Multi-pumping flow systems: the potential of simplicity.

Nowadays, the trend towards more compact, smarter and simpler devices is generally recognized as one of the most challenging aspects in the development of analytical instrumentation. Modern flow-based procedures do not escape this tendency. The level of integration and automation and the operational functionality of Multi-pumping flow systems (MPFS) would, in most of the situations, meet this requirement. The essential elements of MPFS are multiple solenoid actuated micro-pumps strategically positioned in the flow manifold, which are accountable for solutions insertion, propelling and commutation, conditioning the establishment and subsequent detection of the reaction zone. Being the only active components of the flow manifold they provide a great operational simplicity and assure a straightforward run-time control of important analytical variables. Moreover, the reduction of active components minimizes the probability of occurrence of equipment failures, malfunctions or errors. The low size and low cost of solenoid micro-pumps make them ideal tools to build up compact environmentally friendly analytical systems, which are characterized by low solutions consumptions and the minimisation of hazardous waste generation. Furthermore, the reproducible pulsed flowing stream produced by micro-pumps actuation has proven to be a valuable feature regarding sample/reagent mixing and reaction zone homogenisation.

A multipumping flow system for in vitro screening of peroxynitrite scavengers.

Peroxynitrite anion is a reactive nitrogen species formed in vivo by the rapid, controlled diffusion reaction between nitric oxide and superoxide radicals. By reacting with several biological molecules, peroxynitrite may cause important cellular and tissue deleterious effects, which have been associated with many diseases. In this work, an automated flow-based procedure for the in vitro generation of peroxynitrite and subsequent screening of the scavenging activity of selected compounds is developed. This procedure involves a multipumping flow system (MPFS) and exploits the ability of compounds such as lipoic acid, dihydrolipoic acid, cysteine, reduced glutathione, oxidized glutathione, sulindac, and sulindac sulfone to inhibit the chemiluminescent reaction of luminol with peroxynitrite under physiological simulated conditions. Peroxynitrite was generated in the MPFS by the online reaction of acidified hydrogen peroxide with nitrite, followed by a subsequent stabilization by merging with a sodium hydroxide solution to rapidly quench the developing reaction. The pulsed flow and the timed synchronized insertion of sample and reagent solutions provided by the MPFS ensure the establishment of the reaction zone only inside the flow cell, thus allowing maximum chemiluminescence emission detection. The results obtained for the assayed compounds show that, with the exception of oxidized glutathione, all are highly potent scavengers of peroxynitrite at the studied concentrations.

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.

Fluidized beds in flow analysis: use with ion-exchange separation for spectrophotometric determination of zinc in plant digests.

A novel strategy for utilization of solid reagents in flow analysis is proposed. Establishment of diffuse and reproducible geometry enables the solid particles to be maintained in constant floating, reflux, and circulating motion inside a mini-chamber. This is efficiently accomplished with pulsed flows, a characteristic of multi-pumping flow systems. Drawbacks inherent in solid-phase packed columns, for example backpressure, preferential pathways, swelling, etc., and some limitations inherent in immobilized reagents are minimised. Spectrophotometric determination of zinc in plants was selected as an application of the technique. Dowex 1-X8 anionic resin was kept freely inside a mini-chamber. Zinc chloro-complexes were adsorbed on the moving particles and derivatization with zincon was performed after elution. Analytical figures of merit and the potential and limitations of the approach are discussed.

Single reaction interface in flow analysis.

The dual or multiple reaction interface concept, commonly associated to the distinct flow techniques, was replaced by a single interface concept, which do not no rely on the utilisation of a well-defined and compelling sample volume but only on mutual penetration of sample and reagent zones at a single reaction interface where both sample and reagent met together prior to detection. In the proposed approach basic principles of flow analysis, such as controlled dispersion and reaction zone formation, are not influenced by sample and reagent volumes but determined exclusively by the extension of the overlap of two adjoining quasi-infinite zones enhanced by multiple flow reversals and the pulsed nature of the flowing streams. The detector is positioned at the core of the flow manifold (not in the conventional terminal position), and repetitive flow reversals enable interface manipulations, including multi-detection of the entire reaction interface or the monitoring of the evolution of a pre-selected interface zone by using suitable reversal cycle times. The implementation of the developed approach was facilitated due to the configuration simplicity and operational versatility of multi-pumping flow systems. Its performance was evaluated by monitoring processes involving two or four-solution reaction interfaces.

Multi-pumping flow systems: an automation tool.

Multi-pumping flow systems (MPFS) are one of the most recent developments in terms of the design, conception and implementation of continuous flow methodologies, for sample and reagent handling and for the automation of analytical procedures. Based on the utilisation of multiple solenoid micro-pumps they enable the configuring of fully automated and easily controlled and operated analytical systems since all the fundamental operations involved in carrying out a sample analysis, including sample insertion, reagent addition and signal measurement could be carried out by the same manifold component, reducing the number of system parts and minimising its control or the occurrence of mal-functions. On the other hand, micro-pumps actuation produce a pulsed flow characterised by a chaotic movement of the solutions, which contributes to a fast sample/reagent homogenisation with low axial dispersion yielding improved analytical signals. The combination of such advantageous features resulted in simple, compact, versatile, fast, low-cost analytical procedures, exhibiting low reagent and low sample consumption, reducing the production of undesirable wastes and minimising operator intervention.