MSFIA-LOV system for Ra isolation and pre-concentration from water samples previous radiometric detection

An automatic system based on multisyringe flow injection analysis (MSFIA) and lab-on-valve (LOV) flow techniques for separation and pre-concentration of ²²⁶Ra from drinking and natural water samples has been developed. The analytical protocol combines two different procedures: the Ra adsorption on MnO₂ and the BaSO₄ co-precipitation, achieving more selectivity especially in water samples with low radium levels.     

Application of flowing-stream techniques to water analysis Part II. General quality parameters and anionic compounds: halogenated, sulphur and metalloid species

In the first part of this review [Talanta 60 (2000) 867], flowing-stream methods (namely, segmented flow analysis (SFA), continuous-flow analysis (CFA), flow-injection analysis (FIA), sequential-injection analysis (SIA), multicommuted flow-injection analysis (MCFIA) and multisyringe flow-injection analysis (MSFIA)) were presented as powerful analytical tools for nutrient determination in water samples when coupled to photometric/fluorimetric detection, flow-through ion-selective electrodes or amperometric sensors.In the present paper, relevant flow methods applied to the monitoring of anionic species as well as to the determination of general parameters for water quality evaluation (such as pH, alkalinity, chemical and biochemical oxygen demand, conductivity and total ionic content) are reviewed, and their background, detection technique and noteworthy analytical features are detailed. Furthermore, other techniques, such as flow systems connected to hydride-generation atomic absorption spectrometry, should be highlighted as practical approaches for metalloid determination since a series of speciation schemes are demonstrated to be readily adaptable.     

Multisyringe flow injection analysis system for automation of standard addition calibration method

In the present work, the multi-channel features of multisyringe flow injection analysis (MSFIA) were exploited for the first time to implement calibration based on standard addition method (SAM). For this, standard solutions containing different concentrations of target analyte were placed in each syringe of the multisyringe and connected to a flow network where in-line mixing of sample and standard through a merging zone approach was established prior to detection of analyte. Using this strategy, artifacts reported before in SAM using flow injection analysis were avoided as the concentration of the analyte in the resulting mixture was related to the dilution of sample and added standard within the system, and the concentration of all matrix components was kept constant during all measurements. The feasibility of the proposed MSFIA system was assessed through application to potentiometric determination of chloride ion in electroplating bath and milk samples. Results obtained for samples (n = 15) were not statistically different from those provided by titrimetric procedures, with an excellent throughput (20–31 samples h^{− 1}), comprising four-level addition of chloride ion.     

Flow-through optical fiber sensor for automatic sulfide determination in waters by multisyringe flow injection analysis using solid-phase reflectometry

A software-controlled flow-through optical fiber diffuse reflectance sensor capitalized on the implementation of disk-based solid-phase pre-concentration schemes in a multisyringe flow injection analysis (MSFIA) set-up is proposed for the trace determination of sulfide in environmental waters and wastewaters. The fully automated flowing methodology is based on Fischer's coupling reaction of sulfide with N,N-dimethyl-p-phenylenediamine (DMPD) in the presence of Fe(iii) as oxidizing reagent in a 0.5 M HCl medium. The on-line generated methylene blue dye is subsequently delivered downstream to a dedicated optode cell furnished with an octadecyl-chemically modified (C(18)) disk, while continuously recording the diffuse reflectance spectrum of the pre-concentrated compound. A double regeneration protocol is finally executed to warrant minimum background noise and negligible baseline. Under the optimized chemical and hydrodynamic conditions, the optosensing MSFIA method features coefficients of variation better than 0.7%(n= 10) at 50 microg l(-1) concentration, a linear working range of 20-200 microg l(-1) sulfide, a 3sigma(blank) detection limit of 2.9 microg l(-1) sulfide and an injection throughput of 8 h(-1) for a pre-concentration sample volume of 2.9 ml. The interfacing of the robust and versatile multisyringe flow injection-based optode with a plug-in spectrophotometer furnished with a light emitting diode assures the miniaturization of the overall flow analyzer, which is, thus, readily adaptable to real-time monitoring schemes. The potential of the multisyringe flow method was assessed via the determination of sulfide traces in water samples of different complexity (namely, freshwater, seawater and wastewater).     

