A new microdialysis-based glucose-sensing system with an integrated fiber-optic hybrid sensor is presented. Design and dimensions
of the cell are adapted for its coupling with commercially available microdialysis techniques, thereby providing a new system
for continuous glucose monitoring. The glucose level is detected via oxygen consumption which occurs as a consequence of enzymatic
reaction between immobilized glucose oxidase and glucose. The use of gas-permeable Tygon tubing ensures complete and constant
air-saturation of the measuring fluid in the cell. Nevertheless, a reference oxygen optode is used to detect and to compensate
response changes caused by events like bacterial growth, temperature fluctuations, or failure of the peristaltic pump. In
contrast to widely used electrochemical sensors, the response of the microdialysis-based fiber-optic glucose sensor is highly
selective, making this sensor approach particularly advantageous for continuous glucose monitoring of patients in intensive
care units. The effects of flow rate, pH, temperature, and common interferences on the sensor response are presented and discussed
in detail. The sensor is evaluated in vitro using a 3-day continuous test in glucose-spiked plasma. The ability to measure
glucose in humans is demonstrated by coupling the flow-through cell and commercially available microdialysis catheter CMA60.
A 24-h monitoring test using this setup is successfully applied to a healthy volunteer. 相似文献
Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at ?1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L?1 (1 μg L?1 for Mn) to 20 μg L?1 (30 μg L?1 for Zn, Pb and 80 μg L?1 for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L?1 (5 μg L?1 for Cd) to 100 μg L?1 (200 μg L?1 for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol?1, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb nA L μmol?1. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments. 相似文献
Various key variables (biomass, substrate and product) of bioprocesses should be monitored in order to retrieve useful information
on the system, with the biomass (the cell density) the principal target. Although several analytical methods have been adapted
and used to monitor the evolution of cell density evolution in cultures, a general method for performing this determination
has not yet been established, as each technique has its own advantages and drawbacks. In the present work, noninduced glycerol
batch cultures (for which biomass and substrate are the key variables) were monitored using multiwavelength fluorescence spectroscopy.
The data gathered were modelled via PARAFAC-PLS chemometric methodologies, resulting in important qualitative and quantitative
information about the behaviours of different biogenic fluorophors in batch cultures of the yeast Pichia pastoris. This information was used to predict the target process variables in such cultures; this permitted the applicability of
this combined technique to bioprocess monitoring to be assessed. 相似文献
A high-performance liquid chromatography (HPLC) system was developed for the determination of drug photostability and phototoxicity
based on an automated column-switching system with aqueous online UV-A irradiation and hyphenated organic separation of the
drug and its photoproducts. The photoreactor is built with an poly(ethylene-co-tetrafluoroethylene) (ETFE) reaction coil knitted around a UV-A light source. The chromatographic separation was performed
with two special C18 columns, which are also suitable for using with pure water as eluent. Degradation of chlorpromazine (CPZ) by ultraviolet
light was investigated at pH 7 and pH 3. Furthermore chlorpromazine was irradiated in the presence of guanosine-5-monophosphate
(GMP) in pH 7 buffered solution, leading to a new photoproduct. In the pH 3 irradiation studies of CPZ and GMP, no reaction
was detected between the molecules. 相似文献
The mass spectrometric development of an enzymatic assay resulting in enzymatic activity, its reaction pathway and its dissociation constant are described for the first time within a single experiment. The method combines the performance of a mass spectrometry-compatible enzyme assay with the direct detection of specific enzyme complexes using hen egg white lysozyme as a model. The continuous liquid-flow technique applied, when hyphenated with electrospray ionization (ESI)-time-of-flight (ToF)-mass spectrometry (MS), permitted the simultaneous detection of several substances involved in product screening as well as the direct observation of dissociation constants. Dissociation constants for the product inhibitor N, N', N'-triacetylchitotriose were calculated using a Scatchard plot (12 x 10(-6) M) and the law of mass action (18-24 x 10(-6) M), and these are in good agreement with constants obtained in earlier mass spectrometric (6-18 x 10(-6) M) or spectroscopic (6-8 x 10(-6) M) studies. Finally, the enzymatic hydrolysis of glycosidic substrate was monitored by ESI-ToF-MS in the presence of various inhibitors, thus leading to decreased activities in terms of their enzyme affinities. The associated inhibitor-enzyme complexes could be detected for up to lower micromolar K( d ) values. 相似文献
Fundamental measurements in online polymerization reaction monitoring and control seek to avoid empirical and inferential models in data interpretation. One such approach making use of multiple detectors is automatic continuous online monitoring of polymerization reactions (ACOMP), wherein a continuous reactor stream is automatically, continuously diluted and conditioned to where measurements reflect intrinsic particle properties and not the interactions that can dominate measurements in concentrated media. Examples where dilute regime measurements are needed include static and dynamic light scattering, and reduced viscosity. This review focuses on ACOMP to illustrate a number of reaction contexts where fundamental measurements are used to gain a comprehensive picture of reaction characteristics.
