On-line Flow Injection Analysis Research Articles

Online headspace monitoring of volatile organic compounds using proton transfer reaction-mass spectrometry: Application to the multiphase atmospheric fate of 2,4-hexadienedial

Chemical processes in clouds have been suggested to contribute significantly to the mass of organic aerosol particles in the atmosphere. Experimental and theoretical evidence suggest that organic mass production in clouds can be substantial and depends on the concentration of organic precursor compounds available in the gas phase. The present study aims at studying the aqueous phase reactivity of one of these overlooked precursors, i.e. 2,4-hexadienedial, an important and toxic intermediate in the atmospheric oxidation of aromatic species. Cautious synthesis and purification of 2,4-hexadienedial was performed. Its effective Henry's law constant was measured using a new simple and fast method based on online flow-injection analysis. The reactivity of 2,4-hexadienedial in the aqueous phase relevant to atmospheric conditions was studied, including hydrate formation, photolysis, ∙OH- and SO4∙--oxidation as well as reaction with NH3. The results revealed a low hydration constant compared to other dicarbonyls (Khyd1 = 7 × 10−2) and no dihydrate formation, indicating in an intermediate solubility (KH = 1.0 × 104 M atm−1) and high absorption cross sections (σ278nm > 10−16 cm2 molecule−1). Compared to its gas phase photolysis, its aqueous phase photolysis showed low quantum yields (Φ290–380nm = 0.9 %), and a significant red shift of the absorbance maximum, leading to a fast aqueous photolysis kinetics (Jaq,atm = 8.7 × 10−5 s−1) under atmospheric solar radiation, but no triplet state formation was detected. Radical oxidation experiments revealed extremely rapid oxidation kinetics (k∙OH = 1.10 × 1010 M−1 s−1 and kSO4∙- = 1.4 × 109 M−1 s−1) driven by fast addition of the radicals to the unsaturated bonds. In contrast, the reaction with aqueous NH3 (kNH3 = 2.6 × 10−3 M−1 s−1) was found slower than glyoxal and 2-butenedial, likely due to the hyperconjugation of 2,4-hexadienedial. Using these new data complemented with assumed aqueous phase kinetics (for NO3, 3C* and 1O2 reactions) and previous gas-phase kinetic ones, the multiphase atmospheric fate of 2,4-hexadienedial was established under atmospheric conditions reported from previous field measurements and models. The results revealed a short day lifetime (∼1 h) and a long night lifetime (>12 h). It was shown that daytime atmospheric chemistry of 2,4-hexadienedial can be influenced by aqueous-phase reactivity during cloud events, up to ∼50 % under thick cloud conditions (Liquid Water Content >2000 g/m3), indicating that even a compound of intermediate solubility can be strongly affected by condensed-phase reactivity. Besides its fast aqueous phase reactivity towards ∙OH and photolysis, its daytime condensed-phase reactivity may be driven by reactions with dissolved triplet states (3C*), up to 35 %, highlighting the need to study further the kinetics, the nature and concentrations of dissolved 3C* under various atmospheric conditions. In addition, the molecular properties and atmospheric behavior of 2,4-hexadienedial were found different from those of glyoxal and 2-butenedial, highlighting the need for detailed atmospheric reactivity studies of polyfunctional compounds, in particular unsaturated compounds.

On-site and high-resolution spectrophotometric measurement of total dissolved sulfide in natural waters

Reliable high-resolution data is essential for understanding the aquatic sulfur biogeochemical processes. However, the accurate quantification of total dissolved sulfide (TDS) remains challenging due to its low concentration and vulnerability to oxidation. Furthermore, the frequency and the spatial coverage of TDS measurements are constrained by the cost of the laboratory analysis. In this study, an automated portable system was developed for on-site real-time measurement of trace TDS in natural waters. This system was based on the classic methylene blue (MB) spectrophotometric assay combined with on-line solid phase extraction (SPE) and flow injection analysis (FIA). A commercially available weak-cation-exchange cartridge was used as the SPE sorbent. Experimental parameters affecting the performance of the proposed system were optimized. Under the optimized conditions, linear calibration range of 0.02–2.50 μmol L−1 was obtained with a sample loading volume of 5.0 mL and a sample throughput of 12 h−1. The limit of detection could be lowered to 0.003 μmol L−1 by pre-concentrating 10.0 mL sample. The precision, determined as the relative standard deviation (RSD), was <2.75 % (n = 11) and the recoveries from spiked samples ranged from 54.4 % to 97.5 % with RSDs of 1.1–2.3 % (n = 3). Furthermore, the FIA-SPE-MB system was successfully deployed in the Taihu Lake for continuous 48 h monitoring of variations in TDS, demonstrating the applicability of this system for on-site TDS measurement in natural waters.

