Sequential Injection Analysis System Research Articles

Development of a sequential injection analysis system for the potentiometric determination of nitrite in meat products by using a Gran’s plot method

This article describes a potentiometric multi-task flow system, based on the sequential injection analysis (SIA) concept, developed to quantify the nitrite contained in cured meat products. The manifold includes a mixing chamber to provide the automatic on-line generation of the solutions required for the multiple standard additions method, adopted as potentiometric analytical technique of measurement. The assessment of nitrite concentration was accomplished by using the Gran’s plot approach. A 0.16 mol L−1 silver sulphate solution, prepared in ammonia hydroxide, was used to remove the salt present in the samples since chloride ion is one of the most important interfering agents of the nitrite selective electrode. The procedure, when applied to different types of meat samples, showed relative standard deviations better than 3% with a sampling rate of 20 samples h−1. The results obtained statistically agreed with those obtained by application of a modification of the well-known Griess spectrophotometric method adopted as a reference technique.

Determination of (+)-3,3′,5,5′-Tetraiodo-L-thyronine (L-T4) in Serum and Pharmaceutical Formulations using a Sequential Injection Analysis/Immunosensor System

A sequential injection analysis/immunosensor system is proposed for the analysis of thyroxine (L-T4) in serum and in pharmaceutical formulations with a rate of 75 samples/hour. The immunosensor design is based on the physical immobilization of anti-L-T4 in carbon paste. The working concentration range of the immunosensor in the sequential injection analysis system is between 36 and 1080 ng/mL with a limit of detection of 24.6 ng/mL. The system is very reliable and very easy to design and operate.

Applying sequential injection analysis (SIA) and response surface methodology for optimization of Fenton-based processes

This work presents the use of sequential injection analysis (SIA) and the response surface methodology as a tool for optimization of Fenton-based processes. Alizarin red S dye (C.I. 58005) was used as a model compound for the anthraquinones family, whose pigments have a large use in coatings industry. The following factors were considered: [H 2O 2]:[Alizarin] and [H 2O 2]:[FeSO 4] ratios and pH. The SIA system was designed to add reagents to the reactor and to perform on-line sampling of the reaction medium, sending the samples to a flow-through spectrophotometer for monitoring the color reduction of the dye. The proposed system fed the statistical program with degradation data for fast construction of response surface plots. After optimization, 99.7% of the dye was degraded and the TOC content was reduced to 35% of the original value. Low reagents consumption and high sampling throughput were the remarkable features of the SIA system.

Determination of pesticides fenoxycarb and permethrin by sequential injection chromatography using miniaturized monolithic column

Sequential injection chromatography system equipped with miniaturized 10 mm monolithic column was used for fast simultaneous determination of two pesticides—fenoxycarb (FC) and permethrin (PM). The system was composed of a commercial sequential injection analysis (SIA) system (FIAlab ® 3000, 6-port selection valve and 5.0 mL syringe pump), commercially available column Chromolith™ RP-18e (10 mm × 4.6 mm i.d.) (Merck ®, Germany) and CCD UV–vis detector (USB 2000, Ocean-optics) with 1.0 cm Z-flow cell, absorbance was monitored at 225 nm. The mobile phase used for analysis was acetonitrile/water (60:40, v/v), flow rates were 0.6 mL min −1 for elution of fenoxycarb and 1.2 mL min −1 for elution of permethrin. For each analysis 4.8 mL of mobile phase was used. The chromatographic resolution between both compounds was >8 and analysis time was <6.5 min under the optimal conditions. Limits of detection were determined at 2.0 μg mL −1 for fenoxycarb and 1.0 μg mL −1 for permethrin. Samples were prepared by diluting with mobile phase and injected volume was 10 μL for each analysis. Developed method was applied to analysis of both pesticides in veterinary pharmaceutical foams and sprays ARPALIT ® Neo (Aveflor, Czech Republic). SIC method was compared with validated method (HPLC, reverse phase 100 mm monolithic column, gradient elution).

