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Tea plants absorb chromium-contaminated soil and water and accumulate in tea leaves. Hexavalent chromium (Cr6+) is a very toxic heavy metal; excessive intake of tea containing Cr6+ can cause serious harm to human health. A reliable and sensitive surface-enhanced Raman spectroscopy (SERS) method was developed using Au@Ag nanoparticles as an enhanced substrate for the determination of Cr6+ in tea. The Au@AgNPs coated with carbimazole showed a highly selective reaction to Cr6+ in tea samples through a redox reaction between Cr6+ and carbimazole. The Cr6+ in the contaminated tea sample reacted with methimazole—the hydrolysate of carbimazole—to form disulfide, which led to the decrease in the Raman intensity of the peak at 595 cm−1. The logarithm of the concentration of Cr6+ has a linear relationship with the Raman intensity at the characteristic peak and showed a limit of detection of 0.945 mg/kg for the tea sample. The carbimazole functionalized Au@AgNPs showed high selectivity in analyzing Cr6+ in tea samples, even in the presence of other metal ions. The SERS detection technique established in this study also showed comparable results with the standard ICP-MS method, indicating the applicability of the established technique in practical applications. [ABSTRACT FROM AUTHOR]

The effective differentiation and detection of multiple tea polyphenols are often challenging due to their subtle structural similarities. Although post-column derivatization HPLC strategies are commonly employed to distinguish multiple targets, the short physical distance between chromatographic column and detector limits reaction time, thereby reducing the derivatization efficiency. Dopamine (DA) reacts rapidly with resorcinol to form fluorescent azamonardine products, making fast fluorometric derivatization of tea polyphenols containing resorcinol motifs possible. In this study, a DA-driven rapid and post-column fluorescence derivatization method has been applied to sensitively detect eight tea polyphenols. This method is based on fluorescence derivatization and possesses low background interference, high sensitivity, and excellent reproducibility. Moreover, the practical application of this proposed fluorometric derivatization platform was further validated by simultaneous identification of multiple tea polyphenols in different tea samples. This work has great potential to become an alternative to the National Standard method for tea polyphenols determination. [Display omitted] • Dopamine can act as novel fluorescence derivatization agent for tea polyphenols. • The retention time of tea polyphenols is extended after derivatization. • Eight tea polyphenols are distinguished using post-column derivatization HPLC. • The analysis of tea polyphenols contents in different tea samples is realized. [ABSTRACT FROM AUTHOR]

Tea plants absorb chromium-contaminated soil and water and accumulate in tea leaves. Hexavalent chromium (Cr6+) is a very toxic heavy metal; excessive intake of tea containing Cr6+ can cause serious harm to human health. A reliable and sensitive surface-enhanced Raman spectroscopy (SERS) method was developed using Au@Ag nanoparticles as an enhanced substrate for the determination of Cr6+ in tea. The Au@AgNPs coated with carbimazole showed a highly selective reaction to Cr6+ in tea samples through a redox reaction between Cr6+ and carbimazole. The Cr6+ in the contaminated tea sample reacted with methimazole—the hydrolysate of carbimazole—to form disulfide, which led to the decrease in the Raman intensity of the peak at 595 cm−1. The logarithm of the concentration of Cr6+ has a linear relationship with the Raman intensity at the characteristic peak and showed a limit of detection of 0.945 mg/kg for the tea sample. The carbimazole functionalized Au@AgNPs showed high selectivity in analyzing Cr6+ in tea samples, even in the presence of other metal ions. The SERS detection technique established in this study also showed comparable results with the standard ICP-MS method, indicating the applicability of the established technique in practical applications.

Natural product screening in plants has always been a difficult task due to the complex nature of the plant material and diverse structures of the compounds present in them. Flavonoids are important and diverse class of plant secondary metabolites with numerous medicinal activities. The present study focuses on the development of a high-resolution tandem mass spectral library for the rapid and authentic identification of common flavonoids. A total of forty flavonoid standards belong to class flavones, isoflavones, flavanones, flavanols and anthocyanins were pooled into two solutions applying logP-based strategy. The flavonoids were analyzed using LC-QTOF-MS high-resolution mass spectrometer with optimization of different instrumental parameters to achieve good sensitivity. The library was built by incorporating names, molecular formulae, exact masses, and MS, and MS/MS spectra of analyzed flavonoids using Bruker Library Editor tool. The fragmentation pattern observed for the standard compounds were compared to the fragments reported in the literature. To assess the practical implications, an extract of tea sample was analyzed and screened using the developed library, which resulted in the identification of three common flavonoids based on their HR-ESI-MS/MS spectral features. The established LC-HR-MS/MS method can be used for the targeted identification of flavonoids in complex samples like food material from different botanical families.