Chemiluminescence (CL) offers a sensitive detection method for capillary electrophoresis (CE), but the implementation of CE–CL is usually under compromised operating conditions for CE, such as the prerequisite of extreme pH buffer for optimal CL reaction at the capillary outlet. This has sometimes significantly deteriorated the separation of CE. In this study, the development of a new interface makes it possible to optimize the operating conditions for CE separation and CL detection independently. The interface consists of an on-column fracture being installed in a reservoir near the capillary end to create an electrical connection and also serve as reagent addition entrance. The capillary terminal is inserted into an end-column reservoir for CL reaction and detection. In this arrangement, the applied electric field has been decoupled from the CL detection, which is proved to effectively improve CE's performance by allowing the use of optimal CE buffers. At the same time, it enables the optimization of CL detection independently. The applicability of this interface was evaluated by using acridinium ester (AE) and luminol systems. For AE system, the interfering products of CL reagent (−OH, HO2−) have been prevented, and the pH range of CE buffer can be independent to the optimal pH value of AE CL reaction, which is usually below 3. The AE was detected using running buffer at pH 8.7, giving a detection limit of 0.1 nM (S/N = 3), and the theoretical plate numbers is as high as 56 000. The on-column fracture based configuration is simple, sensitive and easy to implement. 相似文献
In this work we have evaluated the performance of two sample preparation methodologies for the large-scale multiresidue analysis of pesticides in olives using liquid chromatography–electrospray tandem mass spectrometry (LC–MS/MS). The tested sample treatment methodologies were: (1) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using GCB, PSA and C18 sorbents (QuEChERS method – modified for fatty vegetables) and (2) matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a final clean-up performed in the elution step using Florisil. An LC–MS/MS method covering 104 multiclass pesticides was developed to examine the performance of these two protocols. The separation of the compounds from the olive extracts was achieved using a short C18 column (50 mm × 4.6 mm i.d.) with 1.8 μm particle size. The identification and confirmation of the compounds was based on retention time matching along with the presence (and ratio) of two typical MRM transitions. Limits of detection obtained were lower than 10 μg kg−1 for 89% analytes using both sample treatment protocols. Recoveries studies performed on olives samples spiked at two concentration levels (10 and 100 μg kg−1) yielded average recoveries in the range 70–120% for most analytes when QuEChERS procedure is employed. When MSPD was the choice for sample extraction, recoveries obtained were in the range 50–70% for most of target compounds. The proposed methods were successfully applied to the analysis of real olives samples, revealing the presence of some of the target species in the μg kg−1 range. Besides the evaluation of the sample preparation approaches, we also discuss the use of advanced software features associated to MRM method development that overcome several limitations and drawbacks associated to MS/MS methods (time segments boundaries, tedious method development/manual scheduling and acquisition limitations). This software feature recently offered by different vendors is based on an algorithm that associates retention time data for each individual MS/MS transition, so that the number of simultaneously traced transitions throughout the entire chromatographic run (dwell times and sensitivity) is maximized. 相似文献
In situ tensile tests were made in a scanning electron microscope (SEM) to investigate the deformation and micro-fracture in the immediate vicinity of a micro-crack tip in commercial pure aluminum with large-size crystal. Examined are the slip line field, stress intensity factor, strain energy density factor and crack tip opening displacement (CTOD) for mixed mode loading. Blunting and sharpening effects are observed. The latter is controlled by localized slip while the former by uniformed slip of the operating slip system with the highest crack tip Schmid factor. The operating slip system depends on the crystallographic orientation of crystal containing micro-cracks.The damage and fracture take place in the blunted region and depend on the coarsening and spacing of uniformed slip lines. The mixed mode micro-crack propagates along the direction where the voids grow and coalesce into the micro-crack. The direction also depends on the orientation of the applied loading. This suggests that the formation of macro-fracture mechanics could be applied. In particular, the minimum strain energy density criterion is suitable for determining the direction of micro-crack instability in the mixed mode. The in situ data were used to yield a nearly constant critical, minimum strain energy density factor for onset of micro-cracking. 相似文献