Potentiometric measurements in sequential injection analysis lab-on-valve (SIA-LOV) flow-system

Advantages of using sequential injection analysis lab-on-valve (SIA-LOV) in potentiometric measurements are studied with Ca²⁺ sensitive solid-contact ion-selective electrodes (SC-ISE) and pH electrode based on polyaniline (PANI). Experiments show that Ca²⁺-SC-ISE requires a stopped flow mode to be used in order to get longer equilibration time. On the other hand, PANI based pH electrode gives better results under flow conditions. SIA-LOV was found to be a flexible solution handling system for potentiometric measurements. The technique gives a possibility to fine-tune the calibration range or even recondition the electrode before every measurement without losing in linear range of calibration.     

An electrochemical assay for the determination of Se (IV) in a sequential injection lab-on-valve system

A sequential injection lab-on-valve (LOV) unit, integrating a miniaturized electrochemical flow cell (EFC), has been constructed for the determination of trace amounts of Se (IV) by employing cathodic stripping voltammetry (CSV) technique. The procedure is carried out on a mercury film coated glassy carbon electrode. The analyte solution and electrolyte solution were continuously aspirated and merged in the holding coil (HC) by using a single syringe pump, which were afterwards pushed into the EFC, where the peak current was generated during the subsequent deposition/stripping procedure and measured as the basis of quantification. Assay parameters were optimized in order to achieve the best analytical performance, including mercury film preparation, supporting electrolyte composition, deposition potential and deposition time, and flow variables in the LOV. By loading a sample volume of 500 μL, a linear calibration graph was derived within 1-600 μg L⁻¹, and a detection limit (3б) of 0.11 μg L⁻¹ was achieved along with a sampling frequency of 20 h⁻¹. By integrating the EFC into the LOV unit, the assembling system not only minimized the sample/reagent consumption and waste generation, but also enhanced the sampling frequency. The work itself extended the applications of electrochemical detection techniques and provided a good platform for Se (IV) electrochemical analysis.     

Spectrophotometric determination of Cu(II) with sequential injection analysis

A sequential injection system, based on the reaction of Cu(II) with diethyldithiocarbamate (DDTC), was developed for the determination of Cu(II) in plant food and water samples. The extraction procedure, generally used to extract the Cu(II)–DDTC complex for subsequent analysis was eliminated in this procedure. The complex was detected spectrophotometrically in aqueous solutions at 460 nm. The physical and chemical parameters depicting the system were studied to obtain optimum conditions for sample analysis. The system developed is fully computerized and able to monitor Cu(II) in samples at seven samples per hour with a relative standard deviation of <4.50%. The calibration curve is linear from 0.5–5.0 mg/l with a detection limit of 0.2 mg/l. Interferences were reduced by introducing multiple flow reversals, to increase mixing between the reagent and sample zones, and subsequently enhance working of the masking agents (EDTA/citrate).     

Reversed flow injection and sandwich sequential injection methods for the spectrophotometric determination of copper(II) with cuprizone

Two new flow methods, flow injection analysis (FIA) and sequential injection analysis (SIA), for the spectrophotometric determination of Cu(II) in water at trace levels have been developed and optimised. Both methods are based on the reaction with oxalic acid bis(cyclohexylidene hydrazide) (cuprizone) in alkaline media. The two procedures have been developed for the final aim to compare their performances and to offer new rapid heavy metals analysis tools, avoiding the use of extraction steps. A detailed study of the physico-chemical parameters affecting the systems performances has been carried out. The reversed FIA and sandwich SIA approaches offered the best sensitivity. In both cases, an extremely good linearity has been obtained within the range 0.06-4 μg ml⁻¹ (correlation coefficient r=0.9999), whereas the observed detection limits were 0.013 and 0.004 μg ml⁻¹, for FIA and SIA, respectively. Furthermore, due to the great similarity of the diffusion zones in the reaction slugs, our approach offers the opportunity to compare the two methods in analogous conditions. This SIA method, besides keeping its typical reagent saving features, offered analytical performances equivalent to those of FIA. To obtain these results, an original “stop-flow like” method was successfully employed in the SIA approach. Both methods were validated by analysis of real water samples, after copper addition, and certified reference samples of fortified and waste waters.     

