Sequential Injection Analysis Research Articles

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.

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, 400–410 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-1) 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.

On-site extraction using a 3D printed device coated with Zn/Co-ZIF-derived carbon followed by an on-line SIA-HPLC-FL system for fluoroquinolones determination in wastewater

A 3D printed device covered with Zn/Co-ZIF-derived carbon allows the on-site extraction of fluoroquinolones (FQs) from wastewater, avoiding the sample transportation to the laboratory, and the subsequent elution, separation and determination using an on-line flow system based on sequential injection analysis (SIA) coupled to HPLC-FL. Several parameters that affect the extraction efficiency and desorption were optimized including the sorption phase immobilization technique on the 3D device, extraction time, pH effect, sample volume as well as the type of eluent, eluent volume, and flow rate. Under optimum conditions, detection limits of 3–9 ng L−1 were achieved for norfloxacin, ciprofloxacin, danofloxacin, enrofloxacin and difloxacin. The precision expressed as relative standard deviation (%RSD, n = 3), showed intraday and interday ranges of 1.5–5.3% and 2.8–5.7%, respectively, demonstrating a good precision of the proposed methodology. To assess matrix effects and accuracy of the proposed method in real samples, recovery studies were performed without and with FQs spiked at different concentrations (0.5–10 μg L−1) to wastewater samples, showing good recoveries in the range of 91–104%. The results allow to confirm the applicability of MOF-derived carbons as adsorbents for on-site extraction, and the satisfactory separation and quantification of FQs by a SIA-HPLC-FL on-line system after their desorption with small eluent volumes.

Automation and Computerization of (Bio)sensing Systems.

Sensing systems necessitate automation to reduce human effort, increase reproducibility, and enable remote sensing. In this perspective, we highlight different types of sensing systems with elements of automation, which are based on flow injection and sequential injection analysis, microfluidics, robotics, and other prototypes addressing specific real-world problems. Finally, we discuss the role of computer technology in sensing systems. Automated flow injection and sequential injection techniques offer precise and efficient sample handling and dependable outcomes. They enable continuous analysis of numerous samples, boosting throughput, and saving time and resources. They enhance safety by minimizing contact with hazardous chemicals. Microfluidic systems are enhanced by automation to enable precise control of parameters and increase of analysis speed. Robotic sampling and sample preparation platforms excel in precise execution of intricate, repetitive tasks such as sample handling, dilution, and transfer. These platforms enhance efficiency by multitasking, use minimal sample volumes, and they seamlessly integrate with analytical instruments. Other sensor prototypes utilize mechanical devices and computer technology to address real-world issues, offering efficient, accurate, and economical real-time solutions for analyte identification and quantification in remote areas. Computer technology is crucial in modern sensing systems, enabling data acquisition, signal processing, real-time analysis, and data storage. Machine learning and artificial intelligence enhance predictions from the sensor data, supporting the Internet of Things with efficient data management.

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.

Determination of N-Acetyl-L-cysteine Ethyl Ester (NACET) by Sequential Injection Analysis.

New sequential injection analysis (SIA) methods with optical sensing for the determination of N-acetyl-L-cysteine ethyl ester (NACET) have been developed and optimized. NACET is a potential drug and antioxidant with advantageous pharmacokinetics. The methods involve the reduction of Cu(II) in its complexes with neocuproine (NCN), bicinchoninic acid (BCA), and bathocuproine disulfonic acid (BCS) to the corresponding chromophoric Cu(I) complexes by the analyte. The absorbance of the Cu(I) complexes with NCN, BCA, and BCS was measured at their maximum absorbance wavelengths of 458, 562, and 483 nm, respectively. The sensing manifold parameters and experimental conditions were optimized for each of the Cu(II) complexes used. Under optimal conditions, the corresponding linear calibration ranges, limits of detection, and sampling rates were 8.0 × 10-6-2.0 × 10-4 mol L-1, 5.5 × 10-6 mol L-1, and 60 h-1 for NCN; 6.0 × 10-6-1.0 × 10-4 mol L-1, 5.2 × 10-6 mol L-1, and 60 h-1 for BCA; and 4.0 × 10-6-1.0 × 10-4 mol L-1, 2.6 × 10-6 mol L-1, and 78 h-1 for BCS. The Cu(II)-BCS complex was found to be best performing in terms of sensitivity and sampling rate. Usual excipients in pharmaceutical preparations did not interfere with NACET analysis.

