Continuous-flow Chemiluminescence Research Articles

Micron-confined microcapturer-triggered Fenton as efficient and environmentally-friendly method for simultaneously capturing bloom-forming cyanobacteria, inhibiting cell-regrowth and degrading microcystins

The frequent outbreak and continuous expansion of harmful cyanobacteria blooms (HCBs) have become important environmental concerns and public health issues globally. In this study, the “micron-confined Fe(II)-modified-microcapturer (FMC)-triggered Fenton” technology was established as advanced process adaptable to the HCB treatment. Results show that 95.7–99.4% of cyanobacteria cells were captured and separated from the HCB water at the optimum doses of Fe(II) and H2O2 within only 30 s. The chain-like cyanobacteria of A. flos-aquae were easier to be collected by FMCs compared with the unicellular M. aeruginosa. It was confirmed by scanning electron microscopic observation and fluorescence staining flow cytometry measurement that the FMC-carrying Fe(II) played the roles of both cell-gripper and Fenton catalyst. During the one-step process, the FMC-triggered Fenton effectively inhibited the cyanobacteria regrowth via inactivating the cells, and meanwhile, the microcystins of LR and RR were removed. The analyses by continuous flow chemiluminescence and X-ray photoelectron spectroscopy denote that FMCs performed efficiently in capture and Fe(II)-catalytic oxidation through increasing mass transfer, exposing sufficient active reactive oxygen species active-sites on the FMC surface and accelerating electron transfer. The micron-field-confined cascade processes retained the robust performance of Fenton against the high pH of bulk HCB water. This novel interface-dependent Fenton method is a promising tool for HCB treatment owing to its great efficiency, versatility, rapidness and eco-environmental friendliness.

Dynamic monitoring and regulation of pentachlorophenol photodegradation process by chemiluminescence and TiO2/PDA

Pentachlorophenol (PCP), a highly toxic halogenated aromatic compound, and its direct photolysis or TiO2 photocatalysis may generate toxic intermediates and induce secondary pollution in the environment. It is urgently needed to design a strategy to inhibit the toxic intermediates in the photodegradation of PCP. To achieve this, polydopamine (PDA), a non-toxic substance, modified TiO2 (P25/PDA) nanoparticles were synthesized and used to improve the PCP photodegradation process. The dynamic tracking of toxic intermediates tetrachloro-1,4-benzoquinone (TCBQ) and trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) produced in the PCP photodegradation process were obtained by continuous flow chemiluminescence. Combined with reactive oxygen species (ROS) measurements, P25/PDA could approximatively depress 70 % TCBQ and 40 % OH-TrCBQ generation through the regulation of ROS especially the generation of a fairly large amount of H2O2 (about 30 μM) and O2− (about 20 μM) on the surface of the P25/PDA. The toxicity evaluation showed that the photodegradation of PCP by P25/PDA was a safer and green approach. Therefore, it was instructive to inhibit the formation of highly toxic intermediates in the photodegradation of environmental contaminants by regulating the ROS generated on the surface of the photocatalysts.

Dynamic Tracking of Highly Toxic Intermediates in Photocatalytic Degradation of Pentachlorophenol by Continuous Flow Chemiluminescence.

Photocatalytic degradation is a powerful technique for the decomposition of pollutants. However, toxic intermediates might be generated which have become a great concern recently. In the present work, a continuous flow chemiluminescence (CFCL) method was developed for dynamic monitoring of toxic intermediates generated in the photocatalytic degradation of pentachlorophenol (PCP). Among the main intermediates, tetrachloro-1,4-benzoquinone (TCBQ) and trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) showed higher or similar toxicity to PCP. As both TCBQ and OH-TrCBQ can produce chemiluminescence (CL) in the presence of H2O2, a CFCL system was established for the dynamic tracking of the two toxic intermediates. A PCP/TiO2 suspension was irradiated in a photoreactor, pumped continuously into a detection cell, and mixed with H2O2 to produce CL. The time-dependent CL response displayed two distinctive peaks at pH 7, which were attributed to the generation of OH-TrCBQ and TCBQ, respectively, by comparing with their changes measured by high-performance liquid chromatography (HPLC). Furthermore, the CL response curve of PCP/TiO2 suspension showed a pattern very similar to their bacteria inhibition. Therefore, the CFCL could be used as a simple and low-cost method for online monitoring of TCBQ and OH-TrCBQ to ensure complete removal of not only PCP but also highly toxic degradation intermediates.

