Chuen-Ying Liu

Stationary phases for capillary electrophoresis and capillary electrochromatography.

An overview of the most recent developments in column technology employed in capillary electrophoresis (CE) and capillary electrochromatography (CEC), mainly for the separation of small molecules and ions, is presented. Particular emphasis is laid on permanent coating. The wall modification methods in CE include covalent modification, adsorbed coatings and polymeric coatings, while those in CEC include packed columns, open‐tubular columns and fritless columns. A short discussion on the characterization and selectivity of the bonded phases is also given.

Preparation and application of ionic liquid-coated fused-silica capillary fibers for solid-phase microextraction

A simple and cost effective solid-phase microextraction device has been developed. Fused-silica capillaries were etched with ammonium hydrogen difluoride prior to coating with an ionic liquid. For comparison, both a bare fused-silica capillary and one pretreated with a Nafion membrane were coated with the ionic liquid. All three coated capillaries were employed for the head space microextraction of polycyclic aromatic hydrocarbons (PAHs) which were then separated with an established GC system. Efforts to optimize the extraction process indicated that the etched fiber displayed the most efficient extraction, giving not only highly reproducible extraction results but also greater extraction efficiency. The Nafion membrane-supported fiber was inferior to the etched fiber, while the untreated fused-silica had the lowest extraction efficiency. The Nafion membrane contains negatively charged sulfonate groups, and the increase in ionic liquid binding was due to electrostatic attractive forces. However, due to the hydrophobic interactions of the PAHs with the polymer matrix in the Nafion membrane, a more complex adsorption/desorption mechanism might reduce the efficiency. The established method was successfully applied for the analysis of PAHs released from burning of mosquito coil incense.

Preparation and analytical properties of a chelating resin containing cysteine groups

Abstract A macroporous, cross-linked polyacrylonitrile copolymer was synthesized, the nitrile groups were converted to carboxylic acid by hydrolysis, and these carboxylic acid groups were treated with L-cysteine and 1,6-hexanediol (binding agent). Studies of the basic characteristics of this resin showed that it was highly selective for silver(I), mercury(II), gold(III) and platinum(IV) in aqueous acidic solution, the maximum capacities being 0.97, 0.65, 1.22 and 0.39 mmol g-1 of dry resin, respectively. These four metal ions can be separated from each other, or concentrated from very dilute solutions, on a short column of the resin. The effects of different acids and of various common metal ions are reported.

Chelation ion chromatography as a technique for trace elemental analysis in complex matrix samples

Abstract A new method for the determination of lanthanides based on chelation and ion chromatography with absorbance detection is described. γ-Aminobutyrohydroxamate resin or its derivative, N -methyl- γ -aminobutyrohydroxamate resin in a column was used to concentrate and separate lanthanides from the alkali and alkaline earth metals and other matrix components. Various complexing agents were investigated as possible eluants. The influence of a sample matrix and parameters important for quantitative analysis are discussed. Using γ-aminobutyrohydroxamate resin as concentrator, and potassium nitrate (0.02 M) as matrix eliminator, with the mobile phase of oxalic acid (0.03 M, pH 4.5)-diglycolic acid (0.005 M), and 4(2-pyridylazo) resorcinol (6 × 10 −5 M )- ZnEDTA (1 ×10 −4 M ) as postcolumn reagent, most of the lanthanides can be separated and determined in the complex matrix samples. The detection limit was found to be 2.5 ng ml −1 for these elements by concentrating 25 ml of sea water.

Electrophoretic separation of inorganic anions with an anion complexone-modified capillary column

Abstract A twenty-eight-membered macrocyclic polyamine, 4,8,12,18,22,26-hexaaza-1,15-dioxacyclooctaeicosane ([28]ane-N6O2), was covalently bound to fused-silica for the electrophoretic separation of simple anions, complex anions and metal-containing anions. Parameters influencing bound ligand complexation properties or the electrophoretic behavior of analytes, such as the nature of the background electrolyte, the pH and concentration were investigated. The separation of metallocyanide complexes, Fe(CN)63− and Fe(CN)64− has been achieved. Supercomplex formation resulting from the second-sphere interaction between metallocyanide and polyamine was indicated. The method was effective for the separation of arsenite, arsenate, dimethylarsinic acid and phenylarsonic acid or selenite as well as selenate species. Better resolution of a mixture of bromide, chloride, sulfate, nitrate, bromate and iodate was achieved using an applied potential of −20 kV, with chromate (5 mM, pH 8.1) as background electrolyte and indirect detection at 270 nm. Linearity of response, expressed as peak height or peak area was in the range of 10−5–10−6 M; detection limits (LODs) based on three times signal-to-noise ratio for bromide, chloride, sulfate, nitrate, bromate, iodate, selenate and selenite were all at the femtomole levels. The anions present in mineral water and rainwater were also analyzed to evaluate the quantitative performance of the proposed method. The response mechanism of the prepared capillary column was briefly discussed in terms of anion complex formation between analytes and the protonated [28]ane-N6O2 bound at the silica surface.

