Sequential Injection Analysis System Research Articles

A violet light-emitting diode-based gas-phase molecular absorption device for measurement of nitrate and nitrite in environmental water

A simple and sensitive device for the detection of nitrite and nitrate in environmental waters was developed based on visible light gas-phase molecular absorption spectrometry. By integrating a detection cell (DC), semiconductor refrigeration temperature-controlling system (SRTCY), and nitrite reactor into a sequential injection analysis system, trace levels of nitrite and nitrate in complex matrices were successfully measured. A low energy-consuming light-emitting diode (violet, 400–405 nm) was coupled with a visible light-to-voltage converter (TSL257) to measure the gas-phase molecular absorption. To reduce the interference of water vapor, an SRTCY was used to condense the water vapor on-line before the gas-phase analyte entered the DC. The DC was radiatively heated by the SRTCY to avoid water vapor condensation in the light path. As a result, the obtained baseline noise reduced 3.75 times than that of without SRTCY. Under the optimized conditions, the device achieved limits of detection (3σ/k) of 0.055 and 0.36 mmol/L (0.77 and 5.04 mg N/L) for nitrite and nitrate, respectively, and the linear calibration ranges were 0.1–15 mmol/L (R2 = 0.9946) and 1–10 mmol/L (R2 = 0.9995), respectively. Precisions of 5.2 % and 9.0 % were achieved for ten successive determinations of 0.3 mmol/L nitrite and 1.0 mmol/L nitrate, and the analytical times for nitrite and nitrate determination were 5 and 13 min, respectively. This method was validated against standard methods and recovery tests, and it was applied to the measurement of nitrite and nitrate in environmental waters. Moreover, a device was designed to enable the field measurement of nitrite and nitrate in complex matrices.

Development of a sequential injection analysis method for the automatic speciation of inorganic selenium in water samples

Selenium is an important micronutrient for the human body, but biological concentrations on either side of its narrow nutritional window can lead to serious health impacts. Furthermore, Se(IV) has been reported to be more toxic than Se(VI). Therefore, prudent control and monitoring of Se intake should involve speciation of this element. Herein, the development and validation of an automatic sequential injection analysis (SIA) system and method for the speciation of Se(IV) and Se(VI) in water samples is reported for the first time. This method is based on the starch-iodide reaction using Se(IV) as the oxidant, which subsequently forms a blue compound with starch. Total selenium is determined after an online pre-reduction of Se(VI) to Se(IV) with HCl at 75 °C. The concentration of Se(VI) is then calculated as the difference between the total Se and Se(IV) concentrations. The calibration curves for Se(IV) and total Se are characterised by linear ranges of 0 – 1.5 mg L-1 and 0 – 2.5 mg L-1, limits of detection (LODs) of 0.02 mg L-1 and 0.07 mg L-1, and averaged relative standard deviations (RSDs) (n = 3) of 1.33 % and 2.95 % respectively, with a sampling rate of 10 h−1. The newly developed SIA method has been successfully applied to drinking water samples spiked with both Se species and good recoveries in the range 94 – 109 % have been achieved.

Monitoring β-Fructofuranosidase Activity through Kluyveromyces marxianus in Bioreactor Using a Lab-Made Sequential Analysis System

The yeast Kluyveromyces marxianus has shown the potential to produce β-fructofuranosidases, which are enzymes capable of hydrolyzing β-fructofuranosides links of fructans to obtain fructooligosaccharides. The thriving market for fructose syrup and the quality standards imposed by food and pharmaceutical industries have generated an increased search for improved, monitored, and controlled production processes. Monitoring β-fructofuranosidase activity in a bioprocess requires the use of adequate sensors and the processing of information using efficient software algorithms; nevertheless, currently, such a sensor does not exist for this purpose. In this contribution, a sequential injection analysis system (SIA) developed in our laboratory was adapted to monitor at-line β-fructofuranosidase activity produced by the yeast K. marxianus. Samples were taken out automatically from the bioreactor and analyzed using 3,5-dinitrosalicylic (DNS). An algorithm was designed to operate the overall components of the lab-made SIA system. The enzymatic activity error obtained with the automatic SIA compared to the off-line laboratory determinations varied from 0.07% at high enzyme concentrations to 20.39% at low β-fructofuranosidase activity. Further development is required to improve the performance of the lab-made SIA system; nevertheless, such a device must be considered as a potential method for monitoring β-fructofuranosidase activity in real time.

