On-line Flow Injection System Research Articles

Restricted access material-ion imprinted polymer-based method for on-line flow preconcentration of Cd2+ prior to flame atomic absorption spectrometry determination

The present paper describes a new restricted access material-ion imprinted polymer for on-line preconcentration of Cd2+ from natural water samples, and simultaneous clean-up of humic acid. Cadmium-imprinted poly(allylthiourea) was synthesized and modified with 2-hydroxyethyl methacrylate (IIP-HEMA) to obtain the restricted access ability. The on-line flow injection system coupled to FAAS (FIA-FAAS) was based on percolation of 20.0 mL of the sample (pH 8.70 and in presence of organic matter) through a mini-column (100.0 mg of IIP-HEMA) at 7.5 mL min−1 flow rate. The elution step was performed using 2.0 mol L−1 HNO3 at 5.0 mL min−1 flow rate. The method provided linearity in the range 0.56–50.00 μg L−1 and limit of detection of 0.17 μg L−1. The preconcentration factor was found to be 37-fold, consumption index of 0.54 mL, preconcentration efficiency of 13.10 min−1 and sample throughput of 21 h−1. The precision of the method was evaluated in terms of intra-day and inter-day repeatability and the relative standard deviation percentage (%RSD) obtained by two-level concentration (2.50 and 40.00 μg L−1) in the presence and absence of humic acid were <5.0%. Low interferences of ions commonly found in water samples as well as the humic acid were observed. The accuracy was attested by addition and recovery tests at two-level of Cd2+ (2.00 and 20.00 μg L−1, both prepared in presence of humic acid) in a real water sample, and the recovery percentages ranged from 93.8 to 108.7%. Cadmium was also analyzed in a certified reference material TORT-2 (lobster hepatopancreas). The method was applied for Cd2+ determination on water after spiking procedure with known concentration, food (linseed, 301.8 ± 15.3 μg kg−1), herbal medicine (Ginkgo biloba L., 221.2 ± 5.8 μg kg−1) and cigarette (77.9 ± 6.3 μg kg−1).

Online rapid sampling microdialysis (rsMD) using enzyme-based electroanalysis for dynamic detection of ischaemia during free flap reconstructive surgery

We describe an enzyme-based electroanalysis system for real-time analysis of a clinical microdialysis sampling stream during surgery. Free flap tissue transfer is used widely in reconstructive surgery after resection of tumours or in other situations such as following major trauma. However, there is a risk of flap failure, due to thrombosis in the flap pedicle, leading to tissue ischaemia. Conventional clinical assessment is particularly difficult in such ‘buried’ flaps where access to the tissue is limited. Rapid sampling microdialysis (rsMD) is an enzyme-based electrochemical detection method, which is particularly suited to monitoring metabolism. This online flow injection system analyses a dialysate flow stream from an implanted microdialysis probe every 30 s for levels of glucose and lactate. Here, we report its first use in the monitoring of free flap reconstructive surgery, from flap detachment to re-vascularisation and overnight in the intensive care unit. The on-set of ischaemia by both arterial clamping and failure of venous drainage was seen as an increase in lactate and decrease in glucose levels. Glucose levels returned to normal within 10 min of successful arterial anastomosis, whilst lactate took longer to clear. The use of the lactate/glucose ratio provides a clear predictor of ischaemia on-set and subsequent recovery, as it is insensitive to changes in blood flow such as those caused by topical vasodilators, like papaverine. The use of storage tubing to preserve the time course of dialysate, when technical difficulties arise, until offline analysis can occur, is also shown. The potential use of rsMD in free flap surgery and tissue monitoring is highly promising. FigureFree flap surgery timeline: The flap is raised and MD probe inserted. Glucose and lactate levels were monitored at 1 minute intervals throughout flap removal and the reconstruction of the tongue. Grey lines indicate key events as communicated by the surgeons in real time.

