Biomimetic enhanced chemiluminescence of luminol-H2O2 system by manganese (III) deuteroporphyrin and its application in flow injection determination of phenol at trace level

A novel, sensitive and high selective flow-injection chemiluminescence (FI-CL) method for the determination of phenol is reported, based upon its decreasing effect on the CL reaction of luminol with hydrogen peroxide catalyzed by manganese (III) deuteroporphyrin [MnDP, Scheme 1, 3] in alkaline solution. Under the selected optimized experimental conditions, the relative CL intensity was linear with phenol in the range of 4.0 × 10⁻⁹ to 4.0 × 10⁻⁷ g mL⁻¹. The detection limit (3σ) was 6.3 × 10⁻¹⁰ g mL⁻¹ and the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ phenol (n = 11) was 2.99%. The regression equation was I = 120.79 + 1.14 × 1010c (R = 0.9936). This method has been applied to the determination of phenol in water with satisfactory results.     

Development of an automatic multi-channel ink-jet ejection chemiluminescence system and its application to the determination of horseradish peroxidase

In this work, an automatic multi-channel ink-jet for chemiluminescence (CL) analysis was developed. The four-channel ink-jet device was controlled by a home-made circuit. Differing from the classic flow injection CL, the whole procedure for CL analysis was automatically completed on a hydrophobic glass side. CL reaction of luminal and hydrogen peroxide for the determination of horseradish peroxidase (HRP) was selected as an application to automatic CL analysis platform. All solutions delivered by different channels were precisely ejected to the same position of the glass slide for the CL analysis. The consumption of reaction solution was reduced to nanoliter level. The whole CL analysis could be completed in less than 4 min, which was benefited from the prompt solution mixing in small size of droplet. The CL intensity increased linearly with HRP concentration in the range from 0.01 to 0.5 μg mL⁻¹. The limit of detection (LOD) (S/N = 3) was 0.005 μg mL⁻¹. Finally, the automatic CL system could also be used for the detection of HRP in HRP–protein conjugates, which showed its practical application in immunoassay.     

纳米银增敏鲁米诺液相化学发光分析法测定4-乙酰氨基酚的研究

研究发现在碱性条件下,纳米银对鲁米诺-铁氰化钾液相化学发光体系发光信号具有明显的增敏作用,而4-乙酰氨基酚对该体系具有强烈的抑制作用。结合流动注射技术,建立了流动注射化学发光分析法测定对乙酰氨基酚的新方法。该方法测定对乙酰氨基酚的线性范围为9.0×10-12～1.0×10-10g/mL(0.9947)和1.0×10-1...     

Employment of 4-(1-imidazolyl)phenol as a luminol signal enhancer in a competitive-type chemiluminescence immunoassay and its comparison with the conventional antigen-horseradish peroxidase conjugate-based assay

This study describes the employment of a novel imidazole-substituted phenol [4-(1-imidazolyl)phenol] as a highly potent signal enhancer in a horseradish peroxidase (HRP)-luminol chemiluminescence (CL) immunoassay. This competitive-type immunoassay for the model antigen fentanyl is based on the use of fentanyl polyclonal antibody immobilized on white microtiter plates and a biotinylated bovine serum albumin (BSA)-fentanyl derivative as a tracer. The latter was detected by means of streptavidin labeled with HRP, resulting in the generation of a high-intensity and relatively stable chemiluminescent signal, immediately after the addition of the substrate solution (NOAS). The developed method fulfilled the requirements of accuracy (percentage recovery ranged from 93.8 to 107%) and precision (intra- and inter-assay CVs were 2.5-5.2 and 4.5-11.9%, respectively). Its plasma detection limit (1.05 pg ml⁻¹) was lower than those of previous immunoassays. The novel assay was compared in terms of sensitivity and concentration range with other common HRP substrate systems: luminol-p-iodophenol-H₂O₂ and TMB-H₂O₂. Finally, the described method was compared with an HRP-fentanyl conjugate-based assay, similar to commercially available kits (SKIT), employing the novel substrate solution for both assays and the differences observed were explained by applying previously described models. The detection limit was 4.82 pg ml⁻¹ for SKIT, recovery values were 94.2-105% and intra- and inter-assay CVs were 2.5-5.2 and 4.5-11.9%, respectively. In conclusion, the proposed assay could be utilized for a wide range of molecules and replace the existing enzyme-labeled antigen-based kits.     