A fluorometric assay was developed for the determination of copper(II) ion based on its quenching effect on the green fluorescent probe of SiO2-anchored CdS nanocrystals (SiO2/CdS NCs). The fluorescent probe was prepared by a surface ion-directing strategy for homogeneous precipitation of CdS NCs onto the carboxyl-capped SiO2 core surfaces. In comparison to CdS NCs, the SiO2/CdS NCs has strong fluorescence emission and good photostability. Moreover, SiO2/CdS NCs show higher fluorescence selectivity for copper(II) ions than for other common metal ions because copper(II) ions have a strong fluorescence quenching effect on SiO2/CdS NCs. At excitation/emission wavelengths of 300/516 nm, the resulting fluorescent probe shows wide linear ranges from 0.01 to 2 μM with a detection limit of 6.3 nM for copper(II) ions. The method has been applied to the determination of trace copper(II) ions in tea infusions with satisfactory results. [ABSTRACT FROM AUTHOR]

Based on the inner filter effect mechanism of quantum dots, a ratiometric fluorescence nanoprobe was constructed for the determination of Pb(II) ion. Green emitting quantum dots conjugated with DNA substrate (DNA2) acted as donors providing green fluorescence, while gold nanoparticles coupled with DNA enzyme (DNA1) as acceptors quench the green fluorescence. Meanwhile, Fe3O4 nanosphere served as magnetic substrates to facilitate separation process and red fluorescence as an "inner rule" to eliminate the background signal. In the presence of Pb(II) ion, the DNA1 specifically recognize and capture Pb(II) ion with enhanced catalytic activity, which can cleave DNA2 and "turn on" the green fluorescence (I540), while the red fluorescence (I630) remained unchanged. In this way, the ratio of I540/I630 reflects the Pb(II) ion in the system, enabling the quantitative and selective determination of Pb(II) ion over nine different metal ions. Under optimal conditions, the ratiometric fluorescence assay showed good linearity (R2 = 0.98) within the range 10 to 100 ng mL−1. The limit of detection (LOD) was calculated to be 1.79 pg mL−1 (S/N = 3, n = 3, ±3.8%). The proposed fluorescence nanoprobe provides better sensitivity and accuracy than non-ratiometric signal evaluation for Pb(II) ion determination. [ABSTRACT FROM AUTHOR]

In this paper, a new type of carbon ceramic electrode modified with reduced graphene oxide (RGO) was fabricated via sol-gel method. The constructed electrode was used in square wave voltammetric (SWV) determination of gallic acid (GA). The electrochemical properties of the fabricated electrode and voltammetric behavior of gallic acid were investigated by cyclic voltammetry (CV). The SWV investigation of GA was performed in Britton-Robinson buffer at pH 2 as a supporting electrolyte. Under the optimized SWV mode parameters, the oxidation peak current (best measured at 0.57 V vs Ag/AgCl) increased linearly in the wide concentration range from 0.51 to 46.40 μmol L −1 . The calculated values of LOD and LOQ were 0.0867 and 0.263 μmol L −1 , respectively. The presented results were obtained without any preconcentration procedure. During the experiment, the effect of common interfering molecules was also investigated. Finally, the usability of the proposed method was verified by the quantitative analysis of GA in red wine, black tea and white tea samples. [ABSTRACT FROM AUTHOR]