Stationary phases for the enrichment of glycoproteins and glycopeptides

The analysis of protein glycosylation is important for biomedical and biopharmaceutical research. Recent advances in LC‐MS analysis have enabled the identification of glycosylation sites, the characterisation of glycan structures and the identification and quantification of glycoproteins and glycopeptides. However, this type of analysis remains challenging due to the low abundance of glycopeptides in complex protein digests, the microheterogeneity at glycosylation sites, ion suppression effects and the competition for ionisation by co‐eluting peptides. Specific sample preparation is necessary for comprehensive and site‐specific glycosylation analyses using MS. Therefore, researchers continue to pursue new columns to broaden their applications. The current manuscript covers recent literature published from 2008 to 2013. The stationary phases containing various chemical bonding methods or ligands immobilisation strategies on solid supports that selectively enrich N‐linked or sialylated N‐glycopeptides are categorised with either physical or chemical modes of binding. These categories include lectin affinity, hydrophilic interactions, boronate affinity, titanium dioxide affinity, hydrazide chemistry and other separation techniques. This review should aid in better understanding the syntheses and physicochemical properties of each type of stationary phases for enriching glycoproteins and glycopeptides.

Capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs with a histidine bonded phase.

An open tubular wall-coated capillary column containing histidine functional groups was prepared and employed for the capillary electrochromatographic separation of non-steroidal anti-inflammatory drugs. The anion exchange along with the hydrogen bonding and hydrophobic properties of the surface coating allowed the separation of analytes with very similar ionic mobility. Selectivity and resolution were studied by changing the pH over the range from 3.5 to 5.0 and the concentration of the buffer from 10 to 25 mM, as well as variation of the organic modifier, such as methanol, ethanol and 1-propanol over the range 7.5 to 20%. The optimum experimental conditions for the separation of a drug mixture, which consisted of indoprofen, ketoprofen, suprofen, naproxen, flurbiprofen, fenoprofen and ibuprofen were using a mixture of acetate buffer (20 mM, pH 5.0)-ethanol (1:5, v/v) as background electrolyte and an applied voltage of -20 kV with UV detection at 220 nm. The separation of these drugs could be achieved with an average plate number of 1.0 x 10(5) m(-1).

Macrocyclic polyamine as a selective modifier in a bonded-phase capillary column for the electrophoretic separation of aromatic acids

The use of a macrocyclic polyamine, 28[ane]-N6O2, as a selective modifier in a bonded-phase capillary column for the electrophoretic separation of 14 aromatic acids is described. Parameters that affect the performance of the separations, such as the type of buffer, the pH and concentration of buffer, the applied potential and the injection mode were studied. By changing the buffer pH (4.0-5.0), buffer concentration (10-50 mM) and applied potential (-10 approximately -20 kV), optimum conditions were obtained at -20 kV, using an acetate buffer (20 mM, pH 4.5), hydrodynamic injection with a vacuum at the buffer reservoir on the detector side and detection at 220 nm. The results showed that the separation was effective under these conditions. The plate number was greater than 4 x 10(4) m-l. Due to the wide variation in the mobilities of the test compounds, injection studies suggested that a vacuum at the buffer reservoir on the detector side would produce a result that is more representative of the initial sample composition. Benzoic acid in soy sauce, salicylic acid in Salic ointment and Aspirin were sampled and analyzed using the established conditions.

Histidine as the functional group for a chelating ion exchanger

Abstract In the chelating ion exchanger synthesized, the amino group of histidine is attached chemically via the azide method to the carboxyl group of Amberlite IRC-50. A flow system based on a spectrophotometric detector, with 4-(2-pyridylazo) resorcinol as reagent, is described for fast assays of eluted cations. The pH dependence of the metal extraction is reported for Ag(I), Au(III), Cu(II), Fe(III), Hg(II), Ni(II) and Zn(II) ions. The resin exhibits no affinity for the alkali or alkaline earth metals. The uptake of traces of the specified elements from synthetic samples by a short (90 mm) column of the histidine-containing resin was in the range 94–100% and the retained metals were readily eluted by means of 2 M hydrochloric or hydrobromic acid. In column operation, mercury was quantitatively recovered even in the presence of large excesses of various ligands. The recoveries of the trace metals were good at the usual pH of natural waters.

Functionalized carbon nanotubes as the pseudostationary phase for capillary EKC separation of non-steroidal anti-inflammatory drugs.

Functionalized multiwalled carbon nanotubes (f‐MWCNTs) can serve as the pseudostationary phase (PSP) for the capillary EKC separation of non‐steroidal anti‐inflammatory drugs (NSAIDs). To increase their hydrophilicity, we treated MWCNTs, with a sonochemical process in a concentrated nitric/sulfuric acid mixture. The oxidized MWCNTs were then characterized by FT‐IR, transmission electron microscopy, and X‐ray photoelectron spectroscopy. We evaluated the potential of the PSP and the effects of buffer composition, pH, addition of organic modifier, and injection temperature on the NSAID separation. The PSP created a network structure of π–π interactions, hydrophobic forces, hydrogen bonding, and electrostatic interactions to separate NSAIDs, providing a different separation mode from SDS micelles. We achieved complete separation of six NSAIDs using a mixture of a borate buffer (75 mM, pH 10) with methanol (5%, v/v) containing 0.02 mg/mL f‐MWCNTs, an applied voltage of +12 kV and detection at 214 nm. Better precision was obtained with a low injection temperature. The method was also satisfactorily applied to the analysis of NSAIDs spiked into a urine sample.