The formation of an ion-association complex (IA) between sulfonephthalein dye and basic nitrogen-containing compound in an organic solvent medium has been for the first time used to develop an ...automated SIA method. In highly polar aprotic solvents, the tautomeric equilibrium for such dyes is strongly shifted towards the colorless lactonic form. The addition of a basic nitrogen-containing substance leads to the formation of IA with a highly colored quinonoid form, which is accompanied by an increase in the absorbance of the dye band at approximately 400 nm. Protonation of pyridine nitrogen in loratadine, structure and binding places of IA were shown using quantum-chemical calculations. The very simple, direct and non-extraction spectrophotometric SIA method with high throughput of 43 h−1 was developed based on the formation of IA between loratadine and bromocresol purple in the medium of acetonitrile used both as solvent and carrier. The calibration graph was linear in the concentration range from 1.0 to 20 mg L−1 with correlation coefficient of 0.9992. The developed method was successfully applied to the analysis of pharmaceutical formulations.
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•Interaction of sulfonephthalein dyes and nitrogen-containing compounds.•Shift of tautomeric equilibrium in an organic solvent medium.•Non-extraction spectrophotometric SIA method for loratadine determination.•Loratadine was determined using its ion associate with bromocresol purple.
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•Sequential injection analysis method for Se(IV) /Se(VI) speciation is developed.•Se(IV) is determined by oxidising I3- to I2 which reacts with starch.•Total Se (Se(IV) + Se(VI)) is ...determined after reduction of Se(VI) to Se(IV) with HCl at 75 °C.•The LOD for Se(IV) and Se(VI) are 0.02 mg L-1 and 0.07 mg L-1, respectively.•The method was successfully applied to spiked tap water and mineral 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 multiparametric sequential injection system for the determination of phosphate, nitrite, nitrate, potassium, and iron(III) in a single manifold was developed. The main goal of the proposed method ...was to develop an efficient tool to assess a number of essential chemical compounds in soils, providing the corresponding information on soil fertility and, additionally, information on possible groundwater contamination. The method was applied for the quantification of the aforementioned parameters in simulated leachates produced in laboratory-scale core columns. The relative standard deviations of ten replicate analyses of a standard were: 6% for phosphate; 2% for nitrite; 2% for nitrate; 5% for potassium; and 6% for iron(III). The limits of detection and quantification were: 2.15 and 7.18 μmol/L for phosphate determination; 0.22 and 0.73 μmol/L for nitrite determination; 3.42 and 8.00 μmol/L for nitrate determination; 39 μmol/L (limit of detection) for potassium determination; and 0.46 and 1.85 μmol/L for iron(III) determination. The sequential injection system was successfully applied for the quantification of multiple soil chemical components (PO43−, NO2−, NO3−, K+, and Fe3+) in soil leachates. The analysis of a sample, involving all the analytes, has a duration of 28 min.
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•Design of a multiparametric flow-based system for soil analysis.•Real-time assessment of soil fertility.•Miniaturized and automatic tool for soil nutrients monitoring in a single manifold.•Easy to adapt to a specific analyte/s or to all the analyte’s quantification.•Successful application to agricultural soil leachates.
One of the most used methods to measure antioxidant capacity in food is the ferric reducing antioxidant power (FRAP) test, which is simple, sensitive, and economical, nevertheless has long analysis ...times, causing measurement errors due to the instability of the FRAP reagent due to its precipitation sequential injection analysis (SIA) is a flow technique that can correct these disadvantages because it is more quickly. So, a novel FRAP-SIA method was developed to evaluate the antioxidant capacity. The system was optimized using a central composite design for hydrodynamic and chemical factors, resulting in a flow rate of 35 μL s−1, and aspirate volumes of 33 μL–38 μL–33 μL for the sequence (FRAP-Antioxidant-FRAP). FRAP reagent was prepared with an HCl solution at 0.005 mol L−1, improving its stability 24 times, concerning when it is in acetate buffer at pH 3.6. The method showed excellent accuracy (RSD <3%) with a LOD of 1.0 μmol L−1 of Trolox for a linear range of 5–120 μmol L−1. The reaction time was diminished by 96% concerning the FRAP-microplate assay (from 30 min to 1.2 min). The method was applied in beverages and extracts, obtaining recovery values ranging from 91.24 to 114.22%.
