Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

Summary A pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH₂CH₃)₄], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.     

Optimization of an electrolytic conductivity detector for determination of toxic nitrogen-containing food contaminants separated by open tubular column gas chromatography

The combination of open tubular column gas chromatography with electrolytic conductivity detection has been evaluated for the determination of nitrogen-containing pesticide residues in food extracts. Optimization of the column position at the column-detector interface was crucial to the successful operation of the detector. The signal-to-noise ratio and response stability of the detector are greatly influenced by the composition of the electrolyte solvent. Large volume splitless injections using retention gaps and optimized detector operating conditions enabled pesticide residues in food extracts to be determined at sub parts-per-million levels. Although the electrolytic conductivity detector is less sensitive than the thermionic ionization detector, its greater nitrogen selectivity can he crucial to the determination of nitrogen-containing contaminants in food extracts, particularly in complex mixtures where phosphorus-containing contaminants or matrix compounds are also present.     

Rapid and sensitive determination of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with on-line regenerating covalent coating

A rapid, sensitive and reproducible micellar electrokinetic chromatographic method using hexamethyldisilazane as on-line regenerating covalent coating was developed for the quantification of ephedrine (E) and pseudoephedrine (PE). E and PE were derivatized with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol for laser-induced fluorescence detection. The on-line regenerating covalent coating formed a combinative double coating with the subsequently produced dynamic SDS coating. The total coating can be easily removed and conveniently regenerated on-line. The simple coating procedure was described. By a series of optimization, a running buffer of 20 mm Na(2)B(4)O(7) + 16 mm SDS was applied for the separation of the derivatives. Linear relationships for E and PE were obtained in the range of 0.044-6.60 microg mL(-1) (correlation coefficients: 0.9975 for E, 0.9981 for PE), and the detection limits for E and PE were 1.71 and 0.67 ng mL(-1), respectively. The separation speed, the reproducibility and the sensitivity were much improved over those of other capillary electrophoresis methods more recently reported. The method was applied to the analysis of the two alkaloids in traditional herbal preparations with recoveries in the range 92.8-104.8%.     

Utility of copper(II) oxide as a packed reactor in flow injection assembly for rapid analysis of some angiotensin converting enzyme inhibitors

A new simple, sensitive, rapid and precise flow injection (FI) procedure based on the formation of copper complexes with some angiotensin converting enzyme (ACE) inhibitors has been developed and evaluated for the analysis of lisinopril (LN), enalapril maleate (EP), ramipril (RP) and perindopril tert-butylamine (PD). In this method, samples were injected into a flowing stream of distilled-deionized water, carried through the packed reactor of CuO for derivatization followed by ultraviolet (UV) detection. The flow rate was 1.5 ml min⁻¹ and column temperature was ambient (25 °C). Lisinopril was injected directly into the flowing stream and the detector response was measured at 262 nm. The hydrolysis products of enalapril maleate, ramipril and perindopril tert-butylamine in 0.2N NaOH were injected after neutralization with 1N HCl and the detector response was measured at 272, 265 and 252 nm, respectively. The developed method was successfully applied to the determination of tested drugs in pharmaceutical preparations at a sampling rate of 60 samples h⁻¹ and a recovery near 100% for all compounds.     

非水滴定法测定苯唑醇含量的研究

建立了农药中间体苯唑醇的分析方法，用指示剂法和电位法对苯唑醇进行了非水滴定的研究，测定结果与高效液相色谱(HPLC)法基本一致，相对标准偏差≤0．20％。     

Multidimensional separation of isomeric species of chlorinated hydrocarbons such as PCB,PCDD, and PCDF

A multidimensional GC-system containing two capillary columns of different polarities, operated within a double oven instrument, was used for the optimized separation of complex isomeric mixtures of various types of chlorinated aromatic compounds such as PCB, PCDD, or PCDF. Electron capture was applied parallel to flame ionization detection to obtain sensitive signals of the PCB or PCDD and the n-alkane standards required for identification by Kovats indices, respectively. Electron capture detection within a valvelessly operated MDGC system forced changes in the usual instrumental set-up, the live-switching coupling piece being located within the second oven of the double oven instrument. This oven is operated isothermally to ensure optimal and interference-free detection, for stable flow conditions within the coupling piece and for the determination of the isothermal retention indices (Kovats), which are much more suitable for identification by retention than the so-called “linear” indices.     

