Multisyringe flow injection analysis: characterization and applications

An overview of automated flow systems for total and isotopic analysis of strontium and yttrium in samples of environmental interest

Due to the different uses of radioactivity during the last decades, there has been an increase in the concentration of natural and artificial radionuclides in the environment. This, along with some accidents with a high affect public opinion (for example, Chernobyl and Fukushima), have led to the growth and establishment of environmental radioactivity monitoring programs. Currently, trends in legislation and research are focused on the development of accurate, precise, reliable and fast analytical methods with low limits of detection (LOD) for radionuclides determination, such as strontium and yttrium, in environmental samples. In this paper, two comprehensive reviews and four automated analytical systems for total and isotopic determination of yttrium and strontium are presented. The developed methods have been applied in the analysis of environmental samples with low concentrations of these analytes. These methodologies have been automated by exploiting flow analysis techniques, such as multi-syringe flow injection analysis (MSFIA), Sequential injection analysis (SIA) and laboratory-on-valve (LOV) systems, achieving a minimal handling and low consumption of samples and reagents, a significant reduction in waste generation and a high frequency of analysis. In the developed methodologies, some spectrometric methods such as ICP-OES and ICP-MS have been implemented as detection techniques instead of radiometric detectors obtaining a fully automated, low-cost and fast yttrium and strontium determinations.

Dynamic Flow Approaches for Automated Radiochemical Analysis in Environmental, Nuclear and Medical Applications

Automated sample processing techniques are desirable in radiochemical analysis for environmental radioactivity monitoring, nuclear emergency preparedness, nuclear waste characterization and management during operation and decommissioning of nuclear facilities, as well as medical isotope production, to achieve fast and cost-effective analysis. Dynamic flow based approaches including flow injection (FI), sequential injection (SI), multi-commuted flow injection (MCFI), multi-syringe flow injection (MSFI), multi-pumping flow system (MPFS), lab-on-valve (LOV) and lab-in-syringe (LIS) techniques have been developed and applied to meet the analytical criteria under different situations. Herein an overall review and discussion on these techniques and methodologies developed for radiochemical separation and measurement of various radionuclides is presented. Different designs of flow systems with combinations of radiochemical separation techniques, such as liquid-liquid extraction (LLE), liquid-liquid microextraction (LLME), solid phase extraction chromatography (SPEC), ion exchange chromatography (IEC), electrochemically modulated separations (EMS), capillary electrophoresis (CE), molecularly imprinted polymer (MIP) separation and online sensing and detection systems, are summarized and reviewed systematically.

Flow Chemistry in Contemporary Chemical Sciences: A Real Variety of Its Applications

Flow chemistry is an area of contemporary chemistry exploiting the hydrodynamic conditions of flowing liquids to provide particular environments for chemical reactions. These particular conditions of enhanced and strictly regulated transport of reagents, improved interface contacts, intensification of heat transfer, and safe operation with hazardous chemicals can be utilized in chemical synthesis, both for mechanization and automation of analytical procedures, and for the investigation of the kinetics of ultrafast reactions. Such methods are developed for more than half a century. In the field of chemical synthesis, they are used mostly in pharmaceutical chemistry for efficient syntheses of small amounts of active substances. In analytical chemistry, flow measuring systems are designed for environmental applications and industrial monitoring, as well as medical and pharmaceutical analysis, providing essential enhancement of the yield of analyses and precision of analytical determinations. The main concept of this review is to show the overlapping of development trends in the design of instrumentation and various ways of the utilization of specificity of chemical operations under flow conditions, especially for synthetic and analytical purposes, with a simultaneous presentation of the still rather limited correspondence between these two main areas of flow chemistry.

Automatic multicommuted flow-batch setup for photometric determination of mercury in drinking water at ppb level

Herein, a multicommuted flow-batch setup and a photometric procedure for the determination of mercury at the ppb level in aqueous samples are described. The setup was designed to implement a versatile solvent extraction and pre-concentration strategy by combining flow-batch and multicommuted flow analysis approaches. The photometric method was based on Hg(II) reaction with dithizone in a chloroform medium, which was also used as the extracting organic solvent. The flow analysis system was composed of a homemade syringe pump module, a set of solenoid valves, two Aquarius mini-pumps, and a flow-batch chamber. The homemade photometer was comprised of a light emitting diode (LED), photodiode, and homemade flow cell (50 mm length). The flow system and photometer were controlled using an Arduino Due board, running custom-written software. After optimizing the operational conditions, the effectiveness of the developed system was evaluated for the determination of the mercury concentration in drinking water. For accuracy assessment, samples were analyzed using a spiking methodology and an independent method, yielding a recovery ranging from 92% to 108%. Other important characteristics of the proposed method were found as follows: linear response range, 0.5-10.0 μg L^-1 (r = 0.9984); limit of detection 0.38 μg L^-1 Hg(II); consumption of dithizone and chloroform, 1.85 μg L^-1 and 0.8 mL per analysis, respectively; coefficient of variation, 2% (n = 10); sampling throughput, 20 determinations per h.