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•A completely novel FRAP-SIA method was developed to determine antioxidant capacity.•The stability of the FRAP reagent was improved up to 24 times.•The reaction time was reduced from 30 min to 1.2 min by the developed SIA method.•The results of antioxidant capacity were comparable with those by reference method.•The FRAP-SIA method substantially improved precision (<3%).
A combination of sequential Injection Analysis (SIA) system and the ion-selective electrode (ISE) detector is considered to be one of a very effective analytical method. Reaction of lactate with ...lactate oxidase produces pyruvic acid and hydrogen peroxide. When the produced hydrogen peroxide is reacted with 4-aminoantipyrine (4-AAP) and 4-fluorophenol (4-FP) in the presence of horseradish peroxidase (HRP), F− ion is produced. The concentration of lactate can be indirectly determined by measuring the F− ion by F− ISE. Based on this principle of detection of lactate, a new measurement method of lactate using an SIA with ISE detector was developed.
The use of saliva for diagnose and surveillance of systemic illnesses, and general health has been arousing great interest worldwide, emerging as a highly desirable goal in healthcare. The collection ...is non-invasive, stress-free, inexpensive, and simple representing a major asset. Glucose, calcium, and magnesium concentration are three major parameters evaluated in clinical context due to their essential role in a wide range of biochemical reactions, and consequently many health disorders. In this work, a spectrophotometric sequential injection method is described for the fast screening of glucose, calcium, and magnesium in saliva samples. The glucose determination reaction involves the oxidation of the aldehyde functional group present in glucose with simultaneous reduction of 3,5-dinitrosalicylic acid (DNS) to 3-amino, 5-nitrosalicylic acid under alkaline conditions, followed by the development of colour. The determination of both metals is based on their reaction with cresolphtalein complexone (CPC), and the interference of calcium in the magnesium determination minimized by ethylene glycol-bisβ-aminoethyl ether-N,N,N′,N′-tetraacetic acid (EGTA). The developed multi-parametric method enabled dynamic ranges of 50 – 300 mg/dL for glucose, 0.1 − 2 mg/dL for calcium, and 0.1 − 0.5 mg/dL for magnesium. Determination rates of 28, 60, 52 h−1 were achieved for glucose, calcium, and magnesium, respectively. Less than 300 µL of saliva is required for the multi-parametric determination due to saliva viscosity and inherent necessity of dilution prior to analysis. RSDs lower than 5% were obtained, and the results agreed with those obtained by reference methods, while recovery tests confirmed its accuracy.
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•SI method for simultaneous determination of glucose, calcium and magnesium in saliva.•Direct glucose assessment with in line glucose digestion prior to determination.•Normalisation of saliva variability by including calcium and magnesium determination.•Application of the multi-parametric SI method to saliva samples (accuracy validation).
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.
•An in situ analyzer with a versatile liquid waveguide capillary cell module was developed to detect nutrients in seawater.•By utilizing 50 cm LWCC, the analyzer can detect nitrite from 0.025 to 0.5 μM and reach a detection limit of 7.6 nM.•Two long-term in situ deployments were completed with the autonomous nitrite analyzers in different environments.
The increase in anthropogenic CO2 concentrations in the Earth's atmosphere since the industrial revolution has resulted in an increased uptake of CO2 by the oceans, leading to ocean acidification. ...Dissolved Inorganic Carbon (DIC) is one of the key variables to characterize the seawater carbonate system. High quality DIC observations at a high spatial-temporal resolution is required to improve our understanding of the marine carbonate system. To meet the requirements, autonomous DIC analyzers are needed which offer a high sampling frequency, are cost-effective and have a low reagent and power consumption.
