Development and evaluation of a diffusive gradients in a thin film technique for measuring ammonium in freshwaters

A new diffusive gradients in a thin film (DGT) technique, using Microlite PrCH cation exchange resin, was developed and evaluated for measuring NH₄–N in freshwaters. Microlite PrCH had high uptake (>92.5%) and elution efficiencies (87.2% using 2 mol L⁻¹ NaCl). Mass vs. time validation experiments over 24 h demonstrated excellent linearity (R² ≥ 0.996). PrCH-DGT binding layers had an extremely high intrinsic binding capacity for NH₄–N (∼3000 μg). NH₄–N uptake was quantitative over pH ranges 3.5–8.5 and ionic strength (up to 0.012 mol L⁻¹ as NaCl) typical of freshwater systems. Several cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺) were found to compete with NH₄–N for uptake by PrCH-DGT, but NH₄–N uptake was quantitative over concentration ranges typical of freshwater (up to 0.012 mol L⁻¹ Na⁺, 0.006 mol L⁻¹ K⁺, 0.003 mol L⁻¹ Ca²⁺ and 0.004 mol L⁻¹ Mg²⁺). Effective diffusion coefficients determined from mass vs. time experiments changed non-linearly with electrical conductivity. Field deployments of DGT samplers with varying diffusive layer thicknesses validated the use of the technique in situ, allowed deployment times to be manipulated with respect to NH₄–N concentration, and enable the calculation of the diffusive boundary layer thickness. Daily grab sample NH₄–N concentrations were observed to vary considerably independent of major rainfall events, but good agreements were obtained between PrCH-DGT values and mean grab sample measurements of NH₄–N (C_DGT:C_SOLN 0.83–1.3). Reproducibility of DGT measurements in the field was good (relative standard deviation < 11%). Limit of detection was 0.63 μg L⁻¹ (equivalent to 0.045 μmol L⁻¹) based on 24 h deployments.     

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.     

A novel dichromate-sensitive fluorescent nano-chemosensor using new functionalized SBA-15

A novel fluorescence nano-chemosensor for Cr₂O₇²⁻ anion has been developed by assembly of fluorescent aluminum complex of 8-hydroxyquinoline (AlQ_x) within the channels of modified SBA-15. SBA-SPS-AlQ_x shows a fluorescence emission at 486 nm. The observed remarkable fluorescence of SBA-SPS-AlQ_x quenches in presence of Cr₂O₇²⁻ anion. The results showed that this fluorescent nano-material can be a useful chemo-sensor for determination of dichromate anions in aqueous solutions. The linear detecting range of fluorescent nano-chemosensor for Cr₂O₇²⁻ anion was 0.16–2.9 μmol L⁻¹. The lowest limit of detection (LDL) was also found to be 0.2 ng mL⁻¹ in aqueous solutions. SBA-SPS-AlQ_x showed selectively and sensitively fluorescent quenching response toward Cr₂O₇²⁻ ion in comparison with I₃⁻, NO₃⁻, CN⁻, CO₃²⁻, Br⁻, Cl⁻, F⁻, H₂PO₄⁻ and SO₄²⁻ ions, which was because of the higher stability of its inorganic complex with dichromate ion.     

Comparison of synchronous and laser-induced fluorescence spectroscopy applied to the Eu(III)-fulvate complexation

The complexation of europium ion (Eu(III)) with a soil fulvic acid (FA) has been studied at pH 5 in 0.01 M NaClO₄ by different experimental methods, i.e. synchronous fluorescence spectroscopy (SyFS) and time resolved laser-induced fluorescence spectroscopy (TRLFS). A series of SyFS quenching spectra was obtained by increasing the Eu(III) concentration and keeping the FA concentration constant. The emission spectra and fluorescence lifetimes of the Eu(III) bound to the FA were also measured by a TRLFS system using the same solution used in the SyFS spectral measurement. From the analysis of the fluorescence data obtained by the SyFS and the TRLFS using a non-linear least-squares method, the concentration of the binding sites (C_L) of the FA accessible for the Eu(III) and the corresponding conditional stability constants (log K) were estimated. The two different methods gave rise to constants being comparable with one another. The log K and C_L values (mean ± standard deviation of three determinations) determined by the SyFS were 6.4 ± 0.2 (6.7 ± 0.1 μmol L⁻¹: by the TRLFS) and 10 ± 1 μmol L⁻¹ (7 ± 1 μmol L⁻¹: by the TRLFS), respectively. The applicability of the FA fluorescence quenching techniques for estimating the europium binding parameters was proved by the direct monitoring of the Eu(III) bound to the FA using the TRLFS system.     