The activity concentrations of natural radionuclides and radiological hazard indices in eleven tea samples collected from local market in Bangladesh have been analyzed by using High Purity Germanium (HPGe) Detector. The average activity concentrations of 226Ra, 232Th and 40K in tea samples have been found to be 21.21±14.04, 32.43±7.48 and 93.47 ± 43.94 Bqkg-1 respectively. The calculated absorbed dose rates due to these radioactive nuclides in tea samples have been found to vary from 26.24 nGyh-1 to 37.95 nGyh-1 and average value was 33.28 nGyh-1. The estimated outdoor annual effective dose rates varied from 38.64 μSvy-1 to 55.89 μSvy-1 with the mean value of 49.02 μSvy-1 which is less than the world average value of 1000 μSvy-1. The values of radium equivalent activity in all samples are less than the permissible maximum value of the radium equivalent activity which is 370 Bqkg-1 according to UNSCEAR 2000 report. The values of external and internal hazard indices for different samples varied from 0.16 to 0.23 with the average value of 0.20 and from 0.21 to 0.29 with an average of 0.26. The value of this index must be less than unity in order to keep the radiation hazard insignificant. It was also found that there is no artificial radionuclide (for example 137Cs) in any of the samples. The data generated in this study will provide baseline radiometric values for natural and artificial radioactivity in tea samples in Bangladesh. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to assess the activity concentration of radionuclides in tea samples which were cultivated in Chitttagong region in Bangladesh. Total thirteen (13) tea samples were collected from different tea garden of Fatickchari, Rangunia and Banshkhali upozilla in Chittagong. The activity concentrations of 238U, 232Th, 40K and 137Cs in thirteen tea samples were measured, using a gamma spectrometry system with multichannel analyzer. The observed activity concentrations of 238U found in tea samples varied from 2.4 ± 0.4 Bq.kg-1 to 18.93 ± 1.72 Bq.kg-1 with mean concentration 5.34 ± 0.38 Bq.kg-1. The observed activity concentration of 232Th found in the tea sample varied 1.4 ± 0.56 Bq.kg-1 to 27.22 ± 3.65 Bq.kg-1 with mean concentration 10.07± 0.83 Bq.kg-1. The 40K activity in these tea samples varied from 151 ± 18.72 Bq.kg-1 to 1243 ± 83.91 Bq.kg-1 with mean concentration 430 ± 35.5 Bq.kg-1. No 137Cs activity was detected at any of the samples in the whole study area. The calculated values of Radium equivalent activity (Raeq) and the internal hazard index (Hin) for the tea samples are lower than the international permissible value of unity UNSCEAR (2000). It was concluded that the activity level of tea samples in the present study was non-threatening to public health. [ABSTRACT FROM AUTHOR]

In this work, a miniaturized optical sensor was developed for fluoride determination in tea samples to evaluate their specific risks of fluorosis for public health based on evanescent-wave interaction. The sensor design was integrated on the optical fiber by utilizing the evanescent wave produced on the fiber surface to react with sensing reagents. According to the absorption change at 575 nm, fluoride could be determined by colorimetric method and evaluated by Beer's law. With improved performances of small detection volume (1.2 μL), fast analysis (0.41 min), wide linear range (0.01–1.4 mg L −1 ), low detection limit (3.5 μg L −1 , 3σ) and excellent repeatability (2.34%), the sensor has been applied to fluoride determination in six different tea samples. Conventional spectrophotometry and ion chromatography were employed to validate the sensor's accuracy and potential application. Furthermore, this sensor fabrication provided a miniaturized colorimetric detection platform for other hazardous species monitoring based on evanescent wave interaction. [ABSTRACT FROM AUTHOR]

A novel voltammetric assay for the simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RS) by using an electrochemically treated pencil graphite electrode modified with cobalt-phthalocyanine is described. Differential pulse voltammetric results showed three well-distinct oxidation peaks for HQ, CC and RS at 102 mV, 203 mV and 591 mV (vs. Ag/AgCl), respectively. Thus, the method can be applied to direct simultaneous determination without previous separation. The detection limits are 3.38 × 10 mol L for HQ, 3.40 × 10 mol L for CC and 7.23 × 10 mol L for RS. The method was successfully applied to the direct determination of dihydroxybenzene isomers in tea samples, and the results were compared with chromatographic data. [ABSTRACT FROM AUTHOR]