Infrared detection in flow analysis - developments and trends (review)

Flow analysis offers an inexpensive and versatile means for the automation of analytical procedures and hence it has been incorporated in many different techniques. However, the use of infrared detection in flow analysis systems is not common. Whereas Fourier transform infrared (FTIR) spectroscopic detection has been routinely used in gas chromatography (GC), its use for liquid chromatography, and now for flow analysis, flow injection analysis, or sequential injection analysis, is not frequent. The most prominent reasons are probably: (i) the strong absorption of most of the common solvents, specially water, (ii) the relative poor sensibility compared to UV–vis, fluorescence, etc. (iii) FTIR is normally not even considered a valuable detection technique, (iv) problems arising from obtaining adequate information from transient IR signals from the injected samples, and (v) only a few analytical chemist uses routinely the FTIR technique. This practice neglects that IR spectroscopy offers some unique features that now, using modern FTIR instrumentation, can be exploited in an advantageous manner. It is important to realize that each sample (analyte/matrix) represents a special and unique analytical problem; which defines the mode of operation and implementation of the IR technique. Flow analysis–IR techniques – as well as all techniques – has a number of shortcomings to solve these problems. In this article, most of these strategies such as the use of: baseline correction, derivative spectroscopy, stopped flow systems, reverse flow systems, multiparametric calibrations, etc., will be discussed. Additionally, recent developments in on-line gas phase generation–FTIR and hydride generation–FTIR spectrometry, as well as the principles of the HPLC–FTIR and capillary electrophoresis–FTIR hyphenation are also discussed. This review aims to provide an account of the state of the art, of these relatively new techniques. Its beginning, developments, applications and new trends, basically in the MID–IR, and by using transmission cells.     

Electronic tongues in flow analysis

This review presents the evolution of recent flow-based analytical systems, characterized by the use of arrays of sensors as a detection scheme. For the proper processing of the complex responses generated, the systems require the use of advanced chemometric treatment, in which received the term “electronic tongue”. Applications employing the flow injection analysis (FIA) and sequential injection analysis (SIA) are described. Chronologically, the progresses made by different research groups are shown, emphasizing their final applications in real problem solving.     

A versatile set up for implementing different flow analysis approaches: Spectrophotometric determination of nickel in steel alloys

An arrangement capable of implementing the four principal types of flow analysis processes, monosegmented flow analysis (MSFA), flow injection analysis with multicommutation and binary sampling (FIA-MBS), flow injection analysis with sandwich sampling (FIA-SS) and sequential injection analysis (SIA) is described. The core of the flow manifold is a six-way solenoid valve that is assembled together with three three-way solenoid valves in order to provide a versatile flow network. Software was written in VisualBasic 3.0 to give a friendly working structure allowing the user to easily choose the flow variables and the kind of flow system. The reliability of the flow set up for implementation of the four flow analysis systems was evaluated by means of the spectrophotometric determination of nickel in steel alloys, based on the formation of a colored complex with dimethylglyoxime (DMG). The performances of the four different flow methodologies were compared. The reagent consumptions per determination were 4.0 mg of triethanolamine, 6.0 mg of potassium persulfate and 0.6 mg of DMG. When the flow set up was instructed through the software to implement MSFA, FIA-MBS, and FIA-SS approaches, a sampling frequency of 40 samples/h was obtained, while 30 samples could be processed per hour in the SIA mode. The precisions, evaluated as the relative standard deviation of ten determinations were 0.7%, 1.6%, 1.8% and 3.1% for the MFSA, FIA-MBS, FIA-SS and SIA systems, respectively. The results for determination of nickel in steel alloys presented good agreement with the reference method (ICP OES), showing no significant difference at a confidence level of 95%.     

Conductometric determination of ammonium by a multisyringe flow injection system applying gas diffusion

A multisyringe flow injection system (MSFIA) coupled to a gas-diffusion cell has been developed for the conductometric determination of ammonium in different water samples. Operation strategies, membrane, reagent concentrations, and flow rates have been studied to optimize the sensitivity of detection and to fit the required working range. The proposed MSFIA system has been compared with former FIA and SIA systems using gas diffusion. The system was applied to the determination of ammonium in water samples of different matrices in order to evaluate its performance. These samples were coastal waters, pond waters, and compost aqueous extracts. Good recoveries of 102?±?13% were obtained and no significant differences with the reference methods were found. The system can be used for a wide concentration range of ammonia, from 0.075 to 360?mg?L^?1, without sample dilution and with a precision better than 2% of RSD. The throughput of the method was 32 injections per hour.     