Synthesis of a novel electrode material containing phytic acid-polyaniline nanofibers for simultaneous determination of cadmium and lead ions

The development of nanostructured conducting polymers based materials for electrochemical applications has attracted intense attention due to their environmental stability, unique reversible redox properties, abundant electron active sites, rapid electron transfer and tunable conductivity. Here, a phytic acid doped polyaniline nanofibers based nanocomposite was synthesized using a simple and green method, the properties of the resulting nanomaterial was characterized by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). A glassy carbon electrode modified by the nanocomposite was evaluated as a new platform for the simultaneous detection of trace amounts of Cd²⁺ and Pb²⁺ using differential pulse anodic stripping voltammetry (DPASV). The synergistic contribution from PANI nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the DPASV analysis. Under the optimal conditions, good linear relationships were obtained for Cd²⁺ in a range of 0.05–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.02 μg L⁻¹, and for Pb²⁺ in a range of 0.1–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.05 μg L⁻¹. The new electrode was successfully applied to real water samples for simultaneous detection of Cd²⁺ and Pb²⁺ with good recovery rates. Therefore, the new electrode material may be a capable candidate for the detection of trace levels of heavy metal ions.     

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CN_x) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CN_x electrode. Thus, an a-CN_x film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L⁻¹ KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CN_x electrode were 0.0656 μmol L⁻¹ for DA and 1.05 μmol L⁻¹ for AA, whereas with the BDD electrode these values were 0.283 μmol L⁻¹ and 0.968 μmol L⁻¹, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CN_x electrode in electroanalysis.     

Poly(methylene blue) functionalized graphene modified carbon ionic liquid electrode for the electrochemical detection of dopamine

An ionic liquid 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was used as the substrate electrode and a poly(methylene blue) (PMB) functionalized graphene (GR) composite film was co-electrodeposited on CILE surface by cyclic voltammetry. The PMB–GR/CILE exhibited better electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behavior of dopamine (DA) was further investigated by cyclic voltammetry and a pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔE_p) as 0.058 V in 0.1 mol L⁻¹ pH 6.0 phosphate buffer solution, which proved a fast quasi-reversible electron transfer process on the modified electrode. Electrochemical parameters of DA on PMB–GR/CILE were calculated with the electron transfer number as 1.83, the charge transfer coefficients as 0.70, the apparent heterogeneous electron transfer rate constant as 1.72 s⁻¹ and the diffusional coefficient (D) as 3.45 × 10⁻⁴ cm² s⁻¹, respectively. Under the optimal conditions with differential pulse voltammetric measurement, the linear relationship between the oxidation peak current of DA and its concentration was obtained in the range from 0.02 to 800.0 μmol L⁻¹ with the detection limit as 5.6 nmol L⁻¹ (3σ). The coexisting substances exhibited no interference and PMB–GR/CILE was applied to the detection of DA injection samples and human urine samples with satisfactory results.     

The Cu-MOF-199/single-walled carbon nanotubes modified electrode for simultaneous determination of hydroquinone and catechol with extended linear ranges and lower detection limits

A novel electrochemical sensor based on Cu-MOF-199 [Cu-MOF-199 = Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylicacid)] and SWCNTs (single-walled carbon nanotubes) was fabricated for the simultaneous determination of hydroquinone (HQ) and catechol (CT). The modification procedure was carried out through casting SWCNTs on the bare glassy carbon electrode (GCE) and followed by the electrodeposition of Cu-MOF-199 on the SWCNTs modified electrode. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were performed to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The composite electrode exhibited an excellent electrocatalytic activity with increased electrochemical signals towards the oxidation of HQ and CT, owing to the synergistic effect of SWCNTs and Cu-MOF-199. Under the optimized condition, the linear response range were from 0.1 to 1453 μmol L⁻¹ (R_HQ = 0.9999) for HQ and 0.1–1150 μmol L⁻¹ (R_CT = 0.9990) for CT. The detection limits for HQ and CT were as low as 0.08 and 0.1 μmol L⁻¹, respectively. Moreover, the modified electrode presented the good reproducibility and the excellent anti-interference performance. The analytical performance of the developed sensor for the simultaneous detection of HQ and CT had been evaluated in practical samples with satisfying results.     

