Gold nanoparticle‐enhanced capillary electrophoresis‐chemiluminescence assay of trace uric acid

A sensitive method based on gold nanoparticle‐enhanced CE‐chemiluminescence (CL) detection was developed for quantifying uric acid (UA) in serum. In this work, gold nanoparticles were added into the running buffer of CE to catalyze the post‐column CL reaction between luminol and hydrogen peroxide, achieving highly efficient CL emission. Negative peaks were produced due to the inhibitory effects on CL emission from UA eluted from the electrophoretic capillary. The decrease in CL intensity was proportional to the concentration of UA in the range of 2.5×10^?7–1.0×10^?5 M. Detection limit was 4.6×10^?8 M UA. Ten human serum samples were analyzed by the presented method. Serum level of UA was found to be in the range from 204 to 324 μM for healthy subjects (n=5), and from 464 to 497 μM for diabetic patients (n=5). The two groups were significantly different (p<0.05). The results suggested a potential application of the proposed assay in rapid primary diagnosis of diseases such as diabetes.     

Use of capillary electrophoresis with chemiluminescence detection for sensitive determination of homocysteine

A sensitive capillary electrophoresis (CE) method with chemiluminescence (CL) detection was developed for the determination of homocysteine (HCys) in human plasma. In this work, N‐(4‐aminobutyl)‐N‐ethylisoluminol was used as tagging reagent to label the analyte for achieving high assay sensitivity. N‐(4‐Aminobutyl)‐N‐ethylisoluminol‐tagged HCys after CE separation reacted with hydrogen peroxide in the presence of horseradish peroxidase, producing CL emission. Experimental conditions for labeling analyte, CE separation, and CL detection were studied. The CL intensity was proportional to the concentration of HCys in the range of 2.5×10^?8 to 5.0×10^?6 M. Detection limit (S/N=3) was 7.6×10^?9 M. Human plasma samples from healthy donors were analyzed by the presented method. HCys levels were found to be in the range of 9.50–15.3 μM.     

Stopped-flow study of the enhanced chemiluminescence for the oxidation of luminol with hydrogen peroxide catalyzed by microperoxidase 8

The presence of carbonate or Tris causes a dramatic enhancement in the cheminluminescence (CL) for the oxidation of luminol with hydrogen peroxide catalyzed by microperoxidase 8 (MP8). A nearly constant enhancement in CL was observed over a wide range of H₂O₂ and luminol concentrations. The enhancement in CL is strongly pH-dependent, varying from 1.3 to 22.2 for carbonate and 1.6 to 10.2 for Tris. The CL enhancement is much more prominent at pH 9-10 than at high pH (>10.5) because of the extremely weak CL emission at pH below 10 when no enhancer is present. The CL enhancement is attributed to an accelerated CL cycle and the existence of alternative routes for luminol CL, possibly involving the carbonate, or Tris radicals. The dramatic enhancement in CL of the MP8-luminol-H₂O₂ system by the readily available reagents, sodium carbonate or Tris, will have general applications for sensitive CL assays. As an example, the presence of antioxidant results in a diminished and delayed CL emission, allowing the determination of its concentration at sub-micromolar level.     

Chemiluminescent Determination of Vitamin B12 Using Charge Coupled Device (CCD)

A method was developed for the determination of vitamin B₁₂ based on the enhancement of cobalt (II) on the chemiluminescence (CL) reaction between luminol and percarbonate (powerful source of hydrogen peroxide). The release of cobalt (II) from the vitamin B₁₂ was reached by a simple and fast microwave digestion (20 s microwave digestion time and a mix of nitric acid and hydrogen peroxide). A charge coupled device (CCD) photodetector, directly connected to the cell, coupled with a simple continuous flow system was used to obtain the full spectral characteristics of cobalt (II) catalyzed luminol-percarbonate reaction.

The optima experimental conditions were established: 8.0 m mol L^?1 luminol in a 0.075 mol L^?1 carbonate buffer (pH 10.0) and 0.15 mol L^?1 sodium percarbonate, in addition to others experimental parameters as 0.33 mL s^?1 flow rate and 2 s integration time, were the experimental conditions which proportionate the optimum CL emission intensity. The emission data were best fitted with a second-order calibration graph over the cobalt (II) concentration range from 4.00 to 300 µ g L^?1 (r² = 0.9990), with a detection limit of 0.42 µ g L^?1. The proposed method was successfully applied to the determination of vitamin B₁₂ in pharmaceuticals.     

