Enhancing the microdialysis recovery for sampling of Cu and Ni by incorporating humic acid in the perfusion liquid

A strategy to enhance the microdialysis relative recovery for sampling of Cu and Ni ions is presented. Enhanced recovery was achieved by incorporating humic acid, a binding agent, in the microdialysis perfusion liquid during sampling from a Cu and Ni standard solution mixture. All microdialysis sampling experiments were carried out at room temperature under quiescent conditions using a concentric type of microdialysis probe with an adjustable effective dialysis length. For all metal determinations electrothermal atomic absorption spectrometry was employed. Metal recoveries were shown to be dependent on the membrane molecular weight cut-off, perfusion rate, sample solution pH, perfusion liquid composition as well as perfusion liquid pH. Complete recoveries (100%) of Cu and Ni were obtained by microdialysis sampling using a 10 kDa molecular weight cut-off polysulfone membrane at a flow-rate of 2 μl/min employing a 0.05% (w/v) optimal composition of humic acid incorporated in the perfusion liquid. The optimal sampling pH of humic acid was determined to be 6 where most oxygen containing functional groups are dissociated and available for metal binding. These data have important ramifications for sampling and determination of metal ions in small sample solutions (∼10 ml) at very low concentrations in the ppb range.     

Determination of Cu and Ni in plants by microdialysis sampling: Comparison of dialyzable metal fractions with total metal content

Microdialysis sampling is presented as an in situ sampling and sample clean-up technique with the potential to be used for determination of metals in plant suspension. Suspensions prepared from ultra pure water and flowers of a Blepharis aspera plant species obtained from a Cu and Ni mineralized site were sampled for Cu and Ni by microdialysis sampling after incorporating an optimal 0.05% (w/v) composition of humic acid in the perfusion liquid. Acid digestion of the plant samples was employed for quantification of Cu and Ni by flame atomic absorption spectrometry. All microdialysis sampling experiments were carried out at room temperature under quiescent conditions using a concentric type of microdialysis probe and electrothermal atomic absorption spectrometry was employed for metal quantification. The versatility of microdialysis as an in situ sampling and sample clean-up technique was demonstrated by the ability to sample Cu and Ni from the complex matrices of plant suspensions. Linear relations between the concentrations of Cu and Ni determined after microdialysis sampling and acid digestion were established and the constant concentration ratios of the metals were found to be 0.0138 and 0.0440 respectively for Cu and Ni thus demonstrating the potential that microdialysis sampling has in prediction of metal concentrations in plant suspension after direct relation with the acid digestion method.     

A study of the use of microdialysis probes as a sampling unit in on-line bioprocess monitoring in conjunction with column liquid chromatography

Summary An automated on-line sampling and analytical set-up for the control of fermentations was studied incorporating a microdialysis probe as the sampling device. Applications to a penicillin broth and an ethanol fermentation were studied. Typical recovery values of carbohydrates were found to be close to 100% even after exposure of the microdialysis probe in the process for about 30 h.     

On-line FT-Raman spectroscopic monitoring of starch gelatinisation and enzyme catalysed starch hydrolysis

The hydrolysis of starch by α-amylase and amyloglucosidase and the kinetics of these technically important reactions were investigated by FT-Raman spectroscopy. During the technical starch hydrolysis process, three reactions proceed one after the other but partly in parallel: the gelatinisation, the hydrolysis of starch to dextrin (liquefaction) by α-amylase, and the hydrolysis of dextrin to glucose (saccharification) by glucoamylase. These three reactions were studied separately. Potato starch or dextrin in concentrations of 50 g/l were suspended or dissolved in water, the reaction chamber was placed in a heated water bath, and defined, varied amounts of enzymes in solution were added. The reactions were monitored on-line in a bypass loop. The greatest spectral changes were observed due to the swelling and gelatinisation of starch. The liquefaction of starch to dextrin was started with the addition of α-amylase at a temperature of 80°C and the spectral changes were monitored. In a similar way, a solution/suspension of dextrin was used to investigate the reaction of glucoamylase at 50°C. Both enzymatic reactions were performed at four different enzyme activities. All reactions showed distinctive spectral changes, which can, in principle, be evaluated for the determination of the degree of starch hydrolysis. As a Nd:YAG laser at 1064 nm was used, fluorescence excitation was not observed despite the use of crude, technical-grade enzymes. The findings demonstrate the potential use of Raman spectroscopy in monitoring and control of technical enzyme reactions.     

