A new resonance scattering spectral method for the determination of trace amounts of iodate with rhodamine 6G

Under the conditions of 0.04 mol L⁻¹ HCl-8.0 × 10⁻⁴ mol L⁻¹ KI, there is a fluorescence peak at 540 nm and a synchronous fluorescence peak at 540 nm for rhodamine 6G (RhG). When there is IO₃⁻, it reacts with exceed I⁻ to form I₃⁻. And I₃⁻ and RhG combine into ion association particles. The particles exhibit three resonance scattering peaks at 320, 400 and 595 nm. And there is fluorescence quenching at 540 nm. Iodine concentration is proportional to the intensity of the resonance scattering intensity at 400 nm in the range of 1.0-20 × 10⁻⁷ mol L⁻¹. And a new resonance scattering spectral (RSS) method has been described for the determination of IO₃⁻ in salt samples. The spectral results have been verified that the formation of (RhG-I₃)_n association particles and solid-liquid interfaces are the main factor that cause the fluorescence quenching and resonance scattering effects.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

Synchronous fluorescence measurement of enrofloxacin in the pharmaceutical formulation and its residue in milks based on the yttrium (III)-perturbed luminescence

A simple, rapid and sensitive synchronous fluorescence method is put forward for the determination of enrofloxacin (ENRO) in the pharmaceutical formulation and its residue in milk based on the yttrium (III)-perturbed luminescence. When Y³⁺ is added into the ENRO solution, the fluorescence of ENRO is significantly enhanced. The synchronous fluorescence technology is employed in the method to determine trace amount of ENRO residue in milks. The synchronous fluorescence intensity of the system is measured in a 1-cm quartz cell with excitation wavelength of 328 nm, Δλ = 80 nm. A good linear relationship between the fluorescence intensity and the ENRO concentration is obtained in the range of 1.0 × 10⁻⁹ to 2.0 × 10⁻⁶ mol L⁻¹ (r² = 0.9992). The limit of detection (LOD) of this method attains as low as 3.0 × 10⁻¹⁰ mol L⁻¹ (S/N = 3). The selectivity of this method is also very good. Common metal ions, rare-earth ions and some pharmaceuticals, which are usually used together with ENRO, do not interfere with the determination of ENRO under the actual conditions. The proposed method can be applied to determine ENRO residue in milks, and limit of quantification (LOQ) determined in the spiked milk is estimated to be 2.8 × 10⁻⁸ mol L⁻¹ (10 μg L⁻¹). Moreover, this method can be used as a rapid screening for judging whether the ENRO residues in milks exceed Minimal Risk Levels (MRLs) or not. In addition, the mechanism of the fluorescence enhancement is also discussed in detail.     

Synchronous fluorescence determination of urinary 1-hydroxypyrene, β-naphthol and 9-hydroxyphenanthrene based on the sensitizing effect of β-cyclodextrin

A novel method for the simultaneous determination of 1-hydroxypyrene (1-OHP), β-naphthol (β-NAP) and 9-hydroxyphenanthrene (9-OHPe) in human urine has been established by using synchronous fluorescence spectrometry. It was based on the fact that synchronous fluorescence spectrometry can resolve the broad-band overlapping of conventional fluorescence spectra, which arise from their similar molecular structures. Only one single scan is needed for quantitative determination of three compounds simultaneously when Δλ = 15 nm is chosen. The signals detected at these three wavelengths, 369.6, 330.0 and 358.0 nm, vary linearly when the concentration of 1-OHP, β-NAP and 9-OHPe is in the range of 2.16 × 10⁻⁸-1.50 × 10⁻⁵ mol L⁻¹, 1.20 × 10⁻⁷-1.10 × 10⁻⁵ mol L⁻¹ and 1.07 × 10⁻⁷-3.50 × 10⁻⁵ mol L⁻¹, respectively. The correlation coefficients for the standard calibration graphs were 0.994, 0.999 and 0.997 (n = 7) for 1-OHP, β-NAP and 9-OHPe, respectively. The limits of detection (LOD) for 1-OHP, β-NAP and 9-OHPe were 6.47 × 10⁻⁹ mol L⁻¹, 3.60 × 10⁻⁸ mol L⁻¹ and 3.02 × 10⁻⁸ mol L⁻¹with relative standard deviations (R.S.D.) of 4.70-6.40%, 2.80-4.20%, 3.10-4.90% (n = 6), respectively. The method described here had been applied to determine traces of 1-OHP, β-NAP and 9-OHPe in human urine, and the obtained results were in good agreement with those obtained by the HPLC method. In addition, the interaction modes between β-cyclodextrin (β-CD) and 1-OHP, β-NAP or 9-OHPe, as well as the mechanism of the fluorescence enhancement were also discussed.     

