Azo calix[4]arene based neodymium(III)-selective PVC membrane sensor

We found that the PVC membrane, containing azo calix[4]arene is a suitable ionophore, exhibited a Nernstian response for neodymium (Nd³⁺) ions (with slope of 19.8 ± 0.2 mV decade⁻¹ for the triply charged ion) over a wide linear range of 4.0 × 10⁻⁸ to 1.0 × 10⁻¹ mol L⁻¹ with a detection limit 1.0 × 10⁻⁸ mol L⁻¹, a relatively fast response time, in the whole concentration range (<10 s), and a considerable life time at least for four months in the pH range of 4.0-8.0. Furthermore, the electrode revealed high selectivity with respect to all the common alkali, alkaline earth, transition and heavy metal ions, including the members of the lanthanide family other than Nd³⁺. Concerning its applications, it was effectively employed for the determination of neodymium ions in industrial waste water as well as in lake water.     

杨树嫩茎质外体微透析液中K+,Na+,Ca2+的分析

采用微透析法获取3种杨树嫩茎质外体汁液的灌流液,流速1μL/min,探针截留分子量为30 kDa,无须处理直接通过原子吸收光谱(石墨炉法)测定样品中Na+,K+,Ca2+浓度,通过建立实时、无损检测离子浓度变化的实验技术,进行杨树生理生化的研究。此方法加标回收率在95.8%~103.1%之间。研究表明,吴屯杨、小胡杨和小美旱的Na+含量分别为1034~1156μg/L,1493~1611μg/L和1586~1703μg/L;K+含量分别为1012~1237μg/L,941~964μg/L和1095~1201μg/L;Ca2+含量分别为4976~5237μg/L,4786~5042μg/L和5893~6142μg/L,本方法为在植物应激反应中通过离子浓度变化来适应外界环境的研究提供可靠数据。     

Determination of fumaric and maleic acids with stacking analytes by transient moving chemical reaction boundary method in capillary electrophoresis

The paper presents an on-line transient moving chemical reaction boundary (MCRB) method for simply but efficiently stacking analytes in capillary electrophoresis (CE). The CE technique was developed for a rapid determination of fumaric and maleic acid. Based on the theory of MCRB, Effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were investigated to acquire the optimum conditions. The optimized separations were carried out in a 20 mmol/L sulphate neutralized with ethylenediamine to pH 6.0 electrolytes using a capillary coated with poly (diallyldimethylammonium chloride) and direct UV detection at 214 nm. The optimized preconcentrations were carried out in 50 mmol/L borax (pH 9.0). The calibration curves were linear in the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L and 5.0 × 10⁻⁷–1.0 × 10⁻⁴ mol/L for fumaric and maleic acid with correlation coefficients higher than 0.9991. The detection limits were 5.34 × 10⁻⁸ mol/L for fumaric acid and 1.92 × 10⁻⁷ mol/L for maleic acid. This method was applied for determination of fumaric acid in apple juice and of fumaric and maleic acid in dl-malic, the recovery tests established for real samples were within the range 95–105%. This work provided a valid and simple approach to detect fumaric and maleic acid.     

Voltametric and Flow Injection Determination of Oxytetracycline Residues in Food Samples Using Carbon Fiber Microelectrodes

A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square‐wave conditions, a linear calibration plot for OTC was obtained in the 1.0×10^?6–1.0×10^?4 mol L^?1 range, with a detection limit of 2.9×10^?7 mol L^?1 (150 ng mL^?1) OTC. The determination of OTC by a flow‐injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL^?1 and 200 ng g^?1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile ?5.0×10^?4 mol L^?1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method.     

Silver nanoparticles fluorescence enhancement effect for determination of nucleic acids with kaempferol-Al(III)

Nucleic acids can greatly enhance fluorescence intensity of the kaempferol (Km)-Al(III) system in the presence of silver nanoparticles (AgNPs). Based on this, a novel method for the determination of nucleic acids is proposed. Under studied conditions, there are linear relationships between the extent of fluorescence enhancement and the concentration of nucleic acids in the range of 5.0 × 10⁻⁹ to 2.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 7.0 × 10⁻⁹ to 2.0 × 10⁻⁶ g mL⁻¹ for salmon sperm DNA (smDNA) and 2.0 × 10⁻⁸ to 3.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits are 2.5 × 10⁻⁹ g mL⁻¹, 3.2 × 10⁻⁹ g mL⁻¹ and 7.3 × 10⁻⁹ g mL⁻¹, respectively. Samples were satisfactorily determined. And the system of Km-Al(III)-AgNPs was used as a fluorescence staining reagent for sensitive DNA detection by DNA pattern of agarose gel electrophoresis analysis. The results indicate that the fluorescence enhancement should be attributed to the formation of Km-Al(III)-AgNPs-nucleic acids aggregations through electrostatic attraction and adsorption bridging action of Al(III) and the surface-enhanced fluorescence effect of AgNPs.     