Development of a push-pull microdialysis sampling technique for the quantitative determination of proteins

Summary An on-line push-pull sampling technique has been developed for continuous analysis of proteins of molecular weight from 5.7 to 67 kDa. The characteristics of the system include gradient elution with a total cycle time of 21 min, membrane stability, unattended automatic operation, and adjustment of the sampling mode and extraction fraction (the ratio of the concentration of analyte in the dialysate to that in the sample) by varying the effective dialysis length. The push and pull flow rates were adjusted in a manner which enabled three different modes of operation. When push-pull microdialysis was compared with conventional microdialysis sampling, significantly higher extraction fractions were obtained for all five model proteins studied. The technique has been applied to the quantification of proteins in cell samples. On-line fractionation enabled complementary MS identification of the proteins present.     

Droplet-based micro-flow chemiluminescence system for in vivo glucose determination by microdialysis sampling.

A micro-flow chemiluminescence (CL) system in vivo for glucose determination by the on-line microdialysis sampling is described in this paper. The micro-flow CL system uses discrete sample droplets, which formed at the tip of the capillary with the sampling volume of 4.5 microl. The sol-gel method is introduced to co-immobilize horseradish peroxidase (HRP) and glucose oxidase (GOD) on the inside surface of the micro-flow cell which was fabricated in polymethyl methacrylate (PMMA). The CL detection involved enzymatic oxidation of glucose to D-gluconic acid and H2O2, then H2O2 oxidizing luminol to produce CL in presence of HRP. The microdialysis probe was utilized for sampling in the rabbit blood; the sample throughput was 20 h(-1). The glucose level in blood of the rabbit was on-line monitored with good results.     

Crystallization and photovoltaic properties of titania-coated polystyrene hybrid microspheres and their photocatalytic activity

The hybrid microspheres with polystyrene core coated by titania nanoparticles were prepared by miniemulsion polymerization, and the as-prepared samples were characterized by SEM, XRD, TG-DTA, XPS, and SPS techniques. TiO2 nanoparticles experienced two processes of phase transition, i.e., amorphous to anatase and anatase to rutile at the calcining temperature range from 400 to 1000 degrees C. The phase transformation temperature of TiO2 hybrid microspheres from anatase to rutile was increased by about 300 degrees C due to the blocking function of calcined polymer remainder. SPS results present that the band-gap of hybrid microspheres is 3.2-3.4 eV, which is larger than that of pure TiO2. The maximum intensity of the SPS signal is about 3 times larger for the hybrid material as compared to the pure TiO2. In addition, the photocatalytic degradation rate of TiO2 hybrid microspheres was 15% faster than that of pure TiO2 in the experiment of the photocatalytic degradation of methyl orange.     

Multi-enzyme electrodes for the determination of starch by flow injection

A tri-enzyme electrode has been developed for determining starch in a flowing stream based on amperometric monitoring of hydrogen peroxide at a potential of +600 mV versus a silver--silver chloride reference electrode. The nylon-based starch-sensing membranes (over a platinum electrode) were prepared from an enzyme cocktail containing various ratios of amyloglucosidase (AMG), mutarotase (MUT) and glucose oxidase (GO). The best starch-sensing membrane (to give the type A electrode) was made from an enzyme cocktail of AMG--MUT--GO (2000 + 100 + 100 U; where 1 U = 16.67 nanokatals), i.e., containing a high level of AMG. In this system, starch samples were first incubated with soluble alpha-amylase (alpha-AMY) (1000 U) for 1 h at room temperature prior to analysis with the tri-enzyme electrode. Attempts were also made to immobilize alpha-AMY on to nylon net, either alone or as a component of a four-membrane starch-enzyme electrode but starch signals were weak compared with those generated by starch pre-treated with soluble alpha-AMY. This system, associated with the type A starch electrode, not only exhibited a calibration of wide linear range (1 x 10(-4)-0.1% m/v starch) but also showed promising operational properties. It has excellent thermal stability over the range 30-70 degrees C.     