Flow Injection Electrochemical Quartz Crystal Microbalance with ICP-OES Detection: Recovery of Silver by Electrodeposition with Redox Replacement in a Flow Cell

We developed a new on-line hyphenated flow injection analysis technique (FI-EQCM-ICP-OES) that allows electrochemical deposition and stripping with mass detection and elemental analysis. This technique was used to study a new system for electrochemical recovery of silver from a 0.5 mM Ag+/5 mM Cu2+/0.5 M H2SO4 solution by pulsed electrodeposition with redox replacement (EDRR) in a small flow cell. The metal ions in a 500 μl sample are injected into the sulfuric acid carrier stream and deposited onto an electrochemical quartz crystal microbalance (EQCM) electrode housed in a 50 μl flow cell. The deposits are subsequently stripped off electrochemically in the same cell and analyzed downstream in an ICP-OES. The stripped metal layer was found to be composed of Ag with no detectable Cu for a redox replacement time of 10 s, and 91 wt.% Ag–9 wt.% Cu for a redox replacement time of 5 s. Microscopy measurements demonstrated that the electrode was covered with silver particles, some of which contain Cu in the case of the 5 s replacement time. This technique allowed the study of mass changes on the electrode during electrodeposition and open circuit times in each EDRR cycle in flowing solutions.

Physical and biological controls of dissolved manganese on the northern slope of the South China Sea

The South China Sea (SCS) is classified as an oligotrophic ocean because it has low nutrient and chlorophyll concentrations. We examined the biogeochemical cycle of dissolved manganese (DMn) on the northern slope of the SCS during two cruises (October 2014 and June 2015), and the effect of DMn enrichment on the growth of phytoplankton in field incubation experiments. DMn was measured spectrophotometrically by an on-line pre-concentration and flow injection analysis method. The concentration of DMn varied from 0.6 to 32.4 nM in the Pearl River Estuary, and decreased with distance from the coast. Moreover, DMn concentrations declined significantly (50–90%) as salinity increased between the Pearl River and the SCS. Vertical profiles of DMn reflected a typical scavenge-type distribution, and decreased with depth. Mixing between the Shelf Water and the Western Philippine Sea led to a Mn-rich plume (> 4 nM), which extended from the northern shelf into the slope regions of the SCS. The export of Mn-rich shelf waters was an important source of DMn for SCS, and this lateral input from the continental shelf could exceed atmospheric input. The incubation experiments showed that the addition of Mn stimulated phytoplankton growth. These results suggest that Mn may play an important role in regulating phytoplankton growth in the SCS.

Revealing the Structure and Mechanism of Palladium during Direct Synthesis of Hydrogen Peroxide in Continuous Flow Using Operando Spectroscopy

The direct synthesis of H2O2 is a dream reaction in the field of selective oxidation and green chemical synthesis. However, the unknown active state of the catalyst and the lack of a defined catalytic mechanism preclude the design and optimization of suitable catalysts and reactor setups. Here direct synthesis of H2O2 over Pd–TiO2 in water was investigated in a continuous flow reactor setup utilizing undiluted oxygen and hydrogen to increase aqueous-phase concentrations safely at ambient temperature and a pressure of 10 bar. In this experiment operando X-ray absorption spectroscopy (XAS) and online flow injection analysis for photometric quantification of H2O2 were combined to build catalyst structure–activity relationships in direct H2O2 synthesis. XAS at the Pd K absorption edge was used to observe the oxidation state and local Pd structure together with H2O2 production for three reactant ratio (H2/O2) regimes: hydrogen rich (>2), hydrogen lean (<0.5), and balanced (0.5–2). During H2O2 production, oxyge...

