A green method for the determination of hypochlorite in bleaching products based on its native absorbance

A new, green method for the determination of hypochloride in bleaching products is here presented. The method, based on a flow injection system and measurement of the native absorbance of hypochlorite at 292 nm, allows the determination of hypochlorite in the range 0.07-0.42 g Cl₂ l⁻¹. In order to achieve high selectivity a mini-column containing cobalt oxide, which effectively catalyses hypochlorite decomposition to chloride and oxygen, was inserted in the flow system. The difference in absorbance of samples no circulated and circulated through the mini-column was selected as analytical signal; thus, the method only requires 20 mg of solid, reusable catalyst, and a NaOH solution of pH 10.4; providing a sample throughput of 12 samples h⁻¹ in triplicate injection. Its usefulness for analysis of bleaching products is demonstrated.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

A multisyringe flow injection Winkler-based spectrophotometric analyzer for in-line monitoring of dissolved oxygen in seawater

An integrated analyzer based on the multisyringe flow injection analysis approach is proposed for the automated determination of dissolved oxygen in seawater. The entire Winkler method including precipitation of manganese(II) hydroxide, fixation of dissolved oxygen, dissolution of the oxidized manganese hydroxide precipitate, and generation of iodine and tri-iodide ion are in-line effected within the flow network. Spectrophotometric quantification of iodine and tri-iodide at the isosbestic wavelength of 466 nm renders enhanced method reliability. The calibration function is linear up to 19 mg L⁻¹ dissolved oxygen and an injection frequency of 17 per hour is achieved. The multisyringe system features a highly satisfying signal stability with repeatabilities of 2.2% RSD that make it suitable for continuous determination of dissolved oxygen in seawater. Compared to the manual starch-end-point titrimetric Winkler method and early reported automated systems, concentrations and consumption of reagents and sample are reduced up to hundredfold. The versatility of the multisyringe assembly was exploited in the implementation of an ancillary automatic batch-wise Winkler titrator using a single syringe of the module for accurate titration of the released iodine/tri-iodide with thiosulfate.     

Time-based multisyringe flow injection system for the spectrofluorimetric determination of aluminium

A time-based multisyringe flow injection procedure with spectrofluorimetric detection is proposed in this paper for the determination of aluminium in drinking water. The flow methodology is based on the simultaneous or sequential injection of sample and chelating reagent (viz. 8-hydroxyquinoline-5-sulphonic acid) plugs using a multicommutation approach so that three successive injections may be performed with a sole displacement of the piston driver bar of the burette. Thus, an injection throughput as high as 154 h⁻¹ is achieved by sampling a 182 μl sample zone. In order to enhance the luminescence, the reaction is carried out in micellar medium using hexadecyltrimethylammonium chloride as surfactant. The influence of geometric and hydrodynamic variables as well as several parameters such as multicommutation timing, ligand and surfactant concentration and reagent pH was assessed.Under the selected working conditions, a linear dynamic range from 10 to 500 μg l⁻¹ Al(III), a 3σ detection limit of 0.5 μg l⁻¹ and a coefficient of variation of 0.6% at the 30 μg l⁻¹ level were obtained. The analytical features were compared with those reported in previous flow injection and sequential injection methods. The multisyringe technique was successfully applied to the determination of aluminium in drinking water at low mineralisation levels, validating the results by inductively coupled plasma atomic emission spectrometry.     

Antimony determination and speciation by multisyringe flow injection analysis with hydride generation-atomic fluorescence detection

A new analytical procedure for determination of inorganic antimony and speciation of antimony(III) and antimony(V) is presented. For this purpose, a software-controlled time-based multisyringe flow injection system, which contains a multisyringe burette provided with a multi-port selection valve, was developed. Hydride generation-atomic fluorescence spectrometry was used as a detection technique. A 0.3% (w/v) reducing sodium tetrahydroborate solution, hydrochloric acid (2 M), an antimony solution and a pre-reducing solution of 10% (w/v) KI and 0.3% (w/v) ascorbic acid are dispensed simultaneously into a gas-liquid separation cell with further propulsion of the reaction product into the flame of an atomic fluorescence spectrometer using argon flow. A hydrogen flow was employed to support the flame.The linear range and the detection limit (3s_b/S) of the proposed technique were 0.2-5.6 μg l⁻¹ and 0.08 μg l⁻¹, respectively. A sample throughput of 18 samples per hour (corresponding to 80 injections per hour) was achieved. The relative standard deviation for 18 independent measurements was 4.6%. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of Sb(III) and Sb(V) by means of the developed technique were obtained.     

