Phenol derivatives as enhancers and inhibitors of luminol–H2O2–horseradish peroxidase chemiluminescence

Systematic studies on phenol derivatives facilitates an explanation of the enhancement or inhibition of the luminol–H₂O₂–horseradish peroxidase system chemiluminescence. Factors that govern the enhancement are the one-electron reduction potentials of the phenoxy radicals (PhO^•/PhOH) vs. luminol radicals (L^•/LH⁻) and the reaction rates of the phenol derivatives with the compounds of horseradish peroxidase (HRP-I and HRP-II). Only compounds with radicals with a similar or greater reduction potential than luminol at pH 8.5 (0.8 V) can act as enhancers. Radicals with reduction potentials lower than luminol behave in a different way, because they destroy luminol radicals and inhibit chemiluminescence. The relations between the reduction potential, reaction rates and the Hammett constant of the substituent in a phenol suggest that 4-substituted phenols with Hammett constants (σ) for their substituents similar or greater than 0.20 are enhancers of the luminol–H₂O₂–horseradish peroxidase chemiluminescence. In contrast, those phenols substituted in position 4 for substituents with Hammett constants (σ) lower than 0.20 are inhibitors of chemiluminescence. On the basis of these studies, the structure of possible new enhancers was predicted. © 1998 John Wiley & Sons, Ltd.     

Enhancer effect of fluorescein on the luminol–H2O2–horseradish peroxidase chemiluminescence: energy transfer process

The chemiluminescence of the luminol–H₂O₂–horseradish peroxidase system is increased by fluorescein. Fluorescein produces an enhancement of the luminol chemiluminescence similar to that of phenolphthalein, by an energy transfer process from luminol to fluorescein. The maximum intesity and the total chemiluminescence emission (between 380 and 580 nm) of luminol with fluorescein was more than three times greater than without fluorescein; however, the emission duration was shorter. The emission spectra in the presence of fluorescein had two maxima (425 and 535 nm) and the enhancement was dependent on pH and fluorescein concentration. A mechanism is proposed to explain these effects. © 1997 John Wiley & Sons, Ltd.     

Determination of ampicillin sodium using the cupric oxide nanoparticles–luminol–H2O2 chemiluminescence reaction

A simple and sensitive chemiluminescence (CL) method has been developed for the determination of ampicillin sodium at submicromolar levels. The method is based on the inhibitory effect of ampicillin sodium on the cupric oxide nanoparticles (CuO NPs)–luminol–H₂O₂ CL reaction. Experimental parameters affecting CL inhibition including concentrations of CuO NPs, luminol, H₂O₂ and NaOH were optimized. Under optimum conditions, the calibration plot was linear in the analyte concentration range 4.0 × 10^‐7–4.0 × 10^‐6 mol/L. The limit of detection was 2.6 × 10^‐7 mol/L and the relative standard deviation (RSD) for six replicate determinations of 1 × 10^‐6 mol/L ampicillin sodium was 4.71%. Also, X–ray diffraction (XRD) and transmission electron microscopy (TEM) analysis were employed to characterize the CuO NPs. The utility of the proposed method was demonstrated by determining ampicillin sodium in pharmaceutical preparation. Copyright © 2013 John Wiley & Sons, Ltd.     

Studies of visible oscillating chemiluminescence with a luminol–H2O2–KSCN–CuSO4–NaOH system in batch reactor

Oscillating chemical reactions are complex systems involving a large number of chemical species. In oscillating chemical reactions some species, usually reaction intermediates, exhibit fluctuation in concentration. Visible oscillating chemiluminescence, produced by the addition of luminol (3‐aminophthalhydrazide) to the oscillating system H₂O₂–KSCN–CuSO₄–NaOH, was investigated. In this study the effect of varying the concentration of H₂O₂, KSCN, CuSO₄, NaOH and luminol was investigated in a batch reactor. We showed that the concentration of all components involved in the oscillating chemilumenscent reaction influenced the light intensity and the oscillation period. Copyright © 2002 John Wiley & Sons, Ltd.     

