Chemiluminescent Determination of Vitamin B12 Using Charge Coupled Device (CCD)

A method was developed for the determination of vitamin B₁₂ based on the enhancement of cobalt (II) on the chemiluminescence (CL) reaction between luminol and percarbonate (powerful source of hydrogen peroxide). The release of cobalt (II) from the vitamin B₁₂ was reached by a simple and fast microwave digestion (20 s microwave digestion time and a mix of nitric acid and hydrogen peroxide). A charge coupled device (CCD) photodetector, directly connected to the cell, coupled with a simple continuous flow system was used to obtain the full spectral characteristics of cobalt (II) catalyzed luminol-percarbonate reaction.

The optima experimental conditions were established: 8.0 m mol L^?1 luminol in a 0.075 mol L^?1 carbonate buffer (pH 10.0) and 0.15 mol L^?1 sodium percarbonate, in addition to others experimental parameters as 0.33 mL s^?1 flow rate and 2 s integration time, were the experimental conditions which proportionate the optimum CL emission intensity. The emission data were best fitted with a second-order calibration graph over the cobalt (II) concentration range from 4.00 to 300 µ g L^?1 (r² = 0.9990), with a detection limit of 0.42 µ g L^?1. The proposed method was successfully applied to the determination of vitamin B₁₂ in pharmaceuticals.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L^?1 KCl electrode in an acidic medium and 1 mol L^?1 H₂SO₄ was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L^?1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L^?1 and a low limit of detection (LD = 1.64 µmol L^?1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.     

A carbon ceramic electrode modified with bismuth oxide nanoparticles for determination of syringic acid by stripping voltammetry

A new type of carbon ceramic electrode modified with bismuth oxide nanoparticles (referred to as Bi-CCE) was fabricated via the sol-gel method. The Bi-CCE was applied to the determination of syringic acid by square wave adsorptive stripping voltammetry. The electrochemical properties of the Bi-CCE and the voltammetric response to syringic acid were investigated by cyclic voltammetry. The effects of the pH value of supporting electrolyte, of accumulation potential, accumulation time, SW mode parameters, and of possible interferents were tested. Under optimized conditions, the oxidation peak current (best measured at 0.8 V vs Ag/AgCl after an accumulation time of 20 s) increases linearly in the 0.4 to 24 μmol·L^?1 syringic acid concentration range. Other figures of merit include an LOD of 47 nmol·L^?1, a sensitivity of 3.3 μA·μmol^?1·L·cm^?2, and a relative standard deviation of 4.7% (for n = 5) at 2 μmol·L^?1 of syringic acid. The method was successfully applied to the determination of syringic acid in red, white and rose wine as well as water samples.

Open image in new window

Graphical abstract Schematic presentation of the preparation of carbon ceramic electrode (CCE) containing Bi₂O₃ nanoparticles and its application in square wave adsorptive stripping voltammetric (SW AdSV) determination of syringic acid.

     

Simultaneous Analysis of Sugars and Polyphenols in Tobacco by CZE with Amperometric Detection Based on a Cu2O/MWCNT-COOH Composite Electrode

A composite electrode was fabricated from Cu₂O powder, carboxyl-functionalized multi-wall carbon nanotubes (MWCNT-COOH), and paraffin oil in the proportions 51:17:32 (w/w). This composite electrode was used for amperometric detection (CZE–AD) in simultaneous capillary zone electrophoretic analysis of chlorogenic acid, rutin, sucrose, glucose, mannose, and fructose in tobacco samples. Under the optimum conditions, the six analytes could be separated in 100 mmol L^?1 NaOH buffer within 30 min. Good linearity was achieved in the range 1 × 10^?7–1 × 10^?4 mol L^?1 for the two polyphenols and 5 × 10^?6–1 × 10^?3 mol L^?1 for the four sugars. The detection limits (S/N = 3) for the polyphenols and sugars were as low as 10^?8 mol L^?1 and 10^?6 mol L^?1, respectively.     

Comparative Analysis of the Distribution of Copper in Green and Brown Brazilian Propolis Extracts

We proposed here a novel analytical procedure for copper speciation in green and brown propolis extracts using SEC—HPLC—GFAAS with 0.5% m v^?1 SDS in 2.5 m mol L^?1 Tris–HCl (pH 7.4) as the mobile phase buffer solution. Both basic (0.05 mol L^?1 NaOH) and acid (0.05 mol L^?1 HCl) conditions were evaluated for sample extraction. Depending on the extraction procedure, differences in copper distribution were identified. Copper was mainly associated with high-molecular-weight (HMW) fractions in green propolis extract when extracted with basic solution, whereas with acid extraction solution, only low-molecular-weight (LMW) fractions were obtained in both samples. Furthermore, combined analysis of results obtained using SEC-UV and GF AAS confirmed the association of copper with LMW and HMW species.     

