Tubular Detector Research Articles

Influence of different covalent immobilization protocols on electroanalytical performance of laccase-based biosensors

This paper presents a simple and effective flow-through electrochemical biosensor, consisting of Trametes versicolor laccase (Lac)-based mini-reactor and a tubular detector of silver solid amalgam (TD-AgSA), capable of rapid and selective detection of phenolic compounds. Amperometric detection relies on the reduction of the quinone molecule (formed during the enzymatic reaction in a mini-reactor) on TD-AgSA at –50 mV vs SCE. Since different enzyme immobilization techniques may contribute to differing biosensor performances, four covalent strategies for Lac attachment were compared: (i) through glutaraldehyde to supports −NH2, (ii) via disuccinimidyl suberate to supports −NH2, (iii) using EDC/NHS for Lac coupling by its −COOH groups to supports −NH2, and (iv) using EDC/NHS to supports −COOH. Additionally, five supports (mesoporous silica (SBA-15, MCM-41), cellulose, carbon-based (glassy carbon, graphite) powders) were investigated. It was found that different methods of immobilization, as well as different types of supports, significantly affect the amount of immobilized Lac and, in turn, the analytical characteristics of the obtained biosensors. Thus, TD-AgSA with enzymatic mini-reactor based on Lac covalently attached via glutaraldehyde to aminated MCM-41 proved to be the most promising biosensor, providing the best detection limit (18.3 μmol L–1) and the long-term stability (47.9 % of the initial response/4 months/100 measurements).

Flow amperometric uric acid biosensors based on different enzymatic mini-reactors: A comparative study of uricase immobilization

This is the first report of a novel strategy for uric acid (UA) determination via newly developed highly stable flow biosensors based on different enzymatic mini-reactors in combination with a four-electron reduction of the consumed oxygen. The design of the biosensors provides a spatial separation of the detection (working electrode) and biorecognition (uricase-based mini-reactor) part. To prepare the most efficient enzymatic mini-reactor, a comparative study focused on three different techniques of the covalent uricase immobilization at two kinds of mesoporous silica powders (SBA−15 and MCM−41) and the physical enzyme adsorption at four types of carbonaceous powders (glassy carbon, graphite, Starbon® 300, and Starbon® 800) has been performed. All investigations were carried out for two kinds of uricase: from Candida sp. (UOx(c)) and from Bacillus fastidiosus (UOx(b)) to estimate the influence of uricase source. The flow-through cell with tubular detector of silver solid amalgam was used for amperometric monitoring of four-electron oxygen reduction at the highly negative potential (−1100 mV vs. SCE). It was found that the developed UA biosensors responses are strongly dependent on the enzyme immobilization strategy. UOx(c) bounded to glassy carbon by physical adsorption has provided good results in terms of sensitivity, stability, and repeatability for UA determination. The biosensor with the mini-reactor based on the covalent immobilization of UOx(b) at glutaraldehyde activated NH2 functionalized MCM–41 has shown extremely high stability (more than 1 year) and reusability (at least 600 measurements) The biosensor’s practical applicability has been tested by successful determination of UA in human urine.

Amperometric Biosensor Based on Enzymatic Reactor for Choline Determination in Flow Systems

AbstractA simple, selective and stable biosensor with the enzymatic reactor based on choline oxidase (ChOx) was developed and applied for the determination of choline (Ch) in flow injection analysis with amperometric detection. The enzyme ChOx was covalently immobilized with glutaraldehyde to mesoporous silica powder (SBA‐15) previously covered by NH2‐groups. This powder was found as an optimal filling of the reactor. The detection of Ch is based on amperometric monitoring of consumed oxygen during the enzymatic reaction, which is directly proportional to Ch concentration. Two arrangements of an electrolytic cell in FIA, namely wall‐jet cell with working silver solid amalgam electrode covered by mercury film and flow‐through cell with tubular detector of polished silver solid amalgam were compared. The experimental parameters affecting the sensitivity and stability of the biosensor (i. e. pH of the carrier solution, volume of reactor, amount of the immobilized enzyme, the detection potential, flow rate, etc.) were optimized. Under the optimized conditions, the limit of detection was found to be 9.0×10−6 mol L−1. The Michaelis‐Menten constant for covalently immobilized ChOx on SBA‐15 was calculated. The proposed amperometric biosensor with the developed ChOx‐based reactor exhibits good repeatability, reproducibility, long‐term stability, and reusability. Its efficiency has been confirmed by the successful application for the determination of Ch in two commercial pharmaceuticals.