A potential visual fluorescence probe for ultratrace arsenic (III) detection by using glutathione-capped CdTe quantum dots

The interaction between mercaptoacetic acid (MA)-capped CdTe QDs, MA-capped CdTe/ZnS QDs or glutathione (GSH)-capped CdTe QDs with As(III) was studied using fluorescence spectrometry. As (III) has a high-affinity to reduced-GSH to form As(SG)₃, and the emission of the GSH-capped CdTe QDs (λ_em. = 612 nm) is quenched effectively. Thus, a novel fluorescence spectrometric method was developed for As (III) determination by using GSH-CdTe QDs. Under optimal conditions, the quenched fluorescence intensity (F₀/F) increased linearly with the concentration of As (III) ranging from 5.0 × 10⁻⁶ to 25 × 10⁻⁵ mol L⁻¹. The limit of detection (3σ) for As (III) was found to be 2 × 10⁻⁸ mol L⁻¹. This method is potentially useful in visual detection of As (III) under irradiation of the ultraviolet light.     

Selective determination of bisphenol A (BPA) in water by a reversible fluorescence sensor using pyrene/dimethyl β-cyclodextrin complex

A bifurcated optical fiber chemical sensor for continuous monitoring of bisphenol A (BPA) has been proposed based on the fluorescence quenching (λ_ex/λ_em = 286/390 nm) of pyrene/dimethyl β-cyclodextrin (HDM-β-CD) supramolecular complex immobilized in a plasticized poly(vinyl chloride) (PVC) membrane, in which pyrene served as a sensitive fluorescence indicator probe. The decrease of the fluorescence intensity of pyrene/HDM-β-CD complex upon the addition of BPA was attributed to the displacement of pyrene by BPA, which has been utilized as the basis of the fabrication of a BPA-sensitive fluorescence sensor. The response mechanism of the sensor was discussed in detail. The sensor exhibited a dynamic detection range from 7.90 × 10⁻⁸ to 1.66 × 10⁻⁵ mol L⁻¹ with a detection limit of 7.00 × 10⁻⁸ mol L⁻¹, and showed excellent reproducibility, reversibility, selectivity, and lifetime. The proposed sensor was successfully used for the determination of BPA in water samples and landfill leachate.     

Highly sensitive and selective spectrofluorimetric determination of tolnaftate through the formation of ternary inclusion complex of beta-naphthol/beta-cyclodextrin/anionic surfactant system

An indirect spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of antifungal drug: tolnaftate (TNF), depending on the supramolecualr multirecognition interaction among the anionic surfactant sodium laurylsulfate (SLS), β-cyclodextrin (β-CD) and β-naphthol (ROH). The mechanism of the inclusion was studied and discussed by means of fluorescence spectrum, infra-red spectrograms and ¹HNMR spectroscopy. Results showed that the naphthalene ring of ROH and the hydrophobic hydrocarbon chain of SLS were included into the β-CD's cavity to form a ROH:SLS:β-CD ternary inclusion complex with stoichiometry of 1:1:1 at room temperature, which provided effective protection for the excited state of ROH. At λ_ex/λ_em = 273/360 nm, the fluorescence intensity was linear over a tolnaftate concentration range of 2.46 × 10⁻⁹ to 2.10 × 10⁻⁶ mol L⁻¹. The detection limit and relative standard deviation was 7.50 × 10⁻¹⁰ mol L⁻¹ and 1.4%, respectively. The interference of 31 foreign substances was slight. The proposed method had been successfully applied to the determination of tolnaftate in artificial mixed samples with almost quantitative recovery.     

