Rapid detection of proteins by enzyme-linked immunofiltration assay after transfer onto nitrocellulose membranes.

Enzyme-linked immunofiltration assay (ELIFA) for labeling transferred proteins is an interesting and powerful technique for the rapid specific detection (15 min) of proteins immobilized on nitrocellulose or nylon membranes (0.20 and 0.45 micron). ELIFA does not require fastidious handling of the membranes. Saturation, specific labeling and washing procedures are achieved by filtration, controlled by a monitoring unit which regulates the flow rate and ensures excellent specificity, repetition and reproducibility. The recycling by closed circuit or by repetitive inversion of the flow direction offers the advantage of reducing the volumes of expensive reagents while simultaneously increasing the sensitivity of the technique. The detection limit is at least as low as 1-5 ng using directly or indirectly enzymatically labelled probes. ELIFA may be extended to the identification of glycoproteins using specific ligands such as lectins or to the immunocapture of an antigen using specific antibodies immobilized on an activated membrane. ELIFA complements fast separation, by e.g., isoelectric focusing, polyacrylamide gel electrophoresis, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis and accelerated electrotransfer to membranes with rapid detection reducing the total time for separation transfer and detection to less than 2 h.     

Significant immunological cross-reactivity of plant glycoproteins

Plant glycoproteins generally cross-react because of the presence of identical or related complex glycans which are highly immunogenic. The use of mild periodate oxidation of glycans after glycoprotein transfer from sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels to nitrocellulose membranes prior to immunodetection is a way of identifying the carbohydrate antigenic determinants of a glycoprotein as the basis for antigenic cross-reaction. Periodate oxidation can distinguish between antibodies directed against carbohydrate and against peptide antigenic determinants, the latter being unaffected by oxidation. Immunoblotting performed after periodate treatment allows the detection of common protein epitopes.     

Three-compartment bipolar membrane electrodialysis for splitting of sodium formate into formic acid and sodium hydroxide: Role of diffusion of molecular acid

Bipolar membrane electrodialysis is used in a three-compartment configuration to regenerate formic acid and sodium hydroxide from sodium formate. A previous study showed that the diffusion of molecular formic acid induces the loss of acid current efficiency. The present study shows the following results: the diffusion of molecular formic acid through the bipolar membrane explains quantitatively the presence of sodium formate in the sodium hydroxide solution. The loss of acid current efficiency is only due to diffusion of molecular acid through both anion-exchange and bipolar membranes. The sodium hydroxide current efficiency is determined by acid diffusion through the bipolar membrane and OH⁻ leakage through the cation-exchange membrane. The flux of acid diffusion through the membranes is proportional to acid concentration and depends on sodium hydroxide concentration for bipolar membrane and on sodium formate concentration for anion-exchange membrane. The flux rates vary with temperature.     

India ink staining after sodium dodecyl sulfate polyacrylamide gel electrophoresis and in conjunction with Western blots for peptide mapping by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

We present an approach that allows matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) peptide mapping of proteins separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and electroblotted onto nitrocellulose (NC). After blocking the nitrocellulose membrane with polyvinylpyrrolidone-40 the immobilized proteins are visualized using India Ink staining which allows the detection of low nanogram amounts of protein. The utilization of a low concentration of Tween 20 (0.05%) in the India Ink staining solution does not negatively impair the quality of the mass spectra. Due to the virtual nondestructive nature of the stain proteolytic peptides could be recovered from the NC membrane. Taking into account minor precautions during the sample manipulation and concentration and by loading the sample onto a pre-crystallized matrix layer, high quality mass spectral data were obtained on <100 femtomoles of protein loaded onto the gel. Finally, the use of India Ink in conjunction with Western blot analysis is also demonstrated. A rat plasma protein, characterized by Western blot as a covalently modified protein-drug compound, was subjected to peptide mapping and post source decay (PSD) sequencing of peptides. The zomepirac-modified protein was identified as the alpha-subunit of fibrinogen.     