Sequential Injection Analysis utilizing Amperometric Biosensors as Detectors for the Simultaneous Determination of L- and D-Pipecolic Acid

Enantioanalysis of biomedical substances is very important for clinical analysis because the L- and D-enantiomers of the same chiral compound may be markers for different illnesses. A sequential injection analysis (SIA) system using amperometric biosensors as detectors is proposed for the simultaneous determination of L- and D-pipecolic acid (PA). The amperometric biosensors were based on L-amino acid oxidase (L-AAOD) or/and horseradish peroxidase (HRP) for the assay of L-PA and D-amino acid oxidase (D-AAOD) and/or HRP for the assay of D-PA. The linear concentration ranges are of pmol/L to nmol/L magnitude order, with very low limits of detection. The SIA/biosensors system can be used reliably on-line for the simultaneous assay of L- and D-PA from serum samples, with a frequency of 34 samples per hour.

Enzymatic Microreactors for the Determination of Ethanol by an Automatic Sequential Injection Analysis System

Enzymatic Microreactors for the Determination of Ethanol by an Automatic Sequential Injection Analysis System

Sequential injection analysis as a tool for implementation of enzymatic assays in ionic liquids

An approach based on the use of water/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) mixtures in a sequential injection analysis (SIA) system is presented. The rapid and robust procedure developed was used to evaluate horseradish peroxidase activity in [bmim][BF4] and is intended to be a generic tool for enzymatic assays in ionic liquids. The horseradish peroxidase activity tests were based on the implementation of the 4-aminoantipyrine (4AAP)/phenol test in the SIA system, using 1-naphtol as substrate. Small volumes (12 μL) of sample, reagents and enzyme were sequentially aspirated to the holding coil before being sent to the spectrophotometric detector ( λ = 510 nm), where a coloured product proportional to the enzyme activity was measured. The results were compared to those obtained when the assay was performed in water/methanol mixtures under the same conditions, to evaluate [bmim][BF4] as an alternative to conventional organic solvents. Comparative evaluation of the enzyme behaviour revealed that the enzyme activity increased significantly when the assay was performed in water/[bmim][BF4] mixtures. The SIA methodology exhibited good repeatability over the full concentration range (R.S.D. < 3.3%, n = 15) studied, produced approximately 1.7 mL of effluent and consumed approximately 36 μL of solutions prepared in water/[bmim][BF4] mixtures for each analytical cycle.

Integrated Biosensor Systems for Ethanol Analysis

Different integrated systems with a bi-enzymatic biosensor, working with two different methods for ethanol detection--flow injection analysis (FIA) or sequential injection analysis (SIA)--were developed and applied for ethanol extracted from gasohol mixtures, as well as for samples of alcoholic beverages and fermentation medium. A detection range of 0.05-1.5 g ethanol/l, with a correlation coefficient of 0.9909, has been reached when using FIA system, working with only one microreactor packed with immobilized alcohol oxidase and injecting free horseradish peroxidase. When using both enzymes, immobilized separately in two microreactors, the detection ranges obtained varied from 0.001 to 0.066 g ethanol/l, without on-line dilution to 0.010-0.047 g ethanol/l when a 1:7,000 dilution ratio was employed, reaching correlation coefficients of 0.9897 and 0.9992, respectively. For the integrated biosensor SIA system with the stop-flow technique, the linear range was 0.005-0.04 g/l, with a correlation coefficient of 0.9922.

Development of an automated DNA purification module using a micro-fabricated pillar chip

We present a fully automated DNA purification module comprised of a micro-fabricated chip and sequential injection analysis system that is designed for use within autonomous instruments that continuously monitor the environment for the presence of biological threat agents. The chip has an elliptical flow channel containing a bed (3.5 x 3.5 mm) of silica-coated pillars with height, width and center-to-center spacing of 200, 15, and 30 microm, respectively, which provides a relatively large surface area (ca. 3 cm(2)) for DNA capture in the presence of chaotropic agents. We have characterized the effect of various fluidic parameters on extraction performance, including sample input volume, capture flow rate, and elution volume. The flow-through design made the pillar chip completely reusable; carryover was eliminated by flushing lines with sodium hypochlorite and deionized water between assays. A mass balance was conducted to determine the fate of input DNA not recovered in the eluent. The device was capable of purifying and recovering Bacillus anthracis genomic DNA (input masses from 0.32 to 320 pg) from spiked environmental aerosol samples, for subsequent analysis using polymerase chain reaction-based assays.