Multicommutated Flow System with Amperometric Detection. Determination of Uric Acid in Urine

In this work an automated flow methodology based on a tubular amperometric detector coupled to a multicommutated flow system was developed and applied in the determination of uric acid in urine. The exploitation of the analytical potential of multicommutated flow systems allowed the implementation of an expeditious and easily controlled on‐line sample dilution, based on the zone sampling approach. The dilution capability exhibited by the developed methodology allowed a direct insertion of the samples in the flow system, without any pretreatment, assuring faster, simpler and less expensive analyses when compared to the enzymatic based methods with spectrophotometric detection commonly used in clinical analyses. The results obtained with the developed system in the determination of uric acid in urine were compared with those obtained by the enzymatic method used in clinical analysis laboratories, and no statistical difference between both methods (for a confidence level of 95%) was found. The proposed system showed good repeatability (RSD<3%, n=10) and a detection limit of 4×10^?7 mol L^?1.     

Evolution of the commutation concept associated with the development of flow analysis

Evolution of the commutation concept has lead to the proposal and development of different generations of flow analyzers. Since the inception of the air-segmented flow systems till the availability of modern flow injection, sequential-injection and other flow-based analytical systems, a noteworthy improvement of the commutating devices has been noted.

Multi-functional manifold is described as a polyvalent approach for methodology implementation in a flow analyzer. It permits the investigation of mixing conditions under different flow patterns (unsegmented, segmented, monosegmented) with optional exploitation of the stopped-flow approach. For this purpose, spectrophotometric or turbidimetric measurements eventually affected by Schlieren noise were considered. Potentialities and limitations of the manifold are discussed in relation with methods based on relatively fast or slow chemical reactions. As applications, phosphate and chloride determinations in plant digests and natural waters were selected.

The manifold is characterized by high versatility and may work in connection with different flow configurations. Development will certainly lead to simple, versatile and miniaturized analyzers, able to run samples in a personalized fashion. In addition, random reagent selection, full automation, expansion of the analytical application range and increasing potentialities of the already existing methodologies are devised.     

Evaluation of different mediator-modified screen-printed electrodes used in a flow system as amperometric sensors for NADH

This work presents a comparative study between two different methods for the preparation of mediator-modified screen-printed electrodes, to be used as detectors in a reliable flow injection system for the determination of the nicotinamide adenine dinucleotide (NADH) coenzyme. The best strategy was selected for the final development of compact biosensors based on dehydrogenase enzymes. For the first immobilisation strategy, different redox mediators were electropolymerised onto the SPE surface. The second immobilisation strategy was carried out using polysulfone–graphite composites, which were deposited by screen-printing technology onto the screen-printed electrode (SPE) surface. Both methods achieved an effective and reliable incorporation of redox mediators to the SPE configuration. Finally, a flow system for ammonium determination was developed using a glutamate dehydrogenase (GlDH)-Meldola's Blue (MB)-polysulfone-composite film-based biosensor.

The stability of the redox mediators inside the composite films as well as the negligible fouling effect observed on the electrode surface improve the repeatability and reproducibility of the sensors, important features for continuous analysis in flow systems. Furthermore, the optimised bio/sensors, incorporated in a flow injection system, showed good sensitivities and short response times. Such a good analytical performance together with the simple and fast sensor construction are interesting characteristics to consider the polysulfone-composite films as attractive electrochemical transducer materials for the development of new dehydrogenase-based SPEs.     

Construction of a New Flow‐through Cell for Screen Printed Electrodes

In this paper a new flow‐through cell for voltammetric determinations using screen printed electrodes is described. This cell is much simpler than one with similar performances described in a previous work. This new flow‐through cell has been coupled to a multisyringe flow injection system (MSFIA) and to a multiport selection valve allowing the online calibration using the standard addition method. The uses of the MSFIA, together with the small volume of the flow cell and the reduced surface area of the solid phase electrode (SPE) have considerably reduced the volume of reagents and samples to be used. This system has allowed obtaining similar or better detection limits than those obtained using other techniques and flow analysis devices such as SIA, FIA, LOV and microfluidic channels. Graphite ink has been used for the development of screen‐printed electrodes. The determination of Cd and Pb with ASV has been made through its co‐deposition with Bi. For this, Bi(III) solution and the sample were mixed in line. Due to the creation of a new Bi film in each voltammetric cycle, very well defined and reproducible peaks corresponding to Cd and Pb have been obtained. The use of Bi is one of the most important advantages of this system, since it is a recognized substitute for Hg, and its impact on the environment is much lower due to its reduced toxicity. The fact of being an automatic system, the low cost of its components, its simplicity and ease of handling, make it a system that could be useful for monitoring tasks in fieldwork, or measurements on board.     