Microwave plasma torch-atomic emission spectrometry for the on-line determination of rare earth elements based on flow injection preconcentration by TiO2–graphene composite

In this work, we synthesized TiO2–graphene composite as a novel preconcentration material. It was enclosed in a microcolumn in the on-line flow injection system to adsorb trace light (La), medium (Tb), and heavy (Ho) rare earth elements (REEs) prior to their determinations by microwave plasma torch-atomic emission spectrometry (MPT-AES). Various experimental parameters, such as sample loading time, sample flow rate, sample pH, eluent flow rate, eluent concentration, and interfering ions, were investigated systematically. Under the optimum conditions, the detection limits (three times of standard deviations of blank by 7 reiterations) of La, Tb, and Ho were found to be 2.2, 1.6, and 2.8μgL−1, with enrichment factors of 17.1, 11.1, and 10.2, respectively. Relative standard deviations for the determination of the target REEs were 3.6%, 1.3%, and 1.4%, respectively (n=7). The developed method was validated by the analysis of La, Tb, and Ho in certified reference material (GBW07313, marine sediment) and high purity REE oxide samples.

Development of a novel on-line flow injection mercury analyzer to determine gaseous elemental mercury over the northern South China Sea

A simple and reliable gaseous elemental mercury analyzer (GEMA) was developed to investigate atmospheric gaseous elemental Hg (GEM) over the northern South China Sea (SCS). This on-line flow injection system couples the main sampling and analytical steps from sample introduction, Au amalgamation/pre-concentration to final detection/data acquisition. This approach provides ease of operation and high analytical performance and is suitable for shipboard use. The analyzer can be fully automated and also be modified to examine other atmospheric Hg species (e.g., reactive gaseous, particulate and methyl-Hg). Here, we present the results of laboratory performance tests and comparison with a traditional manual method, which showed good agreement. The results demonstrate that this approach is accurate and precise. The GEMA allows the reliable GEM determination in ambient air samples (i.e. high recoveries of 107 ± 6%, obtained from 6 spiked gas standards) with a low detection limit of 0.1 ng m−3 for a sample volume of 10 L and an excellent reproducibility (relative standard deviation ≤ 5%, n = 6). Representative field atmospheric GEM data from spring, summer, fall and winter 2003 over the northern SCS are also presented. Seasonal GEM variations with higher GEM (6.9 ± 1.0 ng m−3) in winter and lower in late spring (2.2 ± 0.5) and summer (2.7 ± 0.8) were evident in relation to the East Asian monsoon cycles.

Interaction of surface-attached haemoglobin with hydrophobic anions monitored by on-line acoustic wave detector

The behaviour of proteins on surfaces and at interfaces is an important field with applications in drug development, clinical diagnostics and studies of device biocompatibility. A key factor is the conformation of surface-bound proteins, which can affect chemical signalling and drug binding. A recent study of the interactions of haemoglobin with hydrophobic anions at a liquid-liquid interface has shown that a pH- and orientation-dependent conformational change occurs in the haemoglobin molecule upon interaction with these anions. To corroborate these results, we use an acoustic wave detector to study binding of solution-phase hydrophobic anions to surface-adhered haemoglobin. The orientation of protein is controlled by thiol chemistry, which generates hydrophilic and hydrophobic surfaces. Tetraphenylborate-based anions are introduced to the haemoglobin coated surface via an on-line flow-injection system to monitor the signal in real-time. Changes in the acoustic properties of the surface, measured piezoelectrically, are related to interactions between the protein and the anions. Signal strength is proportional to the degree of interaction between the salts and the haemoglobin, which in turn, is influenced by its conformation.

On-line preconcentration system using a microcolumn packed with Alizarin Red S-modified alumina for zinc determination by flame atomic absorption spectrometry

A simple and sensitive on-line flow injection system for determination of zinc with FAAS has been described. The method is based on the separation and preconcentration of zinc on a microcolumn of immobilized Alizarin Red S on alumina. The adsorbed analyte is then eluted with 250 µL of nitric acid (1 mol L-1) and is transported to flame atomic absorption spectrometer for quantification. The effect of pH, sample and eluent flow rates and presence of various cations and anions on the retention of zinc was investigated. The sorption of zinc was quantitative in the pH range of 5.5-8.5. For a sample volume of 25 mL an enrichment factor of 144 and a detection limit (3S) of 0.2 µg L-1 was obtained. The precision (RSD, n=7) was 3.0% at the 20 µg L-1 level. The developed system was successfully applied to the determination of zinc in water samples, hair, urine and saliva.