Coordination to copper(II) strongly enhances the in vitro antimicrobial activity of pyridine-derived N(4)-tolyl thiosemicarbazones

Five copper(II) complexes with N(4)-ortho, N(4)-meta and N(4)-para-tolyl thiosemicarbazones derived from 2-formyl and 2-acetylpyridine were obtained and thoroughly characterized. The crystal structure of N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone (H2Ac4mT) was determined, as well as that of its copper(II) complex [Cu(2Ac4mT)Cl], which contains an anionic ligand and a chloride in the coordination sphere of the metal. The in vitro antimicrobial activities of all thiosemicarbazones and their copper(II) complexes were tested against Salmonella typhimurium and Candida albicans. Upon coordination a substantial decrease in the minimum inhibitory concentration, from 225 to 1478 μmol L⁻¹ for the thiosemicarbazones to 5–30 μmol L⁻¹ for the complexes was observe against the growth of Salmonella typhimurium and from 0.7–26 to 0.3–7 μmol L⁻¹ against the growth of C. albicans, suggesting that complexation to copper(II) could be an interesting strategy of dose reduction.     

Identification of catecholamine neurotransmitters using fluorescence sensor array

A nano-based sensor array has been developed for identification and discrimination of catecholamine neurotransmitters based on optical properties of their oxidation products under alkaline conditions. To produce distinct fluorescence response patterns for individual catecholamine, quenching of thioglycolic acid functionalized cadmium telluride (CdTe) quantum dots, by oxidation products, were employed along with the variation of fluorescence spectra of oxidation products. The spectral changes were analyzed with hierarchical cluster analysis (HCA) and principal component analysis (PCA) to identify catecholamine patterns. The proposed sensor could efficiently discriminate the individual catecholamine (i.e., dopamine, norepinephrine, and l-DOPA) and their mixtures in the concentration range of 0.25–30 μmol L⁻¹. Finally, we found that the sensor had capability to identify the various catecholamines in urine sample.     

In situ emulsification microextraction using a dicationic ionic liquid followed by magnetic assisted physisorption for determination of lead prior to micro-sampling flame atomic absorption spectrometry

For the first time, a simple and efficient in situ emulsification microextraction method using a dicationic ionic liquid followed by magnetic assisted physisorption was presented to determine trace amounts of lead. In this method, 400 μL of 1.0 mol L⁻¹ lithium bis (trifluoromethylsulfonyl) imide aqueous solution, Li[NTf₂], was added into the sample solution containing 100 μL of 1.0 mol L⁻¹ 1,3-(propyl-1,3-diyl) bis (3-methylimidazolium) chloride, [pbmim]Cl₂, to form a water immiscible ionic liquid, [pbmim][NTf₂]₂. This new in situ formed dicationic ionic liquid was applied as the acceptor phase to extract the lead-ammonium pyrrolidinedithiocarbamate (Pb-APDC) complexes from the sample solution. Subsequently, 30 mg of Fe₃O₄ magnetic nanoparticles (MNPs) were added into the sample solution to collect the fine droplets of [pbmim][NTf₂]₂, physisorptively. Finally, MNPs were eluted by acetonitrile, separated by an external magnetic field and the obtained eluent was subjected to micro-sampling flame atomic absorption spectrometry (FAAS) for further analysis. Comparing with other microextraction methods, no special devices and centrifugation step are required. Parameters influencing the extraction efficiency such as extraction time, pH, concentration of chelating agent, amount of MNPs and coexisting interferences were studied. Under the optimized conditions, this method showed high extraction recovery of 93% with low LOD of 0.7 μg L⁻¹. Good linearity was obtained in the range of 2.5–150 μg L⁻¹ with determination coefficient (r²) of 0.9921. Relative standard deviation (RSD%) for seven repeated measurements at the concentration of 10 μg L⁻¹ was 4.1%. Finally, this method was successfully applied for determination of lead in some water and plant samples.     