Sensitive determination of phenothiazines in pharmaceutical preparation and biological fluid by flow injection chemiluminescence method using luminol-KMnO4 system

A flow injection chemiluminescence method was described for the determination of four phenothiazine drugs, namely, chlorpromazine hydrochloride, perphenazine hydrochloride, fluphenazine hydrochloride and thioridazine hydrochloride. Strong Chemiluminescence (CL) signal was produced when above-mentioned drug was injected into the mixed stream of luminol with KMnO₄. The linear ranges of the method were 0.0020-1.0 μg/mL chlorpromazine hydrochloride, 0.0040-3.0 μg/mL perphenazine hydrochloride, 0.0020-5.0 μg/mL fluphenazine hydrochloride and 0.0050-1.0 μg/mL thioridazine hydrochloride. The detection limits were 0.4 ng/mL chlorpromazine hydrochloride, 0.7 ng/mL perphenazine hydrochloride, 2 ng/mL fluphenazine hydrochloride and 0.7 ng/mL thioridazine hydrochloride. The proposed method was applied to the determination of chlorpromazine hydrochloride in injections and in mental patient's urine samples and the satisfactory results were achieved. The possible CL reaction mechanism was also discussed briefly.     

Stacked films immobilization of MBTH in nafion/sol-gel silicate and horseradish peroxidase in chitosan for the determination of phenolic compounds

The stacked-film immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid nafion/sol-gel silicate film and horseradish peroxidase (HRP) in chitosan, performed in order to allow the determination of phenolic compounds, was investigated via an optical method. The stacked films were deposited onto a microscope glass slide by a spin-coating technique. The quinone or free radical product formed by the enzymatic reactions of phenolic compounds interacts with MBTH to form azo-dye products, which can be measured spectrophotometrically at a wavelength of 500 nm. The color intensity of the product was found to increase in proportion to the phenolic concentration after 5 min of exposure. The response of the biosensor was linear over concentration ranges of 0.025–0.500, 0.010–0.070 and 0.050–0.300 mM for guaiacol, resorcinol and o-cresol, respectively, and gave detection limits of 0.010, 0.005 and 0.012 mM. The sensor exhibited good sensitivity and stability for at least two months.     

A multi-pumping flow system for chemiluminometric determination of ascorbic acid in powdered materials for preparation of fruit juices

A multi-pumping flow-based procedure with chemiluminescent detection is proposed for the determination of ascorbic acid, AA, in fruit juices (powdered form). The method relies on the inhibitory effect of AA on the oxidation of luminol by hydrogen peroxide in alkaline medium. The system comprises several discretely actuated solenoid pumps as the only active components. It handles 100 samples per hour, and requires 96 μl of sample, 42 μg of luminol and 105 μg of potassium hexacyanoferrate(III) per determination. The analytical curve is linear up to about 11 mmol l^− 1 AA, and detection limit is 0.17 mmol l^− 1 AA. The system yields precise measurements (r.s.d. < 1%; n = 11), and recovery ranges from 94% to 106%. Results are in agreement with the reference method (AOAC) at the 95% confidence level.     

Development of an automated chemiluminescence flow-through sensor for the determination of 5-aminosalicylic acid in pharmaceuticals: a comparative study between sequential and multicommutated flow techniques

This work is aimed at demonstrating the potential of the implementation of automatic flow systems in optosensors using chemiluminescence detection. With this purpose, two automatic methodologies, multicommutation and sequential injection analysis (SIA), have been applied to the analysis of 5-aminosalicylic acid (ASA). The analyte is determined for the first time making use of its chemiluminescence reaction with permanganate anion, previously immobilized on an appropriate solid support in the detection area. First, the study of the most appropriate commercial flow-through cell and the optimum conditions for the reaction were performed. Second, the main differences in terms of flow variables and analytical parameters for multicommutation and SIA approaches were stated. Both methodologies were applied to the determination of the analyte in pharmaceuticals obtaining satisfactory results. Finally, the advantages and disadvantages of both proposed methods and the recoveries obtained from pharmaceuticals were statistically compared.     