Continuous generation of hydroxyl radicals for highly efficient elimination of chlorophenols and phenols catalyzed by heterogeneous Fenton-like catalysts yolk/shell Pd@Fe3O4@metal organic frameworks

Core/shell Fe3O4-decorated Pd nanoparticles (NPs) hybrids (Pd@Fe3O4) are prepared through a “green”, and one-pot chemical process. The Pd@Fe3O4 hybrids consisted of faceted quasi-spherical Pd nanoparticles (NPs) cores (∼20 nm) surrounded by close-packed Fe3O4 NPs (∼7 nm). To improve the stability and avoid aggregation of Pd@Fe3O4 hybrids in water, hollow Fe-metal organic frameworks (Fe-MOFs) were applied to enwrap Pd@Fe3O4 to obtain yolk/shell structured composites. Sub-10 nm Fe3O4 and Pd NPs close to each other were distributed evenly in the MOFs shell of Pd@Fe3O4@MOFs. The yolk/shell Pd@Fe3O4@MOFs can catalyze the oxidative degradation of chlorophenols and phenols by hydroxyl radicals (OH) decomposed from H2O2. With low molar ratio of H2O2/pollutants, the pollutants are degraded and mineralized efficiently and rapidly. The outstanding catalytic efficiency of Pd@Fe3O4@MOFs is contributed by the fast and continuous generation of OH radicals in Pd@Fe3O4@MOFs suspension which is detected with the electron spin resonance spin-trap technique and a continuous-flow chemiluminescence system. Lack of consumption of hydroperoxyl radicals/superoxide radicals (HO2/O2−) in the Pd@Fe3O4@MOFs-H2O2 system might suggest that the production of OH radicals results from the electron transferring from Pd to Fe3O4 component both in the inner Pd@Fe3O4 and MOF shell, which facilitates fast Fe(III)/Fe(II) redox cycle.

Quantitative Analysis of Reactive Oxygen Species Photogenerated on Metal Oxide Nanoparticles and Their Bacteria Toxicity: The Role of Superoxide Radicals.

Ecotoxicity of engineered nanoparticles (NPs) has become the focus of considerable attention because of their wide applications. Reactive oxygen species (ROS) play important roles in the toxicity mechanisms of engineered metal oxide NPs. This work aimed to understand quantitatively the contribution of photogenerated ROS on metal oxide NPs to their toxicity. The dynamic generation of O2•-, •OH, and H2O2 in aqueous suspensions of photoilluminated metal oxide nano- and bulk particles (TiO2, ZnO, V2O5, CeO2, Fe2O3, and Al2O3) was measured by a continuous-flow chemiluminescence (CFCL) detection system. Superoxides were generated on all six nanoparticles as well as bulk TiO2 and ZnO, with nano TiO2 producing the highest concentration (180 nM). Hydroxyl radicals were detected on both nano- and bulk TiO2 and ZnO, whereas H2O2 was detected only on TiO2 and ZnO nanoparticles. The generation of ROS can in general be interpreted by the electronic structures and surface defects of the NPs and the ROS redox potentials. Furthermore, acute toxicity of the six metal oxide particles to a luminescent bacterium, P. phosphoreum 502 was assessed after photoillumination. The toxicity effect was attributed to the long-lived O2•- radicals on the nanoparticlce, and its potency follows the order of TiO2 > ZnO > V2O5 > Fe2O3 > CeO2 > Al2O3, which is the same as the order of the O2•- concentration measured by CFCL. Our work revealed quantitatively the important role superoxide radicals play in the toxicity of various metal oxide nanoparticles after photoillumination.