Highly-controllable imprinted polymer nanoshell at the surface of silica nanoparticles based room-temperature phosphorescence probe for detection of 2,4-dichlorophenol

This paper reports a facile and general method for preparing an imprinted polymer thin shell with Mn-doped ZnS quantum dots (QDs) at the surface of silica nanoparticles by stepwise precipitation polymerization to form the highly-controllable core–shell nanoparticles (MIPs@SiO₂–ZnS:Mn QDs) and sensitively recognize the target 2,4-dichlorophenol (2,4-DCP). Acrylamide (AM) and ethyl glycol dimethacrylate (EGDMA) were used as the functional monomer and the cross-linker, respectively. The MIPs@SiO₂–ZnS:Mn QDs had a controllable shell thickness and a high density of effective recognition sites, and the thickness of uniform core–shell 2,4-DCP-imprinted nanoparticles was controlled by the total amounts of monomers. The MIPs@SiO₂–ZnS:Mn QDs with a shell thickness of 45 nm exhibited the largest quenching efficiency to 2,4-DCP by using the spectrofluorometer. After the experimental conditions were optimized, a linear relationship was obtained covering the linear range of 1.0–84 μmol L⁻¹ with a correlation coefficient of 0.9981 and the detection limit (3σ/k) was 0.15 μmol L⁻¹. The feasibility of the developed method was successfully evaluated through the determination of 2,4-DCP in real samples. This study provides a general strategy to fabricate highly-controllable core–shell imprinted polymer-contained QDs with highly selective recognition ability.     

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.     

Dual fluorescence/contactless conductivity detection for microfluidic chip

A new dual detection system for microchip is reported. Both fluorescence detector (FD) and contactless conductivity detector (CCD) were combined together and integrated on a microfluidic chip. They shared a common detection position and responded simultaneously. A blue light-emitting diode was used as excitation source and a small planar photodiode was used to collect the emitted fluorescence in fluorescence detection, which made the device more compact and portable. The coupling of the fluorescence and contactless conductivity modes at the same position of a single separation channel enhanced the detection characterization of sample and offered simultaneous detection information of both fluorescent and charged specimen. The detection conditions of the system were optimized. K⁺, Na⁺, fluorescein sodium, fluorescein isothiocyanate (FITC) and FITC-labeled amino acids were used to evaluate the performance of the dual detection system. The limits of detection (LOD) of FD for fluorescein Na⁺, FITC, FITC-labeled arginine (Arg), glycine (Gly) and phenylalanine (Phe) were 0.02 μmol L⁻¹, 0.05 μmol L⁻¹, 0.16 μmol L⁻¹, 0.15 μmol L⁻¹, 0.12 μmol L⁻¹ respectively, and the limits of detection (LOD) of CCD achieved 0.58 μmol L⁻¹ and 0.39 μmol L⁻¹ for K⁺ and Na⁺ respectively.     

One-step synthesis and applications of fluorescent Cu nanoclusters stabilized by l-cysteine in aqueous solution

Herein, an innovative and simple strategy for synthesizing high fluorescent Cu nanoclusters was successfully established while l-cysteine played a role as the stabilizer. Meaningfully, the current Cu nanoclusters together with a quantum yield of 14.3% were prepared in aqueous solution, indicating their extensive applications. Subsequently, the possible fluorescence mechanism was elucidated by fluorescence, UV–vis, HR-TEM, FTIR, XPS, and MS. Additionally, the CuNCs were employed for assaying Hg²⁺ on the basis of the interactions between Hg²⁺ and l-cysteine; thus facilitating the quenching of their fluorescence. The proposed analytical strategy permitted detections of Hg²⁺ in a linear range of 1.0 × 10⁻⁷ mol L⁻¹ × 10⁻³ mol L⁻¹, with a detection limit of 2.4 × 10⁻⁸ mol L⁻¹ at a signal-to-noise ratio of 3. Significantly, this CuNCs described here were further applied for coding and fluorescent staining, suggesting may broaden avenues toward diverse applications.     

Engineering oxygen into ultrathin graphitic carbon nitride: synergistic improvement of electron reduction and charge carrier dynamics for efficient photocatalysis

The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C₃N₄) materials in the field of photocatalytic hydrogen (H₂) evolution. Here, ultrathin oxygen (O) engineered g-C₃N₄ (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H₂ evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H₂ evolution (93.78 μmol h^?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h^?1. Furthermore, the H₂ evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h^?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C₃N₄ to achieve efficient photocatalytic H₂ evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation.     