Flow analysis based on a pulsed flow of solution: theory, instrumentation and applications

The increased demands placed on solution propulsion by programmed flow systems, such as sequential injection analysis, lab-on-value technology, bead injection and multi-commutation, has highlighted the inability of many conventional pumps to generate a smooth, consistent flow. A number of researchers have examined ways to overcome the inadvertent, uncontrolled pulsation caused by the mechanical aciton of peristaltic pumps. In contrast, we have developed instruments that exploit the characteristics of a reproducible pulsed flow of solution. In this paper, we discuss our instrumental approaches and some applications that have benefited from the use of a reproducible pulsed flow rather than the traditional linear flow approach. To place our approach in the context of the continuously developing field of flow analysis, an overview of other programmed flow systems is also presented.     

Multisyringe flow injection system for solid-phase extraction coupled to liquid chromatography using monolithic column for screening of phenolic pollutants

In this work a fast, automatic solid-phase extraction procedure hyphenated to HPLC-UV is proposed for screening of priority phenolic pollutants in waters at ng mL⁻¹ levels. A flow through column, containing polystyrene-divinylbenzene sorbent, was incorporated to a multisyringe flow injection system (MSFIA), where the sample loading and analyte elution were carried out after computer control. The MSFIA system also directed the eluent to fill the injection loop of the chromatograph, coupling the sample preparation to its determination. High enrichment factors were attained for phenol and ten of its derivatives (mean value 176 for 50 mL of sample), with LOD values lower than 1 ng mL⁻¹ for the maximum volume of sample used (100 mL). For all analytes, mean recoveries between 89 and 103% were obtained for different water matrices. Certified reference material and a contaminated soil (RTC-CRM 112) were also tested successfully. The determination frequency was 4-10 h⁻¹, providing an automatic, fast and reliable tool for water quality and environmental monitoring.     

Valves and flow injection manifolds: an excellent marriage with unlimited versatility

An overview of the functions of valves—both injection and selection valves—in flow injection (FI) for manipulating the manifold as a function of both necessities and imagination of the user is reported. The use of single valves for sample or reagent injection, for housing different devices (namely, minicolumns and other separation units, flow-cells, etc.) is discussed. Multiple injection valve arrangements (in-series, in-parallel and inner coupling) that give place to FI modes as merging-zones (both symmetrical and asymmetrical), trapping-zone and nested-loop approaches are exposed. The possible locations of selection valves in the FI manifold are presented and the problems each design can solve are commented.     

Application of pyridylazo and thiazolylazo reagents in flow injection preconcentration systems for determination of metals

Pyridylazo and thiazolylazo reagents are synthetic dyes widely used in analytical chemistry. These reagents are also very attractive for use in preconcentration systems. This paper covers the application of pyridylazo and thiazolylazo reagents in flow injection systems for the determination of metals. The article discusses flow injection preconcentration systems with solid-phase extraction, precipitation and cloud point extraction. The use of pyridylazo and thiazolylazo reagents in flow injection detection systems is also presented. The relative advantages and drawbacks of these systems are discussed. The application of pyridylazo and thiazolylazo reagents in new systems is presented in the concluding part of this review article.     

Flow injection determinations of citric acid: a review

A review of the flow injection (FI) analytical methods used to determine citric acid (CA) is presented. These flow determinations are described and compared according to the detection technique used. In addition to the advantages involving the use of the continuous flow systems, the analytical figures of merit and interferences are also discussed.     

Multi-syringe flow-injection systems improve antioxidant assessment

Conventionally, measuring antioxidant capacity is time consuming, laborious and costly, especially in routine work. These limitations can be overcome using multi-syringe flow-injection analysis (MSFIA), which has succeeded in automating the most widely applied antioxidant-capacity assays that use chromogen radicals or reactive species found in vivo. We highlight the features of MSFIA and improved methodologies in using MSFIA to measure antioxidant capacity.