Rapid simultaneous analysis of 1-hydroxypyrene, 2-hydroxyfluorene, 9-hydroxyphenanthrene, 1- and 2-naphthol in urine by first derivative synchronous fluorescence spectrometry using Tween-20 as a sensitizer

A novel method of first derivative synchronous fluorescence was developed for the rapid simultaneous analysis of trace 1-hydroxypyrene (1-OHP), 1-naphthol (1-NAP), 2-naphthol (2-NAP), 9-hydroxyphenanthrene (9-OHPe) and 2-hydroxyfluorene (2-OHFlu) in human urine. Only one single scan was needed for quantitative determination of five compounds simultaneously when Δλ = 10 nm was chosen. In the optimal experimental conditions, there was a linear relationship between the fluorescence intensity and the concentration of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in the range of 1.75 × 10⁻⁹ to 4.50 × 10⁻⁶ mol L⁻¹, 3.64 × 10⁻⁸ to 2.20 × 10⁻⁴ mol L⁻¹, 8.18 × 10⁻⁹ to 1.20 × 10⁻⁴ mol L⁻¹, 3.26 × 10⁻⁹ to 8.50 × 10⁻⁵ mol L⁻¹ and 4.88 × 10⁻⁹ to 5.50 × 10⁻⁶ mol L⁻¹, respectively. The limits of detection (LOD) were found to be 5.25 × 10⁻¹⁰ mol L⁻¹ for 1-OHP, 1.10 × 10⁻⁸ mol L⁻¹ for 1-NAP, 2.46 × 10⁻⁹ mol L⁻¹ for 2-NAP, 9.77 × 10⁻¹⁰ mol L⁻¹ for 9-OHPe and 1.46 × 10⁻⁹ mol L⁻¹ for 2-OHFlu. The proposed method is reliable, selective and sensitive, and has been used successfully in the determination of traces of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in human urine samples, whose results were in good agreement with those gained by the HPLC method.     

A reagent-free method based on a photo-induced fluorimetry in a sequential injection system

According to the current demands of environmentally friendly analytical chemistry and with a view to achieving lower reagent consumption with improved analytical performance, an automatic methodology composed of a photoreactor and fluorimetric detection (λ_exc = 287 nm, λ_em = 378 nm) was developed. To this end, a sequential injection analysis (SIA) system was developed for indomethacin determination using ultra-violet (UV) light which promotes an increase in the fluorescence of indomethacin. This increase in sensitivity makes it possible to apply this methodology to a dissolution test and to determine indomethacin in pharmaceutical formulations.The calibration graph for indomethacin was linear between 4.10 × 10⁻⁶ and 9.00 × 10⁻⁵ mol L⁻¹and the detection limit was 1.23 × 10⁻⁶ mol L⁻¹. The method was proven to be reproducible with a R.S.D. < 5% and sampling rate of approximately 20 per hour. The potential effect of several compounds commonly used as excipients on analytical signals was studied and no interfering effect was observed. Statistical evaluation at the 95% confidence level showed good agreement between the results obtained for the pharmaceutical samples with both the SIA system and comparison batch procedures.     

Sensing hydrogen peroxide involving intramolecular charge transfer pathway: A boronate-functioned styryl dye as a highly selective and sensitive naked-eye sensor

The synthesis, properties and applications of a novel boronate-functioned styryl dye, BSD, as a colorimetric sensor for hydrogen peroxide is presented. The dye displayed remarkable color change from colorless (λ_max = 391 nm) to deep red (λ_max = 522 nm) in the presence of H₂O₂ and the behavior could be rationalized by the chemoselective H₂O₂-mediated transformation of arylboronate to phenolate, resulting in the release of the merocyanine dye which featured with strong intramolecular charge transfer (ICT) absorption band. The absorption increment of merocyanine at λ_max = 522 nm (? = 87000 L mol⁻¹ cm⁻¹) is linear with the concentration of H₂O₂ in the range of 1.0 × 10⁻⁷-2.5 × 10⁻⁵ mol L⁻¹ with the detection limit of 6.8 × 10⁻⁸ mol L⁻¹ under optimum conditions. There is almost no interference by other species that commonly exist due to the specific deprotection of H₂O₂ towards arylboronate group on BSD. The chromogenic sensor has been applied to the detection of trace amounts of hydrogen peroxide in rain water.     