Trace aluminium determination in biological samples after microwave digestion followed by solid phase extraction with l-methionine on controlled pore glass

Aluminium is an element found in biological samples at low concentrations and aluminum-related neuropathological diseases in human beings have been reported. For this reason the determination of Al in this type of samples requires the development of enrichment methods capable of improving the instrumental detection for this analyte. l-methionine immobilized on controlled pore glass (CPG) was tested for the retention of aluminium. This adsorbent material was packed in a conical minicolumn and connected to an on-line flow injection system. An inductively coupled plasma optical emission spectrometer associated to an ultrasonic nebulization system (USN-ICP OES) was used for aluminium detection. Al(III) was retained at pH 12.5 and removed from the column with 20% (v/v) HNO 3. The precision of the preconcentration method was evaluated by passing a measured volume of aluminium standard solution (1 μg L − 1 ) through the minicolumn and repeating this procedure five times. The relative standard deviation (RSD) was 2.5%, calculated with the peak heights obtained. A total enhancement factor of 1600 was attained for a sample volume of 10 mL (10-fold for the ultrasonic nebulization system and 160-fold for the preconcentration methodology). The detection limit (DL), calculated as the amount of Al required to yield a net peak equal to three times the standard deviation of the blank solution, was 25 ng L − 1 . The proposed system was successfully applied to the determination of aluminium in urine, hair, and saliva samples, which were pretreated using a microwave digestion methodology with the introduction of a digestion program for saliva. The average aluminium levels found in urine, hair, and saliva samples were 5.5 μg L − 1 , 19 μg g − 1 and 93 μg L − 1 respectively.

On-line preconcentration and speciation analysis of Se(iv) and Se(vi) using l-methionine immobilised on controlled pore glass

A study was undertaken to evaluate the analytical capabilities of the aminoacid L-methionine as a possible substrate for the selective sorption of selenium inorganic species for the determination of Se(IV) and Se(VI) in aqueous solution. Methionine was covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. Se was determined by flow injection hydride generation-inductively coupled plasma optical emission spectrometry (FI-HG-ICP OES). Chemical and physical variables affecting the sorption process were tested in order to select the optimal analytical conditions for the Se retention by methionine. Se(VI) was selectively retained by methionine at pH 3.0, while Se(IV) was not retained. Se(VI) was subsequently removed from the conical minicolumn with 10% HCl and on-line reduced with 12 mol l−1 HCl in a water bath (100 °C). A preconcentration factor of 90 was achieved when 30 mL of sample were processed reaching a detection limit of 11 ng l−1, with a sample throughput of 17 samples h−1 for total selenium determination and 8 samples h−1 for speciation [Se(IV) and Se(VI)]. The speciation analysis of inorganic Se in drinking water was performed following the proposed method and the recoveries were in all cases between 98 and 100%.

Reagents regeneration flow injection analysis (RRFIA) for spectrophotometric determination of methamphetamine coupled with solvent extraction

Methamphetamine (MPA), being a stimulant drug, reacts with tetrabromophenolphthalein ethyl ester (TBPEH) to form a red-violet ion associate, TBPEHMPA, in 1,2-dichloroethane (DCE) at pH 9. The maximum absorption wavelength was at 570 nm. After measuring, yellow TBPEH with DCE could be regenerated by mixing with the buffer solution at pH 3. The regenerated TBPEH/DCE could be reused as an ion association reagent and extracting solvent. In addition, the reagent regeneration could be performed by the on-line flow injection system and the cyclic flow injection analysis system was demonstrated for the determination of MPA without consumption of ion association reagent and organic solvent. The calibration curve was linear in the range of 0.5–3.5 × 10 −5 M with good repeatability. The sample throughput was 20 h −1.