A review on sequential injection methods for water analysis

The development of fast, automatic and less expensive methods of analysis has always been the main aim of flow methodologies. The search for new procedures that still maintain the reliability and accuracy of the reference procedures is an ever growing challenge. New requirements are continually added to analytical methodologies, such as lower consumption of samples and reagents, miniaturisation and portability of the equipment, computer interfaces for full decision systems and so on. Therefore, the development of flow methodologies meeting the extra requirements of water analysis is a challenging work.Sequential injection analysis (SIA) presents a set of characteristics that make it highly suitable for water analysis. With sequential injection analysis, most routine determinations in waters can be performed more quickly with much lower reagent consumption when compared to reference procedures. Additionally, SIA can be a valuable tool for analyte speciation and multiparametric analysis. This paper critically reviews the overall work in this area.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

On-line coupling of sequential injection lab-on-valve to differential pulse anodic stripping voltammetry for determination of Pb in water samples

Sequential injection lab-on-valve (LOV) was first proposed for analyzing ultra-trace amounts of Pb using differential pulse anodic stripping voltammetry (DPASV) with a miniaturized electrochemical flow cell fabricated in the LOV unit. Deposition and stripping processes took place between the renewable mercury film carbon paste electrode and sample solution, the peak current was employed as the basis of quantification. The mercury film displayed a long-term stability and reproducibility for at least 50 cycles before next renewal, the properties of integrated miniature LOV unit not only enhanced the automation of the analysis procedure but also declined sample/reagent consumption. Potential factors that affect the present procedure were investigated in detail, i.e., deposition potential, deposition time, electrode renewable procedure and the volume of sample solution. The practical applicability of the present procedure was demonstrated by determination of Pb in environmental water samples.     

Field speciation of chromium with a sequential injection lab-on-valve incorporating a bismuthate immobilized micro-column

A fully automated and portable analyzer for field speciation of inorganic chromium in wastewater was developed. The instrument consists of a micro-sequential injection lab-on-valve (LOV) system and a miniature USB2000 spectrophotometer. A multi-purpose flow cell was incorporated on one side of the main body of the LOV, which offers vast potentials and versatilities in its compatibility with various detection modes. On-line oxidation of trivalent chromium was performed on a bismuthate immobilized silica micro-column reactor integrated in the LOV. When determining Cr(VI), its chromogenic reaction with 1,5-diphenylcarbazide (DPC) was facilitated in the flow cell and the absorbance was monitored in situ at 548 nm via optical fibers. While for the quantification of total chromium, Cr(III) was oxidized on-line by aspirating sample solution through the oxidizing column reactor, followed by chromogenic reaction with DPC and the absorbance was monitored in the flow cell. With a sampling volume of 200 μl, the detection limits of 5.6 μg l⁻¹ for Cr(VI) and 6.8 μg l⁻¹ for total chromium were achieved along with a sampling frequency of 60 h⁻¹. A R.S.D. value of 2.0% was recorded at 32 μg l⁻¹ of Cr(VI). The practical applicability of the speciation analyzer was validated by analyzing Cr(VI) and total chromium contents in two certified reference materials. The feasibility of performing rapid field speciation of chromium in wastewater samples was also demonstrated.     

Determination of cadmium with a sequential injection lab-on-valve by anodic stripping voltammetry using a nafion coated bismuth film electrode

This work exploited a sequential injection lab-on-valve (LOV) system for the determination of cadmium by anodic stripping voltammetry (ASV). A miniaturized electrochemical flow cell (EFC) was fabricated in LOV, in which a nafion coated bismuth film electrode was used as working electrode. The cadmium was electrodeposited on the electrode surface in bismuth solution, and measured with the subsequential stripping scan. Under optimal conditions, the proposed system responded linearly to cadmium concentrations in a range 2.0-100.0 μg L⁻¹. The detection limit of this method was found to be 0.88 μg L⁻¹. By loading a sample volume of 800 μL, a sampling frequency of 22 determinations h⁻¹ was achieved. The repeatability expressed as relative standard derivation (R.S.D.) was 3.65% for 20 μg L⁻¹ cadmium (n = 11). The established method was applied to analysis of trace cadmium in environmental water samples and the spiked recoveries were satisfactory.     

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.     

Micro solid phase spectrophotometry in a sequential injection lab-on-valve platform for cadmium,zinc, and copper determination in freshwaters

This work describes the development of a solid phase spectrophotometry method in a μSI-LOV system for cadmium, zinc, and copper determination in freshwaters. NTA (Nitrilotriacetic acid) beads with 60–160 μm diameter were packed in the flow cell of the LOV for a μSPE column of 1 cm length. The spectrophotometric determination is based on the colourimetric reaction between dithizone and the target metals, previously retained on NTA resin. The absorbance of the coloured product formed is measured, at 550 nm, on the surface of the NTA resin beads in a solid phase spectrophotometry approach.     