Studies of visible oscillating chemiluminescence in luminol–H2O2–KSCN–CuSO4 system using (2‐hydroxyethyl) trimethylammonium hydroxide

Visible oscillating chemiluminescence (CL) of luminol–H₂O₂–KSCN–CuSO₄ was studied using the organic base (2‐hydroxyethyl)trimethylammonium hydroxide. The effect of concentrations of luminol, H₂O₂, KSCN, CuSO₄ and the base were investigated in a batch reactor. This report shows how the concentration of components involved in the oscillating CL system influenced the oscillation period, light amplitude and total time of light emission. The oscillating CL with different bases was also investigated. Results indicated that using 2‐HETMAOH causes regular oscillating CL with nearly the same oscillating period. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigations of different chemiluminescent peaks in H2O2–SCN−–Cu2+–OH−–luminol flow system

In the H₂O₂–SCN^?–Cu²⁺–OH^?–luminol oscillatory system of chemiluminescence, the effects of the ingredient concentrations, temperature, flow rate and complexing agent on the oscillatory dynamics were investigated in a continuous‐flow stirred tank reactor (CSTR). The dynamical structure of two peaks during a period was discussed in detail. By addition of EDTA to the oscillating system, the peak I height decreased sharply while the peak II height was little affected, and the period kept constant. This may be due to the fast reaction between Cu(II) and EDTA and the highly stable complex Cu(II)–EDTA. From the experimental study and mechanism analysis, the chemiluminescent peak I corresponds to Cu(II) → Cu(I) transformation and the peak II corresponds to the Cu(I) → Cu(II) transformation process. The key species involving in the two‐transformation process are inferred to be superoxide radical and hydroxyl radical. Copyright © 2010 John Wiley & Son, Ltd.     

Evaluation of lophine derivatives as L‐012 (luminol analog)‐dependent chemiluminescence enhancers for measuring horseradish peroxidase and H2O2

8‐Amino‐5‐chloro‐7‐phenylpyrido[3,4‐d]pyridazine‐1,4(2H,3H)dione (L‐012) was recently synthesized as a new chemiluminescence (CL) probe; the light intensity and the sensitivity of L‐012 are higher than those of other CL probes such as luminol. Previously, our group developed four lophine‐based CL enhancers of the horseradish peroxidase (HRP)‐catalyzed CL oxidation of luminol, namely 2‐(4‐hydroxyphenyl)‐4,5‐diphenylimidazole (HDI), 2‐(4‐hydroxyphenyl)‐4,5‐di(2‐pyridyl)imidazole (HPI), 4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenylboronic acid (DPA), and 4‐[4,5‐di(2‐pyridyl)‐1H‐imidazol‐2‐yl]phenylboronic acid (DPPA), and showed that DPPA was suitable for the photographic detection of HRP. In this study, we replaced luminol with L‐012 and evaluated these as L‐012‐dependent CL enhancers. In addition, to detect HRP and/or H₂O₂ with higher sensitivity, each detection condition for the L‐012–HRP–H₂O₂ enhanced CL was optimized. All the derivatives enhanced the L‐012‐dependent CL as well as luminol CL; HPI generated the highest enhanced luminescence. Under optimized conditions for HRP detection, the detection limit of HRP was 0.08 fmol. By contrast, the detection limit of HRP with the enhanced L‐012‐dependent CL using 4‐iodophenol, which is a common enhancer of luminol CL, was 1.1 fmol. With regard to H₂O₂ detection, the detection limits for enhanced CL with HPI and 4‐iodophenol were 0.29 and 1.5 pmol, respectively. Therefore, it is demonstrated that HPI is the most superior L‐012‐dependent CL enhancer. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.     

Trace analysis of N‐acetyl‐L‐cysteine using luminol–H2O2 chemiluminescence system catalyzed by silver nanoparticles

N‐Acetyl‐L‐cysteine (NAC) can inhibit the luminol–H₂O₂, reaction, which is catalyzed by silver nanoparticles. Based on this phenomenon a new method was developed for NAC determination. Under optimum conditions, a linear relationship between chemiluminescence intensity and NAC concentration was found in the range 0.034–0.98 µg/mL. The detection limit was 0.010 µg/mL (S/N =3), and the relative standard deviation (RSD) was <5% for 0.480 µg/mL NAC (n =5). This simple, sensitive and inexpensive method has been applied to measure the concentration of NAC in pharmaceutical tablets. Copyright © 2014 John Wiley & Sons, Ltd.     