Electrodialysis of calcium and carbonate high concentration solutions and impact on composition in cations of membrane fouling

Fouling, which is the accumulation of undesired solid materials at the phase interfaces of permselective membranes, is one of the major problems in electrodialysis. The objectives of the present work were to investigate the effect of the composition in calcium and carbonate of a model solution to be treated by conventional electrodialysis on their migration kinetics and the composition in cations of the membrane fouling. In the absence of sodium carbonate in the solution, no fouling was visually observed on anion-exchange membranes (AEM) and fouling was observed only at 1600 mg/L CaCl2 on cation-exchange membrane (CEM), while at only 800 mg/L CaCl2 with sodium carbonate, a deposit was observed on both membranes. This difference could be explained by the fact that carbonate has a high buffer capacity, and the time to reach pH 4.0 was then longer than the one without carbonate. Consequently, the migration of the ionic species was carried out over a longer period of time during ED treatment with sodium carbonate addition and in extent the demineralization rates were higher: 43 vs 86%. For treatment with sodium carbonate and 1600 mg/L CaCl2, the higher migration during ED treatment, increased the concentration of calcium, from 14.24 to 93.38 mg/g dry membrane and from 0.74 to 10.27 mg/g dry membrane for CEM and AEM, respectively. Due to the basic pH on the side of the membrane in contact with the NaCl solution, the calcium would precipitate to form calcium hydroxide on CEM while the calcium migrated through the CEM was blocked by the AEM where it formed another fouling.     

Direct N-terminal sequence analysis of rat liver plasma membrane glycoproteins separated by two-dimensional polyacrylamide gel electrophoresis

Nine previously uncharacterized membrane glycoproteins from normal rat liver have been analyzed by amino acid sequencing from two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) after transblotting to Immobilon-P membranes. Three of these components show altered levels of expression in liver tumors. A single electroblotted polyacrylamide gel yielded sufficient quantities of these glycoproteins for amino acid sequencing and the N-terminal structure could be determined for four of them. The remaining five glycoproteins of interest were not sequenceable in this manner, presumably because they had blocked N-termini. Prior to electrophoresis, two enrichment methods were applied to the crude liver membrane preparations: affinity chromatography with concanavalin A to isolate the plasma membrane glycoproteins and then fast protein liquid chromatography on Superose 12 to obtain components having a specific range of molecular weights. These materials were next subjected to 2-D PAGE using pH 4-6 carrier ampholytes in the first dimension and 7.5% sodium dodecyl sulfate gels in the second. The proteins were then electroblotted to Immobilon-P membranes and located by staining with Coomassie Brilliant Blue R-250. Our results demonstrate that N-terminal sequencing (gas-phase) can be achieved on polypeptides obtained from approximately 250 micrograms of total glycoproteins applied to a single 2-D gel.     

水中酚的膜萃取分离流动注射技术测定的研究

本文提出了硅橡胶膜在线萃取分离流动注射技术测定水样中苯酚的方法。由于水样中的苯酚透过硅橡胶进入萃取液的萃取量随时间的增加和温度的升高而增大，故采用停流技术及升高温度以降低酚的检出限。     

Conversion of sodium lactate to lactic acid with water-splitting electrodialysis

The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.     

A reproducible method for determination of nitrocellulose in soil

A reproducible analytical method for determination of nitrocellulose in soil is described. The new method provides the precision and accuracy needed for quantitation of nitrocellulose in soils to enable worker safety on contaminated sites. The method utilizes water and ethanol washes to remove co-contaminants, acetone extraction of nitrocellulose, and base hydrolysis of the extract to reduce nitrate groups. The hydrolysate is then neutralized and analyzed by ion chromatography for determination of free nitrate and nitrite. A variety of bases for hydrolysis and acids for neutralization were evaluated, with 5N sodium hydroxide and carbon dioxide giving the most complete hydrolysis and interference-free neutralization, respectively. The concentration of nitrocellulose in the soil is calculated from the concentrations of nitrate and nitrite and the weight percentage of nitrogen content in nitrocellulose. The laboratory detection limit for the analysis is 10mg/kg. The method acceptance range for recovery of nitrocellulose from control samples is 78-105%.     