Exploitation of reaction mechanisms for sensitivity enhancement in the determination of phosphorus by sequential injection analysis

The molybdenum blue method using antimony and ascorbic acid was studied for the determination of phosphorus (as orthophosphate) by means of sequential injection analysis (SIA). In order to avoid the interference of the Schlieren effect in the photometric measurements a stopped-flow kinetic approach was adopted monitoring the absorbance of the reaction bolus inside the flow cell. Aiming at enhancing the sensitivity of the method, the effect of the order of addition of the reactants was studied. It was found that the best sensitivity was attained by adding separate reagents and acidifying only after the phosphate, molybdate and antimony solutions were already mixed; the reductant (ascorbic acid) was then added. In this way a sensitivity enhancement in excess of 10 times was obtained when compared to the addition of the phosphate solution to the acidified mixture of molybdate and antimony. It is proposed that the difference in sensitivities could be explained by the existence of different mechanisms for the formation of the intermediate phosphoantimonyl molybdic acid (PMA). Thus the selected sequence in the order of addition, where sulphuric acid is added to the mixture of the other reactants would lead to higher production of PMA in turn conducting to a faster reduction reaction. The resulting SIA method was validated finding limits of detection (3s/m) and quantification (10s/m) of 0.0077 and 0.026 mg-P L^-1 respectively. Linearity was confirmed in the range up to 2 mg-P L^-1. Precisions (s_r, n = 10) were in the range 1.8%-4.0%. 32 water samples of different types and origins were analysed by the proposed method and by ion chromatography, obtaining a regression curve y = 0.990× - 0.0019, with a determination coefficient R² = 0.973.

Automated on-line liquid-liquid extraction in a multisyringe flow injection analysis manifold for migration studies in food-contact materials: analysis of 4,4´-dihydroxybiphenyl

Packaging may represent a source of food contamination, as different organic compounds and degradation compounds may migrate from packaging to foodstuff. For fatty foods, rectified olive oil is the common simulant, which implies time-consuming and laborious liquid-liquid extraction (LLE) procedures to isolate the contaminant(s) from the oil. Here we propose a Multisyringe Flow Injection Analysis manifold to automate this sample treatment, using the monomer 4,4´-dihydroxybiphenyl as the contaminant. The LLE procedure, using water as extractant, was fully automated. After the on-line LLE, the resulting extract was pumped through a fluorescence detector, inside which a flow-cell filled with C₁₈ silica gel solid support was placed. The analyte was pre-concentrated on the solid support (in which the analytical signal was directly recorded), so improving the sensitivity of the system. Under optimum conditions, the method detection limit is 0.05 mg kg^-1, well within the specific migration limit of 6 mg kg^-1. The method developed was compared with the standard CEN test method (off-line LLE and HPLC determination) observing savings in sample and reagents of 90% and a 7-fold increase in sample throughput.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

Uranium and thorium sequential separation from norm samples by using a SIA system

This study presents a sequential radiochemical separation method for uranium and thorium isotopes using a novel Sequential Injection Analysis (SIA) system with an extraction chromatographic resin (UTEVA). After the separation, uranium and thorium isotopes have been quantified by using alpha-particle spectrometry. The developed method has been tested by analyzing an intercomparison sample (phosphogypsum sample) from International Atomic Energy Agency (IAEA) with better recoveries for uranium and thorium than the obtained by using a classical method (93% for uranium using the new methodology and 82% with the classical method, and in the case of thorium the recoveries were 70% for the semi-automated method and 60% for the classical strategy). Afterwards, the method was successfully applied to different Naturally Occurring Radioactive Material (NORM) samples, in particular sludge samples taken from a drinking water treatment plant (DWTP) and also sediment samples taken from an area of influence of the dicalcium phosphate (DCP) factory located close to the Ebro river reservoir in Flix (Catalonia). The obtained results have also been compared with the obtained by the classical method and from that comparison it has been demonstrated that the presented strategy is a good alternative to existing methods offering some advantages as minimization of sample handling, reduction of solvents volume and also an important reduction of the time per analysis.

