Multicommutated Flow Research Articles

Multicommuted Flow Injection Analysis Using Chemiluminescence Detection (MCFIA-CL) for Olive Oil Analysis

This article describes the applicability of multicommuted chemiluminescence flow injection analysis (MCFIA-CL) to the determination of olive oil quality parameters. Two automated MCFIA methods were developed and validated for the determination of peroxide value (PV) and phenolic compounds in commercial extra virgin olive oil samples. The PV method proposed is based on the chemiluminescent (CL) signal produced from luminol oxidation by the olive oil hydroperoxides in basic conditions using Co(II) as catalyst, while the determination of phenolic compounds is based on CL emission generated from permanganate reduction in acidic media by hydroalcoholic extracts of olive oil. The flow assemblies for automated liquid handling consisted, respectively, of 2 and 3 three-way solenoid valves, which were controlled by a homemade electronic interface and Java-written software together with a CL detector. The signals obtained correlated well against the PV and total phenolic contents measured by the official and the Folin-Ciocalteu methods, respectively. The linear response range observed for PV allows checking whether the samples are in compliance with European Union regulations. On the other hand, the phenolic compounds content also correlated well with data reported by the well-known FC method across the entire typical concentration range of these compounds in virgin olive oils. The proposed methods are faster, safer, and more environmentally friendly than the respective official or classical ones involving lower consumption of solvents, reagents, and sample, as well as less waste generation together with a high sample throughput. Moreover, they are straightforward and cost-effective to implement in routine analysis, and can be regarded as a feasible alternative to the official or classic methods.

Versatile automated continuous flow system (VersAFlo) for bioanalysis and bioprocess control

Flow injection analysis provides a convenient platform for the use of biosensors in the monitoring of bioprocesses. A major requirement in bioprocess monitoring is real time information about various process parameters like concentration of products and substrates, flow rates, and injection volumes. Depending on the application, the monitoring requirements vary and this results in a need for different measurement flow schemes. Common flow schemes employed with biosensing are FIA, SIA, BIA and multi-commuted flow. In this work, a versatile platform to employ biosensors for continuous analysis of bioprocesses with precise control of flow, volume and defined events has been developed. The system is based on National Instruments LabVIEW and employs piston-, peristaltic pumps, motorized injection valves and 2-way and 3-way solenoid valves. The system supports data acquisition, controls interface with devices and visualization of data from multiple detectors used in biosensing. The system was successfully evaluated for the analysis of a model analyte, human immunoglobulin G (IgG), employing continuous flow-ELISA in competitive mode with optical detection. The flow-immunosensor showed very good linearity; from 5 to 400 μg/ml. The system had excellent reproducibility and stability with a relative standard deviation of 4.75%. The immunosensor was also subjected to a model first order kinetics of target analyte concentration and the results from the sensor agreed well with the estimated concentration. The flexibility of the system gives that different flow configurations easily can be set up and the dynamic range of analysis can be adapted by varying different flow conditions for measurement, thereby controlling different reaction times in the biosensor system. The system could be useful for online analysis and control of bioprocesses employing biosensors. Further, with automated data collection and analysis, the system provides excellent basis for cross platform data communication for integrated control.

A critical comparison of analytical flow systems exploiting streamlined and pulsed flows

Multipumping (MPFS) and multicommuted (MCFS) flow systems relying on pulsed and laminar flows were critically compared. The mixing conditions and dispersion associated with both systems were evaluated by simulating the sample with bromocresol green. The molybdenum blue method for phosphate determination in soil extracts was also implemented in both flow systems. Furthermore, laser-induced fluorescence (LIF) was applied to visualize the dispersing sample; rhodamine B was used as the fluorescent species. The pulsed flow enhanced the mixing of the solutions involved, thus reducing reagent consumption (48 and 96 microl for MPFS and MCFS), and improving sampling rate (67 and 144 h(-1) for MCFS and MPFS). For phosphate determination, results obtained with both systems were precise (r.s.d. < 0.5%; n = 10) and accurate. Analyses of the absorbance vs time/space LIF plots revealed that exploitation of pulsed flow led to a pronounced radial dispersion and to a limited axial dispersion, typical aspects of turbulent flows.

Scientometric Picture of the Evolution of the Literature of Automation in Spectroscopy and Its Current State

The current study focuses on the status of automation and mechanization in spectroscopy for analytical chemistry publications compiled during the period 1980–2006, in Analytical s. Flow injection analysis (FIA), sequential injection analysis (SIA), multicommutation, and monosegmented and segmented flow strategies were considered. For assessing the evolution of scientific productivity, the total number of publications concerned with the different methodologies was evaluated. In order to provide a picture of the state of the art of this field, the most important journals, the most active authors, and the most productive countries in the field of automation were evaluated in the period of the first years of this century. The authors were invited to contribute this paper to a special issue of the journal entitled “Spectroscopy and Automation”. This special issue was organized by Miguel de la Guardia, Professor of Analytical Chemistry at Valencia University, Spain.

Multicommuted fluorescence based optosensor for the screening of bitertanol residues in banana samples

A multicommuted flow through optosensor is developed in order to determine bitertanol in banana samples, by measuring the pesticide native fluorescence at 261/326 nm. The solid support used in the flow-through cell, C 18, allows both high selectivity and sensitivity necessary for the screening of the pesticide at residue levels. These characteristics of optosensing are implemented with low sample consumption and automation intrinsic properties of multicommutation, providing a useful tool for pesticide residue routine determination in foods. An acetonitrile extraction/partitioning and dispersive solid-phase extraction clean-up procedure proved to be useful; an additional cleaning step with C 18 solid phase extraction (SPE) cartridges was carried out, eliminating all matrix limitations. Recovery experiments performed on banana samples at different concentrations provided recoveries between 81% and 115%. A detection limit of 0.014 mg kg −1 was obtained. This makes the method suitable for screening bitertanol in banana samples, fulfilling the maximum residue levels of 3 mg kg −1 established by the European Union.

Oxidability Determination in Waste Waters Using an Automatic Titrator Based on a Multicommutated Unsegmented Flow System

The automatic titrator based on a multicommutated unsegmented flow system was applied to redox titrations and used for oxidability determination in waters analysis. This automatic titrator allows the attainment of complete titration curves, being the determination of titrand concentration performed without requiring any prior calibration. After sample treatment (oxidation step), the oxidability determination in waste water samples was accomplished by the automatic flow titrator (titration step). Repeated determinations of standard solutions gave a 3.5% RSD (n=10, 0.010M) for repeatability and a 3.2% RSD (n=2, 0.057M) for reproducibility. Samples results (n=9) were in good agreement (t-test) with those obtained with a reference procedure.

Precipitation titrations using an automatic titrator based on a multicommutated unsegmented flow system

An automatic flow titrator based on a multicommutated unsegmented flow system was used to perform precipitation titrations with potentiometric detection. The titration approach is based on sequential introduction of increasing titrant and decreasing titrand volumes into a mixing chamber. The system allows the attainment of complete curves, the titration end point being determined by the Gran method, as is usually employed in batch potentiometric titrations. The theoretical model for the analytical process is presented and discussed and the determination of titrand concentration is performed without any prior calibration. The automatic flow titrator developed was applied to chloride determination in bottled natural waters and the results obtained were reproducible (RSD 3.2 and 3.8% for repeatability and reproducibility, respectively) and in good agreement with those given by the reference procedure (relative deviation within the range from −4.6 to 4.8%).