On-line preconcentration and speciation analysis of Cr(III) and Cr(VI) using baker's yeast cells immobilised on controlled pore glass

A study was undertaken to evaluate Saccharomyces cerevisiae as a substrate for the biosorption of Cr(III) and Cr(VI) aiming to the selective determination of these species in aqueous solutions. The yeast cells were covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. The effect of chemical and physical variables affecting the biosorption process was tested in order to select the optimal analytical conditions for the Cr retention by S. cerevisiae. Cr(III) was retained by the immobilised cells and Cr(VI) were retained by CPG. The speciation was possible by selective and sequential elution of Cr(III) with 0.05 mol L −1 HCl and 2.0 mol L −1 HNO 3 for Cr(VI). The influence of some concomitant ions up to 20 mg L −1 was also tested. Quantitative determinations of Cr were carried out by means of inductively coupled plasma optical emission spectrometry (ICP OES). Preconcentration factors of 12 were achieved for Cr(III) and 5 for Cr(VI) when 1.7 mL of sample were processed reaching detection limits of 0.45 for Cr(III) and 1.5 μg L −1 for Cr(VI). The speciation of inorganic Cr in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analysed and the recoveries were in all cases between 81 and 103%.

Determination of Cd, Hg, Pb and Se in sediments slurries by isotopic dilution calibration ICP-MS after chemical vapor generation using an on-line system or retention in an electrothermal vaporizer treated with iridium

A method for the determination of Cd, Hg, Pb and Se in sediments reference materials by slurry sampling chemical vapor generation (CVG) using isotopic dilution (ID) calibration and detection by inductively coupled plasma mass spectrometry (ICP-MS) is proposed. Two different systems were used for the investigation: an on-line flow injection system (FI-CVG-ICP-MS) and an off-line system with in situ trapping electrothermal vaporization (CVG-ETV-ICP-MS). About 100 mg of the reference material, ground to a particle size ≤50 μm, was mixed with acid solutions ( aqua regia, HF and HCl) in an ultrasonic bath. The enriched isotopes 111Cd, 198Hg, 206Pb and 77Se were then added to the slurry in an adequate amount in order to produce an altered isotopic ratio close to 1. For the on-line system, a standing time for the slurry of 12 h before measurement was required, while for the batch system, no standing time is needed to obtain accurate results. The conditions for the formation of the analyte vapor were optimized for the evaluated systems. The following altered isotope ratios were measured: 111Cd/ 114Cd, 198Hg/ 199Hg, 206Pb/ 208Pb e 77Se/ 82Se. The obtained detection limits in the on-line system, in μg g −1, were: Cd: 0.15; Hg: 0.09; Pb: 6.0 and Se: 0.03. Similar detection limits were obtained with the system that uses the ETV: 0.21 for Hg, 6.0 for Pb and 0.06 μg g −1 for Se. No signal for Cd was obtained in this system. One estuarine, two marine and two river certified sediments were analyzed to check the accuracy. The obtained values by both systems were generally in agreement with the certified concentrations, according to the t-test for a confidence level of 95%, demonstrating that isotope equilibration was attained in the slurries submitted to a chemical vapor generation procedure and detection by ICP-MS. The relative standard deviations were lower than 10%, adequate for slurry analysis. The almost quantitative analytes extractions to the aqueous phase of the slurry must favor equilibration of the added enriched isotope with the isotope in the sample, allowing the use of isotopic dilution calibration for slurry analysis.

On-line collection/concentration of trace metals for spectroscopic detection via use of small-sized thin solid phase (STSP) column resin reactors.: Application to speciation of Cr(III) and Cr(VI)

A novel and simple on-line flow injection (FI) system using anion- and cation-exchange resin disks was developed for the speciation of chromium species in fresh water samples by inductively coupled plasma-atomic (optical) emission spectrometry (ICP-AES). Two kinds of ion-exchange resin disks packed in line-filters were fixed and serially connected on the loop of each six-way valve. Five milliliters of a sample solution (pH 4.5) was introduced into the system. Anionic chromate ion, Cr(VI), was collected on the anion-exchange resin disk while cationic chromium ion, Cr(III), was collected on the cation-exchange resin disk. The collected species were then sequentially eluted by 2 M nitric acid and nebulized to the plasma of ICP-AES system. The detection limit (3 σ) of Cr(VI) and Cr(III) were 0.04 and 0.02 μg l −1, respectively. The proposed method was applied to the speciation of Cr(III) and Cr(VI) in fresh water samples.

