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Analytica Chimica Acta (v.668, #1)
Downscaling a multicommuted flow injection analysis system for the photometric determination of iodate in table salt by Sivanildo S. Borges; Jailson de Souza Peixoto; Mário A. Feres; Boaventura F. Reis (pp. 3-7).
In this work a downscaled multicommuted flow injection analysis setup for photometric determination is described. The setup consists of a flow system module and a LED based photometer, with a total internal volume of about 170μL. The system was tested by developing an analytical procedure for the photometric determination of iodate in table salt using N,N-diethyl-henylenediamine (DPD) as the chromogenic reagent. Accuracy was accessed by applying the paired t-test between results obtained using the proposed procedure and a reference method, and no significant difference at the 95% confidence level was observed. Other profitable features, such as a low reagent consumption of 7.3μg DPD per determination; a linear response ranging from 0.1 up to 3.0m IO3−, a relative standard deviation of 0.9% ( n=11) for samples containing 0.5m IO3−, a detection limit of 17μgL−1IO3−, a sampling throughput of 117 determination per hour, and a waste generation 600μL per determination, were also achieved.
Keywords: Multicommuted flow analysis; Spectrophotometry; Green chemistry; Iodate; Downsized flow system
New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique by J. Kozak; J. Gutowski; M. Kozak; M. Wieczorek; P. Kościelniak (pp. 8-12).
The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ=530nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 22 factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1–3.0 and 0.9–3.5mgL−1 of both analytes, respectively.
Keywords: Flow injection analysis; Two-component analysis; Simultaneous determination of Fe(II) and Fe(III)
Fructose-selective calorimetric biosensor in flow injection analysis by Sunil G. Bhand; Srimathi Soundararajan; Ioana Surugiu-Wärnmark; Jaqueline Simona Milea; Estera Szwajcer Dey; Maria Yakovleva; Bengt Danielsson (pp. 13-18).
A highly selective, interference free biosensor for the measurement of fructose in real syrup samples was developed. The assay is based on the phosphorylation ofd(−)fructose to fructose-6-phosphate by hexokinase and subsequent conversion of fructose-6-phosphate to fructose-1,6-biphosphate by fructose-6-phosphate-kinase. The heat liberated in the second reaction is monitored using an enzyme thermistor. The major advantages of this biosensor are rapid and selective measurement of fructose without the need to eliminate glucose and inexpensive FIA-based, mediator-free calorimetric measurement suitable for regular fructose analysis. This method was optimised for parameters, such as pH, ionic strength, interference, operational stability and shelf life. Good and reproducible linearity (0.5–6.0mM) with a detection limit of 0.12mM was obtained. Fructose determination in commercial syrup samples and spiked samples confirmed the reliability of this set-up and technique. The biosensor gave reproducible results with good overall stability for continuous measurements over a period of three months besides a useful shelf life of six months. The method could be used for routine fructose monitoring in food samples.
Keywords: Abbreviations; DF; d; (−)fructose; DG; d; (+)glucose; FIA; Flow injection analysis; DF6P; d; (−) fructose-6-phosphate; F6PK; fructose-6-phosphate-kinase; HK; hexokinase; ET; enzyme thermistor; G6P; glucose-6-phosphate; PGI; phosphoglucoisomerase; CPG; controlled pore glassd; -fructose; Fructose-6-phosphate-kinase; Hexokinase; Enzyme thermistor; Immobilised enzymes; Flow injection analysis
Flow injection chemiluminescence determination of the total phenolics levels in plant-derived beverages using soluble manganese(IV) by Edyta Nalewajko-Sieliwoniuk; Iwona Tarasewicz; Anatol Kojło (pp. 19-25).