Online Quantification of O2·-and H2O2and Their Formation Kinetics in Ultraviolet (UV)-Irradiated Nano-TiO2Suspensions by Continuous Flow Chemiluminescence

Online Quantification of O₂^·-and H₂O₂and Their Formation Kinetics in Ultraviolet (UV)-Irradiated Nano-TiO₂Suspensions by Continuous Flow Chemiluminescence

Online detection of reactive oxygen species in ultraviolet (UV)-Irradiated nano-TiO2 suspensions by continuous flow chemiluminescence.

Reactive oxygen species (ROS) play very important roles in the photocatalytic reactions of semiconductors. Using a continuous flow chemiluminescence (CFCL) system, we developed three methods for the selective, sensitive, and online detection of O2(• -), •OH, and H2O2 generated during ultraviolet (UV) irradiation of nano-TiO2 suspensions. TiO2 nanoparticles were irradiated in a photoreactor and pumped continuously into a detection cell. To detect O2(• -), luminol was mixed with TiO2 before it entered the detection cell. For the detection of short-lived •OH, phthalhydrazide was added into the photoreactor to capture •OH, and then mixed with H2O2/K5Cu(HIO6)2 to produce chemiluminescence (CL). To detect H2O2, an irradiated TiO2 suspension was kept in darkness for 30 min, and then mixed with luminol/K3Fe(CN)6 to produce CL. The selectivity of each method for a particular ROS was verified by using specific ROS scavengers. For a given ROS, a comparison between CL and conventional method showed good agreement for a series of TiO2 concentrations. The sensitivity of CL method was approximately 3-, 1200-, and 5-fold higher than the conventional method for O2(• -), •OH, and H2O2, respectively. To demonstrate the utility of the methods, ROS in three different types of TiO2 suspensions was detected by CFCL. It was found that photodegradation efficiency of Rhodamine B correlated the best (R(2) > 0.95) with the amount of photogenerated •OH, implying that •OH was the major oxidant in Rhodamine B photodegradation reaction. CFCL may provide a convenient tool for the studies on the reaction kinetics of ROS-participated decomposition of environmental contaminants.

Determination of piroxicam in pharmaceutical preparations by continuous-flow chemiluminescence

A simple and rapid chemiluminescent method for the assay of piroxicam in pure and in pharmaceutical formulations by flow analysis is proposed. The method is based on the reaction of this drug with N-bromosuccinimide (NBS) in alkaline medium in the presence of fluorescein as sensitizer. The emission intensity is greatly enhanced by the presence of cetyltrimethylammonium bromide (CTAB). The optimum chemical conditions for the chemiluminescence emission were investigated. The calibration graph was linear for the concentration range from 2.0 to 12.0 μg mL−1. The detection limit, according to Clayton et al.(C. A. Clayton, J. W. Hines and P. D. Elkins, Anal. Chem., 1987, 59, 2506), was 0.72 μg mL−1. For analysis of 10 solutions of 8.0 μg mL−1 of this anti-inflammatory, if error propagation theory is assumed, the relative error was less than 1.5%. The present chemiluminescence procedure was applied to the determination of piroxicam in Spanish pharmaceutical formulations, with excellent recoveries, as the determination is free from interference from common excipients.

Droplet detector for the continuous flow luminol–hydrogen peroxide chemiluminescence system

A droplet detector with high sensitivity and low consumption of reagents and sample for continuous flow chemiluminescence (CL) detection has been developed. The proposed system directly mixes sample with luminescence reagents to form a small droplet, thanks to the gravity force and surface tension of water, in front of a photomultiplier tube (PMT) where the CL reaction takes place. The PMT can then instantaneously record the maximum CL light signal emitted from the whole reaction process. This small droplet can replace the conventional spiral-shaped flow cell for flow injection CL analysis and the droplet detector can reduce interference from the reaction products and residual reagents. To evaluate the potential application of the proposed detector, the CL detection of Fe(ii) was assessed under the alkaline luminol-hydrogen peroxide conditions. The CL intensity increased linearly with the concentration of Fe(ii) ranging from 10.0 to 1000 nmol dm(-3) with a detection limit of 7.16 nmol dm(-3) (S/N = 3). The droplet detector allows highly sensitive, stable and fast CL detection of analytes, and thus is promising for application to other analytes having fast CL reaction rates.