Chitosan-based solid electrolyte composite membranes: I. Preparation and characterization

Some chitosan-based solid electrolyte composite membranes were prepared by incorporating potassium hydroxide as the functional ionic source, using glutaraldehyde as cross-linking agent. A three-layer structure with a porous intermediate layer for each composite membrane was observed using SEM. It was found that the concentration of potassium hydroxide solution used to prepare the composite membranes largely influenced the pore volume, porosity, pore size of the intermediate layer, as well as determined the content of potassium hydroxide inside the composite membranes, whereas the degree of cross-linking of composite membrane did not show notable effects. All composite membranes showed significant decreases in both their T_g and onset thermal degradation temperatures with respect to the solid cross-linked chitosan membranes without containing potassium hydroxide. Potassium hydroxide was found to be located inside the intermediate layer of composite membranes with shapes of bulky or fabric crystals. The crystalline properties of matrices of the composite membranes themselves were remarkably modified after being incorporated with potassium hydroxide and main crystalline peaks of matrices almost disappeared for all composite membranes.     

On-line monitoring of cyanide concentration via a gas membrane system in extractive metallurgical processes

The principle of molecular diffusion of gaseous HCN across a tubular microporous hydrophobic PTFE membrane directly immersed in an alkaline solution or in an aqueous mineral suspension has been applied to the design of an on-line sensing system for cyanide. It offers an efficient detection of “available” cyanide and does not require acidification and solution sampling in the reactor. Gaseous HCN diffused through the membrane is dissolved by a sodium hydroxide carder solution which is then submitted to a spectrophotometric analysis by the pyridine-barbituric acid method. The problems related to filtering of sludges are therefore overcome, and many chemical interferences can be eliminated. Complexation reactions of cyanide by metallic cations and the cyanide-consuming properties of sulphide minerals and ores were studied. This method allows the determination of concentrations down to ca. 6 × 10^?7 mol l^?1 HCN + CN^? in the reactor at Ph 10 with a 120-cm membrane tube and a carrier solution flow-rate of 8 cm³ min^?1.     

Determination of cadmium in grains by isotope dilution ICP–MS and coprecipitation using sample constituents as carrier precipitants

A coprecipitation method using sample constituents as carrier precipitants was developed that can remove molybdenum, which interferes with the determination of cadmium in grain samples via isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS). Samples were digested with HNO₃, HF, and HClO₄, and then purified 6 M sodium hydroxide solution was added to generate colloidal hydrolysis compounds, mainly magnesium hydroxide. Cadmium can be effectively separated from molybdenum because the cadmium forms hydroxides and adsorbs onto and/or is occluded in the colloid, while the molybdenum does not form hydroxides or adsorb onto the hydrolysis colloid. The colloid was separated by centrifugation and then dissolved with 0.2 M HNO₃ solution to recover the cadmium. The recovery of Cd achieved using the coprecipitation was >97%, and the removal efficiency of Mo was approximately 99.9%. An extremely low procedural blank (below the detection limit of ICPMS) was achieved by purifying the 6 M sodium hydroxide solution via Mg coprecipitation using Mg(NO₃)₂ solution. The proposed method was applied to two certified reference materials (NIST SRM 1567a wheat flour and SRM 1568a rice flour) and CCQM-P64 soybean powder. Good analytical results with small uncertainties were obtained for all samples. This method is simple and reliable for the determination of Cd in grain samples by ID-ICPMS. Figure Overview of a coprecipitation method using sample constituents     

Determination of DBP and MBP in organic phase by ion chromatography

Dibutyl-and monobutylphosphoric acid in acidic toluene medium were determined by ion chromatography. The procedure involved stripping with dilute sodium hydroxide solution and used carbon tetrachloride as diluent, then detection with a conductivity meter. The effect of flow rate, eluent strength and stripping solution, the effect of chloride and nitrate ion on DBP, the effect on DBP in sodium hydroxide solution, and the effect of organic aliphatic acids were discussed. The detection limits of 0.19 ppm and 0.14 ppm were found for DBP and MBP, respectively.     