A stopped‐flow study of the dual chemiluminescence for the luminol–KIO4–Mn2+ system in strong alkaline solutions

A novel phenomenon of dual chemiluminescence (CL) was observed for the KIO₄–luminol–Mn²⁺ system in strong alkaline solutions using the stopped‐flow technique. Scavenging study of the reactive oxygen species (ROS) suggested that the two CL peaks originated from different CL pathways precipated by distinct ROS (O₂^? and ^?OH for the first peak, mainly ¹O₂ for the second peak). Generation of these ROS at different time intervals from the reactions involving IO₄^?, O₂, and Mn²⁺ and their subsequent reactions with luminol induced the intense CL emission. The relative intensity of the two CL peaks can be tuned over a wide range by varying the concentrations of Mn^2?, luminol and KIO₄. Because of the involvement of different ROS in each pathway, the two CL peaks could respond quite differently to various substances. Moreover, variation of the intensity ratio of the two CL peaks altered the relative proportions of the corresponding ROS, thereby changing their responses to a given substance. The dual CL emission acts like a pair of tunable probes and it is believed that this CL system has great potential in analytical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhanced chemiluminescence of the luminol–AgNO3 system by Ag nanoparticles

The oxidation reaction of luminol with AgNO₃ can produce chemiluminescence (CL) in the presence of silver nanoparticles (NPs) in alkaline solution. Based on the studies of UV‐vis absorption spectra, photoluminescence (PL) spectra and CL spectra, a CL enhancement mechanism is proposed. The CL emission spectrum of the luminol–AgNO₃–Ag NPs system indicated that the luminophore was still 3‐aminophthalate. On injection of silver nanoparticles into the mixture of luminol and AgNO₃, they catalysed the reduction of AgNO₃ by luminol. The product luminol radicals reacted with the dissolved oxygen, to produce a strong CL emission. As a result, the CL intensity was substantially increased. Moreover, the influences of 18 amino acids, e.g. cystine, tyrosine and asparagine, and 25 organic compounds, including gallic acid, tannic acid and hydroquinone, on the luminol–AgNO₃–Ag NPs CL system were studied by a flow‐injection procedure, which led to an effective method for detecting these compounds. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemiluminescence determination of moxifloxacin in pharmaceutical and biological samples based on its enhancing effect of the luminol–ferricyanide system using a microfluidic chip

A sensitive determination of a synthetic fluoroquinolone antibacterial agent, moxifloxacin (MOX), by an enhanced chemiluminescence (CL) method using a microfluidic chip is described. The microfluidic chip was fabricated by a soft‐lithographic procedure using polydimethyl siloxane (PDMS). The fabricated PDMS microfluidic chip had three‐inlet microchannels for introducing the sample, chemiluminescent reagent and oxidant, and a 500 µm wide, 250 µm deep and 82 mm long microchannel. An enhanced CL system, luminol–ferricyanide, was adopted to analyze the MOX concentration in a sample solution. CL light was emitted continuously after mixing luminol and ferricyanide in the presence of MOX on the PDMS microfluidic chip. The amount of MOX in the luminol–ferricyanide system influenced the intensity of the CL light. The linear range of MOX concentration was 0.14–55.0 ng/mL with a correlation coefficient of 0.9992. The limit of detection (LOD) and limit of quantification (LOQ) were 0.06 and 0.2 ng/mL respectively. The presented method afforded good reproducibility, with a relative standard deviation (RSD) of 1.05% for 10 ng/mL of MOX, and has been successfully applied for the determination of MOX in pharmaceutical and biological samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Reactivation of horseradish peroxidase with imidazole for continuous determination of hydrogen peroxide using a microflow injection–chemiluminescence detection system

A method for reactivation of inactivated horseradish peroxidase (HRP) was studied and exploited in an assay for hydrogen peroxide (H₂O₂). Addition of imidazole into a mobile phase made continuous determination of hydrogen peroxide (H₂O₂) possible by micro?ow injection based on horseradish‐catalysed luminol chemiluminescence. For reproducible determination of H₂O₂ with HRP, the inactivation of HRP via protonation of the active sites of HRP caused by reaction with H₂O₂ must be avoided. We successfully reactivated protonated HRP (inactive HRP) with exogenous imidazole in the mobile phase of the micro?ow injection system. The imidazole successfully removed the attached proton from the inactive sites of the HRP. This assay was reproducible (within‐run reproducibility, CV = 4.0%) and the detection limit for H₂O₂ was 5 pmol. Copyright © 2003 John Wiley & Sons, Ltd.     