Simultaneous determination of glucose, fructose and lactose in food samples using a continuous‐flow chemiluminescence method with the aid of artificial neural networks

In this study, a simple continuous-flow chemiluminescence (CL) system was developed for simultaneous determination of glucose, fructose and lactose in ternary mixtures of reducing sugars without previous separation. This method was based on the different kinetics of the individual sugars in the oxidation reaction with potassium ferricyanide. The known luminol-K(3)Fe(CN)(6) CL system was used to measure the kinetic data of the system. The CL intensity was measured and recorded every second from 1 to 300 s. The data obtained were processed chemometrically using an artificial neural network. The relative standard errors of prediction for three analytes were <5%. The proposed method was successfully applied to the simultaneous determination of the three sugars in some food samples.

Simultaneous determination of three organophosphorus pesticides residues in vegetables using continuous-flow chemiluminescence with artificial neural network calibration

In this article, a continuous-flow chemiluminescence (CL) system with artificial neural network calibration is proposed for simultaneous determination of three organophosphorus pesiticides residues. This method is based on the fact that organophosphorus pesticides can be decomposed into orthophosphate with potassium peroxodisulphate as oxidant under ultraviolet radiation and that the decomposing kinetic characteristics of the organophosphorus pesticides with different molecular structure are significantly different. The produced orthophosphate can react with molybdate and vanadate to form the vanadomolybdophosphoric heteropoly acid, which can oxidize luminol to produce intense CL emission. The CL intensity of the solution was measured and recorded every 2 s in the range of 0–250 s. The obtained data were processed chemometrically by use of a three-layered feed-forward artificial neural network trained by back-propagation learning algorithm, in which input node, hidden node and output nodes were 65, 21 and 3, respectively. The proposed multi-residue analysis method was successfully applied to the simultaneous determination of the three organophosphorus pesticides residue in some vegetables samples.

Simultaneous determination of rifampicin and isoniazid by continuous-flow chemiluminescence with artificial neural network calibration

In this paper a continuous-flow chemiluminescence (CL) system with artificial neural network calibration is proposed for simultaneous determination of rifampicin and isoniazid. This method is based on the different kinetic spectra of the analytes in their CL reaction with alkaline N-bromosuccinimide as oxidant. The CL intensity was measured and recorded every second from 1 to 300 s. The data obtained were processed chemometrically by use of an artificial neural network. The experimental calibration set was 20 sample solutions. The relative standard errors of prediction for both analytes were approximately 5%. The proposed method was successfully applied to the simultaneous determination of rifampicin and isoniazid in a combined pharmaceutical formulation.

Improvement of the tetrachloromercurate absorption technique for measuring low atmospheric SO2 mixing ratios

During the Gas‐Phase Sulfur Intercomparison Experiment (GASIE) in 1994 an analytical system for measuring sulfur dioxide mixing ratios at low parts per trillion (pptv) levels was employed. It is based on the absorption of SO2 on a tetrachloromercurate(II)‐impregnated filter. The subsequent analysis uses a chemiluminescence reaction by treating the resulting disulfitomercurate(II) complex with an acidic cerium sulfate solution. An improved sampling device has been introduced that increases the maximum sampling volume from 200 L to 500 L. It is also possible to determine the blank value accurately for each sample. The absorption efficiency of the sampling system is 98.7±6.4% at a nominal flow rate of 10 L/min. The calculated (3σ) detection limit is 3±1 pptv SO2. The sample solution is stable for up to 30 days, which allows the samples to be safely stored or shipped before analysis. This permits the use of a sensitive, compact, and reliable sampling system in the field with subsequent analysis under optimal conditions in the laboratory. A continuous flow chemiluminescence (CFCL) analyzer for on‐line measurements is also presented. The system is based on the same chemical principles as the described filter technique.

Continuous-flow chemiluminescence detection comprising a rotating reactor

This paper describes the implementation of chemiluminescence detection in an unsegmented continuous-flow system by using a detection cell comprising a rotating disk reactor. Rotation introduces convectional movement and facilitates reaction with concomitant enhancement of the chemiluminescence signal. The rotating disk reactor can also be used as a carrier for immobilized rate modifier (catalyst or promoter) of the luminescence reaction. The overall system has been characterized by means of the luminol-H 2O 2 reaction with hexacyanoferrate(III) ions and cobalt phthalocyanine as rate modifiers. The versatility of the device for analytical chemiluminescence measurements is illustrated.

