Analytical Sciences

A highly sensitive and convenient analytical method for the direct determination of selenium in biological samples by GF-AAS with a solid sampling technique using a graphite miniature cup was established by using a Pd solution containing 3 mol/l sulfuric acid or a Pd solution containing 0.1 mol/l nitric acid as a matrix modifier in order to prevent the volatilization of selenium. The determination of μg/g levels of selenium in biological samples was performed using calibration curves prepared by a selenium standard solution containing 100 μg/ml of Pd in 3 mol/l sulfuric acid as the matrix modifier. On the other hand, the pre-ashing concentration technique, which was previously developed by us, was applied to the determination of 10 ng/g levels of selenium in biological samples. The analytes in biological samples were concentrated by decomposing the sample matrix with a conventional electrothermal muffle furnace at 600° C for 30 min, At the pre-ashing stage, a Pd solution containing 0.1 mol/l nitric acid was added, because the addition of the Pd solution containing sulfuric acid caused charring and coagulation of the samples. The concentration factor for selenium in biological samples was 10 to 40. The analytical results of several NIST biological certified reference materials obtained by the proposed method were in good agreement with the certified values. The detection limit of GF-AAS was 0.13 ng of selenium; therefore, 3.3 ng/g levels of selenium in biological samples is detectable by the proposed method.

The surface chemical compositions of solid samples from environmental and geological sources can differ from the bulk or average compositions, because of changes caused by adsorption, dissolution, oxidation, etc. Accordingly, analytical information on surface layers is important for a better understanding of the environmental chemistry involving solid surfaces. The rapid development of surface-analytical techniques has enabled us to probe the surface chemistry of environmental and geological solid samples of complex composition. This article demonstrates some examples of important items of information that can be obtained by applying surface-analytical techniques, such as X-ray photoelectron spectroscopy and secondary ion mass spectrometry, to environmental and geological samples. The surface analysis of fly ashes, soils, sediments and weathered silicate minerals is reviewed.

In the present work, a simple and sensitive turn-on fluorescence method for DNA detection was developed. It was explored based on the N-methyl mesoporphyrin IX (NMM)/G-quadruplex DNA system as a reporter and exonuclease III (Exo III)-aided target recycling amplification to ensure sensitivity. Our method showed an ultra-wide detection range from 10 fM to 100 nM with a low linear detection limit of 0.76 nM. It also had excellent selectivity in a selectivity experiment.

Thermal desorption (TD)–GC/MS, recently developed for the determination of DeBDE in a polystyrene (PS) sample to an order of a few %, was evaluated in detail by using a certified standard PS sample containing 317 ppm of DeBDE. Not only the accuracy and precision of the results, but also the linearity of the working calibration curve were discussed in terms of the catalytic decomposition of DeBDE induced by the degrading macro-radical of the matrix polymer.

A microfluidic solid phase extraction (SPE) array for sample enrichment was prepared by a simple method, a hot embossing technique. Five fused-silica capillaries (250 |xm i.d., 380 |xm o.d.) were partly embedded parallel in a polymethyl methacrylate (PMMA) microchip to serve as the extraction channels. Within each of the channels, a 2-mm- long monolithic porous polymer was prepared by in-situ photoinitiated polymerization. This then acted as the frit for packing of the extraction materials (octadecylsilica beads, ODS). By defining the light-exposure window on the channels, one can easily control the length and location of the polymer frits and the ODS beads can be packed at the desired location. With this method, solid phase extraction channels for microfluidic use can be easily prepared without complex fabrication of microstructures. Several SPE channels can be conveniently made in one microchip since the frits can be prepared in different channels through one polymerization; packing of the different channels can also be performed simultaneously. With the use of dilute ephedrine solutions, the sample loading capacity, linearity, and reproducibility were characterized. Coupled with the fast capillary electrophoresis separation, this microchip SPE array was applied for the detection of ephedrines in human urine.

Rare-earth elements in a limestone geological standard (JLs-1) were determined by inductively coupled plasma mass spectroscopy (ICP-MS) using phosphoric acid 2-ethylhexyl ester solvent extraction, which had been established for seawater analysis. First, the limestone sample was divided into two fractions: acetic acid soluble (carbonate fraction) and insoluble (residue). A modification of the method was undertaken to achieve quantitative recovery. With this method most of the REEs in the carbonate fraction were quantitatively recovered, except for the heaviest three REEs (Tm, Tb and Lu). The reason for the poor recoveries of the three elements was investigated, but still remained unclear. The mass-spectroscopic interference of BaO with Eu made an accurate determination of both lighter REEs and Eu at the same time impossible. The precision of this method was better than 20%. The data adopted after analytical consideration were consistent with those previously reported.

Simple, accurate and real-time analytical methods are required for the detection of metal ions in a complex environment. In the present work, a fluorescent probe CPB based on coumarin was designed for recognizing Cu2+ ions. The fluorescence of CPB gradually quenched with increasing concentration of Cu2+ ions, due to the interactions between CPB and Cu2+ions. With the addition of Cu2+ ions, the emission changes of CPB exhibited a good liner relationship toward the Cu2+ions content in solution. Additionally, CPB could highly selective recognize Cu2+ ions among other metal ions in solution. Bearing the selectivity and fluorescence property toward Cu2+ ions, CPB was successfully applied to monitoring Cu2+ ions in Hela cells and zebrafish.