DPPH Radical Scavenging Activity of Several Naturally Occurring Coumarins and Their Synthesized Analogs Measured by the SIA Method

ABSTRACTCoumarins, naturally occurring compounds derived from benzopyran, have recently been studied extensively for their antioxidant properties. A lot of coumarins have been isolated and identified from natural sources and many others have been synthesized. It is also known that pharmacological and biochemical properties and thus also therapeutic application of simple coumarins depend upon the pattern of their substitution.As a part of studies of biological effects, four naturally occurring coumarins and 18 synthesized analogs of several compounds were assayed for 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) scavenging activity. For this purpose the highly reliable DPPH test modified to be performed by sequential injection analysis (SIA) system was used. This in our laboratory-developed method was originally proposed for antioxidant screening of large series of plant extracts. In this assay, the DPPH test using the SIA method was used for fast and sensitive evaluation of EC50 of coumarins. The evaluation of EC50 of a single compound takes only 15 to 30 min. The structure-activity relationships of tested compounds are also established. The results verified 7,8-dihydroxy-4-methylcoumarins as excellent DPPH radical scavengers. Obtained results correspond with those of other studies and suggest the SIA procedure as a suitable method for fast and sensitive antioxidant analysis of various types of compounds.

Determination of metoprolol, acebutolol and propranolol in pharmaceutical formulations using the same SIA system

A mechanized system for the determination of beta-blockers in pharmaceutical formulations is presented. Using the Sequential Injection Analysis (SIA) technique it was achieved a simple, economical and versatile methodology adaptable to any pharmaceutical control involving these substances. It does not require any pre-treatment for the samples, as they must only be dissolved in acid before analysis. Linear calibration plots were obtained for metoprolol (40.52 - 250 mg L-1), acebutolol (32.85 - 140 mg L-1) and propranolol (16.58 - 120 mg L-1). A R.S.D. lower than 5% was attained. The methodology was used in tablets, injections and prolonged-release capsules. Common excipients used in pharmaceuticals do not interfere. Statistical comparison of the results obtained with the proposed methodology and with the official methods showed good agreement (95% confidence level). SIA system produces only 2.50 mL of effluents per determination whereas the reference methodologies consume around 140 mL.

Use of pulse transient response as input information for an automated SIA electronic tongue

An electronic tongue (ET) employing the transient response of an array of non-specific-response potentiometric sensors was developed for a quantitative application. A sequential injection analysis (SIA) system was used in order to automate its training and operation. This procedure takes profit of the dynamic nature of the sensor's response, which can be of high information content, improving the discrimination ability between primary and interfering ions. This work presents the extraction of significant information contained in the pulse sample transient response of a sensor array formed by eight sensors. The tool employed was the fast Fourier transform (FFT) analysis, from which three coefficients per sensor were fed into an artificial neural network (ANN) model. The studied case was the multidetermination of quaternary mixtures of Ca 2+ , Mg 2+ , Na + and K + in water samples, showing improved resolution when compared to classical ET approaches.

Simultaneous determination of potassium and total fluoride in toothpastes using a SIA system with two potentiometric detectors

A sequential injection analysis (SIA) system has been developed for the first time to quantify potassium and total fluoride in toothpastes and gels used to prevent both dentinal hypersensitivity and dental caries. To enable this simultaneous determination, potentiometric detection, using a conventional fluoride electrode and a tubular potassium selective electrode, formed by a PVC membrane containing valinomycin as ionophore, was carried out. A manifold that uses a three-way solenoid valve was designed. The former under binary sampling conditions, provides reproducible mixing ratios of two solutions. This fact facilitates that the system automatically generates, on-line, the calibration curves required by the analytical procedure. The calibration ranged from 1.0 × 10 −4 to 1.0 × 10 −3 mol L −1 for both potassium and total fluoride determinations. The R.S.D. (11 readings) resulted to be less than 1.5% for both determinations. Off-line studies related to the dissolution of the solid samples, the transformation of monofluorophosphate in fluoride, the elimination of organic matrix interference onto the plastic membrane of the potassium electrode, and the selection of the most adequate TISAB solution for fluoride determination, were also considered. A sampling rate of 18 samples h −1 for both determinations was attained, their precisions and accuracies being statistically indistinguishable from those achieved by atomic emission spectroscopy (for potassium determination) and by a conventional batch potentiometry (for total fluoride determination) adopted as reference techniques.