A selective optical chemical sensor for 2,6-dinitrophenol based on fluorescence quenching of a novel functional polymer

A bifurcated optical fiber based chemical sensor for continuous monitoring of 2,6-dinitrophenol (2,6-DNP) has been proposed based on the reversible chemical reaction between a novel functional poly(vinyl chloride) (PVC) as the sensing material and the analytes. The functional PVC (FPVC), containing a fluorescent curcumin moiety, was synthesized by the nucleophilic substitution of a fraction of the chlorine atoms bound to the PVC backbone by curcumin. When plasticized in a membrane of 5 μm thickness, FPVC extracts 2,6-DNP from aqueous solution into the bulk membrane phase and reacts with the analyte to form a complex with low fluorescence efficiency through hydrogen bonding. Formation of the complex gave a significant fluorescence quenching which is suitable for signalling the occurrence of the host-guest interaction. At pH 3.50, the sensor exhibits a dynamic detection range from 2.5 × 10⁻⁶ to 7.0 × 10⁻³ mol L⁻¹ with a limit of detection of 1.0 × 10⁻⁶ mol L⁻¹. As 2,6-DNP can provide an optimal space geometry matches to the formation of hydrogen bonds, the sensor shows excellent selectivity for 2,6-DNP over other nitrophenols. The forward and reverse response time (t₉₅) of the sensor both was within 1 min. The repeatability, reproducibility, and lifetime of the sensor were also satisfied. The sensor was applied to determine 2,6-DNP in water samples successfully.     

Microtiterplate phosphate assay based on luminescence quenching of a terbium complex amenable to decay time detection

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3-100 μmol L⁻¹ range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H₂PO₄⁻) and secondary phosphate (HPO₄²⁻). The LOD is 110 nmol L⁻¹. A Stern-Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 μmol L⁻¹ of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.     

In situ hydrothermal growth of ZnO/g-C3N4 nanoflowers coated solid-phase microextraction fibers coupled with GC-MS for determination of pesticides residues

In this paper, Zinc oxide (ZnO) hybridized with graphite-like C₃N₄ (ZnO/g-C₃N₄) nanoflowers based solid phase microextraction (SPME) coating was prepared on fiber using in situ hydrothermal growth method for gas chromatographic -mass spectrum (GC- MS) separation and analysis target analytes in complex matrixes for the first time. The proposed hybrid ZnO/g-C₃N₄ fiber exhibited wide linearity for the pesticide residues in range of 0.003–5.0 ng mL⁻¹. The limits of detection (LOD) were 0.001–0.0025 ng mL⁻¹. The relative standard deviation (RSD) for three replicate extractions using one fiber was ranged from 2.3% to 7.6%. The fiber to fiber RSD was 5.3–11.3% (n = 3). This method was successfully used for simultaneous determination of nine pesticide residues in cucumber, pear, Green tea and Minjiang water with satisfactory recoveries of 79.1–103.5%. These results indicated that the ZnO/g-C₃N₄ composite provided a promising alternative in sample pretreatment and analysis.     

Sensitive and selective electrochemical detection of artemisinin based on its reaction with p-aminophenylboronic acid

The electrochemical detection of artemisinin generally requires high oxidation potential or the use of complex electrode modification. We find that artemisinin can react with p-aminophenylboronic acid to produce easily electrochemically detectable aminophenol for the first time. By making use of the new reaction, we report an alternative method to detect artemisinin through the determination of p-aminophenol. The calibration curve for the determination of artemisinin is linear in the range of 2 μmol L⁻¹ to 200 μmol L⁻¹ with the detection limit of 0.8 μmol L⁻¹, which is more sensitive than other reported electrochemical methods. The relative standard deviation is 4.83% for the determination of 10 μM artemisinin. Because the oxidation potential of p-aminophenol is around 0 V, the present method is high selective. When 40 μM, 90 μM and 140 μM of artemisinin were spiked to compound naphthoquine phosphate tablet samples, the recoveries are 107.6%, 105.4% and 101.7%, respectively. This detection strategy is attractive for the detection of artemisinin and its derivatives. The finding that artemisinin can react with aromatic boronic acid has the potential to be exploited for the development of other sensors, such as fluorescence artemisinin sensors.