Direct Growth of Carbon Nanotubes on Silver Substrate for Determination of Fluoroquinolone

Metallic electrodes modified with carbon nanotubes (CNTs) by direct growth have advantages over the ones modified through external connection methods. These advantages are: (i) reduced contact resistance between CNTs and metal substrate, which is required for electroanalytical determinations. (ii) Strong adhesion of the CNTs layer to the metal substrate which in turn prevents the detachment of CNTs from the electrode surface and stops the deterioration of the signal with time and use. This present work shows the use of carbon nanotubes-modified silver (CNTs-Ag) electrode prepared by direct growth of CNTs as indicator electrodes for differential electrolytic potentiometric (DEP) determination of the fluoroquinolone antibiotic, ciprofloxacin. Characterization of CNTs-Ag electrode by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy showed the growth of aligned, crystalline, and graphitized CNTs. Application of CNTs-Ag electrode for the determination of ciprofloxacin by sequential injection analysis (SIA) method exhibited fast and stable response, reproducible signals, and durability for long-term use. Ciprofloxacin has been quantified in the range of 60 – 1000 µmol/L with a good linear relationship. This work combined the advantages of Direct grown CNTs, SIA technique, and the square-wave DEP method. Figure 1

A Rapid and Sensitive Colorimetric Sequential Injection System for Cu(II) ion Determination Using New Azo Reagent

A sensitive and accurate Sequential Injection Analysis technique for determining Cupper (II) ion in different samples, using a new azo derivative reagent of 8-hydroxy quinoline (HQDABA). The reagent and Cu(II) complex diagnosis included Infrared spectroscopy, Ultraviolet-Visual radiation, Elemental Analysis (CHN), Energy dispersive X-ray spectroscopy (EDX), nuclear magnetic resonance spectroscopy 1HNMR and mass spectroscopy techniques. The method depends on the reaction of Cupper (II) with the (Azo derivative of 8-hydroxy Quinoline) reagent in a neutral medium to form a Brown complex which gave a maximum absorbance at 420 nm. The optimum conditions such as flow rate, Copper (II) volume, reagent volume; pH, reagent concentration, and reaction coil length are thoroughly examined. A Copper (II) curve is constructed, and the suggested method obeys Beer's law over ration range of 1-10 mg/ L. The limits of detection (LOD) and on (LOQ) are determined to be (0.361) mg/ L and(1.204) mg/ L, while Sandell's sensitivity and molar absorption coefficient are to be (0.120) µg/ cm2 and (527.05) L/ mol. cm respectively. The recommended method has given good accuracy with recovery rates ranging from (77.82% - 115% ).

Analytical Methods for the Estimation of Levothyroxine and Levothyroxine Sodium in Pharmaceutical Formulations – A Review

Levothyroxine (L-T4) is used in the treatment of hypothyroidism and is a synthetic levoisomer of the thyroid hormone thyroxine produced by the thyroid gland. Levothyroxine sodium (L-T4S) salt has a high clinical utility. There are numerous studies that have been published that describe analytical methods for the estimation of L-T4 and L-T4S in pharmaceutical formulations and also in various biological matrices like blood, plasma, serum, and urine. This review article focused on analytical methods for estimating L-T4 and L-T4S in pharmaceutical formulations such as Thin Layer Chromatography (TLC), UV-visible spectrophotometer, High-Performance Liquid Chromatography (HPLC), Capillary electrophoresis, Luminescence, Sequential Injection Analysis (SIA), Voltammetry, and Hyphenated techniques. All the analytical methods for the estimation of L-T4 and L-T4S are given in tabular form. Out of all the analytical methods reported, HPLC is the most commonly used method for the estimation of L-T4 and L-T4S with optimum separation and resolution.