Gelatinization properties of native starches and their Näegeli dextrins

Cassava, potato, sweet potato, and Peruvian carrot starches were hydrolyzed with 15% v/v sulfuric acid solution for up to 30 days. Näegeli dextrins obtained from 1, 3, 6, 12, and 30 days were evaluated using differential scanning calorimeter (DSC) and scanning electron microscopy (SEM). Two phases of hydrolysis were found. The first phase was attributed to faster degradation of amorphous areas of granules, whereas the second phase corresponded to slower degradation of crystalline regions. Peruvian carrot starch was the most susceptible to acid, whereas potato and sweet potato starches were the most resistant. From DSC, it was observed a progressive reduction in peak height and a broadening of peaks with increasing hydrolysis time. The peaks shifted to higher temperatures. Onset temperature decreased on first day of hydrolysis for cassava and Peruvian carrot starches, and on third day for potato and sweet potato. Enthalpy decreased during first stage of hydrolysis in cassava and Peruvian carrot starches, and during second phase, it reduced in all starches. SEM showed that the granule surfaces were degraded by erosion on the first day of treatment, followed by degradation of amorphous areas. On third day, potato and sweet potato starches still displayed some granules almost intact, whereas cassava and Peruvian carrot starch granules were totally degraded, confirming their high susceptibility to acid attack. On sixth day of hydrolysis, starch granules had faceted structures, characteristic of crystalline material. The effect that acid hydrolysis had on thermal properties of starches depended on both hydrolysis stage and starch source.     

On-line microdialysis-ion chromatographic determination of inorganic anions in olive-oil mill wastewater

A fully automated method is presented for the determination of inorganic anions in olive-oil mill effluents using on-line dialysis-ion chromatography. The wastewater is first of all sonicated at room temperature to make it homogeneous, then diluted and microdialized. Most of the organic load of the effluents is removed in a few minutes without using reagents, while soluble anion quantitation remains unaffected. The clear solution is analyzed for the inorganic anions content by direct injection on to an ion chromatograph equipped with a conductivity detector. In the absence of standards, the separation efficiency of microdialysis has been investigated by spiking wastewater samples as well as standard oil emulsions with varying amounts of inorganic anions and subjecting them to microdialysis for different periods of time prior to performing instrumental analysis. Excellent spike recoveries and low relative standard deviations are obtained for all the anions if a 10 min microdialysis time is overcame. Chloride, nitrite, nitrate, phosphate and sulphate are not affected by the microdialysis procedure and their recovery is between 96 and 104% in wastewater as well as in standard oil emulsion. Calibration plots are linear over about two orders of magnitude. The dialysis membrane has been replaced after more than 100 analyses. The UV photolysis pre-treatment of the same sample evidences the different information that can be obtained by the two sample pre-treatment procedures.     

In vivo microdialysis/liquid chromatography/tandem mass spectrometry for the on-line monitoring of melatonin in rat

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been coupled to in vivo microdialysis for on-line monitoring of melatonin in a freely moving rat for a period of 15 hours. A microdialysis probe was surgically implanted into the jugular vein of the rat, and deionized water was used as the perfusion medium at a flow rate of 1.0 microL/min. Microdialysis samples were collected in an on-line injector with sample injection every 30 minutes. Melatonin was dosed by intraperitoneal (i.p.) injection and then monitored by microdialysis/LC/MS/MS. The whole experiment, including the microdialysis sampling and sample injection into the LC/MS system, was fully automated. Metabolites of melatonin were identified off-line by LC/MSn experiments. Two metabolites were identified as 6-hydroxymelatonin and cyclic 2-hydroxymelatonin, consistent with ones found previously in the literature.     