Multiwalled Carbon Nanotubes-Modified Metallic Electrode Prepared Using Chemical Vapor Deposition as Sequential Injection Analysis Detector for Determination of Ascorbic Acid.

A carbon nanotubes modified silver electrode (CNTs-Ag) was prepared via catalytic chemical vapor deposition and characterized. The morphology, crystallinity, elemental composition, and other quality parameters of the prepared electrode were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman techniques. The characterization results revealed the modification of the silver metal surface with CNTs of good characteristics. A sequential injection analysis (SIA) system was developed for studying the reaction of ascorbic acid with KIO3 using the prepared CNTs-Ag electrode. Electrodes were polarized with both direct current (DC) and periodic square wave (SW). Various experimental conditions affecting the differential electrolytic potentiometric (DEP) peak such as current density, SW bias value, and flow rate were appraised. Under the optimum conditions, good linear responses for ascorbic acid were obtained in the range of 60.0-850.0 µM for both types of polarization with detection limits of 14.0-19.0 µM. The results obtained showed that the periodic polarization method was more sensitive than DC polarization and the electrode response was faster. Ascorbic acid in pharmaceutical tablets was determined with satisfactory results using this method. The prepared CNTs-based electrode exhibited good performance for a long period of use. The method is simple, rapid, and inexpensive for routine analysis.

Sequential Injection Analysis for Rapid Determination of Mercury in Skincare Products Based on Fluorescence Quenching of Eco-Friendly Synthesized Carbon Dots.

This work reports the analysis of mercury using a spectrofluorometric method combined with a sequential injection analysis (SIA) system. This method is based on the measurement of fluorescence intensity of carbon dots (CDs), which is quenched proportionally after adding mercury ions. Herein, the CDs underwent environmentally friendly synthesis using a microwave-assisted approach that provides intensive and efficient energy and shortens reaction time. After irradiation at 750 W for 5 min in a microwave oven, a dark brown CD solution with a concentration of 2.7 mg mL-1 was obtained. The properties of the CDs were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and UV-vis spectrometry. We presented for the first time the use of CDs as a specific reagent for the determination of mercury in skincare products with the SIA system to achieve rapid analysis and full automatic control. The as-prepared CD stock solution was diluted 10 times and used as a reagent in the SIA system. Excitation and emission wavelengths at 360 and 452 nm, respectively, were used to construct a calibration curve. Physical parameters affecting the SIA performance were optimized. In addition, the effect of pH and other ions was investigated. Under the optimum conditions, our method showed a linear range from 0.3 to 600 mg L-1 with an R 2 of 0.99. The limit of detection was 0.1 mg L-1. Relative standard deviation was 1.53% (n = 12) with a high sample throughput of 20 samples per hour. Finally, the accuracy of our method was validated by comparison using inductively coupled plasma mass spectrometry. Acceptable recoveries were also presented without a significant matrix effect. This method was also the first time that uses the untreated CDs for the determination of mercury(II) in skincare products. Therefore, this method could be an alternative for mercuric toxic control in other sample applications.