Study of the influence of silver nanoparticles on the second-order scattering and the fluorescence of the complexes of Tb(III) with quinolones and determination of the quinolones

Quinolones (Qs) can form the complex with Tb(III) ion, and the intramolecular energy transfer from Qs to Tb(III) takes place when excited. And thus the characteristic fluorescence of Tb(III) ion was enhanced and the maximum fluorescence peak locates at 545 nm. The second-order scattering (SOS) peak at 545 nm also appears for the Tb(III)-Qs complexes with the exciting wavelength of 274 nm. When the silver nanoparticles were added to the Tb(III)-Qs system, the luminescence intensity at 545 nm greatly increased. And the relative intensity is proportional to the amount of Qs. Based on this phenomenon, a novel method for determination of quinolones has been developed by using a common spectrofluorometer to measure the intensity of fluorescence and SOS. The luminescence intensity is greatly enhanced by silver nanoparticles in the pH range 5.5-6.2. The calibration graphs for pipemidic acid (PPA) and lomefloxacin (LMFX) are linear in the range 2.0 × 10⁻¹⁰ to 1.0 × 10⁻⁵ and 1.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹, respectively. The limits of detection are 4.7 × 10⁻¹¹ mol L⁻¹ for PPA and 1.1 × 10⁻¹⁰ mol L⁻¹ for LMFX. The method was applied satisfactorily to the determination of the two quinolones (Qs) in tablet, capsule, urine and serum samples. The experimental results showed that it is the certain size and certain concentration of silver nanoparticles that can greatly enhance the fluorescence -SOS intensity.     

Highly sensitive and selective spectrofluorimetric determination of metoclopramide hydrochloride in pharmaceutical tablets and serum samples using Eu ion doped in sol-gel matrix

A simple, sensitive and selective spectrofluorimetric method for the determination of Metoclopramide hydrochloride (MCP) is developed. The MCP can remarkably enhances the luminescence intensity of the Eu³⁺ ion doped in sol-gel matrix at λ_ex = 380 nm in DMSO at pH 8.7. The intensity of the emission band of Eu³⁺ ion doped in sol-gel matrix increases due to energy transfer from MCP to Eu³⁺ in the excited state. The enhancement of the emission band of Eu³⁺ ion doped in sol-gel matrix at 617 nm was found to be directly proportional to the concentration of MCP with a dynamic range of 5 × 10⁻⁹ − 1.0 × 10⁻⁶ mol L⁻¹ and detection limit of 2.2 × 10⁻¹¹ mol L⁻¹.     

Adsorption of a protein-porphyrin complex at a liquid-liquid interface studied by total internal reflection synchronous fluorescence spectroscopy

Interfacial analysis has attracted more and more attention owing to its fundamental and biological importance. Total internal reflection fluorescence (TIRF) spectroscopy is a useful method to study interfacial properties. The synchronous scanning fluorescence technique provides a selective tool to analyze a specific component in a complex system. The interaction and adsorption of bovine serum albumin (BSA) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) at toluene-water interface were studied successfully by the coupling technique of total internal reflection synchronous fluorescence (TIRSF). New methods are provided for the determination of the critical micelle concentration (cmc), apparent adsorption equilibrium constant (K_ad) and maximum amount of adsorption (f_max) at the liquid-liquid interface. The results indicated that BSA could adsorb onto the toluene-water interface as a complex of BSA-TPPS in a ratio of 1:1 ratio based on Langmuir adsorption isothermal model. The cmc, apparent K_ad and f_max for BSA at pH 3.1 were determined to be 1.0 × 10⁻⁴ mol L⁻¹, 1.15 × 10⁵ L mol⁻¹ and 1.14 × 10⁻⁹ mol cm⁻², respectively.     

Synchronous fluorescence determination of DNA based on the interaction between methylene blue and DNA

The fluorescence intensity of methylene blue (MB) quenched by DNA in the pH range of 6.5-8.0 was studied with synchronous fluorescence technology. A novel method for detecting single-stranded and double-stranded DNA was developed. The decreased fluorescence intensity at 664 nm is in proportion to the concentration of DNA in the range of 0.28-11.0 μmol L⁻¹ for ctDNA, 0.14-8.25 μmol L⁻¹ for thermally denatured ctDNA and 0.28-8.25 μmol L⁻¹ for hsDNA. The detection limits (S/N = 3) are 0.11, 0.04 and 0.04 μmol L⁻¹, respectively. The method is rapid, selective, and the reagents are lower toxic. It has been used for the determination of DNA in synthetic samples with good satisfaction. In addition, the interaction modes between MB and ctDNA and the mechanism of the fluorescence quenching were also discussed in detail. The experimental results from absorption spectra and fluorescence polarization indicate that the possible interaction modes between MB and DNA are the electrostatic binding and the intercalation binding.     