Green chemistry and the evolution of flow analysis. A review

Flow analysis has achieved its majority as a well-established tool to solve analytical problems. Evolution of flow-based approaches has been analyzed by diverse points of view, including historical aspects, the commutation concept and the impact on analytical methodologies. In this overview, the evolution of flow analysis towards green analytical chemistry is demonstrated by comparing classical procedures implemented with different flow approaches. The potential to minimize reagent consumption and waste generation and the ability to implement processes unreliable in batch to replace toxic chemicals are also emphasized. Successful applications of greener approaches in flow analysis are also discussed, focusing on the last 10 years.

Validation of a tubular bismuth film amperometric detector

A tubular bismuth film electrode (BFE), installed as part of a multisyringe flow injection system, was used as an amperometric detector to determine the concentration of diclofenac sodium in pharmaceutical formulations. A tubular voltammetric detection cell was employed, in which the hydrodynamic flow conditions were not disturbed. This automated method allows the continuous regeneration of the BFE, preventing passivation of the detector and improving the sensitivity of detection. The influence of several variables on this sensitivity, such as the injection volume, deposition time and flow rate were evaluated; a two-level factorial experimental design was employed for this. In optimal conditions, the linear range of the calibration curve varied from 6.0-50.0 micromol L(-1), with a detection limit of 4.3 micromol L(-1). A sampling rate of 90 determinations/h was achieved; the relative standard deviation of analytical repeatability was <3.5%. After 30 injections the bismuth film on the electrode surface was automatically renewed. The method was validated by comparing the results obtained with those provided by RP-HPLC; no significant difference were seen (p<0.05).

Miniaturization of environmental chemical assays in flowing systems: the lab-on-a-valve approach vis-à-vis lab-on-a-chip microfluidic devices

The analytical capabilities of the microminiaturized lab-on-a-valve (LOV) module integrated into a microsequential injection (muSI) fluidic system in terms of analytical chemical performance, microfluidic handling and on-line sample processing are compared to those of the micro total analysis systems (muTAS), also termed lab-on-a-chip (LOC). This paper illustrates, via selected representative examples, the potentials of the LOV scheme vis-à-vis LOC microdevices for environmental assays. By means of user-friendly programmable flow and the exploitation of the interplay between the thermodynamics and the kinetics of the chemical reactions at will, LOV allows accommodation of reactions which, at least at the present stage, are not feasible by application of microfluidic LOC systems. Thus, in LOV one may take full advantage of kinetic discriminations schemes, where even subtle differences in reactions are utilized for analytical purposes. Furthermore, it is also feasible to handle multi-step sequential reactions of divergent kinetics; to conduct multi-parametric determinations without manifold reconfiguration by utilization of the inherent open-architecture of the micromachined unit for implementation of peripheral modules and automated handling of a variety of reagents; and most importantly, it offers itself as a versatile front end to a plethora of detection schemes. Not the least, LOV is regarded as an emerging downscaled tool to overcome the dilemma of LOC microsystems to admit real-life samples. This is nurtured via its intrinsic flexibility for accommodation of sample pre-treatment schemes aimed at the on-line manipulation of complex samples. Thus, LOV is playing a prominent role in the environmental field, whenever the monitoring of trace level concentration of pollutants is pursued, because both matrix isolation and preconcentration of target analytes is most often imperative, or in fact necessary, prior to sample presentation to the detector.

Multi-syringe flow injection solid-phase extraction system for on-line simultaneous spectrophotometric determination of nitro-substituted phenol isomers

In this paper, a time-based multi-syringe flow injection (MSFI) approach is proposed for automated disk-based sorbent extraction of three nitro-substituted phenol isomers (2-, 3-, and 4-nitrophenol) followed by on-line simultaneous determination of individual species by diode-array spectrophotometry. The method involves the on-line enrichment of the targeted analytes from an acidic medium containing 0.1 mol L(-1) HCl onto a co-polymeric sorbent material, and the concurrent removal of potentially interfering matrix components. The nitrophenol isomers are subsequently eluted with an alkaline solution (0.7 mol L(-1) NaOH), whereupon the eluate is delivered to a diode-array spectrophotometer for recording of the spectral data in the UV-vis region. Deconvolution of strongly overlapped spectra was conducted with multivariate regression models based on multiple linear regression calibration. The analytical performance of the chemometric algorithm was characterized by relative prediction errors and recoveries. The MSFI manifold was coupled to a multiposition selection valve to set a rugged analyzer that ensures minimum operational maintenance via exploitation of membrane switching protocols. As compared with earlier methods for isolation/pre-concentration of nitro-substituted phenols based on liquid-liquid extraction, the proposed flow-through disk-based system should be regarded as an environmentally friendly approach because the use of harmful organic solvents is circumvented. Under the optimized chemical and physical variables, the 3sigma(blank) detection limits for 2-, 3-, and 4-nitrophenol were 1.2, 3.2 and 0.3 micromol L(-1) for a sample loading volume of 1.5 mL, and the relative standard deviations were < or =5.0%. The flowing system, which is able to handle up to 135 samples automatically, was proven suitable for monitoring trace levels of the target isomers in mineral, tap, and seawater.