Synthesis of ionic polybenzimidazoles with broad ion exchange capacity range for anion exchange membrane fuel cell application

In this study, new anion exchange membranes (AEM) based on crosslinked polybenzimidazole (m-PBI) with quaternary ammonium groups, crosslinkable allyl groups, and hydrophobic ethyl groups as side chains are synthesized and characterized. The AEMs are crosslinked by thermal thiol-ene reaction using a dithiol crosslinker. The ion exchange capacity (IEC) values and crosslinking density were controlled by the number of quaternary ammonium groups and allyl groups, respectively. The introduction of ethyl groups improved the solubility of ionic PBIs even at very low IEC values by eliminating the hydrogen bonding interaction of imidazole rings. This method allows ionic PBIs with broad IEC values, from 0.75 to 2.55 mmol/g, to be prepared. The broad IEC values were achieved by independently controlling the numbers of quaternary ammonium groups, allyl groups, and hydrophobic ethyl groups during preparation. The crosslinked ionic PBIs revealed hydroxide conductivity from 16 to 86 mS/cm at 80°C. The wet membranes also showed excellent mechanical strength with tensile strength of 12.2 to 20.1 MPa and Young's Modulus of 0.67 to 1.45 GPa. The hydroxide conductivity of a crosslinked membrane (0.40Q0.60Et1.00Pr, IEC = 0.95 mmol/g) decreased only 7.9% after the membranes was immersed in a 1.0 M sodium hydroxide solution at 80°C for 720 h. A single fuel cell based on this membrane showed a maximum peak power density of 136 mW/cm² with a current density of 377 mA /cm² at 60°C.     

Simultaneous determination of 13 carbohydrates using high‐performance anion‐exchange chromatography coupled with pulsed amperometric detection and mass spectrometry

A simple, accurate, and highly sensitive method was developed for the determination of 13 carbohydrates in polysaccharide of Spirulina platensis based on high‐performance anion‐exchange chromatography coupled with pulsed amperometric detection and mass spectrometry. Samples were extracted with deionized water using ultrasonic‐assisted extraction, and the ultrasound‐assisted extraction conditions were optimized by Box–Behnken design. Then the extracted polysaccharide was hydrolyzed by adding 1 mol/L trifluoroacetic acid before determination by high‐performance anion‐exchange chromatography coupled with pulsed amperometric detection and confirmed by high‐performance anion‐exchange chromatography coupled with mass spectrometry. The high‐performance anion‐exchange chromatography coupled with pulsed amperometric detection method was performed on a CarboPac PA20 column by gradient elution using deionized water, 0.1 mol/L sodium hydroxide solution, and 0.4 mol/L sodium acetate solution. Excellent linearity was observed in the range of 0.05–10 mg/L. The average recoveries ranged from 80.7 to 121.7%. The limits of detection and limits of quantification for 13 carbohydrates were 0.02–0.10 and 0.2–1.2  μg/kg, respectively. The developed method has been successfully applied to ambient samples, and the results indicated that high‐performance anion‐exchange chromatography coupled with pulsed amperometric detection and mass spectrometry could provide a rapid and accurate method for the simultaneous determination of carbohydrates.     