Interfacing in-line gas-diffusion separation with optrode sorptive preconcentration exploiting multisyringe flow injection analysis

An automatic multisyringe flow injection analysis (MSFIA) system coupling a flow-through optical fiber diffuse reflectance sensor with in-line gas-diffusion (GD) separation is proposed for the isolation, preconcentration and determination of traces of volatile and gas-evolving compounds in samples containing suspended solids, with no need for any preliminary batch sample treatment. The flowing methodology overcomes the lost of sensitivity of the in-line separation technique, when performed in a uni-directional continuous-flow mode, through the implementation of disk-based solid-phase extraction schemes. The high selectivity and sensitivity, the low reagent consumption and the miniaturization of the whole assembly are the outstanding features of the automated set-up. The proposed combination of techniques for separation, flow analysis, preconcentration and detection was applied satisfactorily to sulfide determination in environmental complex matrixes. The method based on multicommutation flow analysis involves the stripping of the analyte as hydrogen sulfide from the donor channel of the GD-module into an alkaline receiver segment, whereupon the enriched plug merges with well-defined zones of the chormogenic reagents (viz., N,N-dimethyl-p-phenylenediamine (DMPD) and Fe(III)). The in-line generated methylene blue dye is subsequently delivered downstream to the dedicated optrode cell furnished with a C₁₈ disk, while recording continuously the diffuse reflectance spectrum of the pre-concentrated compound. This procedure provides a linear working range of 20-500 μg l⁻¹ sulfide with a relative standard deviation of 2.2% (n = 10) at the 200 μg l⁻¹ level, and a detection limit of 1.3 μg l⁻¹.     

On-line renewable solid-phase extraction hyphenated to liquid chromatography for the determination of UV filters using bead injection and multisyringe-lab-on-valve approach

For the first time, an automatic sample pre-treatment/detection method is proposed for the multiclass determination of UV filters (namely, benzophenone-3, ethylhexylmetoxycinnamate, butylmethoxydibenzoylmethane and homosalate) in environmental samples. The new methodology comprises in-line solid-phase extraction (SPE) of the target analytes by exploiting the bead injection (BI) concept in a mesofluidic lab-on-valve (LOV) format, with subsequent determination by liquid chromatography (LC). The proposed microanalytical system, using a multisyringe burette as propulsion unit, automatically performed the overall SPE steps, including the renewal of the sorbent in each analytical cycle to prevent sample cross-contamination and the post-extraction adjustment of the eluate composition to prevent chromatographic band broadening effects. In order to expedite the LC separation, a C₁₈ monolithic column was applied and an accelerated isocratic elution was carried out by using a cationic surfactant as mobile phase additive. The LOV-BI-LC method was proven reliable for handling and analysis of complex matrices, e.g., spiked swimming pool water and seawater, with limits of detection ranging between 0.45 and 3.2 μg L⁻¹ for 9 mL sample volume. Linear calibration was attained up to 160 μg L⁻¹ for homosalate and up to 35 μg L⁻¹ for the other target analytes, with good reproducibility (RSD < 13%, for 5 different SPE columns). The hyphenated scheme is able to process a given sample simultaneously and within the same time frame than the chromatographic separation/determination of the formerly pre-treated sample, providing concentration values every 9 min. Hence, the sample throughput was enhanced up to 33 times when compared with previously reported off-line SPE methods. A drastic reduction in reagent consumption and effluent production was also attained, contributing to the development of an environment-friendly analyzer.     