The removal of toxic metals from liquid effluents by ion exchange resins. Part I: Chromium(VI)/Sulphate/Dowex 1x8

The removal of chromium (VI) from sulphuric acid solutions using the Dowex 1x8 resin has been investigated. The influence of several variables such as the stirring speed, temperature, the sulphuric acid and metal concentrations in the aqueous phase and the variation of the amount of resin added has been studied. Various aqueous solutions were used for the elution of the metal. Although concentrated nitric acid elutes chromium, this can be best accomplished using hydrazine sulphate solutions which at the same time reduce the toxic Cr (VI) to the less toxic trivalent chromium state. Results obtained from batch experiments were applied to a continuous system using vertical columns. Moreover, an analytical application of the system in the determination of Cr (VI) presents in the leachate of an EAF dust was investigated by transfering the methodology to an on-line flow injection system.

Rapid determination of 99Tc in environmental samples by high resolution ICP-MS coupled with on-line flow injection system

High resolution inductively coupled plasma mass spectrometry coupled with an on-line flow injection system (FI-HR-ICP-MS) was applied to determine the ultra-trace level 99Tc in soil. The flow injection system (PrepLab™) was composed of two TEVA-SpecOresins, reduced remarkably the sample amounts and the analysis time, compared to the conventional analytical methods. In the flow injection system, Mo and Ru were sufficiently eliminated by using the flow injection system, with the decontamination factors of 1.6.104 and 9.9.105, respectively. With the present method, it was possible to determine ultra-low level of 99Tc in 3-6 g soil at 3–5 hours of analysis time per sample. The relative standard deviation for each sample was less than 4%. The detection limits for 99Tc was 85 fg.ml–1 (0.05 mBq.ml–1), which was calculated from the three times standard deviation of the count rate of the blank.

On-line dissolution of borate melt for simultaneous matrix isolation, concentration and flame atomic absorption determination of lead in phosphate rock

A previously developed on-line flow injection system for solid sample dissolution is described for matrix isolation, concentration and determination of lead in phosphate rock borate melt with flame atomic absorption spectroscopy (FAAS) detection. The flow system can handle slurries and allow solid sample digestion, simultaneous matrix isolation and analyte concentration. Various flow parameters were optimized including, sample size, flow rate, pH and buffer composition. Compared with direct determination by FAAS, the proposed method resulted in almost total elimination of matrix effect and a 15-fold increase in detectability. Ten samples per hour can be processed and analyzed for lead with a detection limit of 0.13 μg g −1 using simple equipment and a flame atomic absorption spectrometer. The analytical results obtained by the proposed method compared favorably with those obtained by mixed-acid digestion of the phosphate rock and graphite furnace atomic absorption spectroscopy (GFAAS).

Optimization of on-line microwave flow injection analysis system by artificial neural networks for the determination of ruthenium

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) was proposed in the optimization of a new on-line microwave flow injection system (FIA) for the determination of ruthenium, grounded on its catalytic effect on the oxidation of dibromocarboxyarsenazo (DBM-AsA) by potassium periodide under the microwave irradiation. The response function (RF) used was a weighted linear combination of two variables related to sensitivity and sampling rate. A neural network with extended delta-bar-delta (EDBD) learning algorithm was applied to predict the maximal RF, according to which the optimized conditions were obtained. The optimized new on-line microwave FIA system is able to determine ruthenium in 5–200 ng ml −1 range with a detection limit of 2.1 ng ml −1 and a recovery of 94.6%. A sampling rate of 58 h −1 was obtained. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization.