Flow/sequential injection sample treatment coupled to capillary electrophoresis. A review

Various flow sample handling approaches coupled to capillary electrophoresis (CE) are reviewed, covering the research in this field in the 12 years since the milestone year of 1997, when practical interfaces to on-line couple flow injection (FI) and capillary electrophoresis were first developed independently by two research groups. Some previous attempts are also presented. Since 1997 a plethora of ingenious coupled systems have been developed. Although several reviews are available on various aspects of the topic, we have opted for a comprehensive overview of all FI-CE systems, as well as related and similar systems. This coupling has thus also led to the development of systems based on hybrids between the classical and microchip approaches. Truly microchip FI-CE systems are also included in this review.The developed systems have been used for various sample treatments, including on-line membrane-assisted sample treatment, column-based preconcentration, on-line derivatization and monitoring, to name just a few. The utility of coupling flow sampling to CE has been demonstrated in various practical applications that are discussed in detail. The current state-of-the-art and foreseeable future developments are also discussed.     

Using sequential injection analysis for fast determination of phosphate in coastal waters

A sequential injection analysis system (SIA) is described which is suited for the fast determination of filterable molybdate reactive phosphate (FRP, 0.2 μm) in coastal waters. It processes up to 270 samples per hour with a detection limit (3σ) of 0.05 μM and is used for surface mapping of phosphate in areas with steep concentration gradients like the Wadden Sea. The determination is based on the reaction of phosphate with acidic molybdate to phosphomolybdate, which builds non-fluorescent ion pairs with rhodamine 6G. The remaining rhodamine fluorescence is detected at 550 nm with an excitation at 470 nm. Syringe pump, valve and detector were controlled by a self made python programme, which was optimised for high speed SIA measurements in monitoring applications.     

Simple sequential injection analysis system for rapid determination of microalbuminuria

A simple, specific and sensitive sequential injection analysis (SIA) system based on non-immunoassay fluorescent detection has been developed for the determination of urinary albumin. The specific binding of the dye Albumin Blue 580 (AB 580) to albumin in urine generated high emission fluorescent signals. The excitation and emission wavelengths were set at 590 and 610 nm, respectively. The analytical range was obtained from 1 to 100 mg L⁻¹, with a detection limit of 0.3 mg L⁻¹ (S/N = 3). The SIA system gave high precision with relative standard deviations (R.S.D.s) of 0.9% and 1.4% when evaluated with 15 and 100 mg L⁻¹ albumin (n = 15), respectively. The method exhibited good reproducibility, as assessed by performing four analytical curves on different days, and intra-run CVs (2.3-3.3%) and inter-run CVs (3.8%) were obtained. Rapid operation was achieved with a sample throughput of 37 h⁻¹. This method was successfully applied to the determination of urinary albumin, and the method was highly correlated with the immunoturbidimetric method (r² = 0.965; n = 72).     

Development of sequential injection spectrophotometric method for determination of mercury (II) using pyrogallol red

A sequential injection analysis (SIA) spectrophotometric method for the determination of trace amount of mercury (II) with pyrogallol red (PGR) was described. The method was based on the measurement of absorbance of the mercury (II)–PGR complex, yielding a light yellow-coloured product at pH 9.0 with absorption maximum at 370 nm. The SIA parameters affecting the signal response were optimised in order to obtain the better sensitivity and minimum reagent consumption. The linear range for determination of mercury (II) was over the range of 0.1–2.0 mg L^?1. The limit of detection and limit of quantification, calculated following IUPAC were 0.06 and 0.10 mg L^?1, respectively. The repeatability was 1.25% (n = 10) for 0.5 mg L^?1 of mercury (II). The proposed method was successfully applied to determine the mercury (II) in commercial cosmetics, local Thai traditional medicines and water samples with a sampling rate of 40 h^?1. Results obtained were in justifiable agreement with those obtained by the official ICP-MS method at the 95% confidence level.     