Durable diagnosis of seminal vesicle and sexual gland diseases using the nano optical sensor thin film Sm-doxycycline complex

A new method in which a nano optical sensor for diagnosis of different diseases of seminal vesicle and sexual gland was prepared. The working principle of the method depends on the determination of the fructose concentration in semen of different patients by using nano optical sensor thin film Sm-doxycycline doped in sol–gel matrix. The assay is based on the quenching of the characteristic emission bands of Sm³⁺ present in silica doped Sm-doxycycline nanooptode thin film by different fructose concentrations in acetonitrile at λ_ex = 400 nm. This method was optimized for parameters, such as, solvent effect, operational stability, shelf life and interference parameters. Good and reproducible linearity (1 × 10⁻⁹ – 5.0 × 10⁻⁵ mol L⁻¹) with a detection limit of 9.0 × 10⁻¹⁰ mol L⁻¹ and quantification limit of detection (LOQ) 2.7 × 10⁻⁹ mol L⁻¹ were obtained. Seminal fructose determination in different patient samples after appropriate dilutions confirmed the reliability of this technique. The method was successfully applied for routine fructose monitoring in human semen samples of different cases such as; obstructive and non-obstructive azoospermia, inflammation of male accessory glands, atrophy of seminal vesicle, congenital vas deferens and retrograde ejaculation.     

Determination of melamine in different milk batches using a novel chemosensor based on the luminescence quenching of Ru(II) carbonyl complex

A novel, simple, sensitive and precise spectrofluorimetric method was developed for measuring the melamine concentration in different milk batch samples. The method was based upon measuring the quenching of the luminescence intensity of the produced yellow colored ruthenium^(II) carbonyl complex of the general formula [Ru(CO)₂(L)] (where L = anion of tetradentate Schiff base). The Ru^(II) complex exhibited characteristic luminescence band in the visible region. The remarkable quenching of the luminescence intensity of [Ru(CO)₂(L)] complex by various concentrations of melamine was successfully used as a chemosensor for the assessment of melamine in different milk samples at λ_ex = 400 nm and pH 7.4 in DMSO with a linear dynamic range 1.0 × 10⁻⁶ to 3.0 × 10⁻⁹ mol L⁻¹ and lower detection limit (LOD) and quantification detection limit (QOD) of 3.3 × 10⁻¹⁰ and 1.0 × 10⁻⁹ mol L⁻¹, respectively.     

Post-column terbium complexation and sensitized fluorescence detection for the determination of norepinephrine, epinephrine and dopamine using high-performance liquid chromatography

Terbium sensitized fluorescence was used as a post-column detection system to develop a simple, sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of catecholamines norepinephrine (NE), epinephrine (E) and dopamine (DA).Catecholamines were separated by an ion-pair reversed-phase chromatography on a BDS-Hypersil analytical column with a mobile phase of methanol and 50 mmol l⁻¹ acetate buffer (pH 4.7) containing 1.1 mmol l⁻¹ SOS and 0.11 mmol l⁻¹ EDTA (15+85 v/v).Catecholamines and the internal standard (3,4-dihydroxybenzylamine, DHBA) were post-column derivatized by the addition to the eluent of an alkaline solution containing a stoichiometric mixture of terbium(III) chloride and EDTA. Fluorescence detection (λ_ex=300 nm, λ_em=545 nm) is based on the sensitization of terbium ion fluorescence after complexation with catecholamines.The chemical compatibility between the eluent and the post-column reagent was studied and the analytical characteristics of the method were established. Detection limits found were 1.0×10⁻⁸, 4.0×10⁻⁸ and 7.0×10⁻⁸ mol l⁻¹ for NE, E and DA, respectively. The method has been successfully applied to the determination of catecholamines in urine samples after solid-phase extraction (SPE) pre-treatment. Recoveries from urine spiked with NE (4.0×10⁻⁷, 2.0×10⁻⁶ and 4.0×10⁻⁶ mol l⁻¹), E (8.2×10⁻⁸, 4.1×10⁻⁷ and 8.2×10⁻⁷ mol l⁻¹) and DA (1.0×10⁻⁶, 5.0×10⁻⁶ and 1.0×10⁻⁵ mol l⁻¹) varied from 98 to 100% (mean=99.3%), from 106 to 107% (mean=106.3%) and from 98 to 101% (mean=99.3%), respectively. The between-run precision (relative standard deviation, R.S.D.) for the method for three urine samples at different concentration levels of each catecholamine varied from 3.6 to 7.0%.     