Fabrication of new solid state phosphate selective electrodes for environmental monitoring

A highly selective and sensitive phosphate sensor has been fabricated by constructing a crystal disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO₄) and powdered copper (Cu). The membrane sensor exhibits linear potential response in the concentration range of 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹. The proposed sensor also exhibits a fast response time of <60 s. Its detection limit is lower than 1.0 × 10⁻⁶ mol L⁻¹. The electrode has a long lifetime and can be stored in air when not in use. The selectivity of the sensor with respect to other common ions is excellent.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Determination of p-nitroaniline by the tartrate-acetone-Mn2+-KBrO3-H2SO4 double organic substrate oscillating system using non-equilibrium stationary state

This paper described the determination of p-nitroaniline in a double organic substrate oscillating system of tartrate-acetone-Mn²⁺-KBrO₃-H₂SO₄. Under the optimum conditions, temperature was chosen as a control parameter to design the bifurcation point and proposed a convenient method for determination of p-nitroaniline. Results showed that the system consisting of 3.5 mL 0.06 mol L⁻¹ tartrate, 4.0 mL 0.7 mol L⁻¹ H₂SO₄, 1.5 mL 1.5×10⁻⁴ mol L⁻¹ MnSO₄, 4.0 mL 0.4 mol L⁻¹ acetone and 7.0 mL 0.05 mol L⁻¹ KBrO₃ was very sensitive to the surrounding at 33.5°C. A good linear relationship between the potential difference and the negative logarithm concentration of p-nitroaniline was obtained to be in the range of 2.50×10⁻⁷∼3.75×10⁻⁵ mol L⁻¹ with a lower detection limit of 2.50×10⁻⁸ mol L⁻¹.      

Flow injection determination of hydrogen peroxide using diperiodatoargentate- and diperiodatonickelate-luminol chemiluminescence

A novel chemiluminescence (CL) method for the determination of hydrogen peroxide is described. Method is based on the transition metals in highest oxidation state complex, which include diperiodatoargentate (DPA) and diperiodatonickelate (DPN) and show excellent sensitisation on the luminol-H₂O₂ CL reaction with low luminol concentration in alkaline medium. In particular, the sensitiser which was previously reported (such as Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe³⁺, Cr³⁺, KIO₄, K₃Fe(CN)₆ etc.) to be unobserved CL due to poor sensitisation with such low concentration of luminol which makes the method hold high selectivity. Based on this observation, the detection limits were 6.5?×?10^?9?mol?L^?1 and 1.1?×?10^?8?mol?L^?1 hydrogen peroxide for the DPN- and DPA-luminol CL systems, respectively. The relative CL intensity was linear with the hydrogen peroxide concentration in the range of 2.0?×?10^?8–6.0?×?10^?6?mol?L^?1 and 4.0?×?10^?8–4.0?×?10^?6?mol?L^?1 for the DPN- and DPA-luminol CL systems, respectively. The proposed method had good reproducibility with a relative standard deviation of 3.4% (8.0?×?10^?7?mol?L^?1, n?=?7) and 1.0% (2.0?×?10^?6?mol?L^?1, n?=?7) for the DPN- and DPA-luminol CL systems, respectively. A satisfactory result has been gained for the determination of H₂O₂ in rainwater and artificial lake water by use of the proposed method.     

Voltammetric Determination of Proguanil in Malarone and Spiked Urine with a Renewable Silver Amalgam Film Electrode

Electrochemical properties of proguanil were investigated by a voltammetric method (SWV) using a renewable silver amalgam film electrode. The influence of buffer pH as well as potential amplitude, frequency, and step potential was studied. The repeatability, precision and recovery of the developed method were examined. The reduction peak current was used for proguanil voltammetric determination in the range 1×10^?7–6×10^?6 mol L^?1, LOD=2.9×10^?8 mol L^?1, LOQ=9.7×10^?8 mol L^?1. The standard addition method was used to determine proguanil in a commercial formulation (Malarone) and in spiked urine.     