Silver Amalgam Tubular Detector Combined with Platinum Auxiliary Electrode for Electrochemical Measurements in Flow Systems

AbstractA new type of tubular detector with platinum auxiliary electrode inside the silver amalgam tube (TD+AuxE) was proposed, fabricated, tested and compared with a typical silver amalgam tubular detector developed earlier. Non‐stop‐flow differential pulse voltammetric anodic stripping method (AS‐DPV) and amperometric method in a glucose oxidase biosensor arrangement were tested. Both detectors were applied for AS‐DPV detection in flow systems for the first time. Solutions of zinc and cadmium cations were used as the testing species for voltammetry, and detection of oxygen concentration was used for amperometry. All these experiments require application of highly negative potentials, which is possible to realize with detectors made of silver solid amalgam. The proposed combination of TD+AuxE provides a much greater current response than the arrangement with three individual electrodes. All relevant parameters were optimized for the developed TD+AuxE. The simple and fast measuring protocol for the determination of the zinc content in commercial food supplement tablets has been developed.

Electrochemical Biosensors Based on Enzymatic Reactors Filled by Various Types of Silica and Amalgam Powders for Measurements in Flow Systems

AbstractTwo enzymatic biosensors with amalgam powder reactors and twelve enzymatic biosensors with various silica powder reactors were fabricated and tested in this work. The enzymatic reactors based on silver amalgam powder provide high sensitivity and they are convenient for faster flow rates. Experiments with six silica materials showed that mesoporous silica SBA‐15 was the best one in terms of covering by enzymes, sensitivity and lifetime of biosensors. The current response of the SBA15‐glucose oxidase (GOx) sensor started to decrease only after 200 day testing and after 406 days the peak current was still 35.9 % of the initial value. The used amalgam tubular detector in a flow system allowed working at highly negative potentials, which significantly increased the sensitivity of determinations. Statistical results of parallel measurement of model solutions with the fabricated biosensors show their high accuracy (RSD=0.28–1.81 %) and sensitivity (6.2–14.3 µmol L−1). The proposed SBA15‐GOx biosensor was successfully used for determination of glucose in commercial honey.

New potentiometric transducer based on a Mn(II) [2-formylquinoline thiosemicarbazone] complex for static and hydrodynamic assessment of azides

A new potentiometric transducer for selective recognition of azide is characterized and developed. The PVC plasticized based sensor incorporates MnII [2-formylquinoline thiosemicarbazone] complex in the presence of tri dodecyl methyl ammonium chloride (TDMAC) as a lipophilic cationic additive. The sensor displayed a near-Nernstian response for azide over 1.0×10−2–1.0×10−5molL−1, with an anionic slope of −55.8±0.6mVdecade−1 and lower limit of detection 0.34µgmL−1. The sensor was pH independent in the range 5.5–9 and presented good selectivity features towards several inorganic anions, and it is easily used in a flow injection system and compared with a tubular detector. The intrinsic characteristics of the detector in a low dispersion manifold were determined and compared with data obtained under a hydrodynamic mode of operation. This simple and inexpensive automation, with a good potentiometric detector, enabled the analysis of ~33 samples h−1 without requiring pre-treatment procedures. The proposed method is also applied to the analysis of trace levels of azide in primer mixtures. Significantly improved accuracy, precision, response time, stability and selectivity were offered by these simple and cost-effective potentiometric sensor compared with other standard techniques. The method has the requisite accuracy, sensitivity and precision to determine azide ions.

Application of Non‐Stop‐Flow Differential Pulse Voltammetry at a Tubular Detector of Silver Solid Amalgam for Electrochemical Determination of Lomustine (CCNU)

AbstractAn application of the flow differential pulse voltammetry with tubular detector based on silver solid amalgam for determination of antineoplastic drug lomustine in pharmaceutical preparations is presented. The highest sensitivity was obtained in [0.10 mol dm−3 MES; 2.00 mol dm−3 NaCl; pH 6.0]:EtOH (9 : 1) with flow rate 0.50 mL min−1, and the magnitude of the modulation amplitude −0.070 V. The calibration dependence was linear in the range 1×10−6–1 × 10−4 mol dm−3 (R2=0.999). The limit of detection was 1.5×10−7 mol dm−3. This method was successfully used for determination of lomustine in real samples of chemotherapy drug CeeNU Lomustine 40 mg.