Sequential injection analysis for mercury ion with modified screen – printed carbon electrode

In this study, we developed a simple high-throughput and cost-effective method for monitoring toxic metal ion in an environmental aqueous sample. Mercury ion determination with Sequential Injection Analysis system (SIAs) coupled with the electrochemical detection on the modified screen-printed carbon working electrode (SPCE) is an alternative green analysis of mercury ion. The gold film was used as the modified material for improved mercury ion analysis in the automated system without memory effect on the electrode. Mercury oxidation signal was found at the potential of 0.7 V in 0.1 M HNO3 and 1.0 M HCl with the concentration low to 0.25 ± 0.18 mg×L-1. Online sample preparation and separation will study in the further experiment.

Automatic Identification of Myeloperoxidase Natural Inhibitors in Plant Extracts.

The aim of this study is the development of an automated method for myeloperoxidase activity evaluation and its application in testing the inhibitory action of different plant extracts on the activity of the enzyme. This enzyme has its concentration increased in inflammatory and infectious processes, so it is a possible target to limit these processes. Therefore, an automatic sequential in-jection analysis (SIA) system was optimized and demonstrated that it is possible to obtain results with satisfactory accuracy and precision. With the developed method, plant extracts were studied, as promising candidates for MPO inhibition. In the group of selected plant extracts, IC50 values from 0.029 ± 0.002 mg/mL to 35.4 ± 3.5 mg/mL were obtained. Arbutus unedo L. proved to be the most inhibitory extract for MPO based on its phenolic compound content. The coupling of an automatic SIA method to MPO inhibition assays is a good alternative to other conventional methods, due to its simplicity and speed. This work also supports the pharmacological use of these species that inhibit MPO, and exhibit activity that may be related to the treatment of infection and inflammation.

Sequential Injection System for Analysis of Degree Brix, Orthophosphate and pH in Raw Sugarcane Juice Applicable to Sugar Industry.

This work presents, for the first time, a new sequential injection analysis (SIA) method to simultaneously analyze degree Brix, orthophosphate and pH in raw cane juice. These key parameters relate to price of harvested sugarcane and quality of cane juice for sugar production. The SIA system employed two detectors: the first detector is a diode-array spectrophotometer, equipped with a regular flow cell, for measurements of degree Brix and orthophosphate. Quantitative of degree Brix (°Bx; ca. % (w/w) sucrose) was based on manipulation of the schlieren effect at the interface between plugs of sample and water. Orthophosphate analysis was carried out based on the molybdenum blue method with significant reduction in consumption of the reagents. Compensation of the schlieren effect from sucrose for determination of orthophosphate was achieved by using a dual-wavelength spectrometric detection. Second detector is a pH-sensing device, called ion-selective field-effect transistors (ISFET). The ISFET is based on the current through the ISFET arising according to the H+ concentration in solution. Our developed SIA system provides linear calibration graphs fitting for purpose in analysis of sugarcane juice (pH: 0–14, °Bx: 1.0–7.0 and P2O5: 20–200 mg L−1). Simultaneous analysis of sugarcane juice for pH, °Bx and P2O5 is carried out within 5 min (12 sample per h). Precision of SIA system is acceptable (RSD < 3%). Our SIA system gave quantitative results insignificantly different, as compared with conventional methods for analysis of pH, °Bx and P2O5 in sugarcane juice.

Development of an automated yeast-based spectrophotometric method for toxicity screening: Application to ionic liquids, GUMBOS, and deep eutectic solvents

Saccharomyces cerevisiae has been used as a eukaryotic model organism for studying the toxic effects of various compounds. In this context, an automated spectrophotometric method based on the enzymatic reduction of methylene blue dye to a colorless product by living yeast cells was implemented in a sequential injection analysis system. Loss of yeast viability/impaired metabolic activity was monitored by an increase in optical density at 664 nm. To prove the usefulness of this approach, the toxicity of ILs (ionic liquids), GUMBOS (group of uniform materials based on organic salts), and DESs (deep eutectic solvents) was examined. Differences obtained between IC50 values confirmed the impact of structural elements on each compounds’ toxicity. While DESs appeared to be less toxic than ILs, GUMBOS were found to be among the most toxic compounds to yeast cells and thus can be viewed as promising antimicrobial candidates. The automated methodology showed satisfactory repeatability and reproducibility (RSD < 9%), which is in good agreement with Green Chemistry principles. In fact, the method required consumption of only 40 μL of reagents and produced less than 2 mL of effluents per cycle. Thus, the developed assay can be used as an alternative tool for toxicity screening.