Determination of total and oxidized glutathione in human whole blood with a sequential injection analysis system

This work reports the development of a simple, robust, automated sequential injection analysis (SIA) system for the enzymatic determination of total (tGSH) and oxidized (GSSG) glutathione in human whole blood. The reduced (GSH) glutathione concentration is then obtained as the difference between the tGSH and GSSG concentrations. The determination was based on the DTNB–GSSG reductase recycling assay, which couples the specificity of the GSSG reductase (GR) with an amplification of the response to glutathione, followed by spectrophotometric detection of the 2-nitro-5-thiobenzoic acid (TNB) formed ( λ = 412 nm). The implementation of this reaction in a SIA flow system with an in-line dilution strategy permitted the necessary distinct application ranges for tGSH and for GSSG. It also guaranteed the exact timing of fluidic manipulations and precise control of the reaction conditions. The influence of parameters such as reagents concentration, temperature, pH, flow rate of the carrier buffer solution, as well as reaction coil length, etc., on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions subsequently selected. Linear calibration plots were obtained for GSH and GSSG concentrations up to 3.00 and 1.50 μM, with detection limits of 0.031 and 0.014 μM, respectively. The developed methodology showed good precision, with a relative standard deviation (R.S.D.) < 5.0% ( n = 10) for determination of both glutathione forms. Statistical evaluation showed good compliance, for a 95% confidence level, between the results obtained with the SIA system and those furnished by the comparison batch procedure.

Automated electronic tongue based on potentiometric sensors for the determination of a trinary anionic surfactant mixture

An automated electronic tongue consisting of an array of potentiometric sensors and an artificial neural network (ANN) has been developed to resolve mixtures of anionic surfactants. The sensor array was formed by five different flow-through sensors for anionic surfactants, based on poly(vinyl chloride) membranes having cross-sensitivity features. Feedforward multilayer neural networks were used to predict surfactant concentrations. As a great amount of information is required for the correct modelling of the sensors response, a sequential injection analysis (SIA) system was used to automatically provide it. Dodecylsulfate (DS −), dodecylbenzenesulfonate (DBS −) and α-alkene sulfonate (ALF −) formed the three-analyte study case resolved in this work. Their concentrations varied from 0.2 to 4 mM for ALF − and DBS − and from 0.2 to 5 mM for DS −. Good prediction ability was obtained with correlation coefficients better than 0.933 when the obtained values were compared with those expected for a set of 16 external test samples not used for training.

Assay of radical scavenging activity of antidotes against chemical warfare agents by DPPH test using sequential injection technique

Free radicals are believed to play an important role in many pathological states. Consequently antioxidants are receiving increased attention in medicinal research. As part of studies of the biological effects of the antidotes against chemical warfare agents currently used in the Czech Armed Forces, eleven compounds were assayed for their free radical scavenging activity. An optimized PC-controlled sequential injection analysis (SIA) system with spectrophotometric detection was used for evaluation of the antioxidation activity of the antidotes. The automated method is based on the known reaction of 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH) with antioxidants. Only the radical scavenging activity of the tested compound 2,3-dimercaptopropanol (BAL) was found to be weaker compared to the reference antioxidant acidum ascorbicum. Other tested antidotes did not possess any DPPH radical scavenging activity. The results obtained show that a correlation between the required biological activity (prophylaxis or treatment of intoxications by warfare agents) and possible antioxidation activity of the tested antidotes is doubtful.

Quasi-simultaneous determination of antioxidative activities against superoxide anion and nitric oxide by a combination of sequential injection analysis and flow injection analysis with chemiluminescence detection