Flow‐Through Potentiometric Sensors for Alizarin Red S Dye and Their Application for Aluminum Determination

AbstractNovel selective and sensitive poly (vinyl chloride) membrane sensors are developed for measuring alizarin red S (AR) based on the use of aliquate 336, MgIIphthalocyanine (MgPc), CuIIphthalocyanine (CuPc) and FeII phthalocyanine (FePc) plasticized poly (vinyl chloride) membrane. The sensors display Nernestian response with slopes of ‐50.6 ± 0.6 , ‐37.4 ± 0.5 , ‐37.7 ± 0.8 and ‐35.0 ± 0.7 mV decade−1 over the range of 5.2 × 10−6 to 1 × 10−2 mol L−1 for all of them and detection limits of 5.9 × 10−7, 1.9 × 10‐−6 2.3 × 10−6 and 1.9 × 10−6 mol L−1 for aliquate, MgPc, CuPc and FePc membrane based sensor, respectively. The sensors exhibit long life span, long term potential stability, high reproducibility, fast response and good discrimination ability towards alizarinate ion in comparison with many other anions. A tubular detector based on aliquate, MgPc, CuPc and FePc was further developed and coupled to a flow‐injection system for alizarin (AR) determination. Under optimized conditions, the linearity range is 1.0 × 10−5‐ 1.0 × 10−1 mol L−1, with a slope of ‐52.1 ± 0.8, 20.9 ± 0.7, 23.6 ± 0.4 and 25 ± 1.1 mV decade−1 and a reproducibility of ± 0.8 mV (n = 6) for aliquate, MgPc, CuPc and FePc membrane based sensors, respectively. The sensor based on aliquate is further utilized for a potentiodynamic quantification of aluminum in sludge samples and deodorants. The buffered solution of alizarin was allowed to react in a flow system with aluminum. The calibration curve of Al was found to be linear over a concentration range of 0.1 to 1.8 and 1.0 ‐ 40 μg mL−1 with a slope = 16.9 (r2 = 0.993) and 1.76 (r2 = 0.994) mV (μg/mL)−1 and a detection limit of 0.08 and 0.5 μg mL−1 for 10−4 and 10−3 mol L−1 AR− as a carrier, respectively. The method was successfully used for determining aluminum in sludge samples and deodorants. The data agree fairly well the nominal values and with results obtain by continuous flow hydride generation inductively coupled plasma (ICP) method.

Flow electrochemical biosensors based on enzymatic porous reactor and tubular detector of silver solid amalgam

A flow amperometric enzymatic biosensor for the determination of glucose was constructed. The biosensor consists of a flow reactor based on porous silver solid amalgam (AgSA) and a flow tubular detector based on compact AgSA. The preparation of the sensor and the determination of glucose occurred in three steps. First, a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) was formed at the porous surface of the reactor. Second, enzyme glucose oxidase (GOx) was covalently immobilized at MUA-layer using N-ethyl-N′-(3-dimethylaminopropyl) carboimide and N-hydroxysuccinimide chemistry. Finally, a decrease of oxygen concentration (directly proportional to the concentration of glucose) during enzymatic reaction was amperometrically measured on the tubular detector under flow injection conditions. The following parameters of glucose determination were optimized with respect to amperometric response: composition of the mobile phase, its concentration, the potential of detection and the flow rate. The calibration curve of glucose was linear in the concentration range of 0.02–0.80mmolL−1 with detection limit of 0.01mmolL−1. The content of glucose in the sample of honey was determined as 35.5±1.0mass % (number of the repeated measurements n=7; standard deviation SD=1.2%; relative standard deviation RSD=3.2%) which corresponds well with the declared values. The tested biosensor proved good long-term stability (77% of the current response of glucose was retained after 35 days).