A Combined Kinetic and Thermodynamic Approach for the Interpretation of Continuous‐Flow Heterogeneous Catalytic Processes

The heterogeneous proline-catalyzed aldol reaction was investigated under continuous-flow conditions by means of a packed-bed microreactor. Reaction-progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate-determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow-injection analysis.

On-line flow injection analysis using gold particle modified carbon electrode amperometric detection for real-time determination of glucose in immobilized enzyme hydrolysate of waste bamboo chopsticks

Dual on-line flow injection analysis (FIA) systems were coupled to an immobilized enzyme reactor. The primary system was detected by amperometric enzyme electrode through a specifically designed three-electrode flow cell and a stopped-flow sampling and injection device to perform the successive real-time determination of glucose in the enzyme hydrolysate of waste bamboo chopsticks fibers. The secondary system was established via high-performance liquid chromatography-refractive index detection for comparison purpose. The novel enzyme electrode was made by chemically bonding both the redox mediator ferrocenecarboxaldehyde and glucose oxidase to a gold-particles modified pencil lead carbon electrode that possessed the widest linear standard calibration concentration range of 0–39.0 mM ( r 2 = 0.9956), a limit of detection of 7.8 μM, fast response time of 5 s, and a detection sensitivity of 2212 nA mM −1. The electrode was usable more than 50 days. The greatest amount of glucose produced from hydrolysis was 0.46 mM at 32 h. Interference from mannose and galactose was 7% and 5%, respectively, that was neglected by their small concentration in hydrolysate. The on-line FIA of amperometric enzyme electrode detection has good analytical precision (RSD 2.2–4.5%) and accuracy (94.4–97.7%) for the real-time glucose determination. The statistical analysis shows that no systematic error exists between the quantitative results of two FIA systems.

Spectrophotometric Determination of Ultra trace Tri & Hexavalent Chromium by Using on-line Flow Injection Analysis with Dual Pre-concentration Column

An on-line flow injection analysis with dual pre-concentration method was developed to determine the ultra trace tri and hexavalent chromium in water. In this system, the cation and anion pre-concentration columns were combined with a 10-port injection valve and then used to separate and concentrate Cr (III) and Cr (VI) selectively. The two species of concentrated chromium were sequentially eluted and determined by using HCl-KCl buffer of pH 1.8 as an eluent. Cr (III) was oxidized by hydrogen peroxide to Cr (VI). It was detected spectrophotometrically at 548 nm by complexation with DPC (diphenylcarbazide). Several factors such as concentration of <TEX>$H_2O_2$</TEX>, DPC and coil length in reaction condition were optimized. The linear range for Cr (III) and Cr (VI) was 0.1-50 <TEX>${\mu}g$</TEX>/L. The limit of detections (<TEX>$3{\sigma}$</TEX>) of Cr (III) and Cr (VI) were 52 ng/L and 44 ng/L under the optimized FIA system, and their recoveries 98% and 103%, respectively. This method was applied to analyze contamination level of chromium species in tap water, groundwater and bottled water.

Mycobial enhancement of ergothioneine by submerged cultivation of edible mushroom mycelia and its application as an antioxidative compound

Ergothioneine (2-mercaptohistidine trimethylbetaine, ESH) in mushroom is one of bioactive and functional components. In the present study, a method of producing ESH within a short period and with high productivity was established by applying submerged fermentation of edible Shiitake mushroom (Lentinula edodes) mycelia. High-resolution mass spectrometry and online flow injection analysis of 2,2-diphenyl-1-picrylhydrazyl scavenging activity clearly confirmed that ESH was the most potent antioxidant in the mycelial extract. Among several mushroom mycelia, Shiitake produced the highest amount of ESH (0.60mg/g dry weight (DW)). Optimisation of the culture medium was performed to achieve higher ESH production. The monosaccharide content in the medium, particularly fructose in combination with aspartic acid, was one of the factors that enhanced ESH production by 3.15-fold (1.89mg/g DW). Individual supplementation of 2mM methionine as an amino acid precursor yielded a significantly higher amount of ESH (3.45mg/g DW) compared to that of the control medium (1.85mg/g DW). The mycelial extracts containing ESH were effective in retarding the formation of secondary lipid oxidation products in the yellowtail red meat model during chilled storage as well as in the oxidation of linoleate and bleaching of beta-carotene in an oil-in-water emulsion system.