Flow-injection chemiluminescence determination of ascorbic acid by use of the cerium(IV)-Rhodamine B system

A highly sensitive flow-injection (FI) method with chemiluminescence (CL) detection is used for the determination of l-ascorbic acid. The method is based on the CL reaction of Rhodamine B with cerium(IV) in sulfuric acid media. l-Ascorbic acid is suggested to be a catalyst utilized in the energy-transferred excitation process. The proposed procedure allows quantitation of l-ascorbic acid in the range 3.8×10⁻¹³ to 1.0×10⁻¹⁰ mol l⁻¹ with a correlation coefficient of 0.9998 (n=5) and relative standard deviation (R.S.D.) of 0.92% (n=11) at 1.0×10⁻¹¹ mol l⁻¹. The detection limit (3×blank) was 1.0×10⁻¹³ mol l⁻¹. The method is successfully used to determine l-ascorbic acid in fresh vegetables. The possible mechanism of the chemiluminescence in the system is discussed.     

Time-resolved fluorescence study of the single tryptophan in thiocyanate and azide derivatives of horseradish peroxidase: Implication for a p H-induced conformational change in the heme cavity

Detailed pH-dependent steady state and picosecond time-resolved tryptophan fluorescence studies on thiocyanate and azide complexes of horseradish peroxidase have been carried out. The fluorescence decay of the single tryptophan in these species was fitted to a discrete three exponential model. Maximum entropy method analysis also gave three distinct regions of lifetime distributions. The fast subnanosecond lifetime component was found to have > 97% amplitude contribution while other two longer lifetime components have small contributions. Small contributions from the nanosecond lifetime components possibly arise from apoprotein impurity or some small amount of disordered heme conformer of the protein. pH dependence of the fast picosecond lifetime components was found to show a systematic behavior which has been interpreted in the light of obligatory conformation change associated with activation of the enzyme at low pH.     

A carbon quantum dots‐enhanced chemiluminescence method for the determination of gallic acid in food samples

In this work, we show that gallic acid can significantly inhibit the chemiluminescence (CL) intensity of carbon quantum dots (CQDs)‐enhanced K₃Fe(CN)₆–luminol system. Under optimum conditions, the decrease in the CL intensity is proportional to the concentration of gallic acid over the range 0.01–1.0 μM, and the detection limit is 1.0 nM. The relative standard deviation of repeated intraday and interday determinations of gallic acid was 1.2–4.2%. This method was successfully applied to the determination of gallic acid in food samples, with recoveries in the range 94.0–103.0%. A possible mechanism of CL is discussed.     

Isolation of free phenolic compounds from arboreal leaves by use of the Florisil/C<Subscript>18</Subscript> system

In studies of the phenolic compounds present in leaves and needles, GC and GC–MS have so far been applied only sporadically. This is probably because of the greater difficulties encountered in preparing the samples for this method than those used for liquid chromatography. When preparing a sample for gas chromatography the analyst is faced with two difficult stages—separation of the compound from the matrix without losses (stage 1) so that the final sample can be derivatized to make it suitable for analysis on a non-polar capillary column of the gas chromatograph (stage 2). This paper presents a procedure for extraction of phenolic compounds from the matrix by means of a Florisil/C₁₈ sorbent system and their analysis by GC. After passage through the adsorbents the recovery ranges from 32% for ferulic acid to 88% for gentisic acid. It was found that this extraction method and the GC analysis are very precise (particularly for samples of a mass <1 g) and can be used for quantification. The high-precision quantification of 15 phenolic acids, shikimic acid, and six other compounds present in pine needles has been achieved. The conditions used for GC analysis and construction of calibration curves for quantitative determination are given.     