Characterisation of absorptive sampling with SPME fibres in the EUPHORE photoreactor

The implementation of an experimental set-up for sampling, and characterisation of parameters related to absorptive sampling solid phase microextraction (SPME) in the EUPHORE photoreactor is described. Toluene was taken as probe compound. Optimisation of the sampling and calibration curves are presented. Equilibrium was achieved in just 30 s due to the good agitation in the chambers and the LOD was 0.24 ppbV. The precision was ±0.02 expressed as relative standard deviation (n = 9). The inter-fibre reproducibility was ±0.03 expressed as relative standard deviation. The effect of the temperature and the sun radiation on absorption in the fibre is also studied using a relative method to calculate the ratio K/K₀ (ratio of absorption constants at two different times during the experiment at which temperature and radiation conditions experimented important variations) calculated through known parameters, avoiding in this way the need for external calibrations in the calculation of K. The results showed a difficult to predict dependence of absorption over the combination of temperature and sun radiation and the need to develop sampling systems with absorptive SPME in which sun radiation has no influence. The stability in different conditions of compounds absorbed in the fibre was also subject to study. At room temperature half of the compound absorbed is expected to desorb in 1.21 h. Conversely, when fibres were kept at low temperatures (−86 °C) after 21 days, desorption was negligible.     

Bio-ceramic hollow fiber membranes for immunoisolation and gene delivery: I: Membrane development

Zirconia bio-ceramic hollow fiber membranes were developed using a sequence of mixing, extrusion, phase inversion and sintering steps. ZrO₂ partially stabilized by Y₂O₃ was chosen as the starting membrane material. The prepared membranes were characterized by SEM, EDX, XRD and gas permeation techniques. Effects of the starting ZrO₂ particle size and sintering temperature on the physical properties of the resulted hollow fiber membranes were extensively studied. Sintered at 1400 °C for 10 h, membranes made from 80 nm sized ZrO₂ particles display cubic fluorite as the major crystalline phase and give rise to interesting microstructure for cell response. Without any surface modification, this tailor-made membrane with high mechanical strength and pore size less than 1 μm was selected for further test of osteoblast attachment. In vitro bio-compatibility was evaluated by using mouse MC-3T3-E1 osteoblast cell culture. A series of cell interactions with fiber surface (i.e. cell adhesion, proliferation, formation of bone nodules, mineralization, etc.) verified the bio-compatibility of the prepared membranes.     

A Review of Microdialysis Sampling Systems

The most important aspects of microdialysis are a theoretical understanding of the process, the microdialysis membrane and the design of the microdialysis probe including the inner cannula dimensions. Several efforts have been made to theoretically account for the processes that take place during microdialysis. These have been employed to develop optimal sampling conditions so as to increase the applicability of the technique for in situ sampling and as a sample clean-up technique prior to chromatography. On the occasion of Prof. Lo Gorton’s 60th birthday, this review highlights the challenge presented by low analyte recoveries that is the major bottleneck in the wider use of microdialysis. The discussion concludes by considering how to increase analyte recovery through a multiple probe approach or by an increase in recovery in the light of the advantages of nanotechnology. Both approaches could impact on the use of microdialysis as a sampling and sample clean-up technique for liquid chromatography.     

Gold nanocatalysts supported on protonic titanate nanotubes and titania nanocrystals

Gold nanoparticles were first supported on protonic titanate nanotubes with the formation of Au/titanate nanocomposites. They were further transformed to Au/titania nanocomposites via an acetic acid treatment at 70 °C for 60 h. The porosity, crystal structure and morphology of those composites have been studied by X-ray diffraction (XRD), High-resolution transmission electron microscope (HRTEM), and low-temperature nitrogen adsorption. Catalytic tests for CO oxidation show that the Au/titanate nanocomposites had a promising activity with complete conversion of CO at 70 °C and that of Au/titania was at room temperature (25 °C). Both catalysts exhibited good thermal and long-term stabilities. The influence of the crystal vacancies and surface properties of the titanate and titania supports on the catalytic activities were evaluated.     