New Potentiometric Sensors for Picrate Determination Using Flow‐Through System: Application to Kinetic Assessment of Se(IV)

AbstractTwo new selective and sensitive poly(vinyl chloride) membrane sensors are developed for measuring picrate ions based on the use of nitron picrate [(Nit)(Pic)] and iron(II)‐bathophenanthroline picrate [Fe(bphen)3)(Pic)2] ion pairs in plasticized poly(vinyl chloride) membrane. The sensors display Nernstian response with slopes of −57.2±0.8 and −58.8±0.5 mV decade−1 over the range of 3.0×10−5 to −1.0×10−2 and 4.6×10−6–1.0×10−2 mol L−1 and detection limits of 7.4×10−6 and 3.07×10−6 mol L−1 for [(Nit)(Pic)] and [Fe(bphen)3)(Pic)2] membrane‐based sensors, respectively. The sensors exhibit long life‐span, long term potential stability, high reproducibility, fast response and good discrimination ability towards picrate ions in comparison with many other anions. A tubular detector based on [Fe(bphen)3][Pic]2 was further developed and coupled to a flow‐injection system for picrate (Pic) determination. Under optimized conditions, the linearity range is 1.0×10−5–1.0×10−1 mol L−1, with a slope of −47.9±0.1 mV decade−1 and a reproducibility of ±0.3 mV (n=5). The sensor is utilized for a kinetic quantification of selenium in pharmaceutical preparations. The alkaline solution of picrate is allowed to react in a batch system with Na2S, in the presence of selenium(IV) as a catalyst. The changes in potential, resulting from the decrease of the picrate anions are monitored with the picrate sensor. The calibration curve of Se is linear in the concentration range 0.14–0.7 µg mL−1, with a lower limit of detection of 1.0 ng mL−1.

Intelligent, net or wireless enabled fluorosensors for high throughput monitoring of assorted crops

Phenotypic characterization of assorted crops of different genotypes requires large data sets of diverse types for statistical reliability. Temporal monitoring of plant fluorescence is able to capture the dynamics of the photosynthesis process that is summarized in a number of parameters for which the genotypic heritability can be calculated. In this paper, an intelligent sensor system is presented that is capable of high-throughput production of baseline-corrected temporal fluorescence curves with many feature points. These are obtained by integrating several (direct and modulated) measurement methods applied at different wavelengths. Simultaneously, temporal change of the sample's emission and the ambient reference temperatures are recorded. Multiple sensors can be deployed easily in large span greenhouse environments with centralized data collection over wired or wireless infrastructure. The unique features of the sensors are a compact, embedded signal guiding fibre optic system, instrument-standard variable tubular detector and source modules, net or wireless enabling for remote control and fast, quasi real-time data collection. Along with the instrumentation, some representative phenotyping data are also presented that were taken on a subset of pepper recombinant inbred line population. It is also demonstrated that transient fluorescence feature points yield high heritability, offering a high confidence level for distinguishing the pepper genotypes.

Tubular Detector of Silver Solid Amalgam for Electrochemical Measurements in Flow Systems

AbstractThis paper presents the application of the tubular detector based on silver solid amalgam (TD‐AgSA) for electrochemical determinations of reducible inorganic (Cd2+, Zn2+) and organic (4‐nitrophenol) compounds under flow injection analysis conditions. The newly developed TD‐AgSA is simple, robust and inexpensive. The limits of detections of Zn2+, Cd2+ and 4‐nitrophenol are 1.4×10−6, 7.0×10−7, and 5.0×10−7 mol dm−3, respectively (i.e. 0.09, 0.08 and 0.07 ppm). The obtained results proved the long‐term stability of the detector (RSD of the determination of Zn2+, Cd2+, and 4‐nitrophenol were 0.8, 0.9 and 0.8 % (n=10; cZn=7.7×10−5 mol dm−3, cCd=4.5×10−5 mol dm−3 and c4‐NPh=3.6×10−5 mol dm−3), respectively and its applicability for cathodic measurements in aqueous solutions at potentials up to −2 V.

New potentiometric sensors based on selective recognition sites for determination of ephedrine in some pharmaceuticals and biological fluids