A method that combines sequential injection analysis (SIA), flow injection analysis and chemiluminescence (CL) detection was developed for the quasi-simultaneous determination of antioxidative activities against superoxide anion (O2-) and nitric oxide (NO). The antioxidative activity was expressed as the decrease in luminol CL intensity caused by the quenching of O2- or NO by an antioxidant. The SIA system consisted of two syringe pumps, two selection valves, two holding coils, an HPLC pump to deliver luminol solution, and a CL detector. Operation of the syringe pumps and multiport valves was controlled automatically using a personal computer with appropriate software. A hypoxanthine (HX)-xanthine oxidase (XOD) system was used for the generation of O2-, and (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexenamide (NOR1) was employed as NO donor agent. The repeatability of the method was evaluated with 35.2 microg ml(-1) L-ascorbic acid, and the relative standard deviations (RSD) of the antioxidative activities were less than 3.8%. The quasi-simultaneous determination of the antioxidative activities in one sample was completed within 2.0 min. The antioxidative activities of some antioxidants and commercially available supplements containing certain antioxidants were successfully determined using this system. The proposed system is rapid and reproducible, and thus may be useful for the screening of functional foods, supplements and pharmaceutical formulations that exhibit antioxidative activity.

Development of a sequential injection analysis system for monitoring of trehalose concentrations

A sequential injection analysis (SIA) system was developed to on-line monitor the concentrations of trehalose in biological processes. The system is based on the enzymatic reaction of trehalose to glucose in an immobilized trehalase reactor and the subsequent reaction of glucose in the presence of glucose oxidase. The peroxide produced is detected using horseradish peroxidase with a redox indicator (ABTS, 2,2′-azino-di(3-ethylbezthiazoli-sulfonic acid-6)) and a spectrophotometer set at 435 nm. The SIA was fully automated using software written in the LabVIEWTM development environment. A number of system variablese.g. flow rate of the carrier buffer solution and volume ratio of sample to reagents, were evaluated to increase the sensitivity and performance of the SIA system. The performance of the trehalose-SIA system was linear under partially optimized operating conditions in the concentration range of 0.3 to 2.0 g/L (R2=0.999) with a sample frequency of 6 1/h. The SIA system was successfully employed to on-line monitor the concentrations of trehalose in a continuously stirred tank reactor. The on-line monitored data were in good agreement with the off-line data measured by a HPLC with a refractive index detector (n=14, R2=0.9865).

Enzymatic microreactors for the determination of ethanol by an automatic sequential injection analysis system

A sequential injection analysis system with two enzymatic microreactors for the determination of ethanol has been designed. Alcohol oxidase and horseradish peroxidase were separately immobilized on glass aminopropyl beads, and packed in 0.91-mL volume microreactors, working in line with the sequential injection analysis system. A stop flow of 120 s was selected for a linear ethanol range of 0.005-0.04 g/L +/- 0.6% relative standard deviation with a throughput of seven analyses per hour. The system was applied to measure ethanol concentrations in samples of distilled and nondistilled alcoholic beverages, and of alcoholic fermentation with good performance and no significant difference compared with other analytical procedures (gas chromatography and high-performance liquid chromatography).

Determination of Rh, Pd and Pt in urine samples using a pre-concentration sequential injection analysis system coupled to a quadrupole-inductively coupled plasma-mass spectrometer

The proposed flow system was developed in order to minimize the drawbacks related to the PGEs determination by quadrupole-inductively coupled plasma-mass spectrometry (Q-ICP-MS). It was intended not only to lower the limits of detection (LODs) but also to eliminate the interferences originating from some atomic and molecular ions produced in the argon plasma. This was accomplished by means of an on-line sample clean-up/pre-concentration step, using a chelating resin (Metalfix™ Chelamine™) in which Rh, Pd and Pt were preferably retained when compared with the interfering species. The results obtained by using the developed flow system in the analysis of urine samples are presented. With a sampling rate of 9 samples h −1 (i.e., 27 determinations) and a sample consumption of ca. 10 mL, the developed flow system allowed linear calibration plots up to 100 ng L −1 with detection limits of 1.2 ng L −1 (Rh), 0.4 ng L −1 (Pd) and 0.9 ng L −1 (Pt). Repeatability studies showed good precision (R.S.D.%, n = 5): 3.7% (Rh); 2.6% (Pd) and 2.4% (Pt), for 10 ng L −1; 2.4% (Rh); 1.4% (Pd) and 1.9% (Pt), for 50 ng L −1; and 1.3% (Rh); 0.58% (Pd) and 0.62% (Pt), for 100 ng L −1. By spiking human urine samples, recovery tests were performed, and the values obtained ranged between 89% and 105% (Rh); 90% and 104% (Pd); and 93% and 105% (Pt).