Determination of carbaryl by flow injection with luminol chemiluminescence inhibition detection

A flow-injection procedure is described for the determination of carbaryl based on its inhibition effect on luminol-cobalt(II) chemiluminescence reaction in alkaline medium in the presence of hydrogen peroxide. The calibration data over the range 5.0?×?10^?7 to 20?×?10^?6?M give a correlation coefficient (r ²) of 0.9972 with relative standard deviations (RSD; n?=?4) in the range of 1.0–2.1% with a limit of detection (3?×?blank noise) of 2.37?×?10^?7?M for carbaryl. The sample throughput was 120?h^?1. The effects of some carbamates, anions, and cations were studied on luminol CL system for carbaryl determination. The proposed method has been applied to determine carbaryl in natural waters.     

On the Effect of Hydrogen Peroxide on the Flow‐Injection Determination of Platinum Based on Luminol Chemiluminescent Reaction

Abstract

A flow‐injection chemiluminescent (CL) method for the determination of trace amounts of Pt(IV) based on the oxidation reaction of luminol in alkaline solution is proposed. The effect of Pt(IV) on the oxidation of luminol was studied in the absence and in the presence of hydrogen peroxide. The positive effect of hydrogen peroxide as well as chloride ions on the sensitivity of measurements was observed. The developed method is characterized by a low limit of detection of Pt (LOD=0.06 ng mL^?1) and good reproducibility (RSD=2.2%). The addition of hydrogen peroxide to the reaction medium resulted in decreasing of platinum detection limit to 0.03 ng mL^?1.     

Screening of chemiluminescent systems for the determination of some biologically important organic compounds

Screening tests are described for the development of chemiluminescence systems (oxidizing systems) capable of detecting biological organic compounds. The light emission depends strongly on the oxidizing systems employed. Acidic permanganate system gives rise to light emission for many compounds, including catechols, catecholamines, triphenols and indoles. The following oxidizing systems led specifically to chemiluminescence for hydroquinone, adrenaline or phenylpyruvic acid: 10^?1 M thiosulphate with 10^?1 M sodium hydroxide and 10^?4 M Ag (I), 0.3 % hydrogen peroxide with 10^?3 M sodium hydroxide/50% acetonitrile and 10^?4 M Fe (II), and 0.3% hydrogen peroxide with 10^?2 M sodium hydroxide/10^?2 M didodecyldimethylammonium bromide and 10^?4 M Co(II), respectively.     

A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

Evaluation of peroxide value of olive oil and antioxidant activity by luminol chemiluminescence

Three procedures are developed and investigated for the simple and fast determination of peroxide value of olive oil by luminol chemiluminescence. The procedure using hemin as catalyst in carbonate alkaline solution allows the determination of hydrogen peroxide within the range 0.014-50 μM. The method can be used for the determination of peroxide value within the range 2.00-30.0 mequiv. O₂/kg oil and results correlate very well (r² = 0.99) with those of the official method. All reagents are aqueous solutions and olive oil is dissolved in acetone:ethanol mixed solution and, hence, the method is using minimal amounts of organic solvents and can be successfully applied to field analysis. Antioxidant activity of five common compounds found in natural products was determined by using luminol CL with Co(II) as EDTA complex as catalyst at pH 9.00.     

Determination of Gallic Acid by Flow Injection Analysis Based on Luminol‐AgNO3‐Ag NPs Chemiluminescence System

A novel flow injection procedure has been developed for the determination of gallic acid based on the enhancement function for luminol‐AgNO₃‐Ag NPs chemiluminescence (CL) system by gallic acid. The enhancement mechanism was proposed for the reinforcing effect of the gallic acid on the CL system. The UV‐vis absorption spectrum and CL emission spectrum were applied to confirm the mechanism. The method is simple, rapid and sensitive with a detection limit of 5×10^?10 g·mL^?1 and a linear range of 8.0×10^?10–1.0×10^?7 g·mL^?1. The relative standard deviation (RSD) is 1.3% for eleven measurements of 5×10^?8 g·mL^?1 gallic acid. The method has been successfully applied to the determination of gallic acid in Chinese proprietary medicine–Jianmin Yanhou tablets and synthesized samples.     

Flow injection determination of hydrogen peroxide using diperiodatoargentate- and diperiodatonickelate-luminol chemiluminescence

A novel chemiluminescence (CL) method for the determination of hydrogen peroxide is described. Method is based on the transition metals in highest oxidation state complex, which include diperiodatoargentate (DPA) and diperiodatonickelate (DPN) and show excellent sensitisation on the luminol-H₂O₂ CL reaction with low luminol concentration in alkaline medium. In particular, the sensitiser which was previously reported (such as Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe³⁺, Cr³⁺, KIO₄, K₃Fe(CN)₆ etc.) to be unobserved CL due to poor sensitisation with such low concentration of luminol which makes the method hold high selectivity. Based on this observation, the detection limits were 6.5?×?10^?9?mol?L^?1 and 1.1?×?10^?8?mol?L^?1 hydrogen peroxide for the DPN- and DPA-luminol CL systems, respectively. The relative CL intensity was linear with the hydrogen peroxide concentration in the range of 2.0?×?10^?8–6.0?×?10^?6?mol?L^?1 and 4.0?×?10^?8–4.0?×?10^?6?mol?L^?1 for the DPN- and DPA-luminol CL systems, respectively. The proposed method had good reproducibility with a relative standard deviation of 3.4% (8.0?×?10^?7?mol?L^?1, n?=?7) and 1.0% (2.0?×?10^?6?mol?L^?1, n?=?7) for the DPN- and DPA-luminol CL systems, respectively. A satisfactory result has been gained for the determination of H₂O₂ in rainwater and artificial lake water by use of the proposed method.     