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.

Determination of o-phthalaldehyde for dose verification of the clinical disinfectant by fluorescent sequential injection analysis.

A new automated, generic analytical approach for determining the clinical disinfectant o-phthalaldehyde (OPA) is reported in this study. The proposed sequential injection analysis (SIA) is based on the online reaction of the OPA with glycine/N-acetylcysteine (NAC) in a neutral medium (pH = 7.0) to form a highly fluorescent isoindole derivative. All critical flow and reaction variables were investigated, while validation was carried out in the linearity detection range (0.0075-0.02%). As a result, excellent linearity (R2 > 0.99) and precision (1.5-2.4% for repeatability and 0.7-2.2% for reproducibility) were achieved for the reference OPA solutions. Furthermore, reasonable concentration verification of OPA disinfection (0.2-0.6%) in healthcare institutes can be achieved using the developed fluorescent SIA due to its good sensitivity (0.111V/%) and precision (1.0-2.3% for intermediate precision) around the minimum effective concentration (MEC) of 0.3% for Cidex-OPA disinfectant.

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.

Innovated single flush on-line solid-phase extraction in bead injection format for flow programming-based determination of creatinine in human urine

Reaction-based assays are commonly automated and miniaturized via flow analysis. However, aggressive reagents can affect or destroy even the chemically resistant manifold during long-term use. Using on-line solid-phase extraction (SPE) can eliminate this drawback and allow for high reproducibility and further advanced automation, as presented in this work. Determination of creatinine in human urine, an important clinical marker, by sequential injection analysis was achieved using bead injection on-line SPE with specific UV spectrophotometric detection, providing the necessary sensitivity and selectivity of the method for bioanalysis. The automated SPE column packing and disposal, calibration, and fast measurement highlighted the improvements in our approach. Variable sample volumes and a single working standard solution eliminated matrix effects, broadened the calibration range, and accelerated the quantification.Our method comprised an injection of 20 μL of 100 × times diluted urine with aqueous acetic acid solution pH 2.4, sorption of creatinine in a strong cation exchanger SPE column, washing out urine matrix with 50% aqueous acetonitrile, and elution of creatinine with 1% ammonium hydroxide. The SPE step was accelerated by a single flush of the column when the eluent/matrix wash/sample/standard zones sequence was created in the pump holding coil, and then the sequence of the zones was flushed into the column at once. The whole process was continually spectrophotometrically detected at 235 nm, subtracted from the signal at 270 nm. A single run duration was less than 3.5 min. Method relative standard deviation was <5.0% (n = 6). A calibration range was linear within the range of 0.02–0.30 μg creatinine (R > 0.999), covering 1.0–15.0 mmol/L creatinine in urine. The standard addition method used two different volumes of a single working standard solution for quantification. Results proved the effectiveness of our improvements in the flow manifold, bead injection, and automated quantification. The accuracy of our method was comparable to the routine enzymatic assay of real urine samples in a clinical laboratory.

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.

Spectrophotometric Determination of N-acetyl-L-Cysteine in Pharmaceutical Formulations by Flow Injection and Sequential Injection Analysis: Comparison of the Methods

Spectrophotometric Determination of N-acetyl-L-Cysteine in Pharmaceutical Formulations by Flow Injection and Sequential Injection Analysis: Comparison of the Methods

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.