This study established a flow injection (FI) methodology for the determination of the total phenolic content in plant-derived beverages based on soluble manganese(IV) chemiluminescence (CL) detection. It was found that mixing polyphenols with acidic soluble manganese(IV) in the presence of formaldehyde evoked chemiluminescence. Based on this finding, a new FI-CL method was developed for the estimation of the total content of phenolic compounds (expressed as milligrams of gallic acid equivalent per litre of drink) in a variety of wine, tea and fruit juice samples. The proposed method is sensitive with a detection limit of 0.02ngmL−1 (gallic acid), offers a wide linear dynamic range (0.5–400ngmL−1) and high sample throughput (247samplesh−1). The relative standard deviation for 15 measurements was 3.8% for 2ngmL−1 and 0.45% for 10ngmL−1 of gallic acid. Analysis of 36 different samples showed that the results obtained by the proposed FI-CL method correlate highly with those obtained by spectrophotometric methods commonly used for the evaluation of the total phenolic/antioxidant level. However, the FI-CL method was found to be far simpler, more rapid and selective, with almost no interference from non-phenolic components of the samples examined.
Keywords: Polyphenols; Antioxidants; Food analysis; Soluble manganese(IV) chemiluminescence; Flow injection analysis
Computer controlled-flow injection potentiometric system based on virtual instrumentation for the monitoring of metal-biosorption processes by A. Florido; C. Valderrama; S. Nualart; L. Velazco-Molina; O. Arias de Fuentes; M. del Valle (pp. 26-34).
A completely automated flow-injection system was developed for the monitoring of biosorption studies of Cu(II) ion on vegetable waste by-products. The system employed flow-through Cu(II)-selective electrodes, of epoxy-resin-CuS/Ag2S heterogeneous crystalline type, and computer controlled pumps and valves for the flow operation. Computer automation was done through a specially devised virtual instrument, which commanded and periodically calibrated the system, allowing for the monitoring of Cu(II) ions between 0.6 and 6530mgL−1 at a typical frequency of 15h−1. Grape stalk wastes were used as biosorbent to remove Cu(II) ions in a fixed-bed column with a sorption capacity of 5.46mgg−1, obtained by the developed flow system, while the reference determination performed by FAAS technique supplied a comparable value of 5.41mgg−1.
Keywords: Grape stalk wastes; Copper sorption; Virtual instrument; Ion-selective electrode; Flow-injection potentiometry; On-line monitoring
Development of a sequential injection dispersive liquid–liquid microextraction system for electrothermal atomic absorption spectrometry by using a hydrophobic sorbent material: Determination of lead and cadmium in natural waters by Aristidis N. Anthemidis; Kallirroy-Ioanna G. Ioannou (pp. 35-40).
A novel on-line sequential injection (SI) dispersive liquid–liquid microextraction (DLLME) system coupled to electrothermal atomic absorption spectrometry (ETAAS) was developed for metal preconcentration in micro-scale, eliminating the laborious and time consuming procedure of phase separation with centrifugation. The potentials of the system were demonstrated for trace lead and cadmium determination in water samples. An appropriate disperser solution which contains the extraction solvent (xylene) and the chelating agent (ammonium pyrrolidine dithiocarbamate) in methanol is mixed on-line with the sample solution (aqueous phase), resulting thus, a cloudy solution, which is consisted of fine droplets of xylene, dispersed throughout the aqueous phase. Three procedures are taking place simultaneously: cloudy solution creation, analyte complex formation and extraction from aqueous phase into the fine droplets of xylene. Subsequently the droplets were retained on the hydrophobic surface of PTFE-turnings into the column. A part of 30μL of the eluent (methyl isobutyl ketone) was injected into furnace graphite for analyte atomization and quantification. The sampling frequency was 10h−1, and the obtained enrichment factor was 80 for lead and 34 for cadmium. The detection limit was 10ngL−1 and 2ngL−1, while the precision expressed as relative standard deviation (RSD) was 3.8% (at 0.5μgL−1) and 4.1% (at 0.03μgL−1) for lead and cadmium respectively. The proposed method was evaluated by analyzing certified reference materials and was applied to the analysis of natural waters.