Highly sensitive and selective detection of biothiols using graphene oxide-based “molecular beacon”-like fluorescent probe

A fluorometric method for quantity analysis of biothiols was developed using a graphene oxide (GO)-based “molecular beacon”-like probe, which consisted of FITC labeled thymine (T)-rich single-stranded DNA (ssDNA), GO and Hg²⁺ ions. The labeled ssDNA containing T–T mismatches would self-hybridize to duplex in the presence of Hg²⁺, which can avoid its adsorption on GO and the fluorescence of this GO-based probe was recovered. The fluorescence of the probe quenched after the addition of biothiols such as glutathione (GSH) and cysteine (Cys) owing to thiol groups can selectively competitive ligation of Hg²⁺ ions with T–T mismatches. In the present work, the GO-based probe was used for the determination of GSH and Cys. Under the optimal conditions, a linear correlation was established between fluorescence intensity ratio I₀/I and the concentration of GSH in the range of 2.0 × 10⁻⁹–5.0 × 10⁻⁷ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. The linear range for Cys is from 5.0 × 10⁻⁹ to 4.5 × 10⁻⁷ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁹ mol L⁻¹. The proposed method was applied to the determination of GSH in human serum and cell extract samples with satisfactory results.     

Determination of various alcohols based on a new immobilized enzyme fluorescence capillary analysis

A novel method for the determination of ethanol in tequila based on the immobilized enzyme fluorescence capillary analysis (IE-EFCA) has been proposed. Alcohol dehydrogenase (ADH) was immobilized in inner surface of a capillary and an immobilized enzyme capillary bioreactor (IE-ECBR) was formed. After nicotinamide adenine dinucleotide (NAD⁺) as an oxidizer is mixed with alcohol sample solution, it was sucked into the IE-ECBR. The fluorescence intensity of the mixed solution in the IE-ECBR was detected at λ_ex = 350 nm and λ_em = 459 nm. The experimental conditions are as follows: The reaction time is 20 min; temperature is 40 °C; the concentrations of phosphate buffer solution (pH 7.5) and NAD⁺ are 0.1 mol L⁻¹ and 5 mmol L⁻¹, respectively; immobilization concentration of ADH is 10 U L⁻¹. The determination range of ethanol is 2.0-15.0 g L⁻¹ (F = 10.44C + 6.6002, r > 0.9958); its detection limit is 1.11 g L⁻¹; and relative standard deviation is 1.9%. IE-EFCA method is applicable for the determination of the samples containing alcohol in medicine, industry and environment.     

Ultrasensitive fluorometric determination of hydrogen peroxide and glucose by using multiferroic BiFeO3 nanoparticles as a catalyst

BiFeO₃ magnetic nanoparticles (BFO MNPs) are used as a catalyst to develop an ultrasensitive method for the determination of H₂O₂. It is found that BFO MNPs can catalyze the decomposition of H₂O₂ to produce OH radicals, which in turn oxidize the weakly fluorescent benzoic acid to a strongly fluorescent hydroxylated product with a maximum emission at 405 nm. This makes it possible to sensitively quantify traces of H₂O₂. Under optimized conditions, the fluorescence intensity is observed to be well linearly correlated with H₂O₂ concentration from 2.0 × 10⁻⁸ to 2.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 4.5 × 10⁻⁹ mol L⁻¹ (S/N = 3). In addition, a selective method for glucose determination is developed by using both glucose oxidase and BFO MNPs, which has a linear range for glucose concentration from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁷ mol L⁻¹. These new methods have been successfully applied for the determination of H₂O₂ in rainwater and glucose in human serum samples.