Slurry sampling and high-resolution continuum source flame atomic absorption spectrometry using secondary lines for the determination of Ca and Mg in dairy products

The present paper proposes a simple and fast analytical procedure for the sequential multi-element determination of Ca and Mg in dairy products employing sampling slurry and high resolution-continuum source flame atomic absorption spectrometry (HR-CS FAAS). Considering the high concentration of these species in these matrices, the analytical measurements were carried out at the secondary lines of 239.856 and 202.852 for Ca and Mg, respectively. The experimental conditions established for the preparation of the slurries during the optimization step were: 2.0 mol L^{− 1} hydrochloric acid, sonication time of 20 min and sample mass of 1.0 g for a slurry volume of 25 mL. Experiments demonstrated that the analytical curves can be established using the external calibration technique employing aqueous standards. The method allows the determination of Ca and Mg with limits of quantification of 0.038 and 0.016 mg g^{− 1}, respectively. The precision was evaluated under reproducibility and repeatability conditions and expressed as relative standard deviation. The results varied from 2.7 to 2.9% (all tests with n = 10) and using a yogurt sample containing Ca and Mg concentrations of 1.40 and 0.13 mg g^{− 1}, respectively.The accuracy was confirmed by the analysis of a certified reference material of non-fat milk powder furnished by the National Institute of Standard and Technology. The proposed method was applied for the determination of Ca and Mg in yogurt, cow milk and milk powder samples. The samples were also analyzed after complete acid digestion and Ca and Mg determination by HR-CS FAAS. No statistical difference was observed between the results obtained by both of the procedures performed.     

Rapid Determination of Hydrogen Peroxide in Milk with Non-enzymatic Amperometric Sensor Based on Porous Gold Modified Screen-printed Electrode in Online Dialysis System

A rapid method for determination of hydrogen peroxide based on a non-enzymatic amperometric sensor with an online dialysis unit was developed for analysis of sample with complicated matrices. A porous gold modified gold screen-printed electrode was prepared by a simple method using 9 V-battery electrodeposition. Based on data from amperometry, a linear dynamic range can be obtained in the range of 10 to 1000 μmol L⁻¹, with a limit of detection of 0.37 μmol L⁻¹. The proposed system was successfully applied to determine H₂O₂ in various milk samples with rapid analysis, high electrode stability, and excellent repeatability (1.95 % RSD with 100 replications).     

Voltammetric Determination of Acibenzolar‐S‐Methyl Using a Renewable Silver Amalgam Film Electrode

Acibenzolar‐S‐methyl (ASM) is a novel fungicide applied for crop protection. A renewable silver amalgam film electrode was used for the determination of ASM in pH 3.4 Britton? Robinson buffer using square wave adsorptive stripping voltammetry (SW AdSV). The parameters of the method were optimized. The electroanalytical procedure made possible to determine ASM in the concentration range of 5×10^?8–3×10^?7 mol L^?1 (LOD=4.86×10^?9, LOQ=1.62×10^?8 mol L^?1). The effect of common interfering pesticides and heavy metal ions was checked. The validated method was applied in ASM determination in spiked water samples.     

Determination of Cr(VI) by Catalytic Adsorptive Stripping Voltammetry with Application of Nitrilotriacetic Acid as a Masking Agent

A selective and sensitive method for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) by differential pulse catalytic adsorptive stripping voltammetry is presented. For minimization of Cr(III) interference nitrilotriacetic acid was used as a masking agent. The determinations were performed in a flow system. The calibration plot was linear from 1×10⁻¹⁰ to 1×10⁻⁸ mol L⁻¹ for accumulation time 60 s. The relative standard deviation for 3×10⁻⁹ mol L⁻¹ Cr(VI) was 4.1% (n=5). The detection limit for an accumulation time of 60 s was 4×10⁻¹¹ mol L⁻¹. The influence of common foreign ions is also presented. The performance of the method was verified by analysis of certified reference material for Cr(VI) and comparing the results of analyses of natural water samples with those obtained by another accepted electrochemical method.     