Application of silver nanoparticles to the chemiluminescence determination of cefditoren pivoxil using the luminol–ferricyanide system

A new simple, accurate and sensitive sequential injection analysis chemiluminescence (CL) detection method for the determination of cefditoren pivoxil (CTP) has been developed. The developed method was based on the enhancement effect of silver nanoparticles on the CL signal arising from a luminol–potassium ferricyanide reaction in the presence of CTP. The optimum conditions relevant to the effect of luminol, potassium ferricyanide and silver nanoparticle concentrations were investigated. The proposed method showed linear relationships between relative CL intensity and the investigated drug concentration at the range 0.001–5000 ng/mL, (r = 0.9998, n = 12) with a detection limit of 0.5 pg/mL and quantification limit of 0.001 ng/mL. The relative standard deviation was 1.6%. The proposed method was employed for the determination of CTP in bulk drug, in its pharmaceutical dosage forms and biological fluids such as human serum and urine. The interference of some common additive compounds such as glucose, lactose, starch, talc and magnesium stearate was investigated. In addition, the interference of some related cephalosporins was tested. No interference was recorded. The obtained sequential injection analysis‐CL results were statistically compared with those from a reported method and did not show any significant differences. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of chemiluminescence from luminol solution and luminol–TiO2 suspension after illumination of a 355 nm pulse laser

Chemiluminescence (CL) from luminol solution and luminol–TiO₂ suspension after illumination of a 355 nm pulse laser is compared. Both the CL systems showed the CL spectra with maximum wavelength of 430 nm, suggesting that the emission was from the excite state of 3‐aminophthalate ion. The TiO₂ photocatalytically induced luminol CL could be separately detected either when the pulse laser power was smaller than 0.15 mJ/pulse or a slit was placed beyond ?2–2 mm in the vertical direction of the laser beam. The TiO₂ photocatalytically induced luminol CL intensity was linear to the laser power, while that of the 355 nm pulse laser‐induced was nonlinear. A log–log plot between the 355 nm pulse laser‐induced luminol CL intensity and laser power showed a near‐linear regression fit with a slope of 2.11, suggesting that a two‐photon absorption process of luminol was present in the 355 nm pulse laser‐induced luminol CL. Adsorbed oxygen on the surface of TiO₂ seemed to greatly contribute to the photocatalytically induced CL. Copyright © 2010 John Wiley & Sons, Ltd.     

Flow‐injection chemiluminescence of the luminol–potassium periodate system enhanced by TGA–capped CdTe quantum dots for the determination of theophylline

The chemiluminescence (CL) behaviour of the luminol–potassium periodate system enhanced by CdTe quantum dots capped with thioglycolic acid (TGA–CdTe QDs) was studied using kinetic experiments, CL spectra, UV–vis absorption spectra and fluorescence spectra. The production of oxygen‐containing reactant intermediates (O₂^?? and OH^?) in the present CL system was verified by CL. The possible CL mechanism was discussed in detail. Furthermore, theophylline (THP) was determined based on its enhancement of the CL intensity of the CdTe QDs–luminol–potassium periodate system coupled with a flow‐injection technique. Under these optimized conditions, the linear range was found to be from 1.0 × 10^?8 to 1.0 × 10^?5 g/mL with a detection limit of 2.8 × 10^?9 g/mL (3σ). The recoveries for the determination of THP in tablets were from 98.2 to 99.6%.     

Development of chemiluminescence method for determination of 10‐hydroxycamptothecin based on luminol–[Ag(HIO6)2]5− reaction in alkaline solution

A novel chemiluminescence (CL) method was developed for the determination of 10‐hydroxycamptothecin(HCPT) based on the CL reaction between [Ag(HIO₆)₂]^5? and luminol in alkaline solution. CL emission of Ag(III) complex–luminol in alkaline medium was very different from that in acidic medium. A possible mechanism of enhanced CL emission was suggested. The enhanced effect of HCPT on CL emission of the [Ag(HIO₆)₂]^5?–luminol system was found. The enhanced degree of CL emission was proportional to HCPT concentration. The effect of the reaction conditions on CL emission was examined. Under optimal conditions, the limit of detection was 6.5 × 10^?9 g mL^?1. The proposed method was applied for the determination of HCPT in real samples with the recoveries of 93.2–109% with the RSD of 1.7–3.3%. Copyright © 2010 John Wiley & Sons, Ltd.     