On-line flow injection solid sample introduction digestion and analysis: spectrophotometric and atomic absorption determination of iron, copper and zinc in multi-vitamin tablets

An on-line flow injection system with solid sample introduction, digestion, treatment and analysis was proposed. The solid sample powder is inserted into a special chamber and carried by the digestion solution to a thermally heated PVC coil (1.4 mm i.d.). The analyte metal as the chloro-complex was retained on a coarse-particle (>0.5 mm) anion exchange resin mini column. The resin beads are held between two plastic screens which allow insoluble residue to pass through to waste. After a brief column wash, the analyte is eluted with diluted HNO 3 and determined spectrophotometrically or by atomic absorption. The proposed novel configuration of the multi-channel pinch valve allows handling slurries without tube blockage or valve damage. The system performance was tested by the determination of Fe, Zn and Cu in multi-vitamin tablets. Fe was determined spectrophotometrically as the thiocyanate complex while Zn and Cu were determined by atomic absorption. Compared with conventional digestion and analysis procedures the flow system yields a reasonably accurate relative error (RE) <2% and precise results with relative standard deviation (R.S.D.) in the range of 2.5–4.2%.

Determination of bismuth in aluminium and in steels by electrothermal atomic absorption spectrometry after on-line separation using a minicolumn of activated carbon

A simple on-line separation and preconcentration flow injection system for the determination of Bi in steels and aluminium solutions by electrothermal atomic absorption spectrometry is proposed. The system requires only a manual injector–commutator and a peristaltic pump. Bismuth is separated after complexation with the ammonium salt of dithiophosphoric acid O,O-diethyl ester and sorption in a minicolumn filled with activated carbon, using ethanol as eluent, which is received in the autosampler cup of the electrothermal atomic absorption spectrometer. A L’vov platform covered with 500 µg of Ir allows a pyrolysis temperature of 900 °C. The preconcentration, pre-elution and elution flow rates were optimized. The column was cleaned with 2 mL of ethanol followed by 5 mL of water. For 10 mL of sample solution, an enrichment factor of about 14 was obtained for Bi in Al or Fe matrices. The detection limit, in the sample solution, was 0.048 µg L–1. The linear regression coefficients of the calibration curves were better than 0.997. For the certified steel samples, the results were in agreement with the reference values. For the non-certified aluminium sample, the recoveries of spiked samples were in the range 87–105%. The fact that the complexing agent does not complex Al and Fe(II) allows the separation of more than 99.5% of the major components.

Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line prereduction of Se(VI) to Se(IV)

An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters by hydride generation atomic absorption spectrometry with microwave-aided heating prereduction of Se(VI) to Se(IV). The samples and the prereductant solutions (4 mol l −1 HCl for Se(IV) and 12 mol l −1 HCl for Se(VI)) which circulated in a closed-flow circuit were injected by means of a time-based injector. This mixture was displaced by a carrier solution of 1% v/v of hydrochloric acid through a PTFE coil located inside the focused microwave oven and mixed downstream with a borohydride solution to generate the hydride. The linear ranges were 0–120 and 0–100 μg l −1 of Se(IV) and Se(VI), respectively. The detection limits were 1.0 μg l −1 for Se(IV) and 1.5 μg l −1 for Se(VI). The precision (about 2.0–2.5% RSD) and recoveries (96–98% for Se(IV) and 94–98% for Se(VI)) were good. Total selenium values were also obtained by electrothermal atomic absorption spectrometry which agreed with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is that the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters is performed in a closed system with a minimum sample manipulation, exposure to the environment, minimum sample waste and operator attention.

Determination of total phosphorus in waters and wastewaters by on-line UV/thermal induced digestion and flow injection analysis

An on-line flow-injection system for the determination of total phosphorus in waters and wastewaters is described. Digestion was performed using a UV photoreactor and a thermal digestion unit connected in series. The orthophosphate formed was detected as phosphomolybdenum blue after on-line filtration. Reagent and digestion conditions required to give optimal oxidation and hydrolysis of organic and condensed model compounds are reported. The flow-injection method gave complete recovery for all the model organic P compounds tested, and >85% recovery for condensed phosphates. When the proposed method was applied to a series of wastewater samples, the results obtained were in close agreement with those from a conventional batch digestion method. The technique was rapid (8 samples h −1 4 replicates), with a linear range of interest for wastewaters 0–18 mgPl −1 and a detection limit of 0.15 mgPl −1.