Man Qiao

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0μmolL(-1), with a limit of detection (3σ/k) of 79.6nmolL(-1). Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

A novel method for detecting allura red based on triple-wavelength overlapping resonance Rayleigh scattering

A method is presented for the sensitive and selective determination of trace allura red (AR) with ethyl violet (EV) in drink samples, based on triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS). At pH 10.0 in a Britton–Robinson (BR) buffer medium, AR combined with EV to form an ion-association complex, which resulted in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 341, 508 and 666 nm. The scattering intensities of the three peaks were proportional to the concentration of AR in the range of 0.057–5.0 μmol L−1 (0.028–2.48 μg mL−1). The detection limits for the three single peaks were 0.048 μmol L−1 (0.024 μg mL−1), 0.050 μmol L−1 (0.025 μg mL−1), and 0.057 μmol L−1 (0.028 μg mL−1), while that of the TWO-RRS method was 0.017 μmol L−1 (0.008 μg mL−1), indicating that the TWO-RRS method could detect trace AR with high sensitivity. In addition, the optimum reaction conditions and the effects of foreign substances were studied. The composition of the ion-association complex, and the reasons for the enhancement of RRS were also investigated. The proposed method was successfully applied in a real sample analysis with satisfactory results.

Enhanced spectrofluorimetric determination of hypochlorite based on the catalytic oxidation of thiamine to thiochrome in the presence of trace ferrocyanide

An enhanced spectrofluorimetric method for highly selective and sensitive determination of nmol L−1 of hypochlorite has been performed. In alkaline medium, ferrocyanide was specifically oxidized by hypochlorite to form ferricyanide, which further reacted with non-fluorescent thiamine, resulting in the formation of blue fluorescent thiochrome. Notably, the fluorescence intensities were positively correlated with the concentration of hypochlorite over the range of 0.02–12.5 μmol L−1. The detection limit was 6.1 nmol L−1, which was lower than for most of the recently published methods. The experimental conditions were optimized and effects of coexisting substances were evaluated and the results showed excellent priority since a certain amount of other anions, including ClO3−, BrO3−, IO3−, Cr2O72− and other acid radicals, would not interfere with the measurement.

Highly selective speciation and fluorimetric determination of Se(IV) in infant formulas using micelle-capped nile blue A

A simple and very selective spectrofluorimetric method for the detection of ng mL−1 levels of inorganic selenium species in infant formulas has been performed. It is based on the oxidation of micelle-capped nile blue A (MCNBA) by sodium selenite under neutral conditions (pH 7.0). A specific quenching of the fluorescence of MCNBA was observed and the response signals were linearly correlated with the concentration of sodium selenite over the ranges of 4.17 × 10−9 to 4.5 × 10−6 mol L−1 (0.73–787.1 ng mL−1). The limit of detection was 1.25 nmol L−1 (0.22 ng mL−1). Different parameters such as selectivity, recovery, linearity, limits of detection and quantification of the measurements were evaluated in order to validate the proposed method. Then, the new method was applied to the analysis of several infant formula samples with satisfactory results.

Fluorescence quenching and spectrophotometric methods for the determination of daunorubicin with meso-tera (4-sulphophenyl) porphyrin as probe

In this work, a synthetic meso-tera (4-sulfophenyl) porphyrin (TPPS4) was used as a probe to determine daunorubicin (DNR) by fluorescence quenching and spectrophotometric methods. At pH 4.6 potassium acid phthalate-NaOH buffer solution, a 1:1 complex of DNR interacted with TPPS4 formed via the electrostatic attractions and hydrophobic interactions, thus resulted in TPPS4 fluorescence quenching and absorption spectra change. The maximum excitation wavelength (λex) and the maximum emission wavelength (λem) are 435 nm and 672 nm, respectively. The fluorescence quenching values (ΔF) are the good linear relationship to the concentration of DNR in the range of 0.8-6.0 mgL(-1). The method exhibits high sensitivity with the detection limit (3σ) being 27.0 ng mL(-1). Meanwhile, a decrease of absorbance is detected at 433 nm with the appearance of a new absorption peak at 420 nm. The optimum reaction conditions, influencing factors and the effect of coexisting substances have been investigated in our experiment. The results showed that the method had a good selectivity and could be applied to determine DNR in serum and urine samples. In addition, the combine ratio between DNR and TPPS4 was measured and the charge distribution before and after reaction was calculated by quantum chemistry calculation AM1 method. The type of fluorescence quenching was discussed by the absorption spectra change, Stern-Volmer plots and fluorescence lifetime determination.

Spectrofluorometric determination of ascorbic acid using thiamine and potassium ferricyanide

ABSTRACT A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367 nm and an emission peak at 441 nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5 µmol L−1 with a correlation coefficient of 0.9996. The detection limit of 0.026 µmol L−1 was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice with satisfactory results.

Study on erythrosine-phen-Cd(II) systems by resonance Rayleigh scattering, absorption spectra and their analytical applications.