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G₄ dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K_SV = 65(5) × 10⁴ M⁻¹; ACNB, K_SV = 19(2) × 10⁴ M⁻¹; and, MNP, K_SV = 33(1) × 10² M⁻¹. These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L⁻¹ for MNB and ACNB and about 0.1 mg L⁻¹ for MNP. No interferences or small interferences are observed for trinitrotoluene [K_SV = 10(2) × 10² × M⁻¹], 2,4-dinitrotoluene [K_SV = 20(3) × 10 M⁻¹], 2,6-dinitrotoluene [K_SV = 11(4) × 10 M⁻¹] and nitrobenzene [K_SV = 2(1) × 10³ × M⁻¹].     

Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Direct and Simple Electrochemical Determination of Morphine at PEDOT Modified Pt Electrode

A simple and rapid method for morphine detection is described based on PEDOT electrode in the presence of SDS. The electrochemistry of morphine is investigated by CV, LSV and SWV. The effect of common interferences on the current response of morphine namely AA and UA is studied. The electrode is applied to the selective determination of morphine in urine samples in the linear ranges 0.3–8 µmol L^?1 and 10–60 µmol L^?1, with low detection limits of 50 and 68 nmol L^?1, respectively and recovery of 96.4 %. The application of PEDOT is realized in determination of morphine in tablets successfully.     

Determination of Nanomolar Concentrations of Pb(II) Using Carbon Paste Electrode Modified with Zirconium Phosphated Amorphous Silica

A sensitive and selective method for the determination of Pb(II) with a zirconium phosphated silica gel (SiZrPH) modified carbon paste electrode has been developed. The measurements were carried out in three steps including an open circuit accumulation following by electrolysis of accumulated Pb(II) at the modified carbon paste electrode and differential pulse voltammetric determination. The analytical performance was evaluated with respect to the carbon paste composition, pH of solution at the accumulation step, pH and concentration of supporting electrolyte, electrolysis potential, accumulation time and electrolysis time. Two linear calibration graphs were obtained in the concentration ranges 2.5×10^?9 mol L^?1–5.0×10^?8 mol L^?1 and 5.0×10^?8 mol L^?1–5.0×10^?6 mol L^?1 with an accumulation time of 120 s. The detection limit was found to be 3.5×10^?10 mol L^?1. The effects of potential interfering ions were studied, and it was found that the proposed procedure is free from interferences of common interfering ions such as tin, thallium and etc. The developed method was applied to Pb(II) determination in a wastewater sample.     

Chemometric Strategies to Develop a Nanocomposite Electrode for Simultaneous Determination of Ascorbic Acid,Dopamine, and Uric Acid

A simple and sensitive method for simultaneously measuring dopamine (DA), ascorbic acid (AA), and uric acid (UA) using a poly(1‐aminoanthracene) and carbon nanotubes nanocomposite electrode is presented. The experimental parameters for composite film synthesis as well as the variables related to simultaneous determination of DA, AA, and UA were optimized at the same time using fractional factorial and Doehlert designs. The use of carbon nanotubes and poly(1‐aminoanthracene) in association with a cathodic pretreatment led to three well‐defined oxidation peaks at potentials around ?0.039, 0.180 and 0.351 V (vs. Ag/AgCl) for AA, DA, and UA, respectively. Using differential pulse voltammetry, calibration curves for AA, DA, and UA were obtained over the range of 0.16–3.12×10^?3 mol L^?1, 3.54–136×10^?6 mol L^?1, and 0.76–2.92×10^?3 mol L^?1, with detection limits of 3.95×10^?5 mol L^?1, 2.90×10^?7 mol L^?1, and 4.22×10^?5 mol L^?1, respectively. The proposed method was successfully applied to determine DA, AA, and UA in biological samples with good results.     

Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental Materials

A sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)? H₂DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential ?1.0 V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO₃. In order to stabilize the signal of Cr(III) the measurements were performed at 5 °C. The calibration graph for chromium for an accumulation time of 60 s was linear in the range from 5×10^?10 to 5×10^?8 mol L^?1. The relative standard deviation for a chromium concentration of 1×10^?8 mol L^?1 was 3.9% (n=5). The detection limit for accumulation time of 60 s was about 8×10^?11 mol L^?1. The validation of the procedure was performed by the analysis of the certified reference materials.