Development of a new high performance low pressure chromatographic system using a multisyringe burette coupled to a chromatographic monolithic column

A novel combination of high performance low pressure chromatography with multisyringe flow injection analysis is presented. This system comprises a multisyringe module, three low pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometer. UV detection is carried out at 250 nm. AutoAnalysis software is used for instrumental control and automated data collection. The results obtained with multisyringe liquid chromatography (MSC) were compared with those obtained with a HPLC system using similar conditions. The chromatographic parameters were calculated from a mixture of anthracene and thiourea using a mobile phase containing acetonitrile-water (60:40) at a flow rate of 2 ml min⁻¹. The proposed MSC system has been successfully applied to the determination of amoxicillin, ampicillin and cephalexin using a mobile phase of sodium acetate buffer (pH 6.2, 0.1 mol l⁻¹)-methanol (90:10) at a flow rate of 2 ml min⁻¹. The low-cost, flexibility and simplicity of MSC should be highlighted.     

Multisyringe flow-injection system for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry

A software-controlled time-based multisyringe flow-injection system for total inorganic arsenic determination by hydride generation atomic fluorescence spectrometry (HGAFS) has been developed. By using a multisyringe burette coupled with one multiport selection valve, the time-based injection provides precise known volumes of sample, a reducing sodium tetrahydroborate solution and a pre-reducing solution which are dispensed into a gas-liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame.Linear calibration graphs for arsenic concentrations between 0.25 and 12 μg l⁻¹ were obtained. The detection limit of the proposed technique (3σ_b/S) was 0.07 μg l⁻¹. A sample throughput of 36 samples/h (108 injections) has been achieved. The proposed technique has been validated by means of reference solid and water materials with good agreement with the certified values. This method was compared with those reported in previous sequential injection analysis (SIA) and flow-injection analysis (FIA) systems. The proposed method offers a number of advantages in front the usual AFS applications, which are mainly a higher sampling frequency and a significant reduction in reagent consumption.     

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.     

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.     

Speciation analysis of inorganic arsenic by a multisyringe flow injection system with hydride generation-atomic fluorescence spectrometric detection

In this study, a new technique by hydride generation-atomic fluorescence spectrometry (HG-AFS) for determination and speciation of inorganic arsenic using multisyringe flow injection analysis (MSFIA) is reported. The hydride (arsine) was generated by injecting precise known volumes of sample, a reducing sodium tetrahydroborate solution (0.2%), hydrochloric acid (6 M) and a pre-reducing solution (potassium iodide 10% and ascorbic acid 0.2%) to the system using a multisyringe burette coupled with one multi-port selection valve. This solution is used to pre-reduce As(V) to As(III), when the task is to speciate As(III) and As(V). As(V) is determined by the difference between total inorganic arsenic and As(III). The reagents are dispensed into a gas-liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame. Nitrogen has been employed as a drier gas (Fig. 1).Several variables such as sample and reagents volumes, flow rates and reagent concentrations were investigated in detail. A linear calibration graph was obtained for arsenic determination between 0.1 and 3 μg l⁻¹. The detection limit of the proposed technique (3σ_b/S) was 0.05 μg l⁻¹. The relative standard deviation (R.S.D.) of As at 1 μg l⁻¹ was 4.4 % (n = 15). A sample throughput of 10 samples per hour was achieved. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of As(III) and As(V) by means of the developed technique were obtained.     

Development of flow injection potentiometric methods for the off-line and on-line determination of fluoride to monitor the biodegradation of a monofluorophenol in two bioreactors

Water treatment has become a source of concern as new pollutants and higher volumes of waste water must be treated. Emerging biological approaches, namely the use of bioreactors, for cleaning processes have been introduced. The use of bioreactors requires the development of efficient monitoring tools, preferably with real-time measurements. In this work, a couple of flow injection systems were developed and optimized for the potentiometric determination of fluoride to monitor a rotating biological contactor (RBC) bioreactor and a sequencing batch reactor (SBR) with off-line and on-line sampling. Both the RBC and the SBR bioreactors were set up for the biodegradation of the halogenated organic compound 2-fluorophenol and, as fluoride was a degradation byproduct, the process was monitored by following up its concentration.The described flow injection potentiometric methods enabled the fluoride determination within the required quantification range 0.10-100 mM. The possible interferences from the growth medium were minimized in-line. The determination rate was 78 h⁻¹ for the off-line monitoring of RBC and 50⁻¹ h for the on-line monitoring of the SBR, with a sample consumption of 0.500 mL and 0.133 mL per determination, respectively. Furthermore, the overall reagent consumption was quite low. The accuracy of the system was evaluated by comparison with a batch procedure. The SBR efficiency was monitored both on-line by the flow system and off-line by HPLC, for comparison purposes.     

