a wide range of applications including the analysis of various organic and inorganic compounds, and sample concentration. It has been directly interfaced with gas chromatography, spectrophotometry, capillary electrophoresis, electrochemical detectors, liquid chromatography, and mass spectrometry. A wide range of liquids, slurries, and solids samples has been analyzed using these techniques. This review highlights the basic principles of the pervaporation and the state of its current development as applied to analytical chemistry.     

Effect of carbon nanotube functionalization in micro-solid-phase extraction (μ-SPE) integrated into the needle of a syringe

In this paper, we report the implementation of polar and nonpolar functionalized multiwalled carbon nanotubes (MWCNTs) as sorbent in μ-SPE integrated into the needle of a syringe. Excellent preconcentration of diverse pharmaceutical analytes was possible without the need for specific pH adjustments using just 300 μg of functionalized nanotubes. Enrichment factors were as high as 6.4, extraction efficiencies were as high as 25.6%, and detection limits as low as 0.08 ng/ml were obtained. The sorption on nanotubes followed Freundlich isotherms, and it was seen that polar analytes adsorbed more strongly on carboxylated MWCNTs, while amphoteric, relatively less polar and basic analytes had greater affinity for MWCNT and those with octadecylamine functionalization.     

Simultaneous determination of bisphenol-A-diglycidyl ether, bisphenol-F-diglycidyl ether, and their derivatives in oil-in-water and aqueous-based canned foods by high-performance liquid chromatography with fluorescence detection

A gradient reversed-phase liquid chromatography with fluorescence detection method for simultaneous identification and quantification of bisphenol-A-diglycidyl ether (BADGE), bisphenol-F-diglycidyl ether (BFDGE), and their 10 derivatives in food matrixes was developed and validated for the analysis of oil-in-water- and aqueous-based foodstuffs. The method linearity range 0.016-10 ppm which are hundred-fold below and tenfold above the EU restriction at 1 ppm (mg/kg). The method detection limits range 0.72-4.20 ppb and the method quantitation limits range 2.40-14.85 ppb, respectively. The validation data indicate excellent precision, acceptable recovery, and good robustness, all supporting a good potential to further develop the method as a standard method for the determination of migrations from interior can coatings into foodstuffs.     

Carbon nanotubes as the sorbent for integrating μ-solid phase extraction within the needle of a syringe

In this research we report the implementation of micro-solid-phase extraction (μ-SPE) in the needle of a syringe for integrating sampling, analyte enrichment and sample introduction into a single device. Both single- and multi-walled carbon nanotubes (CNTs) were explored as high performance sorbents for μ-SPE in packed and self assembled formats. The need for such a sorbent was critical because the needle probe could hold only a small amount of material (around 300 μg). Conventional C-18 and self-assembled CNTs were found to be ineffective with enrichment factors less than one. However, packed beds of CNTs were found to be excellent sorbent phases, where high extraction efficiencies (as high as 27%) as well as enrichment factors (close to 7) could be achieved. The overall method showed excellent linearity, reproducibility, and low method detection limit (0.1–3 ng/mL for MWNTs). The sorption on CNTs followed Freundlich isotherms, and the functionalized CNTs were more effective for enriching the polar compounds.     

Effects of polymer wrapping and covalent functionalization on the stability of MWCNT in aqueous dispersions

The colloidal behavior of aqueous dispersions of functionalized multiwall carbon nanotubes (F-CNTS) formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is presented. The presence of polymer on the nanotube surface provided steric stabilization, and the aggregation behavior of the colloidal system was quite different from its covalently functionalized analog. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.