We present the development and validation of a novel analyzer for autonomous measurements of DIC in seawater using conductometric detection. The analyzer employs a gas diffusion sequential injection approach in a “Tube In A Tube” configuration that facilitates diffusion of gaseous CO2 from an acidified sample through a gas permeable membrane into a stream of an alkaline solution. The change in conductivity in the alkaline medium is proportional to the DIC concentration of the sample and is measured using a detection cell constructed of 4 hollow brass electrodes. Physical and chemical optimizations of the analyzer yielded a sampling frequency of 4 samples h−1 using sub mL reagent volumes for each measurement. Temperature and salinity effects on DIC measurements were mathematically corrected to increase accuracy. Analytical precision of ±4.9 μmol kg−1 and ±9.7 μmol kg−1 were achieved from measurements of a DIC reference material in the laboratory and during a field deployment in the southwest Baltic Sea, respectively.
This study describes a simple, cost-effective, autonomous, on-site benchtop DIC analyzer capable of measuring DIC in seawater at a high temporal resolution as a step towards an underwater DIC sensor. The analyzer is able to measure a wide range of DIC concentrations in both fresh and marine waters. The achieved accuracy and precision offer an excellent opportunity to employ the analyzer for ocean acidification studies and CO2 leakage detection in the context of Carbon Capture and Storage operations.
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•Development of an autonomous DIC analyzer based on Conductometric technique using a cell with 4 hollow brass electrodes.•CO2 extraction from seawater using a gas diffusion cell with a “Tube In A Tube” configuration and a gas permeable membrane.•Formulation of mathematical temperature and salinity correction to determine accurate DIC concentration.•Demonstration of the analyzer performance in the southwest Baltic Sea.
Synthetic cathinones are a class of new psychoactive substances (NPS), an emerging group of analogues to traditional illicit drugs which are functionalized to circumvent legal regulations. The ...analytical investigation of NPS by traditional methods, such as gas chromatography-mass spectrometry (GC-MS), is challenging because newly emerging NPS may not yet appear in spectral libraries and because of the inability to determine certain positional isomers. Low-field or “benchtop” proton nuclear magnetic resonance spectroscopy (NMR) is an alternative that provides significant qualitative information but is particularly susceptible to matrix interferences. To this end, the development of a Sequential Injection Analysis (SIA) method which uses solid-phase extraction (SPE) to remove interfering matrix components prior to NMR determination is described. Factors including the type of SPE sorbent, column dimensions, and sample loading and elution conditions were examined. Several cathinone simulants (primary, secondary, and tertiary amines), “DEA exempt” cathinone standards, as well as authentic case samples were studied. The selectivity of the SIA-NMR-UV method was investigated against a broad range of “cutting agents” and was found to successfully remove all compounds tested with the exception of other basic drugs (e.g., acetaminophen). The limit of detection and reproducibility of the method were optimized using a Plackett-Burman screening design and Sequential Simplex optimization. Using a UV detector for dual (in series) quantification, the multivariate-optimized method produced a method limit of detection (3σ) for the cathinone simulant Phenylpropanolamine (PPA) of 23 μmol L−1, and a calibration model, in terms of UV peak area, of Area = 0.19 PPA, mmol L−1 – 0.04. The optimized method generated ~2 mL of waste per day, and had a footprint of ~1 m2 Finally, the multivariate-optimized SIA-NMR-UV method was successfully applied to several more case samples and the cathinones were definitively identified.
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•Sequential Injection Analysis (SIA) was successfully hyphenated to benchtop proton NMR.•An on-line solid-phase extraction (SPE) method was developed for cathinone isolation.•Method selectivity using a broad range of interferences was investigated.•Authentic forensic case samples were studied and cathinones were definitively determined.•Multivariate optimization was performed to improve the method selectivity and sensitivity.
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