Keywords: Sequential injection; Dispersive liquid–liquid microextraction; Atomic spectrometry; Cadmium; Lead
A thionine-based reversible redox sensor in a sequential injection system by Marieta L.C. Passos; M. Lúcia M.F.S. Saraiva; José L.F.C. Lima (pp. 41-46).
According to the current demands of Green Analytical Chemistry and regarding the need for lower reagent consumption with improved analytical performance, an automatic methodology with a flow-through optosensor incorporating solid-phase spectrophotometric detection was developed. The sensor used in this work was based on the redox state of thionine whose oxidized form is blue and reduced form is colorless with monitoring carried out at 621nm. This redox indicator was immobilized on gel beads and subsequently packed into a flow-through cell. It was then assembled into a sequential injection system and was shown to be an excellent alternative to monitor enzymatic redox reactions automatically as the redox catalysis is performed by glucose dehydrogenase. This enzyme is a representative dehydrogenase enzyme and uses NAD+ as cofactor, promoting the oxidation of glucose to glucono-lactone and reduction of NAD+ to NADH. The produced NADH promotes color depletion on the surface of the sensor. The calibration graph for glucose was linear between 5.74×10−4 and 2.00×10−3molL−1 and detection limit was 1.72×10−4molL−1. Glucose concentration in different samples including sera, salines, perfusion solutions, powder for preparing oral solutions and solutions for hemodialysis was determined. The method proved to be reproducible with a RSD<5% for glucose determinations.
Keywords: Sequential injection analysis; Glucose; Glucose dehydrogenase; Redox sensor; Immobilized thionine; Solid-phase spectrophotometry
A reagent-free SIA module for monitoring of sugar, color and dissolved CO2 content in soft drinks by S. Teerasong; S. Chan-Eam; K. Sereenonchai; N. Amornthammarong; N. Ratanawimarnwong; D. Nacapricha (pp. 47-53).
This work presents a new sequential injection analysis (SIA) method and a module for simultaneous and real-time monitoring of three key parameters for the beverage industry, i.e., the sugar content (measured in Brix), color and dissolved CO2. Detection of the light reflection at the liquid interface (the schlieren effect) of sucrose and water was utilized for sucrose content measurement. A near infrared LED (890±40nm) was chosen as the light source to ensure that all the ingredients and dyes in soft drinks will not interfere by contributing light absorption. A linear calibration was obtained for sucrose over a wide concentration range (3.1–46.5Brix). The same module can be used to monitor the color of the soft drink as well as the dissolved CO2 during production. For measuring the color, the sample is segmented between air plugs to avoid dispersion. An RGB-LED was chosen as the light source in order to make this module applicable to a wide range of colored samples. The module also has a section where dissolved CO2 is measured via vaporization of the gas from the liquid phase. Dissolved CO2, in a flowing acceptor stream of water resulting in the change of the acceptor conductivity, is detected using an in-house capacitively coupled contactless conductivity detector (C4D). The module includes a vaporization unit that is also used to degas the carbonated drink, prior the measurements of sucrose and color within the same system. The method requires no chemicals and is therefore completely friendly to the environment.
Keywords: Sucrose content; Dissolved CO; 2; Schlieren effect; Membraneless; Soft drink; Sequential injection analysis
Determination of trace heavy metals in herbs by sequential injection analysis-anodic stripping voltammetry using screen-printed carbon nanotubes electrodes by Uthaitip Injang; Peeyanun Noyrod; Weena Siangproh; Wijitar Dungchai; Shoji Motomizu; Orawon Chailapakul (pp. 54-60).