Chemiluminescence analysis of nitric oxide in small-volume samples by a modified injection method

To detect NO in samples of the headspace of static cores, a sample-mixing unit was developed which made it possible to detect NO in small-volume samples (50μl to 10 ml) by a continuous flow chemiluminescence NO analyzer. The sample-mixing unit enables the detector of the NO analyzer to reach a steady-state response. The detection limit was 3.5 pmol NO in a sample, which is equivalent to 8.5 ppbv NO in a 10-ml sample or 85 ppbv No in a 1-ml sample at room temperature. The coefficient of variation between replicates varied between 6.4% at low NO levels and 0.6% at high NO levels. The linear response was good, theR2 value was above 0.99 even in the lowest detection range. The sample-mixing unit in combination with an NO analyzer provides a sensitive, reliable, easy to use method for the detection of NO in incubation systems with small headspace volumes such as static cores.

Determination of ammonia/ammonium ion in water by continuous-flow chemiluminescence after derivatization to an isoindole.

アンモニウムイオンをオルトフタルジアルデヒド及び2-メルカプトエタノールを用いて蛍光性の誘導体に変換した後,シュウ酸アリール-過酸化水素化学発光系で定量する方法を検討した.誘導体化反応は約200秒で完了するので,連続的なフロー分析が可能となった.最適化した条件で検出限界はNH3として2.9ng ml-1であり,6μg ml-1まで直線的な応答が得られた.第一アミン類は定量的に誘導体化・検出されるが,その他の共存物質の影響は小さい.雨水試料に適用し,従来法とよく一致することを確認した.

Determination of thiamine by continuous flow chemiluminescence measurement

The chemiluminescence produced by oxidation of thiamine by ferricyanide in alkaline medium has been investigated by using a simple continuous flow analyser and a procedure developed for the determination of thiamine hydrochloride or nitrate in the range 2.00 × 10 −5−5.00 × 10 −4 M (equivalent to 6.75-169 μg/ml thiamine hydrochloride) with coefficients of variation <2%. A measurement rate of 112/hr can be obtained. When applied to pharmaceutical formulations, the only interferent among common excipients and coexisting drugs is ascorbic acid. The results obtained for the assay of dosage forms compared well with those obtained by an official method and demonstrated an error <4%.

Determination of quinine and quinidine by continuous-flow chemiluminescence

A rapid and precise continuous-flow method is described for the determination of quinine and quinidine (5.00–500 μg ml −1) which is based on the sensitizing effect of the compounds on the chemiluminescent oxidation of sulphite by cerium(IV). When applied to tablets, the procedure is relatively free from interferences from common excipients. The results obtained for the assay of commercial formulations compared well with those obtained by an official method and demonstrated good accuracy and precision.

Continuous-flow chemiluminescence determination of some corticosteroids

A continuous-flow method for the determination of cortisone, hydrocortisone, prednisolone and methylprednisolone in the range 0.100–1.00 µg ml–1 and of dexamethasone and betamethasone in the range 0.500–5.00 µg ml–1 is described. The procedure is based on the action of each corticosteroid as a sensitiser on the chemiluminescent oxidation of sulphite by cerium(IV). The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 40 per hour with a relative error of <6%. The method was evaluated by carrying out recovery experiments and by analysing commercial formulations. Results agreed well with those given by an official method.

Continuous-flow chemiluminescence determination of isoniazid by oxidation with N-bromosuccinimide

A rapid and precise continuous-flow method is described for the determination of isoniazid (0.050-20.0 micrograms ml(-1)) based on the chemiluminescence produced during its reaction with N-bromosuccinimide in alkaline medium. The emission intensity is greatly enhanced by the presence of ammonia. The procedure is automated and samples can be analysed at a rate of 112 solutions per hour with a relative error of about 2%. When applied to tablets, the method is relatively free from interferences from common excipients and co-existing compounds. The results obtained for the assay of commercial preparations compared well with those obtained by an official chemical method and demonstrated good accuracy and precision.