Empirical investigation of precipitation of hexadecanoic acid from toluene/brine system: Implication to naphthenic acid precipitation from crude oils

Naphthenic acids, due to their tendency to precipitate out of solution when in contact with formation water, present a formidable challenge for the petroleum industry. In this study, precipitation of hexadecanoic acid from an idealized oil-water (toluene/brine) system was investigated. The FTIR results revealed that the acid was mainly precipitated as calcium hexadecanoate. Experiments designed to study the effect of water cut, acid concentration, brine concentration, and pH of the brine on the amount of the precipitate formed revealed that the amount of precipitate formed increased with increase in brine pH, concentration of the acid and calcium ions. Similar effect was observed with respect to water cut but with maximum amount of the precipitate formed at water cut of about 40%, below and above which relatively lower amount of the acid was precipitated irrespective of the levels of the other factors. In general, the observed effects of the factors suggest that precipitation of the naphthenic acid can be minimized with acidic formation water that contains relatively low concentration of calcium ions particularly when the concentration of the acid in the oil is as low as possible.     

l-Ascorbic acid in organic synthesis: DBU-catalysed one-pot synthesis of tetramic acid derivatives from 5,6-O-isopropylidene ascorbic acid

Reaction of 5,6-O-isopropylidene-2,3-bis-O-alkyl ascorbic acid with different amines in the presence of DBU at ambient temperature resulted in the formation of 3,4-bis-O-alkyl-1-alkyl-5-(2-hydroxy ethyl)-5-hydroxy-1,5-dihydropyrrol-2-ones in moderate yields.     

Chemically enhanced liquid chromatography/tandem mass spectrometry determination of glutamic acid in the diffusion medium of retinal cells

A rapid, reproducible and highly sensitive method, based on liquid chromatography mass spectrometry, was developed for the determination of the excitatory amino acid glutamic acid released in the diffusion medium of control, ischemic and mutant cells from retinas. Signal intensity of glutamic acid was enhanced by dansyl chloride derivatization giving rise to a detection limit in the order of pmol/mL. Further, in HPLC-ESI-MS detection an MS-friendly dansyl group to glutamic acid enhanced both ionization efficiency in the ESI source and collision-activated dissociation in the collision cell. The sample processing procedure included liquid-liquid extraction, derivatization with dansyl chloride and a final cation-exchange extraction to generate clean extracts for LC/MS/MS analysis. This approach has been validated as sensitive, linear (20-300 ng/mL), accurate and precise for the differential quantification of glutamic acid in the diffusion medium of retina cells. This is the first report of using chemical derivatization to enhance MS/MS detection of the glutamic acid released in the diffusion medium of wild-type and mutant retina cells, under ischemic conditions.     

Using an on-line microdialysis/HPLC system for the simultaneous determination of melamine and cyanuric acid in non-dairy creamer

The recent revelation of melamine (MEL) contamination in foodstuffs in China has rocked the international public health community. Many food categories have been involved in this scandal, including non-dairy creamer (NDC). In this study, we investigated the use of hollow-fiber microdialysis (MD) sampling coupled on-line with high-performance liquid chromatography (HPLC) as an alternative to sample pretreatment for the direct determination of MEL and its analogue cyanuric acid (CYA) in NDC. After MD sampling, the dialysate was injected on-line into the chromatographic system for analysis of MEL and CYA with UV detection at 203 nm. We monitored the effects of various parameters affecting the MD efficiency, namely the characteristics of the MD probe membrane, the flow-rate and the nature of the polarity modifier in the perfusion stream, and the addition of salt in the sample solution. The optimal enrichment efficiency for collecting MEL and CYA from aqueous NDC samples occurred with MD sampling using a hollow polysulfone MD fiber and MeOH as the perfusate at a flow rate of 10 μL min⁻¹. The optimized chromatographic conditions involved using a reversed-phase phenyl column and a mobile phase of 5 mM phosphate buffer in 10% (v/v) MeOH, buffered at pH 6.5. Detection was linear in the concentration range from 0.02 to 5 ppm for MEL and from 2 to 100 ppm for CYA, with detection limits of 1 ppb for MEL and 30 ppb for CYA. The volume of perfusate required to extract MEL and CYA from the NDC solution was only 21 μL. The total MD sampling time was 2.1 min. This method allows the sensitive, eco-friendly, and rapid determination of MEL and CYA in NDC—a risk food for economically motivated adulteration.     