A method for the simultaneous determination of Pb(II), Cd(II), and Zn(II) at low μgL−1 concentration levels by sequential injection analysis-anodic stripping voltammetry (SIA-ASV) using screen-printed carbon nanotubes electrodes (SPCNTE) was developed. A bismuth film was prepared by in situ plating of bismuth on the screen-printed carbon nanotubes electrode. Operational parameters such as ratio of carbon nanotubes to carbon ink, bismuth concentration, deposition time and flow rate during preconcentration step were optimized. Under the optimal conditions, the linear ranges were found to be 2–100μgL−1 for Pb(II) and Cd(II), and 12–100μgL−1 for Zn(II). The limits of detection ( Sbl/ S=3) were 0.2μgL−1 for Pb(II), 0.8μgL−1 for Cd(II) and 11μgL−1 for Zn(II). The measurement frequency was found to be 10–15stripping cycleh−1. The present method offers high sensitivity and high throughput for on-line monitoring of trace heavy metals. The practical utility of our method was also demonstrated with the determination of Pb(II), Cd(II), and Zn(II) by spiking procedure in herb samples. Our methodology produced results that were correlated with ICP-AES data. Therefore, we propose a method that can be used for the automatic and sensitive evaluation of heavy metals contaminated in herb items.
Keywords: Heavy metals; Sequential injection analysis; Anodic stripping voltammetry; Carbon nanotubes electrodes
Two-column Sequential Injection Chromatography—New approach for fast and effective analysis and its comparison with gradient elution chromatography by Petr Chocholouš; Dalibor Šatínský; Hana Sklenářová; Petr Solich (pp. 61-66).
This work presents novel approach in low-pressure chromatography flow systems—two-column Sequential Injection Chromatography (2-C SIC) and its comparison with gradient elution chromatography on the same instrument. The system was equipped with two different chromatographic columns (connected to selection valve in parallel design) for isocratic separation and determination of all components in composed anti-inflammatory pharmaceutical preparation (tablets). The sample was first injected on the first column of length 30mm where less retained analytes were separated and then the sample was injected on the second column of length 10mm where more retained analytes were separated. The SIC system was based on a commercial SIChrom™ manifold (8-port high-pressure selection valve and medium-pressure syringe pump with 4mL reservoir) (FIAlab®, USA) with two commercially available monolithic columns the “first column” Chromolith® Flash RP-18e (25mm×4.6mm i.d. with guard column 5mm×4.6mm i.d.) and the “second column” Chromolith® RP-18e (10mm×4.6mm i.d.) and CCD UV–vis detector USB 4000 with micro-volume 1.0cm Z flow cell. Two mobile phases were used for analysis (one for each column). The mobile phase 1 used for elution of paracetamol, caffeine and salicylic acid (internal standard) was acetonitrile/water (10:90, v/v, the water part of pH 3.5 adjusted with acetic acid), flow rate was 0.9mLmin−1 (volume 3.0mL of mobile phase per analysis). The mobile phase 2 used for elution of propyphenazone was acetonitrile/water (30:70, v/v); flow rate was 1.2mLmin−1 (volume 1.5mL of mobile phase per analysis). Absorbance was monitored at 210nm. Samples were prepared by dissolving of one tablet in 30% acetonitrile and 10μL of filtered supernatant was injected on each column (2×10μL). The chromatographic resolution between all compounds was >1.45 and analysis time was 5.5min under the optimal conditions. Limits of detection were determined at 0.4μgmL−1 for paracetamol, at 0.5μgmL−1 for caffeine and at 0.7μgmL−1 for propyphenazone. The new two-column chromatographic set-up developed as an alternative approach to gradient elution chromatography shows evident advantages (time and solvent reduction more than one-third) as compared with single-column gradient SIC method with Chromolith® Flash RP-18 (25mm×4.6mm i.d. with guard column 5mm×4.6mm i.d.).
Keywords: Sequential injection chromatography; Two-column chromatography; Monolithic column; Paracetamol; Caffeine; Propyphenazone
Automated determination of diazepam in spiked alcoholic beverages associated with drug-facilitated crimes by David S.M. Ribeiro; João A.V. Prior; João L.M. Santos; José L.F.C. Lima (pp. 67-73).