LabVIEW virtual instrument for zone penetration studies in flow-based analytical systems

In the flow method development, zone penetration studies are usually conducted as a part of the initial screening phase. A lack of an appropriate tool can keep these studies on the level of rough estimations. The developed LabVIEW virtual instrument (VI) which processes peak signals and calculates the overlapping area and fundamental peak-related parameters was used for the calculations in experiments that are modelling sample and reagent plug interaction within liquid conduits. The reliability of the predictions was initially confirmed on the artificial data set based on thirty-six files covering all the different types of cases that can be foreseen. To continue, the volumes of model solutions, propelling flow rate, and the coil length in the sequential injection analysis system, were varied by following the Box?Behnken response surface design. In three examples, it is demonstrated how the VI can help the planning of further experiments in the range which ensures the efficient zone overlapping, the economic exploitation of reagent plug and the adequate dispersion. The application of the VI is not limited just to the flow-based chemistry, it can also be used in spectroscopy and chromatography. In order to use the graphical user interface, it is not necessary to have the LabVIEW program installed.

Successive Determination of Vanadium and Creatinine in Urine Samples Using a Sequential Injection Analysis System Coupled to ICP-MS and Spectrophotometer

Successive Determination of Vanadium and Creatinine in Urine Samples Using a Sequential Injection Analysis System Coupled to ICP-MS and Spectrophotometer

Use of a Polymer Inclusion Membrane and a Chelating Resin for the Flow-Based Sequential Determination of Copper(II) and Zinc(II) in Natural Waters and Soil Leachates.

A bi-parametric sequential injection method for the determination of copper(II) and zinc(II) when present together in aqueous samples was developed. This was achieved by using a non-specific colorimetric reagent (4-(2-pyridylazo)resorcinol, PAR) together with two ion-exchange polymeric materials to discriminate between the two metal ions. A polymer inclusion membrane (PIM) and a chelating resin (Chelex 100) were the chosen materials to retain zinc(II) and copper(II), respectively. The influence of the flow system parameters, such as composition of the reagent solutions, flow rates and standard/sample volume, on the method sensitivity were studied. The interference of several common metal ions was assessed, and no significant interferences were observed (<10% signal deviation). The limits of detection were 3.1 and 5.6 µg L−1 for copper(II) and zinc(II), respectively; the dynamic working range was from 10 to 40 µg L−1 for both analytes. The newly developed sequential injection analysis (SIA) system was applied to natural waters and soil leachates, and the results were in agreement with those obtained with the reference procedure.

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis.

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter–detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 × 2 × 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffé reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm−1).

Sequential injection analysis Ferrozine spectrophotometry versus Luminol chemiluminescence for continuous online monitoring of the concentration and speciation of iron

We designed two sequential injection analysis systems (Luminol chemiluminescent and Ferrozine spectrophotometric) that are capable of monitoring the concentration of soluble iron(II) and reducible iron(III) in natural waters over extended periods (>120 h). The method based on Luminol chemiluminescence estimated the iron(II) concentration as the difference in signal with or without the addition of the strong iron(II) ligand, FerrozineTM (iron complexing reagent). Iron(II) in the sample without the iron complexing reagent induced a chemiluminescence signal whereas iron(II) in the presence of the iron complexing reagent did not induce a signal. The second method, based on FerrozineTM spectrophotometry, measured iron(II) and reducible iron(III) in a 100 cm path length liquid wave capillary cell. Both methods provided stability for >120 h and yielded similar analytical detection limits equal to ten standard deviations of the blank; 2.2 nM for Luminol chemiluminescence with a calibration concentration range of 0−12 nM, and 3.9 nM for FerrozineTM spectrophotometry with a calibration concentration range of 0−120 nM. The two chemical techniques do not appear to be directly comparable for practical monitoring purposes, and we suggest that Luminol-chemiluminescence is unable to measure strong ligand complexes of iron(II). Both methods used iron(II) as the analytical standard rather than a reduced iron(III) standard. The analysis based on the iron(II) standard was able to be performed without additional buffers and reducing reagents, which significantly minimized contamination.