Carbon dots-enhanced luminol chemiluminescence and its application to 2-methoxyestradiol determination

In this study, the fluorescent carbon dots (CDs) of good biocompatibility and low toxicity was prepared by a carbonation route, and a strong enhancement effect of CDs on the luminol-K₃Fe(CN)₆ chemiluminescence (CL) system was observed. 5?±?1?nm CDs were used as catalysts to enhance the reaction sensitivity. In the presence of 2-methoxyestradiol (2-ME), the CL intensity of CDs-luminol-K₃Fe(CN)₆ was significantly inhibited. The relative CL intensity was linearly related to the 2-ME concentration in the range of 1.0?×?10^?9 –1.0?×?10^?7?g?mL^-1 with a lower detection limit of 4.1?×?10^?10?g?mL^?1. As a preliminary application, the highly sensitive method was successfully applied to the determination of 2-ME in both pharmaceutical preparation and serum samples with satisfactory results. The possible mechanism of CL reaction catalyzed by CDs was investigated and the CDs played a role of catalyst in the reaction which could promote the generation of oxygen radicals.

It could be concluded that the enhancement effect on CL by CDs was attributed to the formation of oxygen radicals. The oxidation reaction of luminol was accelerated by oxygen radicals, which led to the enhanced CL emission.     

Investigation of the Photodecomposition of Hemin and Trace Amount Determination of Hemin with Flow Injection Chemiluminescence Method

Using the hemin‐H₂O₂‐Na₂CO₃‐NaOH chemiluminescence (CL) system, the study on the photodecomposition behavior of hemin under ultraviolet light and solar light were carried out and the determination of hemin was developed coupled with simple flow injection technique. The results showed that the decomposition reaction of hemin in different light irradiations corresponded with a first‐order reaction. And then the determination of hemin was completed by the CL emission from the reaction of hemin with H₂O₂ in aqueous carbonate. The linear range was 2.2 × 10^?10 to 6.88 × 10^?7 M and the detection limit was 2.2 × 10^?11 M (S/N = 3). The relative standard deviation (RSD) was 2.82% for ten independent detections of 1.72 × 10^?8 M hemin. As a preliminary application, the proposed method was successfully applied for the analysis of hemin in pharmaceutical formulations and animal blood with a recovery of 96?108%. A possible CL mechanism of the present system was discussed, and free radicals were suggested to be involved in this reaction.     

H2O2-鲁米诺-荧光素钠-K2CO3高灵敏化学发光法测定二氧化碳

在碱性介质中, CO₃^2－对H₂O₂氧化鲁米诺化学发光反应具有重要作用, 荧光素钠对该反应具有很强的增敏作用. 据此, 建立了化学发光法测定二氧化碳的新方法. 方法的线性范围为1.0×10^－10～5.0×10^－6 mol•L^－1 CO₃^2－, 检出限为 1.2×10^－11 mol•L^－1 CO₃^2－ (相当于5.3×10^－10 g•L^－1 CO₂). 该方法用于室内外空气中二氧化碳含量的测定, 相对标准偏差1.8%～2.1% (n＝11), 加标实验回收率97.6%～101.4%. 论文还探讨了反应的发光机理, 发光反应很可能是由溶液中的CO₃^2－与H₂O₂作用而产生的活性自由基引发, 荧光素钠对发光的增敏作用为化学能量转移过程.     

Development and validation of a sequential-injection method with chemiluminescence detection for the high throughput assay of the total antioxidant capacity of wines

This work reports a sequential-injection analysis (SIA) method with chemiluminescence (CL) detection for the rapid assay of the total antioxidant capacity (TAC) in wines. The method exploited the Co(II)-catalysed CL reaction of luminol with hydrogen peroxide in alkaline medium. Zones of sample, hydrogen peroxide, catalyst (Co(II) solution) and alkaline luminol were sequentially aspirated into the holding coil of the SIA manifold. Then, the flow was reversed and the stacked zones were directed to the CL detector. As the zones overlapped, antioxidants in the samples scavenged a portion of hydrogen peroxide and the decrease in the CL intensity was monitored and related to the TAC. The chemical and geometric conditions were studied and the method was validated in terms of linearity, accuracy (trueness and precision), matrix effects, signal additivity and robustness. The reproducibility of the method (expressed as the between-days % relative standard deviation) was between 2.5 and 3.4% and the trueness (expressed as the % recovery in wines spiked with gallic acid) was in the range 96.7-97.3%. The sampling frequency was 60 samples h⁻¹. The proposed SIA-CL method was compared with the DPPH method and the Folin-Ciocalteau (FC) method for the analysis of 25 wine samples.     