In this work, a multipumping flow system (MPFS) coupled to a photodegradation unit was developed, for the first time, for the determination of diazepam (a benzodiazepine) in spiked alcoholic beverages by fluorimetry. The main features of MPFS such as, high portability, versatility and straightforward automation and control combined with the efficiency and simplicity of photodegradation and the selectivity and sensitivity of fluorimetric detection makes the developed analytical methodology an attractive tool and a valuable contribution for the prevention of drug-facilitated crimes (DFC). Drug-facilitated crimes involve the unauthorized administration of strong central nervous system depressant drugs, which have the capability of preventing victims from resist to the action of the perpetrator or fighting off. Most often, the drugs identified as being used in DFC are surreptitiously placed in drinks served to potential victims in entertainment places, like night clubs.Five commercial alcoholic beverages (Eristoff®, Smirnoff®, Bacardi®, Dry Gin® and Brazilian Cachaça 51®) spiked with diazepam were analyzed by the proposed methodology, and the results revealed good agreement with those obtained through a HPLC comparison procedure. Relative deviations comprised between −1.97 and 2.05% were achieved, and additionally, the application of a paired t-test, revealed the absence of any statistical difference for a confidence level of 95% ( n=5). The detection limit was approximately 2.02mgL−1.
Keywords: Drug-facilitated crimes; Benzodiazepines; Multipumping; Drink spiking; Photodegradation
On-line analysis of volatile fatty acids in anaerobic treatment processes by Edwin Palacio-Barco; Fabien Robert-Peillard; Jean-Luc Boudenne; Bruno Coulomb (pp. 74-79).
In this paper, an on-line spectrofluorimetric system is proposed for a simple, rapid and accurate measurement of volatile fatty acids (VFA) in anaerobic treatment processes. The determination method is based on the derivatization of VFA with N-(1-naphthyl)ethylenediamine (EDAN) followed by a spectrofluorimetric detection of the corresponding amide. The analytical procedure is automated with a flow analysis technique, coupling multisyringe (MSFIA) and multi-pumping (MPFS) methods. Operative conditions have been investigated with a special attention paid to the activation and amidation steps and to the liquid–liquid extraction of the derivatized final product. Fluorescence intensities ( λem=335nm, λex=395nm) were found to be proportional to the concentration of VFA, expressed as acetic equivalent, in the range 19–1000mgL−1, with a detection limit (3σ) of 5.1mgL−1. Our results showed a good selectivity for VFA as compared to other organic and inorganic compounds usually found in sewage sludges. Validation of the on-line system developed has been assessed by application of the procedure to aqueous samples originating from sewage sludge treatment plants. The results were in good agreement with ion chromatography measurements.
Keywords: Multisyringe flow injection analysis; Multi-pumping flow analysis; Volatile fatty acids; Fluorimetry; Anaerobic digestion; Process control
A study of glycoprotein–lectin interactions using quartz crystal microbalance by Maria E. Yakovleva; Gulnara R. Safina; Bengt Danielsson (pp. 80-85).
A study of biospecific interactions between lectins and glycoproteins using a quartz crystal microbalance biosensor with dissipation monitoring (QCM-D) was reported. Four lectins were covalently immobilised on the thiol-modified gold electrode of the QCM chips in order to obtain sensing surfaces. The frequency shift served as analytical signal and the dissipation shift provided additional information about the viscoelastic properties of the glycoprotein–lectin complex formed on the surface of the QCM chip. The working conditions of the assay were optimised. The interaction between different lectins and glycoproteins was characterised by specific frequency shifts and each glycoprotein displayed its own unique lectin-binding pattern. This lectin pattern can serve as a finger print for the discrimination between various glycoproteins. The biosensor enabled quantitative determination of glycoproteins in the concentration range of 50μgmL−1 to 1mgmL−1 with good linearity and R.S.D. of less than 6.0%. An additional advantage of the proposed biosensor was the possibility to re-use the same lectin surfaces during a long period of time (2 month) without changes in analytical response. This was experimentally achieved by the application of a proper regeneration solution (10mM glycine–HCl, pH 2.5). The lectin-based quartz crystal microbalance technique is suitable both for rapid screening and for quantitative assay of serum glycoproteins.
Keywords: Biosensor; Flow-injection analysis; Quartz crystal microbalance; Glycoprotein; Lectin panel