A membraneless gas-diffusion unit-multisyringe flow injection spectrophotometric method for ammonium determination in untreated environmental samples

A new design of a membraneless gas-diffusion (MGD) unit coupled to a multisyringe flow injection system is proposed. The spectrophotometric determination of ammonium using an acid-base indicator was chosen to show the feasibility of this approach. Hence, in alkaline medium, ammonium ions are transformed into ammonia (donor channel) which diffuses through the headspace into the acceptor stream (bromothymol blue solution), causing a pH change and subsequently a colour change. The exploitation of the enhanced potentialities of this re-designed MGD device was the main purpose of the present work. Hence, several strategies concerning flow management were studied seeking to characterize and improve the analytical features of the methodology and moreover, untreated environmental samples were analysed without previous filtration. Consequently, stopped flow in acceptor channel with continuous flow in donor channel was chosen for the application to wastewater and spiked river water samples. A linear concentration range between 10.0 and 50.0 mg L⁻¹ of NH₄⁺, a limit of detection of 2.20 mg L⁻¹ and a determination frequency of 11 h⁻¹ were obtained.     

Spectrophotometric Determination of Bromate in Water Using Multisyringe Flow Injection Analysis

A multisyringe flow injection system for the spectrophotometric determination of bromate in water is proposed, based on the oxidation of phenothiazine compounds by bromate in acidic medium. Several phenothiazines were tested, including chlorpromazine, trifluoperazine, and thioridazine. Higher sensitivity and lower LOD were attained for chlorpromazine. Interference from nitrite, hypochlorite, and chlorite was eliminated in-line, without any changes in the manifold. The automatic methodology using chlorpromazine allowed the determination of bromate between 25 and 750 µg L^?1, with LOD of 6 µg L^?1, good precision (RSD < 1.6%, n = 10), and determination frequency of 35 h^?1.     

Lab on valve-multisyringe flow injection system (LOV-MSFIA) for fully automated uranium determination in environmental samples

The hyphenation of lab-on-valve (LOV) and multisyringe flow analysis (MSFIA), coupled to a long path length liquid waveguide capillary cell (LWCC), allows the spectrophotometric determination of uranium in different types of environmental sample matrices, without any manual pre-treatment, and achieving high selectivity and sensitivity levels. On-line separation and preconcentration of uranium is carried out by means of UTEVA resin. The potential of the LOV-MSFIA makes possible the fully automation of the system by the in-line regeneration of the column. After elution, uranium(VI) is spectrophotometrically detected after reaction with arsenazo-III. The determination of levels of uranium present in environmental samples is required in order to establish an environmental control. Thus, we propose a rapid, cheap and fully automated method to determine uranium(VI) in environmental samples. The limit of detection reached is 1.9 ηg of uranium and depending on the preconcentrated volume; it results in ppt levels (10.3 ηg L⁻¹). Different water sample matrices (seawater, well water, freshwater, tap water and mineral water) and a phosphogypsum sample (with natural uranium content) were satisfactorily analyzed.     

Interfacing on-line solid phase extraction with monolithic column multisyringe chromatography and chemiluminescence detection: An effective tool for fast, sensitive and selective determination of thiazide diuretics

A new, multisyringe flow injection set-up has been developed for the completely automated determination of trace thiazide compounds with diuretic action in different types of samples. The proposed instrumental set-up exploits for the first time, a low pressure on-line solid phase extraction-liquid chromatography-chemiluminescence detection method. This novel combination of sample treatments in flow systems expands the current applicability of low pressure liquid chromatography due to the isolation/preconcentration of the target compounds, besides high selectivity and sensitivity.For the determination of three thiazide compounds named hydroflumethiazide, furosemide and bendroflumethiazide, the proposed set-up provided with the preconcentration of only 1 mL of sample, limits of detection of 3, 60 and 40 μg L⁻¹, respectively. Furthermore wide linear dynamic ranges of 6-4000, 140-20,000 and 90-40,000 μg L⁻¹, respectively, were obtained. Besides of this, a high injection throughput of 12 h⁻¹ was also achieved. As in sports, thiazide diuretics are prohibited substances, the proposed method has been applied to their determination in urine samples. Furthermore the potential of the proposed method as a fast-screening approach for emerging contaminants in waters has been also tested by applying it to well water and leachates from a solid waste landfill.     