Effect of calcium and carbonate concentrations on anionic membrane fouling during electrodialysis

A previous study on electrodialysis of calcium and carbonate high concentration solutions demonstrated that calcium migrated through the cation-exchange membrane (CEM) was blocked by the anion-exchange membrane (AEM) where it formed another fouling. The aim of the present work was to complete the identification of the deposit formed on AEM during electrodialysis and to characterize its physical structure at the interface of the membrane. No fouling was found on the anionic membranes treated without calcium chloride in presence of sodium carbonate, while membranes used during ED process of solutions containing calcium chloride and sodium carbonate were slightly fouled. A thin layer of precipitates was observed on the anionic membrane surface. The appearance of precipitates was typical of a crystalline substance. The size and form of crystal increased in proportion to the concentration of calcium chloride in solution. Large and cubic crystals were the best defined on the membrane treated at 1600 mg/L of CaCl2. The precipitate was identified as calcium hydroxide. However, this fouling was not found to affect significantly the electrical conductivity and the thickness of the membranes. Furthermore, the fouling formed was reversible.     

Artificial Formation and Tuning of Glycoprotein Networks on Live Cell Membranes: A Single‐Molecule Tracking Study

We present a method to artificially induce network formation of membrane glycoproteins and show the precise tuning of their interconnection on living cells. For this, membrane glycans are first metabolically labeled with azido sugars and then tagged with biotin by copper‐free click chemistry. Finally, these biotin‐tagged membrane proteins are interconnected with streptavidin (SA) to form an artificial protein network in analogy to a lectin‐induced lattice. The degree of network formation can be controlled by the concentration of SA, its valency, and the concentration of biotin on membrane proteins. This was verified by investigation of the spatiotemporal dynamics of the SA‐protein networks employing single‐molecule tracking. It was also proven that this network formation strongly influences the biologically relevant process of endocytosis as it is known from natural lattices on the cell surface.     

Determination of Lead(II) by a Nitrocellulose Membrane Fluorescent Biosensor Based on G-Quadruplex Conformational Changes

A simple, label-free fluorescence method was developed for the sensitive determination of lead(II) using a nitrocellulose membrane biosensor. The surface of the nitrocellulose membrane was modified by glutaraldehyde to conjugate streptavidin, followed by the immobilization of a DNA probe via a biotin modifier. The biotinylated DNA probe can fold into a G-quadruplex structure in the presence of potassium ion that selectively binds to N-methyl mesoporphyrin IX and yields a strong fluorescence signal. The presence of lead(II) can induce a conformational change of the G-quadruplex to a more compact structure, which results in the release of potassium ion and N-methyl mesoporphyrin IX with a concomitant reduction of the fluorescence signal. The biosensor displayed a detection limit as low as 10 nM with excellent selectivity for lead(II) over other metal ions. The developed biosensor was employed for the determination of lead(II) in spiked river water.     

黄钠铁矾中铁的测定

准确快速测定黄钠铁矾中铁的含量有利于控制铁湿法冶金的流程。采用氢氧化钠溶液分解试样,盐酸(1+9)溶解滤渣,蒸发除过量酸,氨水沉淀分离铜、镍、钴等元素,再用稀盐酸溶解沉淀。在盐酸介质中,SnCl_2将大部分Fe(Ⅲ)还原为Fe(Ⅱ),钨酸钠为指示剂,用TiCl_3还原呈钨蓝色,重铬酸钾滴定至蓝色褪去。再以二苯胺磺酸钠为指示剂,重铬酸钾标准溶液滴定测定样品中铁的含量。实验表明,黄钠铁矾中共存干扰元素绝大部分被分离,同时与酸溶解法进行比较,测定数据一致,相对标准偏差(n=9)小于0.1%。     

Determination of sodium azide in beverages by ion chromatography

A convenient method for determination of sodium azide in beverages using ion chromatography is described. This method combines the specificity for azide with a simple sample preparation using a bubble and trap apparatus that removes any interferences. Sodium azide in a sample was acidified, and the azide was converted to the volatile hydrazoic acid, which was trapped in 2.5 mM sodium hydroxide solution. Determination was performed by isocratic ion chromatography using suppressed conductivity detection. Calibration curves were linear for 0.5 to 20 microg/mL sodium azide and the detection limit was 0.05 microg/mL. Recoveries of sodium azide from spiked samples (10.0 microg/g) were more than 82.6%. The method was then used to analyze various beverages.