Hyphenating Multisyringe Flow Injection Lab-on-Valve Analysis with Atomic Fluorescence Spectrometry for On-Line Bead Injection Preconcentration and Determination of Trace Levels of Hydride-Forming Elements in Environmental Samples

In this work the third generation of flow injection analysis, that is, the so-called micro-lab-on-valve (microLOV) approach, is proposed for the first time for the separation, preconcentration, and monitoring of metalloids as hyphenated with atomic fluorescence spectrometry (AFS). This was made feasible by interfacing the micromachined LOV-module with AFS by a multisyringe flowing stream network for on-line postcolumn derivatization of the eluate aimed at generation of hydride species. The potential of this new hyphenated technique for environmental assays was ascertained via determination of ultratrace level concentrations of total inorganic arsenic in freshwater. Employing quantitative preoxidation of As(III) to As(V) in the samples by means of permanganate, the method involves preconcentration of arsenate at pH 10 on a renewable anion exchanger, namely, Q-Sepharose, packed in a LOV microcolumn. The analyte species is afterward stripped out and concurrently prereduced by a 300 microL eluent plug containing 6 mol L(-)1 HCl and 10% KI. The eluate is downstream merged with a metered volume of sodium tetrahydroborate (0.3% w/v) for generation of arsine, which is subsequently quantified by AFS. The flow system facilitates on-column reduction of the retained arsenic with no need for application of programmable stopped flow. Yet, the high concentration of reductant and extreme pH conditions for elution hinder the sorbent to be reused due to gradual deactivation of the functional moieties, so that maximum benefit can be taken from the application of the bead renewable strategy. The proposed procedure is characterized by a high tolerance to metal species and interfering hydride-forming elements. In fact, ratios of Se(IV) to As < or = 5000 and Sb(V) to As < or = 500 are tolerated at the 10% interference level. Under the optimized experimental conditions, a detection limit (3sigma) of 0.02 ng mL(-1) As, a dynamic linear range of 0.05-2.0 ng mL(-1) As (by tailoring the AFS gain), an enrichment factor of 8.8 for arsenate, and a precision better than 6.0% at the 0.1 ng mL-1 level were obtained for the bead-injection mode whenever the loading sample volume was affixed at 3.0 mL. The reliability and accuracy of the automated procedure was ascertained by determining total inorganic arsenic in both spiked environmental waters and certified reference materials of variable matrix complexity (TMDA-54.3 and ERM-CA010) at the low ng mL(-1) level. No significant differences were found between the experimental results and the certified values at a significance level of 0.05.

A smart multisyringe flow injection system for analysis of sample batches with high variability in sulfide concentration

A fully automated smart multisyringe flow injection analysis (MSFIA) system for the monitoring of sulfide in a wide concentration range is proposed. It allows the determination of sulfide in samples containing suspended solids without requiring any preliminary batch sample treatment. The smart system is able to choose by itself the best approach to quantify the analyte, selecting either a spectrophotometric or a reflectometric detection. The method, carried out in a multi-commuted system, is based on the analyte release as hydrogen sulfide from the donor channel of the gas-diffusion module into an alkaline acceptor channel solution, which is merged with N,N-dimethyl-p-phenylenediamine (DMPD) and Fe(III). The in-line generated methylene blue (MB) dye can be delivered to an optical fiber diffuse reflectance sensor or to a flow-cell spectrophotometer according to the analyte concentration. The detection limit (3s(b)/S) was 4.6 microg l(-1). Two linear calibration graphs between 50-1000 and 500-10000 microg l(-1) sulfide for reflectometry and spectrophotometry, respectively, were obtained. The potentialities of this method were assessed via the determination of sulfide at a wide range of concentrations (4.6 microg l(-1) to 100 mg l(-1)). The high selectivity and sensitivity, the low reagent consumption and the miniaturization of the proposed automated method should be highlighted.