New cost-effective potentiometric membrane sensors with cylindrical configuration responsive to ephedrine are described. The sensors setup is, based on the use of triacetyl-β-cyclodextrin [(triacetyl-β-CD)] as a neutral ionophore embedded in a plasticized poly (vinyl chloride) (PVC) matrix (sensor I) and carboxylated poly(vinyl chloride) [(PVC–COOH)] as a simultaneous plastic matrix and ion exchanger (sensor II). Both sensors showed significant enhancement of response towards ephedrinium cation (EPD+) over a concentration range of 3.0×10−5–8.0×10−3molL−1 at pH 4–9 and 3–8 with low detection limits of 5.7×10−6 and 6.2×10−6molL−1 for sensors (I) and (II), respectively. The sensors displayed near-Nernstian cationic slope of 57.0 and 55.6mV decade−1 for EPD+ and the effects of lipophilic salts and various foreign common ions were examined. The sensors were also satisfactorily used as tubular detectors in a double channel flow injection system. The intrinsic characteristics of the detectors in a low dispersion manifold under hydrodynamic mode of operation were determined and compared with data obtained under batch mode of operation. Validation of the method revealed good performance characteristics including long life span, good selectivity for EPD+ over a wide variety of other organic compounds, long term stability, high reproducibility, fast response, low detection limit, wide measurement range, acceptable accuracy and precision. Applications of the sensors to the determination of EPD+ in pharmaceutical formulations and spiked biological fluid samples were carried out and compared with standard techniques. Notably, the sensors introduced offer several advantages over many of those previously described that are amenable to quality control/quality assurance assessment of the homogeneity, stability and purity of ephedrine drug tablets.

Biomimetic ciprofloxacin sensors made of molecularly imprinted network receptors for potential measurements

A molecularly imprinted polymer (MIP), with special molecule recognition properties of ciprofloxacin CIP), was prepared by thermal polymerization in which ciprofloxacin acted as the template molecule, methacrylic acid (MAA), acrylonitrile (AN) and 2-vinylpyridine (2-VP) acted as the functional monomer and ethylene glycol dimethacrylate (EGDMA) acted as the crosslinker. A biomimetic potentiometric field monitoring device was developed for the assessment of cirofloxacin (CIP) antibiotics based on these newly synthezised imprinted polymers. The sensing elements were fabricated by the inclusion of CIP imprinted polymers in polyvinyl chloride (PVC) matrix. The sensors showed a high selectivity and a sensitive response to the template in an aqueous system. Electrochemical evaluation of these sensors revealed near-Nernstian response with slopes of 29.9 ± 0.7, 27.9 ± 0.5, and 30.3 ± 0.8 mV decade−1 with a detection limit 41.3, 46.3, and 32 μg mL−1CIP with MIP/MAA, MIP/2-VP and MIP/AN membrane based sensors plasticized with DOP, respectively. The effects of lipophilic salts and various foreign common ions were tested. The sensors were easily used in a single channel flow injection system and compared with a tubular detector. The intrinsic characteristics of the detectors in a low dispersion manifold were determined and compared with data obtained under a hydrodynamic mode of operation. Significantly improved accuracy, precision, response time, stability, selectivity and sensitivity were offered by these simple and cost-effective potentiometric sensors compared with other standard techniques. The method had the requisite accuracy, sensitivity and precision to assay CIP in pharmaceutical formulations and biological fluids.

Conventional and planar chip sensors for potentiometric assay of uric acid in biological fluids using flow injection analysis

The potentiometric response properties of several PVC-based membrane sensors using phthalocyanine complexes of cobalt(II) (CoPC) and Fe(II) (FePC) as anion carriers, towards uric acid were constructed and characterized. The sensors demonstrated fast near-Nernstian response for uric acid over the concentration ranges 9.1 × 10 −6 to 9.1 × 10 −2 and 3.1 × 10 −5 to 3.1 × 10 −2 M with detection limits 0.67 and 2.85 μg mL −1 over pH 6.5–8 for CoPC and FePC based membrane sensors plasticized with o-NPOE and 1% TDMAC, respectively. A novel solid-state planar chip urate sensor was developed, characterized according to IUPAC recommendations, easily used in a single channel wall-jet flow injection system and compared with a tubular detector. The intrinsic characteristics of the detectors in a low dispersion manifold were determined and compared with data obtained under hydrodynamic mode of operation. Validation of the assay methods with the proposed sensors by measuring the lower limit, range, accuracy, precision, repeatability and between-day-variability revealed good performance characteristics confirming applicability for continuous determination of uric acid. The sensors were used for determining urate in biological fluids at an input rate of 50 samples per hour. The results compare favorably with data obtained by the standard spectrophotometry.