Determination of free catecholamines in urine by tandem affinity/ion-pair chromatography and flow injection analysis

Background A system was developed for the simultaneous measurement in urine of free catecholamines (i.e., dopamine, norepinephrine, epinephrine) and creatinine (i.e., an indicator of urine output and volume). This method was based on the use of tandem affinity/ion-pair HPLC and flow injection analysis. Methods The free catecholamines were extracted directly from urine by using an on-line phenylboronic acid affinity column. The extracted solutes were then separated and measured by ion-pair chromatography followed by amperometric detection. Creatinine was measured by an on-line flow injection analysis system based on the Jaffe reaction, which analyzed creatinine as it eluted non-retained from the phenylboronic acid column. Results Various factors were considered in the design and optimization of the phenylboronic acid column, the tandem affinity/ion-pair HPLC columns and the flow injection analysis system. The total analysis time for the final combined system was approximately 16 min per injection at 1 ml/min. This method was found to have good agreement with the expected results for control urine samples. The limits of detection for 20 µl samples (S/N = 3.0) were 1.8, 1.0 and 4.3 µg/l for norepinephrine, epinephrine and dopamine, respectively, while the limit of detection of creatinine was 5.0 mg/l. The linear response of this method extended over a 450 to 930-fold range in concentration for the catecholamines and covered the range of clinical interest. The within-day precision of this method was ± 2.0–2.7%. Conclusions The ability of this method to simultaneously monitor both creatinine and other analytes makes this HPLC/FIA system an attractive method for use in monitoring urinary compounds. With this approach it was possible to provide fast results for small volumes of random urine samples that were collected as part of a psychological study. The same method could also be utilized with 12 or 24 h urine specimens.

On-line solid-phase extraction and multisyringe flow injection analysis of Al(III) and Fe(III) in drinking water

A new analytical method was developed for on-line monitoring of residual coagulants (aluminium and iron salts) in potable water. The determination was based on a sequential procedure coupling an extraction/enrichment step of the analytes onto a modified resin and a spectrophotometric measurement of a surfactant-sensitized binary complex formed between eluted analytes and Chrome Azurol S. The optimization of the solid phase extraction was performed using factorial design and a Doehlert matrix considering six variables: sample percolation rate, sample metal concentration, flow-through sample volume (all three directly linked to the extraction step), elution flow rate, concentration and volume of eluent (all three directly linked to the elution step). A specific reagent was elaborated for sensitive and specific spectrophotometric determination of Al(III) and Fe(III), by optimizing surfactant and ligand concentrations and buffer composition. The whole procedure was automated by a multisyringe flow injection analysis (MSFIA) system. Detection limits of 4.9 and 5.6 microg L(-1) were obtained for Al(III) and Fe(III) determination , respectively, and the linear calibration graph up to 300 microg L(-1) (both for Al(III) and Fe(III)) was well adapted to the monitoring of drinking water quality. The system was successfully applied to the on-site determination of Al(III) and Fe(III) at the outlet of two water treatment units during two periods of the year (winter and summer conditions).

On-column polymer-imbedded graphite inlet electrode for capillary electrophoresis coupled on-line with flow injection analysis in a poly(dimethylsiloxane) interface.

A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 microm ID) in the PDMS structure, enabling independent flow characterization.

Quinoline-8-ol and its derivatives as preconcentration agents in flow injection analysis coupled to atomic and molecular spectrometric techniques.

Quinoline-8-ol, one of the most popular and versatile organic reagents, is known to react with several metals, because it has both a basic nitrogen and a phenolic group. Hence, quinoline-8-ol and its derivatives have been widely used as chelating and/or sorbent extraction agents in on-line flow injection analysis (FIA) along with a suitable detection technique. The state of the art for using quinoline-8-ol and its derivatives in FIA was studied in terms of the selectivity, sensitivity and precision. Emphasis was placed on validating these procedures by analyzing certified reference materials and applying these analytical methodologies to real samples for the determination of inorganics.