Comparison of Pulsed Electrochemical Detection Modes Coupled with Microchip Capillary Electrophoresis

There is a need to develop analytical methods that are capable of rapidly measuring small biological markers in the field of metabolomics. Among others, carbohydrates play an important role biologically yet are traditionally hard to detect since they have no chromophore or fluorophore. In the present report, the first application of integrated pulsed amperometric detection (iPAD) coupled with microchip electrophoresis to the analysis of glucose, mannose, sucrose, maltose, glucosamine, lactose, maltotriose and galactose is demonstrated. iPAD is an electrochemical detection mode that can be used for direct detection of carbohydrates, amines and sulfur containing compounds. The effect of different solution parameters, including the buffer concentration, pH and the concentration of SDS on both separation and detection response was analyzed. In addition, a comparison study between PAD and iPAD was performed using glucose, glucosamine, sucrose and maltose as model carbohydrates.     

Surface-modified CdSe quantum dots as luminescent probes for cyanide determination

Luminescent surface-modified CdSe semiconductor quantum dots (QDs), with nanoparticle (NP) size distribution in the order of 2-7 nm, have been synthesized for optical determination of cyanide ions. The nanoparticles have been functionalised with tert-butyl-N-(2-mercaptoethyl)-carbamate (BMC) groups and exhibit a strong fluorescent emission at about 580 nm with rather long fluorescence lifetimes (several hundred nanoseconds) in aerated methanolic solution. The observed luminescence emitted by the synthesized nanocrystals was tremendously increased by photo-activation under sunlight exposure. The functionalised QDs turned out to exhibit excellent long-term stability when stored in the dark (no significant changes in QDs luminescence emission intensity was observed even after two months from synthesis). The functionalisation of the NPs with carbamate ligand allowed a highly sensitive determination of free cyanide via analyte-induced changes in the photoluminescence (fluorescence quenching of intensity at 580 nm and lifetime changes) of the modified quantum dots (excited at 400 nm). A detection limit of 1.1 × 10⁻⁷ M (2.9 μg l⁻¹) of cyanide ions was obtained, while the interfering effect of other inorganic anions (including NO₃⁻, Cl⁻ or SCN⁻) was negligible even at 200-fold level concentrations in excess of cyanide.     

Evaluation of behaviour of linear monoamines CH3-(CH2)n−1-NH2 (n=1-6) in ion chromatography

This paper reports the results on a study of ion chromatography (IC) behaviour on strong cationic exchange column of CH₃-(CH₂)_n−1-NH₂ (n=1-6) type linear monoamines. The eluents were mixtures of HCl-NaCl, HNO₃-NaNO₃, HClO₄-NaClO₄, H₂SO₄-Na₂SO₄, HClO₄-NaClO₄-CH₃CN. Amines were revealed with an amperometric detector. The influence of different counter-ions on retention factors, k′, is discussed. Relationships between k′ and pE (E=sum of Na⁺ and H⁺ concentrations), and length of alkylic chain, and sensitivity coefficient S, are reported and discussed. The addition of acetonitrile (ACN) in the eluent was also taken into account. Suitable considerations are derived from these data. An example of monoamines separation is given.     

Simultaneous operation of plural separation modes in capillary electrophoresis with a chemiluminescence detector possessing a micro-space area for reaction/detection

Analysis of alpha-amino acids, proteins, and phenolic compounds was simultaneously performed using three capillaries in capillary electrophoresis with chemiluminescence detection, taking advantage of the micro-space area for reaction/detection at the tip of the capillary. The three capillaries included usual, polymer-containing, and sodium docley sulfate (SDS)-containing migration buffers for separation. The eluted samples from the capillaries, which were inserted into the chemiluminescence detection cell, were mixed with chemiluminescence reagent at the tips of the capillaries to generate visible light. The specific micro-space area for reaction/detection at the tips of the capillaries enabled the simultaneous operation of the three separation modes in the present system.