Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na⁺), ammonium (NH₄⁺) and hydrazine (N₂H₅⁺) ions was developed by connecting an anion-exchange column in the I⁻-form after the separation column. For example, NH₄⁺ is converted to a UV-absorbing molecule, NH₄I, by the anion-exchange column in the I⁻-form after the ion-exclusion separation on anion-exchange column in the OH⁻-form with water eluent. As a result, the direct UV detection of Na⁺, NH₄⁺ and N₂H₅⁺ could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001-5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH₄⁺ in river and rain waters, or that of N₂H₅⁺ in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H⁺-form as the separation column and the anion-exchange conversion column.     

Electrochemical characterization of poly(vinyl alcohol)/formyl methyl pyridinium (PVA-FP) anion-exchange membranes

To explore electrodialysis for purification of negatively charged large organic molecules (e.g., amino acids and medicine), water-swollen formyl methyl pyridinium-immobilized polyvinyl alcohol (PVA-FP) anion-exchange membranes were prepared and characterized in terms of their electrochemical properties. The PVA-FP membranes exhibited low electrical resistance (1.0–3.0 Ω cm²), high swelling properties (water content ratio, 0.62–0.73), and reasonable transport number ( for Cl⁻). For glutamic acid solutions, the electrical resistance of the PVA-FP membrane was low (1.0–3.0 Ω cm²) in a wide pH range, with no membrane fouling. Since the resonance effect of quaternary aromatic ammonium contributed to the structural stability of the PVA-FP membrane, the water-splitting with the PVA-FP membrane was approximately one order of magnitude lower than that with a commercial ion-exchange membrane at a same current density.     

Group separation of non-sulphated and 3-sulphated bile acids by disposable anion-exchange cartridges

Summary A rapid and simple method has been developed for the group fractionation of the major unsulphated and mono-sulphated bile acids in human body fluids. After extraction with Bond Elut C₁₈ cartridges, the bile acids are separated into the unconjugated, glycine-, taurine- and sulphate-conjugated forms on pre-packed Bond Elut SAX columns by increasing the ionic strength of the methanol-acetate buffer eluent. The procedure was found to be accurate and reproducible and to give complete resolution between the different groups. The levels of 3-sulphate bile acids in human serum and urine from patients with liver disease were determined by high-performance liquid chromatography, after group separation and solvolysis of the sulphate fraction.     

Determination of saccharides by high performance anion-exchange chromatography with pulsed amperometric detection

Summary High performance anion-exchange chromatography (HPAC) coupled with pulsed amperometric detection (PAD) under alkaline conditions (pH 13) separates neutral saccharides based upon their molecular size, saccharide composition, and glycosidic linkages. Carbohydrates were detected by oxidation with a gold-working electrode. HPAC-PAD was compared to high performance liquid chromatography (HPLC) with refractive index (RI) detection in terms of selectivity and sensitivity of saccharides. The results indicate that HPAC-PAD was more precise, two orders of magnitude more sensitive (pmol range) and gives better resolution of saccharides than HPLC-RI. HPAC-PAD required less sample preparation and was not subjected to matrix interferences. The use of HPAC-PAD was applied to the analysis of organic materials (plant residues, animal wastes and sewage sludge) and soil.     

Multi-step sol-gel process and its effect on the morphology of polyethylene oxide (PEO)/SiO2 anion-exchange hybrid materials

Polyethylene oxide (PEO)/SiO₂ anion-exchange hybrid materials were prepared through the sol-gel process of alkoxysilane functionalized PEO-1000 (PEO-[Si(OCH₃)₃]₂) and N-[3-(trimethoxysilyl)propyl] ethylene diamine (A-1120). The influence of the multi-step sol-gel processing procedure, i.e. the pre-hydrolysis of either of the two precursors on the homogeneity of the hybrid materials was investigated. Results showed that the sol-gel reaction of A-1120 and PEO-[Si(OCH₃)₃]₂ from the same time would result in hybrid materials with the highest homogeneity, and pre-hydrolysis of A-1120 or PEO-[Si(OCH₃)₃]₂ could only decrease the materials’ compatibility.     

Electrodialytic transport properties of anion-exchange membranes in the presence of α-cyclodextrin

Electrodialysis of mixed salt solutions, sodium chloride and sodium sulfate, and sodium chloride and sodium nitrate, was carried out in the presence of α-cyclodextrin using commercial anion-exchange membranes. It was confirmed by several methods that the compound existed in the membrane matrix when the membrane had been immersed in its aqueous solution, though the molecular weight of α-cyclodextrin is relatively high. In electrodialysis, sulfate ions, large and strongly hydrated anions, easily permeated through the membranes and nitrate ions, less hydrated anions, permeated with difficulty through the membranes in the presence of α-cyclodextrin. Because α-cyclodextrin is a hydrophilic compound, which has many ether and alcoholic groups, the hydrophilicity of the anion-exchange membranes is thought to increase. Thus, sulfate ions easily permeate and nitrate ions permeate with difficulty. This proves that the hydrophilicity of the anion-exchange membranes controls permselectivity between anions through the membranes. Received: 8 August 2000 Accepted: 24 October 2000     