Hyphenation of flow injection/sequential injection with chemical hydride/vapor generation atomic fluorescence spectrometry

The dominant role played by flow injection/sequential injection (FI/SI, including lab-on-valve, LOV) in automatic on-line sample pretreatments coupling to various detection techniques is amply demonstrated by the large number of publications it has given rise to. Among these, its hyphenation with hydride/vapor generation atomic fluorescence spectrometry (HG/VG-AFS) has become one of the most attractive sub-branches during the last years, attributed not only to the high sensitivity of this technique, but also to the superb separation capability of hydride/vapor forming elements from complex sample matrices. In addition, it also provides potentials for the speciation of the elements of interest.It is worth mentioning that quite a few novel developments of sample pretreatment have emerged recently, which attracted extensive attentions from the related fields of research. The aim of this mini-review is thus to illustrate the state-of-the-art progress of implementing flow injection/sequential injection and miniaturized lab-on-valve systems for on-line hydride/vapor generation separation and preconcentration of vapor forming elements followed with detection by atomic fluorescence spectrometry, within the period from 2004 up to now. Future perspectives in this field are also discussed.     

Spectrofluorimetric determination of aluminum in drinking waters by sequential injection analysis

A selective procedure for the determination of Al³⁺ in drinking and natural waters is proposed. The analytical procedure is based both on the complex formation between Al³⁺ and 8-hydroxyquinoline-5-sulfonic acid (HQS) and on a fluorimetric detection of the complex. The reaction was carried out in presence of thioglycolic acid as a masking agent. This procedure has been adapted to a sequential injection analysis (SIA) system. Operative conditions both for batch and SIA procedures were investigated including reagent concentration, volumes, pH and wavelengths used for the fluorimetric detection. Batch procedure allows determination of Al³⁺ at ppb level (LOQ: 2.8 μg l⁻¹) within a working range of 2.2-300 μg l⁻¹. The SIA procedure was successfully employed for the determination of Al³⁺ in several commercial drinking and tap waters.     

Immersed single-drop microextraction interfaced with sequential injection analysis for determination of Cr(VI) in natural waters by electrothermal-atomic absorption spectrometry

Single-drop microextraction (SDME) and sequential injection analysis have been hyphenated for ultratrace metal determination by Electrothermal-Atomic Absorption Spectrometry (ETAAS). The novel method was targeted on extraction of the Cr(VI)-APDC chelate and encompasses the potential of SDME as a miniaturized and virtually solvent-free preconcentration technique, the ability of sequential injection analysis to handle samples and the versatility of furnace autosamplers for introducing microliter samples in ETAAS.     

On-line sequential injection dispersive liquid-liquid microextraction system for flame atomic absorption spectrometric determination of copper and lead in water samples

A simple, sensitive and powerful on-line sequential injection (SI) dispersive liquid-liquid microextraction (DLLME) system was developed as an alternative approach for on-line metal preconcentration and separation, using extraction solvent at microlitre volume. The potentials of this novel schema, coupled to flame atomic absorption spectrometry (FAAS), were demonstrated for trace copper and lead determination in water samples. The stream of methanol (disperser solvent) containing 2.0% (v/v) xylene (extraction solvent) and 0.3% (m/v) ammonium diethyldithiophosphate (chelating agent) was merged on-line with the stream of sample (aqueous phase), resulting a cloudy mixture, which was consisted of fine droplets of the extraction solvent dispersed entirely into the aqueous phase. By this continuous process, metal chelating complexes were formed and extracted into the fine droplets of the extraction solvent. The hydrophobic droplets of organic phase were retained into a microcolumn packed with PTFE-turnings. A portion of 300 μL isobutylmethylketone was used for quantitative elution of the analytes, which transported directly to the nebulizer of FAAS. All the critical parameters of the system such as type of extraction solvent, flow-rate of disperser and sample, extraction time as well as the chemical parameters were studied. Under the optimum conditions the enhancement factor for copper and lead was 560 and 265, respectively. For copper, the detection limit and the precision (R.S.D.) were 0.04 μg L⁻¹ and 2.1% at 2.0 μg L⁻¹ Cu(II), respectively, while for lead were 0.54 μg L⁻¹ and 1.9% at 30.0 μg L⁻¹ Pb(II), respectively. The developed method was evaluated by analyzing certified reference material and applied successfully to the analysis of environmental water samples.     

顺序注射催化动力学光度法测定织物和室内空气中痕量甲醛

在磷酸介质中 ,甲醛可以催化溴酸钾氧化　花青的反应使其退色 ,据此建立了顺序注射催化动力学光度法测定织物和室内空气中痕量甲醛的新方法。方法的线性范围 0 .5～ 7.0 μg mL ,检出限 0 .1 μg mL。用于树脂整理特殊织物和室内空气中痕量甲醛的测定 ,回收率在 97.0 %～ 1 0 5 .0 %之间。