A novel chemiluminescent flow injection analysis of trace amounts of rutin by its inhibition of the luminol–hydrogen peroxide reaction catalyzed by tetrasulfonated colbalt phthalocyanine

Based on the inhibition effect of rutin on the luminol–hydrogen peroxide chemiluminescence (CL) system catalyzed by tetrasulfonated colbalt phthalocyanine (CoTSPc), a sensitive flow‐injection CL method has been developed for the determination of rutin. The CL reaction mechanism was carefully investigated by examining CL emission spectra, UV–visible spectra and variation of reaction conditions. It was found that there existed a linear relationship between CL intensity and the concentration of rutin in the range of 8.0 × 10^?9 to 1.0 × 10^?6 mol L^?1, and the detection limit is 3.8 × 10^?9 mol L^?1. This proposed method is sensitive, convenient and simple, and has been applied to the determination of rutin in commercial rutin tablets with satisfactory results. Copyright © 2009 John Wiley & Sons, Ltd.     

A kinetic treatment of stopped‐flow time courses for multiple chemiluminescence of the KIO4‐luminol‐Mn2+ system

Stopped‐flow time courses for chemiluminescence (CL) of the KIO₄‐luminol‐Mn²⁺system showed an instantaneous jump in initial signal followed by two distinct bands. A kinetic model of the form with ten adjustable parameters was proposed to account for CL intensity (I) versus time (t) profiles. The three terms in the model represent the three CL bands. Each band was comprised of a rise part and an exponential decay corresponding to the formation and deactivation of the CL emitter. CL bands could have originated from different CL pathways with the participation of reactive species such as O₂^?, ^?OH and ¹O₂ generated in the reactions involving IO₄^?, O₂ and Mn²⁺. Subsequent reactions of these reactive species with luminol induced CL emissions. Simulation parameters together with peak positions and intensities of the three CL bands were found to vary in different manners by changing conditions such as reagent concentration, pH and temperature. The temperature‐dependence of the rate constants yielded activation energies of 73.2 ± 2.8, 70.1 ± 2.4 and 67.2 ± 1.2 kJ?mol^‐1 for the three decay processes. Moreover, different substances exhibited a significant influence on the three CL bands and their simulation parameters. The numerous parameters and characteristics of CL emissions could serve as multiple probes for detecting analytes, making this system promising for potential analytical applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Employment of 4‐(1,2,4‐triazol‐1‐yl)phenol as a signal enhancer of the chemiluminescent luminol–H2O2–horseradish peroxidase reaction for detection of hepatitis C virus in real samples

Highly sensitive detection of hepatitis C virus (HCV) in serum is a key method for diagnosing and classifying the extent of HCV infection. In this study, a p‐phenol derivative, 4‐(1,2,4‐triazol‐1‐yl)phenol (4‐TRP), was employed as an efficient enhancer of the luminol–hydrogen peroxide (H₂O₂)–horseradish peroxidase (HRP) chemiluminescence (CL) system for detection of HCV. Compared with a traditional enhancer, 4‐TRP strongly enhanced CL intensity with the effect of prolonging and stabilizing light emission. The developed CL system was applied to detecting HCV core antigen (HCV‐cAg) using a sandwich structure inside microwells. Our experimental results showed that there was good linear relationship between CL intensity and HCV‐cAg concentration in the 0.6–3.6 pg/mL range (R = 0.99). The intra‐ and inter‐assay coefficients of variation were 4.5–5.8% and 5.0–7.3%, respectively. In addition, sensitive determination of HCV‐cAg in serum samples using the luminol–H₂O₂–HRP–4‐TRP CL system was also feasible in clinical settings. Copyright © 2015 John Wiley & Sons, Ltd.     

Post‐chemiluminescence determination of chloramphenicol based on luminol–potassium periodate system

A post‐chemiluminescence (PCL) phenomenon was observed when chloramphenicol was injected into a mixture of luminol and potassium periodate after the chemiluminescence (CL) reaction of luminol–potassium periodate had finished. The possible reaction mechanism was proposed based on studies of the CL kinetic characteristics, the CL spectra, the fluorescence spectra and the UV‐vis absorption spectra of the related substances. Based on the PCL reaction, a rapid and sensitive method for the determination of chloramphenicol was established. The linear response range was 6.0 × 10^?7–1.0 × 10^?5 mol/L, with a correlation coefficient of 0.9986. The relative standard deviation (RSD) for 5.0 × 10^?6 mol/L chloramphenicol was 2.3% (n = 11). The detection limit was 1.6 × 10^?7 mol/L. The method has been applied to the determination of chloramphenicol in pharmaceutical samples with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.