Jongman Park

Direct extraction of alkylphenols, chlorophenols and bisphenol A from acid-digested sediment suspension for simultaneous gas chromatographic-mass spectrometric analysis.

The direct extraction of alkylphenols, chlorophenols and bisphenol A from an acid-digested sediment suspension for GC-MS analysis was studied. The sediment was digested with acid while the hydrolyzed analytes were being extracted with dichloromethane. The conditions of the acid digestion and extraction were optimized in terms of time, acidity of digestion, and extracting solvent. It is possible to complete the extraction within 20 min with 5 ml of 0.1 M HCl digesting solution and three portions of 5 ml of dichloromethane. The recoveries of analytes were mostly around 90% with about 10% relative standard deviations. With this technique parallel treatment of large numbers of sediment samples is possible without any expensive special equipment or heating process. The analytical characteristics of this extraction technique were compared with Soxhlet extraction and the pressurized liquid extraction technique. The technique was examined and evaluated for real environmental sediment samples and certified reference material of natural matrix.

Screen-printed anodic stripping voltammetric sensor containing HgO for heavy metal analysis

A screen-printed disposable sensor for the anodic stripping voltammetric (ASV) analysis of heavy metals was prepared by integrating a HgO-modified working electrode, Ag/AgCl reference electrode, and carbon counter electrode on a polycarbonate strip. The working electrode was screen-printed with phenol resin-based carbon ink containing fine particles of mercuric oxide as a built-in mercury precursor. The mercuric oxide particles exposed on the surface were reduced to fine mercury droplets by in situ or pre-cathodic conditioning in order to allow them to behave as heavy metal collectors in the anodic stripping analysis. The reference and counter electrodes were also screen-printed using commercial silver paste ink modified with finely ground AgCl powder and commercial carbon ink, respectively. The analytical characteristics of the sensor were evaluated using Pb and Cd as probe metals. Detailed preparation procedures and analytical characteristics of the sensor are described.

Silver-cemented frit formation for the stabilization of the packing structure in the microchannel of electrochromatographic microchips.

A simple but effective frit formation technique was developed to stabilize the packing structure inside the microchannel of capillary electrochromatographic microchips, utilizing the electroless plating technique. A Ag(NH(3))(2)(+) solution was allowed to diffuse through the colloidal silica packing in the microchannel from the reservoir of the microchip for a limited amount of time, and then it was reduced by an excess amount of formaldehyde solution. A frit structure of ~70 μm in length was formed at the entrance of the microchannel without clogging when treated with 1mM Ag(NH(3))(2)(+) ion and formaldehyde for 30s and 150 s, respectively. The formation of the frit structure was confirmed by a scanning electron microscopy. The stability of the packing structure was tested rigorously and then confirmed by applying alternating electroosmotic flows back and forth with pulsed potential steps on both sides of the frit structure. The effect of the treatment on the electrochromatograms was evaluated after the microchips were repeatedly used and stored for a long period of time. The results indicated that the silver-cemented frit structure extended the lifetime of the fully packed CEC microchips distinctly.

Nickel oxide-modified composite electrode for electrochemical detection of polyhydroxyl compounds in liquid chromatographic analysis

Nickel oxide-modified polymeric composite electrode was prepared for electrochemical detection in liquid chromatography (LC-ECD) or flow injection analysis of polyhydroxyl compounds. The composite electrode was prepared by incorporating semigraphitic carbon black and nickel oxide particles in polystyrene polymer matrix cross-linked with divinylbenzene. The analytical characteristics of the electrodes in LC-ECD and flow injection analysis of polyhydroxyl compounds were evaluated in terms of sensitivity, reproducibility, stability and surface renewability. The electrode revealed three–four orders of dynamic concentration ranges from sub-micromolar to 10 −3 M with high correlation coefficients from 0.9998 to 0.9999 for various polyhydroxyl compounds. The standard deviation for the surface restoration was <2%. High reproducibility, stability, and the renewability of surface are thought to be due to the catalyst particles highly dispersed through robust polymeric electrode matrix.