In pH 7.0-8.0 KH2PO4-Na2HPO4 buffer solution, Cd(II) reacted with 1,10-phenanthroline to form chelate cation [Cd(phen)3]2+, which further reacted with anion of erythrosine to form ternary ion-association complex through electrostatic attraction and hydrophobic effect. This process could result in remarkable absorption spectra change and produce obvious fading reaction at 528 nm. Absorbance change (ΔA) of system was directly proportional to the concentration of Cd(II). Hereby, a highly sensitive spectrophotometric method for the determination of Cd(II) was established. The molar absorption coefficient was 2.29×10(5) L mol(-1) cm(-1) and the detection limit of Cd(II) was 26.5 ng mL(-1). Furthermore, the resonance Rayleigh scattering (RRS) of this system with two peaks located at 371 and 590 nm enhanced significantly, and second-order scattering (SOS) and frequence doubling scattering (FDS) of this system changed notably at 640 and 350 nm, respectively. Under the optimum conditions, the scattering intensities (ΔIRRS, ΔIDWO-RRS, ΔISOS and ΔIFDS) had good linear relationship with the concentration of Cd(II) in certain ranges. The detection limits of Cd(II) were 1.27 ng mL(-1), 1.39 ng mL(-1), 4.03 ng mL(-1), 5.92 ng mL(-1) and 14.7 ng mL(-1) for dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS), RRS (371 nm), RRS (590 nm), SOS and FDS, respectively. In addition, the suitable reaction conditions and effects of coexisting substances were investigated. The methods had been successfully applied to the determination of Cd(II) in environmental water samples. The recovery range was between 93.0% and 103.0% and the relative standard deviation (RSD) was between 2.5% and 4.3%. The results were in agreement with those obtained from atomic absorption spectroscopy.

Study on interactions of aminoglycoside antibiotics with calf thymus DNA and determination of calf thymus DNA via the resonance Rayleigh scattering technique

A simple and sensitive resonance Rayleigh scattering (RRS) spectra method was developed for the determination of calf thymus DNA (ctDNA). The enhanced RRS signals were based on the interactions between ctDNA and aminoglycoside antibiotics (AGs) including kanamycin (KANA), tobramycin (TOB), gentamicin (GEN) and neomycin (NEO) in a weakly acidic medium (pH 3.3-5.7). Parameters influencing the method were investigated. Under optimum conditions, increments in the scattering intensity (∆I) were directly proportional to the concentration of ctDNA over certain ranges. The detection limit ranged from 12.2 to 16.9 ng/mL. Spectroscopic methods, including RRS spectra, absorption spectra and circular dichroism (CD) spectroscopy, coupled with thermo-denaturation experiments were used to study the interactions, indicating that the interaction between AGs with ctDNA was electrostatic binding mode.

Resonance Rayleigh scattering technique for simple and sensitive analysis of tannic acid with carbon dots

Carbon dots (CDs) are raising a substantial amount of attention owing to their many unique and novel physicochemical properties. Herein one-pot synthesized CDs, to the best of our knowledge, were first served as the robust nanoprobe for detection tannic acid (TA) based on resonance Rayleigh scattering technique. The as-prepared CDs can combine with TA via hydrogen bond, resulting in remarkable enhancement of scattering signal with no changes in the fluorescence of CDs. Therefore, a novel protocol for TA determination was established and this strategy allowed quantitative detection of TA in the linear range of 0.2-10.0μmolL-1 with an excellent detection limit of 9.0nmolL-1. Moreover, the CDs based nanoprobe can be applied to the determination of TA in water sample with satisfactory results. Our study can potentially influence our current views on CDs and particularly impressive and offers new insights into application of CDs beyond the traditional understanding of CDs.

A rapid and sensitive resonance Rayleigh scattering spectra method for the determination of quinolones in human urine and pharmaceutical preparation

A new method based on resonance Rayleigh scattering (RRS) was proposed for the determination of quinolones (QNS) at the nanogram level. In pH 3.3-4.4 Britton-Robinson buffer medium, quinolones such as ciprofloxacin, pipemidic acid (PIP), lomefloxacin (LOM), norfloxacin (NOR) and sarafloxacin (SAR) were protonated and reacted with methyl orange (MO) to form an ion-pair complex, which then further formed a six-membered ring chelate with Pd(II). As a result, new RRS spectra appeared and the RRS intensities were enhanced greatly. RRS spectral characteristics of the MO-QNS-Pd(II) systems, the optimum conditions for the reaction, and the influencing factors were investigated. Under optimum conditions, the scattering intensity (∆I) increments were directly proportional to the concentration of QNS with in certain ranges. The method had high sensitivity, and the detection limits (3σ) ranged from 6.8 to 12.6 ng/mL. The proposed method had been successfully applied for the determination of QNS in pharmaceutical formulations and human urine samples. In addition, the mechanism of the reaction system was discussed based on IR, absorption and fluorescence spectral studies. The reasons for the enhancement of scattering spectra were discussed in terms of fluorescence-scattering resonance energy transfer, hydrophobicity and molecular size.