On-line dilution and determination of the amount of concentrated hydrochloric acid in the final products from a hydrochloric acid production plant using a sequential injection titration system

An on-line sequential injection titration system for the determination of the concentration of concentrated hydrochloric acid as final product from a hydrochloric acid production plant is described. The system involves on-line dilution of the concentrated hydrochloric acid solution to an acceptable range for direct measurement by merging the sample stream with a de-ionized water diluent stream, followed by mixing in a dilution coil, before aspiration into the sequential injection system. Concentrated standard solutions were treated in exactly the same way as the samples. The system was evaluated for reproducibility, linearity, accuracy, and sample throughput. A linear relationship between peak width and logarithm of acid concentration was found in the range 5.934–8.995 mol l⁻¹ and a concentration of 0.005 mol l⁻¹ NaOH solution was used as titrant. Samples from the production plant showed excellent agreement when compared with the manual and automated batchwise titrations. The relative standard deviation was found to be less than 0.4% with a sample frequency of 30 samples per hour.     

Modified platinum electrode with phytic acid and single-walled carbon nanotube: Application to the selective determination of dopamine in the presence of ascorbic and uric acids

A platinum (Pt) electrode modified by single-walled carbon nanotubes (SWNTs) and phytic acid (PA) was investigated by voltammetric methods in buffer solution. The PA-SWNTs/Pt-modified electrode demonstrated substantial enhancements in electrochemical sensitivity and selectivity towards dopamine (DA) in the presence of L-ascorbic acid (AA) and uric acid (UA). The PA-SWNTs films promoted the electron transfer reaction of DA, while the PA film, acting as a negatively charged linker, combined with the positively charged DA to induced DA accumulation in the film at pH under 7.4. However, the PA film restrained the electrochemical response of the negatively charged AA due to the electrostatic repulsion. The anodic peak potentials of DA, AA and UA could be separated by electrochemical techniques, and the interferences from AA and UA were effectively eliminated in the DA determination. Linear calibration plots were obtained in the DA concentration range of 0.2-10 μM and the detection limit of the DA oxidation current was determined to be 0.08 μM at a signal-to-noise ratio of 3. The results indicated that the modified electrode can be used to determine DA without interference from AA and UA, while ensuring good sensitivity, selectivity, and reproducibility.     

Rapid and cost-effective LC–MS/MS method for determination of hydroxycitric acid in plasma: Application in the determination of pharmacokinetics in commercial Garcinia preparations

Garcinia cambogia is one of the most commonly used anti-obesity dietary supplements, and hydroxycitric acid (HCA) is a major constituent in the commercial preparations of Garcinia. High doses of HCA are often consumed without much awareness of its pharmacokinetic and toxicokinetic parameters, and therefore, a complete understanding of its effects is lacking. The first step in understanding these parameters is the availability of a reliable bioanalytical method. Here, we present the first report on a UPLC–MS/MS method for analysis of HCA in rat plasma after a simplified and cost-effective protein precipitation. Chromatographic separation of the analytes in the supernatant was achieved using hydrophilic interaction liquid chromatography, where mass parameters were optimized and a rapid 5-min quantitative assay was developed. The method was highly sensitive, accurate, precise and linear in the concentration range of 10.5–5000 ng/mL (validated according to the United States Food and Drug Administration guidelines). Further, the method was successfully used to describe the pharmacokinetic profile of HCA in rat plasma after the administration of pure HCA and commercial Garcinia preparations.