Integration of microcolumns and microfluidic fractionators on multitasking centrifugal microfluidic platforms for the analysis of biomolecules

This work demonstrates the development of microfluidic compact discs (CDs) for protein purification and fractionation integrating a series of microfluidic features, such as microreservoirs, microchannels, and microfluidic fractionators. The CDs were fabricated with polydimethylsiloxane (PDMS), and each device contained multiple identical microfluidic patterns. Each pattern employed a microfluidic fractionation feature with operation that was based on the redirection of fluid into an isolation chamber as a result of an overflow. This feature offers the advantage of automated operation without the need for any external manipulation, which is independent of the size and the charge of the fractionated molecules. The performance of the microfluidic fractionator was evaluated by its integration into a protein purification microfluidic architecture. The microfluidic architecture employed a microchamber that accommodated a monolithic microcolumn, the fractionator, and an isolation chamber, which was also utilized for the optical detection of the purified protein. The monolithic microcolumn was polymerized “in situ” on the CD from a monolith precursor solution by microwave-initiated polymerization. This technique enabled the fast, efficient, and simultaneous polymerization of monoliths on disposable CD microfluidic platforms. The design of the CD employed allows the integration of various processes on a single microfluidic device, including protein purification, fractionation, isolation, and detection.      

Sensitive high-performance anion-exchange chromatographic determination of paeoniflorin and albiflorin by pulsed amperometric detection after solid-phase extraction

We developed a method to simultaneously determine paeoniflorin and albiflorin levels using high-performance anion-exchange liquid chromatography with pulsed amperometric detection (HPAEC-PAD). The main principle of our method includes solid-phase extraction step using Amberlite XAD-2 sorbent to remove sugars and to selectively determine glycosides by PAD. Under these conditions, the linear dynamic range was 0.01–100 μg/mL, and the albiflorin and paeoniflorin detection limits (S/N = 3) were 5 and 10 pg, respectively. The intra- and inter-day precisions (RSDs) were <5.07%, and the average recoveries from Paeoniae Radix and Si-ni-san ranged from 97.12 to 101.15%. Our method showed high selectivity, high sensitivity, and good repeatability for analyzing albiflorin and paeoniflorin in oriental medicinal preparation.     

聚砜阴离子交换膜的制备及结构与性能研究

以1,4-二氯甲氧基丁烷(BCMB)为氯甲基化试剂,使聚砜(PSF)发生氯甲基化反应,制得了氯甲基化聚砜(CMPSF),考察了主要因素对聚砜氯甲基化反应的影响,并使用FTIR及1H-NMR等法对CMPSF的化学结构进行了表征.采用三乙胺(TEA)、三丙胺(TPA)及三丁胺(TBA)等3种叔胺对CMPSF进行了季铵化反应,并以4,4′-联吡啶为交联剂实施了交联反应,制备了聚砜阴离子交换膜(PSFAEM).测定了交换膜PSFAEM的主要性能,包括离子交换容量(IEC)、含水量(WC)及膜电阻(Rm).实验结果表明,使用BCMB,聚砜的氯甲基化反应可顺利进行,以氯仿为溶剂,以SnCl4为Lewis酸催化剂,可制得氯甲基化程度为1.75mmol/g的CMPSF.交换膜PSFAEM的IEC、WC及Rm与季铵化反应时间及叔胺的种类密切相关.季铵化反应时间相同时,采用烷基中碳原子数少的叔胺TEA所制备的交换膜具有高的IEC与WC,低的Rm;使用同一种叔胺时,随季铵化反应时间的增长,交换膜的IEC与WC增大,Rm减小.     

Determination of inorganic arsenic in white fish using microwave-assisted alkaline alcoholic sample dissolution and HPLC-ICP-MS

An analytical method for the determination of inorganic arsenic in fish samples using HPLC-ICP-MS has been developed. The fresh homogenised sample was subjected to microwave-assisted dissolution by sodium hydroxide in ethanol, which dissolved the sample and quantitatively oxidised arsenite (As(III)) to arsenate (As(V)). This allowed for the determination of inorganic arsenic as a single species, i.e. As(V), by anion-exchange HPLC-ICP-MS. The completeness of the oxidation was verified by recovery of As(V) which was added to the samples as As(III) prior to the dissolution procedure. The full recovery of As(V) at 104±7% (n=5) indicated good analytical accuracy. The uncertified inorganic arsenic content in the certified reference material TORT-2 was 0.186±0.014 ng g^–1 (n=6). The method was employed for the determination of total arsenic and inorganic arsenic in 60 fish samples including salmon from fresh and saline waters and in plaice. The majority of the results for inorganic arsenic were lower than the LOD of 3 ng g^–1, which corresponded to less than one per thousand of the total arsenic content in the fish samples. For mackerel, however, the recovery of As(III) was incomplete and the method was not suited for this fat-rich fish.