Probe flow injection analysis

Fast Fourier Transform Flow Injection Analysis Field Ion Atom Probe Flame-Ionization Detector Field Ion Microscopy... 

Since mass spectrometry is a rapid analytical technique, the sample throughput will be -20 per hour when using FAB/LSIMS and >60 per hour when using flow injection analysis with APCI or ESI. The rate-limiting step for FAB/LSIMS is the time (1 to 2 min) required to introduce the direct insertion probe through the vacuum interlock. During LC/MS and LC/MS/MS, the slow step is the time required for chromatographic separation. 

A miniaturized thermal flow-injection analysis biosensor was coupled with a microdialysis probe for continuous subcutaneous monitoring of glucose [34]. The system (Scheme 1) consisted of a miniaturized thermal biosensor with a small column containing co-immobilized glucose oxidase and catalase. The analysis buffer passed through the column at a flow rate of 60 pl/min via a 1-pl sample loop connected to a microdialysis probe (Fig. 11). 

Identification or quantification of molecules up to 1 kDa represents the majority of mass spectrometric analyses. The simplest analysis is probably that of a single product from a synthetic chemical reaction where the required information is only the molecular mass. Such samples used to be introduced using a direct insertion probe. Nonpolar compounds are now analyzed by GC-MS with El or Cl. For polar compounds the usual method of introduction is in a liqnid flow, e.g., in methanol (without an LC column), that then is vaporized and the analyte ionized using ESI or APCl. This approach is termed flow injection analysis (FIA). While quadrupole analyzers are applicable for ether GC-MS or FIA, TOF and FT instruments provide the added dimension of accurate mass determination. 

Flow injection analysis (FIA), using ESI or APCI (Sections 22.2.2 and 2.2.2.3), where samples are introduced in a liquid flow without a chromatographic column (and without vacuum locks), has become the modern equivalent of the direct insertion probe. In addition, FIA combined with API methods usually eliminates problems of sample decomposition and limited mass range encountered with solids probes. 

Bond and coworkers [36] have probed the ability of microelectrodes to determine low concentrations of electroactive species using flow injection analysis. Ferrocene was chosen as a test system to avoid any complications associated with irreversible reactions. Measuring concentrations of the order of 10 nM proved challenging and required the use of a battery operated two-electrode potentiostat because of 50-Hz noise coming from the mains power supply. Bond has also shown that it may be easier to realize low limits of detection using macro- rather than microelectrodes [37]. For example, the electrochemical detection of As (111) at a platinum electrode in an HPLC system becomes less favorable as the electrode radius decreases. Thus, while 10 nM As(III) could be detected at a 50- xm-radius microelectrode, the limit of detection increased to 500 nM when a 2.5-pm-radius electrode was used. This falloff in performance appears to arise because of imperfect seals and high stray capacitance for the smaller electrodes. 

ABEI produces ECL when oxidized at 1.0 V versus Ag/AgCl in alkaline aqueous solution. In contrast to luminol, ABEI labels do not markedly lose their CL efficiency when conjugated with proteins. ECL immunoassays with a flow injection analysis (FIA) system using ABEl-isothiocyanate as a label were proposed, which have a better performance than either single-radial immunodiffusion or nephelometric immunoassays. ABEI can also be used as an oligonucleotide marker to label a DNA probe. The intensity of the ABEI ECL was linearly related to the concentration of the complementary sequence in the range 96-96 nM, and the detection limit was down to 30 pM. 

Various analytical methods now employ amperometric measurements as part of their procedures. In particular, amperometric titrations have been widely used for the analysis of various substances in samples ranging from water to radioactive materials. Also, amperometric sensors, such as the dissolved oxygen probe and various amperometric biosensors, are widely used for clinical, environmental, and industrial monitoring. Furthermore, amperometric detectors have gained considerable use since the 1970s in high-performance liquid chromatographic determination of various substances and in flow injection analysis. 

Redox indicators have been widely used to detect the endpoint of titrimetric redox analyses. Potentio-metric detection of endpoints has now largely replaced the use of indicators, but redox indicators are still in use because of their simplicity. Redox indicators can be used to assess redox potentials in many redox systems where visual rather than electrical measurements can sometimes be more helpful. Recent applications of redox indicators include flow-injection analysis with colorimetric monitoring, or the measurement of electrode potentials of solutions using an immobilized redox indicator on the end of a fiber-optic probe. In studies of the metabolism of cells, redox indicators with their color or fluorescence changes are sometimes more convenient than potentiometry. Redox indicators suffer from their dependence on pH changes, and there is not yet a universal redox indicator that can show the redox potential of a solution over a wide range of potentials... 

See also Extraction Solvent Extraction Principles Solid-Phase Extraction Solid-Phase Microextraction. Flow Injection Analysis Principles Instrumentation. Ion Exchange Principles. Ion-Selective Electrodes Liquid Membrane Gas Sensing Probes Enzyme Electrodes. Membrane Techniques Dialysis and Reverse Osmosis Ultrafiltration Pervaporation. Solvents. 

Such a filtration probe has been tested with very good results in a number of analyses with a special enzyme thermistor version designed for use in industrial environments. Figure 2 is a schematic illustration of an enzyme thermistor arranged for process monitoring by repeated flow injection analysis. The interval between sample injections is chosen with respect to how fast the analyte concentration changes. A typical figure is four to five sample injections per hour. The injection valve and a sample selector valve for selection of different samples or calibration solutions and the pumps are controlled with a personal computer with a 386 processor, which also... 

Hapten monolayer electrode sensor assembly was used to detect triazine in a flow injection analysis mode. The interaction of the electrode with different antibody concentrations resulted in the formation of an antibody-antigen (Ab-Ag) complex which insulated the electrode towards the [Fe(CN)6] /Fe(CN)6] " redox probe and diis in turn resulted in no charge transfer. The extent of insulation depends on the antibody concentration and the time of exposure to the antibody solution. The decrease in amperometric response of the antigenic monolayer to corresponding antibody solution for a fixed time produces a quantitative measurement of the antibody concentration. Typical responses obtained for cyanazine-hapten monolayer electrode to different antibody concentrations is shown in Figure 4. The lowest detection limit achieved for cyanazine sensor was 4.0 pg/ml at a response time of few minutes and a less-than 2% cross-reactivity to atrazine, simazine and other metabolites. 

Takamura, K., S. Ohtsuki, and F. Kusu. 2001. Development of a new amperometric sensor for probing the total acid of beverages. Anal. Sci. 17(Suppl.) i737-i739. Takahashi, K., A. Kotani, S. Ohtsuki, and F. Kusu. 2004. Flow-injection analysis with electrochemical detection for determining the titratable acidity of a pH adjuster for foods. Bunseki Kagaku 53 271-274. 

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