Characterisation of two novel cyclodextrinases using on-line microdialysis sampling with high-performance anion exchange chromatography

In this work, a real-time sampling/analytical method for on-line measurements of two newly discovered cyclomaltodextrinases (CDases) has been developed and evaluated. This novel methodology not only allows the final products to be investigated, but it also reveals enzyme-specific differences in the degradation pathways during the hydrolysis of different substrates, which is a great advantage in the important tasks of investigating the mechanisms of and classifying new hydrolases, and is an advantage that conventional techniques cannot offer. Two different enzymes, one CDase from Laceyella sacchari (LsCda13) and one from Anoxybacillus flavithermus (AfCda13), were investigated during the hydrolysis of α-, β- and γ-cyclodextrin, and the hydrolysis products were sampled via a microdialysis probe and injected on-line every 30 min into a high-performance anion exchange chromatography system equipped with a pulsed amperometric detector (HPAEC–PAD), where they were identified. The enzymes yielded the same end-products, maltose and glucose, in an approximate molar ratio of 2:1, but they exhibited distinctly different patterns of intermediate product formation before reaching the end-point. LsCda13 had a more random distribution of the intermediate products, whereas AfCda13 showed the distinct intermediate production of maltotriose, which in some cases accumulated.     

堇青石栽体表面ilicalite-1沸石膜的合成与表征

本文首次采用堇青石为载体,用水热合成方法,制备了致密的高硅MFI沸石膜,并对其结构、成分以及气体渗透性质进行表征。     

Optimisation of microdialysis sampling recovery by varying inner cannula geometry

In vitro microdialysis recoveries of glucose were evaluated and optimised by varying the inner cannula dimensions for a concentric type microdialysis probe. The recovery was shown to be significantly dependent on the outer radius of the inner cannula (r alpha). Increasing r alpha by 50% while holding all other microdialysis variables constant caused a 26% increase in recovery under the conditions tested. Mass transport modeling of microdialysis sampling showed that the magnitude of the recovery change in response to changes in r alpha may depend on other experimental variables such as effective dialysis length, membrane dimensions, membrane type and medium composition. These data indicate that microdialysis recovery may be substantially improved by optimising the outer diameter of the inner cannula. These data also suggest that in order to fully characterise and compare data from microdialysis experiments, r alpha should become one of the reported variables.     

Diffusion and calibration properties of microdialysis sampling membranes in biological media

The diffusion and calibration properties for three commercially available microdialysis membranes (polycarbonate-polyether (PC), polyacrylonitrile (PAN), and cuprophan (CUP)) were evaluated. The analytes studied had molecular weights between 94 (phenol) and 1355 (vitamin B12). For each analyte-membrane pair, an effective membrane diffusion coefficient was calculated. Effective membrane diffusion coefficients varied considerably between the microdialysis membranes. For Vitamin B12, CUP and PAN membranes gave relative recovery values of greater than 20% at 0.5 microl min(-1), while the PC membrane had a 1% recovery. When backpressure was applied. PC and PAN membranes exhibited more ultrafiltration than CUP membranes. Ultrafiltration did not affect analyte relative recovery through either PC or PAN membranes. Effective membrane diffusion coefficients were not significantly altered for some membrane-analyte combinations when exposed to 4% bovine serum albumin or 0.3% fibrinogen. These data suggest that reductions in relative recovery during long-term microdialysis sampling experiments may be due to other physiologically relevant proteins or to tissue reactions near the dialysis membrane.     

一种气相合成Silicalite-1沸石膜的新方法

由于在分离和催化领域的潜在应用前景 ,沸石膜近年来受到人们的广泛重视 .制备沸石膜的方法很多 ,如原位水热合成、微波合成、电金属沉积、嵌入法等等 .90年代以来 ,由于可减少昂贵的模板剂用量 ,以及能在不同载体上合成沸石膜等优点 ,蒸汽相合成法 (ＶＰＴ)受到关注[1 3] .通常采用浸渍方法或正硅酸乙酯 (ＴＥＯＳ)的水解在载体上形成一层致密的无定形凝胶作为引入的硅源 ,随即在有机模板剂和水的蒸汽相中转晶得到沸石膜 .自 1 992年Ｄｏｎｇ等[1 ] 首先采用ＶＰＴ方法合成ＺＳＭ 5和ＺＳＭ 35沸石膜以来 ,已经成功制备了多种结构类型的沸…