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Abstract: A gold nanoparticles/TiO2 composite modified Indium tin oxide (ITO) electrode has been constructed to study the electrochemical behaviour of catechol (CC) and hydroquinone (HQ) using cyclic voltammetry and differential pulse voltammetry (DPV). Increasing of separation of the oxidative peak potentials and peak current for CC and HQ in pH 6.0 phosphate buffer solution (PBS), make it suitable for selected determination of CC. After the optimization of the conditions, CC was determined by DPV and the linear range is from 1.0×10−7 to 5.0×10−4 molL−1 with a correlation coefficient of 0.999 and limit of detection as 5.0×10−8 molL−1. Interference and stability study showed a satisfactory result. The proposed method has been applied to determine catechol in tea samples, and comparing with the chromatography the results are satisfactory. [Copyright &y& Elsevier]

Natural product screening in plants has always been a difficult task due to the complex nature of the plant material and diverse structures of the compounds present in them. Flavonoids are important and diverse class of plant secondary metabolites with numerous medicinal activities. The present study focuses on the development of a high-resolution tandem mass spectral library for the rapid and authentic identification of common flavonoids. A total of forty flavonoid standards belong to class flavones, isoflavones, flavanones, flavanols and anthocyanins were pooled into two solutions applying logP-based strategy. The flavonoids were analyzed using LC-QTOF-MS high-resolution mass spectrometer with optimization of different instrumental parameters to achieve good sensitivity. The library was built by incorporating names, molecular formulae, exact masses, and MS, and MS/MS spectra of analyzed flavonoids using Bruker Library Editor tool. The fragmentation pattern observed for the standard compounds were compared to the fragments reported in the literature. To assess the practical implications, an extract of tea sample was analyzed and screened using the developed library, which resulted in the identification of three common flavonoids based on their HR-ESI-MS/MS spectral features. The established LC-HR-MS/MS method can be used for the targeted identification of flavonoids in complex samples like food material from different botanical families. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a method was developed for determination of ultra-trace levels of Cd in tea samples by atomic fluorescence spectrometry (AFS). A flow injection solid phase extraction (FI-SPE) separation and preconcentration technique, to on-line couple with a sequential injection hydride generation (SI-HG) technique is employed in this study. Cd was preconcentrated on the SPE column, which was made from a neutral extractant named Cyanex 923, while other matrix ions or interfering ions were completely or mostly separated off. Conditions for the SPE separation and preconcentration, as well as conditions for the HG technique, were studied. Due to the separation of interfering elements, Cd hydride generation efficiency could be greatly enhanced with the sole presence of Co2+ with a concentration of 200μgL−1, which is much lower than those in other works previously reported. Interferences on both the Cd separation and preconcentration, and Cd hydride generation (HG) were investigated; it showed that both the separation and preconcentration system, and the HG system had a strong anti-interference ability. The SPE column could be repeatedly used at least 400 times, a R.S.D. of 0.97% was obtained for 6 measurements of Cd with 0.2μgL−1 and a correlation coefficiency of 1.0000 was obtained for the measurement of a series of solutions with Cd concentrations from 0.1 to 2μgL−1. The method has a low detection limit of 10.8ngL−1 for a 25mL solution and was successfully validated by using two tea standard reference materials (GBW08513 and GBW07605). [Copyright &y& Elsevier]

[Display omitted] • A water-soluble FONs-based sensor was constructed by facile hydrothermal method. • The acquired sensor shows highly specific recognization capability to Hg2+. • The FONs-based sensor was firstly applied to detect Hg2+ in tea samples. In this study, a novel FONs-based sensor P-M(w) was synthesized using 1-Pyrenecarboxaldehyde and L-methionine through facile hydrothermal strategy. The fluorescence emission peaks of the acquired P-M(w) would show specific changes after the addition of Hg2+ due to interfering the PET process and inducing nano-structure conformational rigidification of P-M(w). Notably, the water-soluble FONs-based sensor was firstly used to detect Hg2+ in tea samples providing a new material choice for the fluorescence sensor construction of metal ion detection. Besides, the qualitative and quantitative analysis of Hg2+ could be carried out with P-M (w) at a very low concentration (1 μg/mL) meaning that the acquired P-M(w) synthesized by few grams of reactants may satisfy the detection of approximate fifty thousand samples. [ABSTRACT FROM AUTHOR]