Demonstration of no catalytical activity of Fe‐N‐C and Nb‐N‐C electrocatalysts toward nitrogen reduction using in‐line quantification

AbstractAmmonia (NH3) production via the electrochemical nitrogen reduction reaction (NRR) is a promising method for sustainable generation of this important chemical. Efforts are ongoing in finding an efficient, stable, and selective catalyst that will enable the reaction. However, progress is hindered in the field due to lack of reproducibility, most likely a consequence of reports of false‐positive results due to improper measurement control and methods. In this study, we explore the NRR activity of a promising class of single atom catalysts, transition metal‐nitrogen‐carbon (M‐N‐C) electrocatalysts. Using a state‐of‐the‐art in‐line ammonia quantification methodology, with detection limit as low as 1 ppb for ammonia, we show that single atom Nb and Fe embedded in a stable carbon and nitrogen framework do not electrochemically reduce N2 to NH3. Critically, this demonstrates that our experimental setup with in‐line sequential injection analysis successfully excludes ammonia contamination from the gas supply and atmospheric sources, allowing for thorough and high‐throughput examination of potential NRR catalysts.

Development of Sequential Injection Analysis for the Determination of Lead in Vegetables

A sequential injection analysis incorporated with spectrophotometric method was developed for determination of lead, based on reaction of dithizone with lead producing pink complex and absorbance of the complex was measured at 515 nm. The analytical parameters of the system were optimized by univariate method such as reagent concentration, fl ow rate of reagent and injection volume. Linear calibration curve over the range of 0.02-0.08 mg L-1 and 0.1-2.0 mg L-1 lead was obtained. The detection limit of lead was 0.012 mg L-1. The relative standard deviations for fi ve replicate injections was 0.77-1.54% for intra-day and 0.86-1.80% for inter-day. The recovery of 98.75-101.20% was achieved with sample throughput of 45 samples per hour. The proposed method has been applied to the determination of lead in vegetable samples. The obtained results were in good agreement with those obtained by the ICP-MS standard method, verifi ed by the student t-test at the 95% confi dence level.

Use of dimethylglyoxime for the spectrophotometric flow-based determination of nickel in natural waters

A spectrophotometric flow-based method for the determination of nickel in recreational waters is proposed. In this scenario, the strategy was to devise a miniaturized and automatic system based on sequential injection analysis, aiming for an expeditious, real-time and low-cost determination. For the spectrophotometric determination, dimethylglyoxime was used as color reagent due to its selectivity for nickel. Considering the expected low concentration and low sensitivity of the coloured reaction, a long pathlength flow cell was used to increase the sensitivity. The potential interference of metal ions commonly present in freshwaters was assessed and no significant differences (<10%) were observed, except for manganese. This interference was overcome by adding manganese to the reagent, thus acting as a fixed interference strategy. The limit of detection and quantification were 6.3 and 21.1 µg L−1, respectively. The method was applied to the quantification of nickel in certified water samples and the results were in agreement with the certified values. Additionally, the method was successfully applied to the quantification of nickel in spiked freshwaters and the results were in agreement with those obtained with the reference method.

An in situ analyzer for long-term monitoring of nitrite in seawater with versatile liquid waveguide capillary cells: Development, optimization and application

An automatic analyzer coupled with a versatile liquid waveguide capillary cell (LWCC) of different lengths for long-term in situ monitoring of nitrite in seawater was developed based on sequential injection analysis and spectrophotometry. Laboratory experiments have been carried out to analyze the impact of system parameters and environmental factors to obtain the optimal in situ detection performance of the analyzer. By utilizing 10 cm and 50 cm LWCCs, the analyzer can detect nitrite ([NO2−]) concentrations from 0.063 to 6.5 μM and 0.025 to 0.5 μM, and reach detection limits of 0.0189 μM and 0.0076 μM respectively. The short optical path (10 cm) analyzer was tested in situ during a scientific research cruise and then deployed at a coastal experiment station for one month to test the analyzer long-term measurement reliability and monitor nitrite temporal variation. The long optical path (50 cm) analyzer was deployed in a low nutrient coral reef waters over 50 days and the CTD, turbidity, dissolved oxygen and chlorophyll a data were synchronously acquired through a multi-parameter probe, and the distinct relationship between the in situ monitoring results was discussed.