Peroxidase-catalysed luminol chemiluminescence method for the determination of glutathione

A luminol chemiluminescence (CL) method was developed for the determination of glutathione (GSH). GSH was indirectly determined by measuring the amount of hydrogen peroxide formed during the Cu(II)-catalysed oxidation of GSH with oxygen. The amount of hydrogen peroxide formed was continuously measured using the Arthromyces ramosus peroxidase-catalysed luminol CL reaction. The CL intensities at maximum light emission were linearly correlated with the concentration of GSH over the range 7.5 x 10(-7)-3.0 x 10(-5) M. The detection limit for GSH was about 10 times better than that of the spectrophotometric method using Ellman reagent.     

New Approach to Determination of Phenoxyl Free Radicals by Stopped‐Flow Spectrofluorimetry

Abstract

A simple and highly sensitive method to quantify the rates of production of phenoxyl radicals in enzyme reaction is described. This method employs the peroxidase‐catalyzed reaction between chlorophenols and hydroperoxide to generate phenoxyl free radicals, which can enhance dimerization of L‐tyrosine. The product, dityrosine, was monitored fluorometrically at the excitation/emission wavelength of 320/410 nm and the initial rate of accelerated‐accumulation of dityrosine represents the formation rate of phenoxyl free radicals. With this method, the phenoxyl radicals generated in oxidation of chlorophenols with hydrogen peroxide, catalyzed by horseradish peroxidase, were investigated. Phenoxyl radicals generated from as low as 5.0×10^?9 M 2,4‐dichlorophenol, for example, can be readily detected with a relative standard deviation of 2.6% for 9 replicated determination. The detection limits of phenoxyl radicals produced by various chlorophenols are 4.2×10^?9, 1.1×10^?9, 1.0×10^?10, 2.8×10^?8, and 1.1×10^?7 M for 2‐chlorophenol, 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, and 2,3,4,6‐tetrachlorophenol, respectively. The possible pathway of the reaction is proposed. The protocol is suitable for quantification of free radicals in enzyme reaction and shows promise in being applied to biological systems.     

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Enhanced chemiluminescence for the oxidation of luminol with m-chloroperoxybenzoic acid catalyzed by microperoxidase 8

The use of m-chloroperoxybenzoic acid (mCPBA) in stead of hydrogen peroxide causes an increase in chemiluminescence (CL) of luminol oxidation catalyzed by microperoxidase 8 (MP8) by an order of magnitude. The accelerated formation of an intermediate plays a major role in the CL enhancement, which also leads to a significant reduction in CL duration. The presence of guanidine hydrochloride, sodium carbonate, or sodium chloride further increases the CL emission drastically. The CL emission enhancement is strongly pH dependent. The enormous enhancement of the CL signal is due to an accelerated CL cycle and an improved CL efficiency in the presence of the enhancer. The CL signal covers several orders of magnitude over a wide range of concentrations of luminol and mCPBA. The intense CL of MP8-luminol-mCPBA in the presence of the enhancer will have great potential for extremely sensitive CL assays.     

Enzymatic assay with detection by enhanced luminol chemiluminescence in a reversed micellar system: determination of l-amino acids and glucose

A detection system for hydrogen peroxide, i.e., luminol chemiluminescence (CL) in a hexadecyltrimethylammonium bromide (CTAB) reversed micellar system, was coupled to enzyme reactions. The use of CTAB reversed micellar medium allows one to conduct both the oxidase enzymatic and CL detection reactions simultaneously at mild pH (l-amino acid system, pH 8.7; glucose system, pH 8.5) in the absence of any co-oxidant or catalyst. Based on this result, simple and unique determinations of l-amino acids and glucose as substrates were developed. The calibration graph for a representative amino acid, l-phenylalanine, was linear in the concentration range 4.0×10^?6?200×10^?6M with a relative standard deviation of 5.78% (five determinations). The method established for l-phenylalanine was also applicable for the assay of fourteen other l-amino acids. The calibration graph for glucose was linear in the concentration range 5.4×10^??540×10^?6M with a relative standard deviation of 4.27% (eight determinations). This method was compared with a standard spectrophotometric method (hexokinase) and successfully applied to the determination of glucose in human serum.