Sequential injection analysis system with DGA resin for sample pretreatment in ICP-MS determination of 239Pu in nuclear industry samples

The monitoring of the presence of plutonium isotopes is a very important issue in both nuclear energy industry and environmental protection for human health risk assessment. The developed method for the determination of 239Pu isotope with ICP-QMS detection is based on the use of sequential injection analysis (SIA) system for the pretreatment of samples to be analyzed with the use of a commercial sorbent called diglycolamide (DGA-b) for the analyte preconcentration and separation from 238U, which is the source of the most significant isobaric interference 238U1H+. Optimizing the size of the sorbent bed and the conditions of analyte sorption and elution of plutonium and uranium provides the analytical procedure for 239Pu determination, where at total analysis time of 45 min (at flow rate 10 mL min−1) the evaluated method detection limit (MDL) for 100 mL sample volume was 88 mBq L−1. This is satisfactory detectability for applications in both technological and environmental samples.

Sequential Injection Analysis for Determination of Lead(II) using Extract of Caesalpinia Pulcherrima as a Natural Reagent

The lead(II)-contaminated aquatic environment may endanger humans and living organism. The maximum tolerable limit of lead(II) in river water is 1 mg/L. Therefore, the development of a sensitive and green analytical method to determine lead(II) is required. In this work, we developed a Sequential Injection Analysis (SIA) system equipped with a valve-mixing and a flow-based UV detector for highly sensitive detection of lead(II). In order to deal with the green chemistry system, the environmentally friendly natural reagent is prepared from the extract of Caesalpinia pulcherrima instead of a commercial synthetic reagent. The extract of Caesalpinia pulcherrima contains several flavonoid compounds which can bind lead(II) ion to form an orange complex compound at a wavelength of 672.4 nm. Various parameters affecting the sensitivity of the proposed method, which includes pH, reaction time, the flow rate to the detector, and stability of Caesalpinia pulcherrima extract, were investigated in detail. The optimum conditions for a complex formation of Pb-Caesalpinia pilcherrima extract were found at pH 4 along with a reaction time of 10s, and the product flow rate to the detector was 200 µL/s. Under the optimum conditions, a linear calibration graph can be constructed in the lead(II) concentration range of 0-800 ppb with a detection limit of 8.9 ppb. The proposed method is successfully applied to determine lead(II) in industrial wastewater samples with satisfied results.

Screening of extraction properties of nanofibers in a sequential injection analysis system using a 3D printed device

A novel application of the three-dimensional printing technology for the automation of solid phase extraction procedures in a low-pressure sequential injection analysis system is presented. A 3D printed device was used as a housing for nanofiber membranes in solid phase extraction. The applicability of the device is demonstrated with the extraction of substances of various physical-chemical properties. Pharmaceuticals including non-steroidal anti-inflammatory drugs, antihistaminics, and steroidal structures, as well as emerging pollutants such as bisphenols and pesticide metsulfuron methyl were used as model analytes to study the extraction performance of the nanofibers. Six different nanofiber types comprising polyamide, polyethylene, polyvinylidene fluoride, polycaprolactone combined with polyvinylidene fluoride, and polyacrylonitrile, produced by electrospinning were tested in solid phase extraction. The suitability of specific nanofibers for particular analytes is demonstrated.