Sequential injection analysis for automation of the Winkler methodology, with real-time SIMPLEX optimization and shipboard application

A multipurpose analyzer system based on sequential injection analysis (SIA) for the determination of dissolved oxygen (DO) in seawater is presented. Three operation modes were established and successfully applied onboard during a research cruise in the Southern ocean: 1st, in-line execution of the entire Winkler method including precipitation of manganese (II) hydroxide, fixation of DO, precipitate dissolution by confluent acidification, and spectrophotometric quantification of the generated iodine/tri-iodide (I₂/I₃⁻), 2nd, spectrophotometric quantification of I₂/I₃⁻ in samples prepared according the classical Winkler protocol, and 3rd, accurate batch-wise titration of I₂/I₃⁻ with thiosulfate using one syringe pump of the analyzer as automatic burette.In the first mode, the zone stacking principle was applied to achieve high dispersion of the reagent solutions in the sample zone. Spectrophotometric detection was done at the isobestic wavelength 466 nm of I₂/I₃⁻. Highly reduced consumption of reagents and sample compared to the classical Winkler protocol, linear response up to 16 mg L⁻¹ DO, and an injection frequency of 30 per hour were achieved. It is noteworthy that for the offline protocol, sample metering and quantification with a potentiometric titrator lasts in general over 5 min without counting sample fixation, incubation, and glassware cleaning. The modified SIMPLEX methodology was used for the simultaneous optimization of four volumetric and two chemical variables. Vertex calculation and consequent application including in-line preparation of one reagent was carried out in real-time using the software AutoAnalysis. The analytical system featured high signal stability, robustness, and a repeatability of 3% RSD (1st mode) and 0.8% (2nd mode) during shipboard application.     

A spectrophotometric procedure for DNA assay with a micro-sequential injection lab-on-valve meso-fluidic system

A micro-sequential injection spectrophotometric procedure for DNA assay was developed based on the employment of a lab-on-valve (LOV) meso-fluidic analytical system. A small amount of crystal violet solution (10 μl) was de-colored inside the flow cell of the LOV at the presence of 5 μl λ-DNA/HindIII within a certain pH range, and the absorbance decrease of crystal violet solution at 591 nm was measured via optical fibers and was employed as the basis of quantification. A uni-variant approach was adopted for the optimization of experimental parameters, including buffer pH, concentration and volume of crystal violet solution, reaction time and sample/reagent loading flow rates. A linear calibration graph was obtained within 0.2-6.0 μg ml⁻¹, along with a detection limit of 0.07 μg ml⁻¹. The procedure was applied for the determination of λ-DNA/HindIII in synthetic samples in comparison with a documented procedure.     

On-line determination of mercury(II) by membrane separation flow injection analysis

A rapid and inexpensive gas-diffusion (GD) flow injection method for the on-line determination of Hg(II) in aqueous samples is described. The analytical procedure involves the injection of a Hg(II) sample into a 1.5 M H₂SO₄ carrier stream which is merged with a reagent stream containing 0.6% SnCl₂ and 1.5 M H₂SO₄. Under these conditions Hg(II) is reduced to metallic mercury which partially evaporates through a Teflon membrane into an acceptor stream containing 1.75×10⁻⁴ M KMnO₄ in 0.3 M H₂SO₄. The decrease in the absorbance of the acceptor stream at 528 nm corresponding to the absorption maximum of the permanganate anion can be related to the original concentration of Hg(II) in the sample. The method is characterized by a detection limit of 4 μg l⁻¹ and a sampling frequency of 8 h⁻¹. The flow system was successfully applied to the analysis of river samples spiked with Hg(II).