On-line incorporation of cloud point extraction to flow injection analysis.

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is demonstrated for the first time. The technical difficulties of inducing the cloud point phenomenon, separating the surfactant-rich phase from the aqueous phase, and detecting trace amounts of analyte(s) in the presence of the highly scattering surfactant medium in an on-line FIA system were resolved by the following: (1) mixing the sample solution containing the analyte(s) and CPE surfactant with an appropriate salting-out agent, (2) using a collection column to entrap the analyte-containing surfactant aggregates, and (3) employing the peroxyoxalate chemiluminescence reaction for the sensitive and selective determination of the analyte(s) in the presence of surfactant micelles. The figures of merit for the determination of coproporphyrin in pretreated urine samples were as follows: precision, 1.1-2.2% (RSD); limit of detection, 2.0 microg/L; and the calibration curve was linear from 46 to 2319 (micro/L (r = 0.9996).

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%.

Kinetic Determination of Ruthenium by on-line Microwave Flow Injection Analysis

ABSTRACT A new rapid, high sensitive and selective on-line microwave flow injection method has been developed for the determination of micro-amounts of ruthenium, based on its catalytic effect on the oxidation of dibromocarboxyarsenazo (DBM-AsA) by potassium periodide in acidic medium. The assay is performed in a microwave-induced flow injection analyzer by measuring the absorption of DBM-AsA at 538 nm spectrophotometrically.

Fed-batch production of a soluble β-1,4-galactosyltransferase with Saccharomyces cerevisiae

A feedback-controlled fed-batch process for the recombinant production of a soluble human β-1,4-galactosyltransferase (NdrGal-T) with Saccharomyces cerevisiae was developed and scaled up to the pilot scale. A 5000 U NdrGal-T fermentation run was performed on a 300 l scale. Indirect feedback control of the glucose feeding with RQ data at a set-point of RQ = 1.1 resulted in higher NdrGal-T activities (30 U/l) than direct feedback control of glucose with on-line flow-injection analysis (9 U/l). This increase in final activity of NdrGal-T by a factor of 42 compared to published data makes the fed-batch production of glycosyltransferases with a Saccharomyces cerevisiae expression system competitive with cell-culture systems.

Fast on-line flow injection analysis system for IgG monitoring in bioprocesses

An automated immunoassay, with one affinity component immobilized on a solid surface, has been developed to monitor the production of different immunoglobulins during mammalian cell cultivation processes. The whole analysis device is based on the principle of flow injection analysis (FIA) and a cartridge with the immobilized affinity component is implemented into the FIA system. This cartridge is filled with a carrier material to which protein G is covalently bound. After sample injection, binding of the IgG on the protein G within the cartridge takes place while after a washing step, the IgGs are eluted by a pH shift, and the IgG concentration is monitored via fluorescence. In the automated immunoassay, undiluted cell free samples from the reactor or from down-stream processing can be analyzed directly. Due to the separation the IgG can be detected without interference from other sample components by protein fluorescence. The results are obtained with analysis times below 6 min. Sample volumes of less than 100 μl may be used. The assay is sensitive to concentrations from 5 up to 500 μg ml −1. Using this FIA-System, immunoglobulins G, produced in different media, were successfully monitored. The results of the assay were validated by ELISA.

Automated determination of levodopa and carbidopa in plasma by high-performance liquid chromatography-electrochemical detection using an on-line flow injection analysis sample pretreatment unit

An automated analytical procedure is described for the parallel determination of l-3,4-dihydroxyphenylalanine (levodopa, l-dopa, LD) and the analogous hydrazine compound carbidopa (CD) in dog plasma by ion-pair high-performance liquid chromatography with electrochemical detection (HPLC-ED). After deproteinization of the plasma samples with perchloric acid the catecholamines were extracted from the supernatant by adsorption on a small column filled with alumina. The extraction and redissolution were automatically performed in a flow injection analysis unit (FIA) coupled to the HPLC system. The performance of the whole system was tested on dog plasma samples including specimens taken after oral administration of the anti-Parkinsonism drug Duellin ®, which is a combination tablet of levodopa and carbidopa.