Fully automated method based on on-line molecularly imprinted polymer solid-phase extraction for determination of lovastatin in dietary supplements containing red yeast rice.

A fully automated method for the determination of lovastatin in dietary supplements containing red yeast rice has been developed. It uses a sequential injection analysis system combined with solid-phase extraction applying highly selective molecularly imprinted polymer sorbent. A miniaturized column for on-line extraction was prepared by packing 4.5mg of the sorbent in a 5.0 × 2.5-mm-i.d. cartridge, which was used in the flow manifold. Sequential injection analysis manifold enabled all steps of lovastatin extraction and continuous spectrophotometric detection at 240nm. A limit of detection of 60μgg-1, a limit of quantitation of 200μgg-1, and a linear calibration range of 200-2000μgg-1 were achieved. Intra-day and inter-day precision values (RSD) were ≤ 6.7% and ≤ 4.9%, respectively, and method recovery values of spiked red yeast rice extracts at 200, 1000, and 2000μgg-1 concentration levels were 82.9, 95.2, and 87.7%. Our method was used for determination of lovastatin lactone in four dietary supplements containing red yeast rice as a natural source of lovastatin, also known as monacolin K. The extracted samples were subsequently analyzed by the reference UHPLC-MS/MS method. Statistical comparison of results (F test, t test, α = 0.05) obtained by both methods did not reveal significant difference. A substantial advantage of the new automated approach is high sample throughput thanks to the analysis time of 7.5min, miniaturization via down-scaling the extraction column, and smaller sample and solvent consumption, as well as reduced generation of waste. Graphical abstract ᅟ.

Automatic methodologies to perform loading and release assays of anticancer drugs from mesoporous silicon nanoparticles

Two automatic methodologies were developed to perform the loading and release assays of drugs from porous silicon (PSi) nanoparticles. 5-Fluorouracil (5-FU) was selected as a model drug, and different functionalized PSi nanoparticles were used. While for drug loading studies the reproducible characteristics of flow systems were explored regarding mixture and volumes taken, in the drug release flow methodology versatility in accommodating different devices around the valve were tested. Fluorescent properties of 5-FU were used with detection limit of 9 × 10−4 mg L−1 and a linear response up to 5 mg L−1 The drug loading and release procedures were optimized in sequential injection analysis (SIA) systems obtaining a huge economy regarding the time spent (4 min towards 2 h). Batch and SIA methods were tested and compared for the different behaviours of the PSi nanoparticles towards both methodologies and no noteworthy differences were obtained with Student's t-test for loading with a calculated t value of 2.04 showing the absence of statistical differences. All the results present a RSD less than 10%. So, the developed automatic methodologies are a viable alternative to load drugs and to study the release profiles from PSi nanoparticles.

Automated dispersive liquid-liquid microextraction based on the solidification of the organic phase

In this work, the dispersive liquid-liquid microextraction technique based on the solidification of the organic phase (DLLME-SFO) has been automated for the first time. DLLME-SFO is automated by hyphenating a sequential injection analysis (SIA) system with a custom-made robotic phase separator. Automated in-syringe DLLME is followed by phase separation in a 3D printed device integrating a Peltier cell set, mounted on a multi-axis robotic arm. The combined action of the flow system and the robotic arm is controlled by a single software package, enabling the solidification/melting and collection of the organic phase for further analyte quantification.As proof-of-concept, automated DLLME-SFO was applied to the extraction of parabens followed by separation using liquid chromatography, obtaining LODs between 0.3 and 1.3 µg L−1 (4 mL of sample extracted in 1 mL of 1-dodecanol: MeOH, 15:85, v-v). The method showed a high reproducibility, obtaining intraday RSDs between 4.6% and 5.8% (n = 6), and interday RSDs between 5.6% and 8.6% (n = 6). The developed method was evaluated for the determination of parabens in water, urine, saliva, and personal care products.