Tubular potentiometric detector used to determine As(V) in sediment extracts by flow injection

The construction and evaluation of a tubular potentiometric detector sensitive to As(V) ions is described. This electrode, with no inner reference solution, is comprised of a FeOOH–SiO2–graphite composite agglutinated with an epoxy resin. For As(V) ion concentrations in the range 1.0 × 10−5 to 1.0 × 10−1 mol L−1, the sensor is used as the selective electrode in an FIA system along with a commercial Ag/AgCl reference electrode. In optimal conditions, the practical limit of detection is 4 × 10−6 mol L−1 and a sampling rate of 40 h−1 can be achieved. The system was applied to estimate As(V) levels in sediments of a drinking water distributor in Zimapán (Mexico), an area known to be polluted with this element. The As(V) concentrations detected in the different extracts of sediments generated by the sequential modified BCR three-step extraction procedure (BCR-SEP) were comparable to those obtained by electrothermal atomic absorption spectroscopy (ET-AAS).

Analysis of phenolic acids in plant materials using HPLC with amperometric detection at a platinum tubular electrode

AbstractThe suitability of a simple amperometric platinum tubular detector for HPLC analysis of selected phenolic acids in yacon (Smallanthus sonchifolius, Asteraceae) is reported. The detector offers good overall limits of detection for the phenolic acids of interest. Three different types of extracts from yacon leaves were analyzed and compared with respect to their content of phenolic acids. Caffeic acid was found in all yacon extracts, whereas the content of chlorogenic acid depends more on the extraction procedure used. It has been demonstrated that no complicated and sophisticated equipment is needed and HPLC with amperometric detection seems to be a very useful technique for analysis of plant extracts containing phenolic acids.

Relocation of a Tubular Voltammetric Detector for Standard Addition in FIA

In this work a new strategy for the automation of the standard addition method by FIA with voltammetric detection is described, based on the concept of multi-site detection. In the system developed, a single voltammetric detector with mobility in the FIA manifold, carried out sequential measurement of the sample plug before and after addition of the standard solution. The construction and evaluation of the voltammetric detector of tubular configuration and internal diameter similar to the tubing of the FIA manifold, whose incorporation in the system allowed the measurement process to be carried out without change of the hydrodynamic characteristics of the sample plug, is also mentioned. To evaluate the usefulness of the proposed multi-site voltammetric detection system, this was used in the amperometric determination of ascorbic acid in fruit juices where the standard addition method is frequently required to overcome the matrix effect. The results obtained with the FIA system were compared with those from the reference procedure proposed by AOAC. No statistical difference between methods was found at the 95% confidence level. The relative deviations between both methods were always less than or equal to 3.8%. The sampling rate was about 55 samples per hour (110 measurements).

Capillary electrophoresis with an integrated on-capillary tubular detector based on a carbon sol-gel-derived platform

An integrated on-capillary tubular electrochemical detector for capillary electrophoresis systems has been fabricated based on sol-gel technique. It consists of a sol-gel carbon composite tubular electrode attached permanently onto the outlet of the separation capillary. The device greatly eases the setting up of capillary electrophoresis with electrochemical detection (CEEC) as it makes possible electrode/capillary alignment without the aid of a micromanipulator since this integrated unit can be simply immersed in the CE separation buffer in an ordinary three-electrode stationary cell. To improve analytical performance of the integrated unit, the external wall of the exit capillary was etched with HF after the polyimide coating of the capillary had been removed. Influences of the working electrode length and the wall thickness at the outlet of capillary on the separation efficiency and amperometric sensitivity were assessed and optimized. The practical applicability of this configuration is demonstrated with the detection of both catecholamines and carbohydrates. The advantages, namely, versatility, convenience, ease of operation, and low-cost, of the new design combined with an excellent performance lead to high stability and low detection limits.

Design of the Fluoride Ion-Selective Electrode as Tubular Detector for Flow Injection Analysis

ABSTRACT Design of the fluoride ion-selective electrode (FISE) as the tubular detector used in the flow injection analysis (FIA) has been described. Among other things, this design makes it possible to use various internal contacts. The effect of pH on peak height and detection limit in the pH range from 2.8 to 8.0 has been examined. The effect of flow rate and sample injection volume on peak height and range of linear response has also been examined. The flow rates range from 0.56 mL/min to 4.05 mL/min, while the injection volumes are 100 and 200 μL. The optimum conditions are carrier solution (0.1 M KNO3 buffer pH 4 and 10-6 M NaF), flow rate 1.54 mL/min and sample injection volume 100 μL. Applicability of the FISE as the tubular detector in determination of Fe(III)-ions and AI(III)-ions by flow infection analysis has been examined at pH values of 2.8 and 3.4.