Flow Injection Spectrophotometric Determination of N-Acetylcysteine and Captopril Employing Prussian Blue Generation Reaction

A novel flow injection procedure to determine N-acetylcysteine and captopril in pharmaceutical formulations is proposed. The flow procedure developed was based on oxidation of the analytes by Fe(III) in acidic medium and subsequent reaction of the Fe(II) generated with excess hexacyanoferrate(III) to produce soluble Prussian blue (KFe[Fe(CN)₆]) measured at 700 nm. Detection limits of 1.0 × 10^?5 mol L^?1 and 3.0 × 10^?5 mol L^?1 for N-acetylcysteine and captopril, respectively, were found. The sample throughput was 70 h^?1 for both analytes and the results obtained were in agreement at a 95% confidence level with those obtained using reference methods.     

Automated Determination of Hydrogen Peroxide at the Micro-Molar Level in Rainwater and Snow Using a Stopped-Flow Approach in a Hybrid Sequential Injection/Flow Injection Manifold

A new automated method is reported for the determination of H₂O₂ in real samples. The method is based on the quenching effect of the analyte on the reaction between tris(2-carboxyethyl)phosphine (TCEP) and Ellman's reagent (DTNB). All necessary steps were accomplished under flow conditions using a hybrid sequential injection (SI)/flow injection (FI) setup. The sensitivity was enhanced by applying a stopped-flow step (120 s) in order to promote the reaction between H₂O₂ and TCEP. The proposed analytical protocol was validated for linearity (10–75 µmol L^?1), limits of detection (c _L = 1.0 µmol L^?1), quantitation (c _Q = 3.3 µmol L^?1), precision (s _r = 1.3–1.7%), accuracy, and selectivity. It was then applied successfully to the analysis of H₂O₂ in spiked rainwater and snow samples.     

Comparison of HPLC Methods for the Determination of Amino Sugars in Soil Hydrolysates

A study on the suitability of chromatographic techniques such as high performance anion exchange chromatography (HPAEC) with fluorescence detection (FL) and pulsed amperometric detection (PAD) and reversed phase (RP) chromatography for the determination of galactosamine, glucosamine, mannosamine, and muramic acid in soil hydrolysates was carried out. The reversed phase fluorescence method was rapid, provided good validation parameters, and employed relatively inexpensive instrumentation. The HPAEC methods had slightly higher limits of quantification, 0.6–5.0 µmol L^?1 (HPAEC-FL) and 1.0–10.0 µmol L^?1 (HPAEC-PAD), compared to the reversed phase fluorescence method (0.5–5.0 µmol L^?1). Various sample pretreatment methods and chromatographic methods were investigated and the advantages and disadvantages of the HPLC methods are discussed.     

Electrochemical detection of ursolic acid from spruce (Picea abies) essential oils using modified amperometric microsensors

Ursolic acid (UA) is a natural pentacyclic triterpenoid carboxylic acid found in some medicinal plant species. In this paper, amperometric microsensors based on a powder which contained graphite (G) and carbon nanoparticles (CN) (G-CN) unmodified and modified with chitosan (CHIT) and tetraphenyl-porphine cobalt(II) (Co(II)TPP) are proposed for the analysis of UA plant source essential oils obtained from spruce (Picea Abies). Differential pulse voltammetry (DPV) was used to optimize the method and for the determination of ursolic acid from different types of botanical samples. The optimum working pH was 5.00 for the G-CN and (Co(II)TPP)/G-CN microsensors and pH 3.00 for CHIT/G-CN in the presence of a 0.1?mol L^?1 KCl supporting electrolyte. The linear concentration ranges for ursolic acid (UA) were between 0.1 and 100 µmol L^?1 for the unmodified microsensor (G-CN), 0.01, 1 µmol L^?1 for the microsensor modified with chitosan (CHIT/G-CN), and 0.01 and 10 µmol L^?1 for the microsensor modified with (Co(II)TPP)/G-CN). It is the first time these amperometric microsensors have been used for the reliable analysis of ursolic acid (UA) in three original botanical samples obtained from different parts of spruce (Picea abies): resin essential oil, cons essential oil, cons and sprouts essential oil, with recovery rate values up to 99.29%.     

Voltammetric determination of herbicide molinate in river water and rice samples using solid silver amalgam electrode fabricated with nanoparticles

The evaluation of the voltammetric behaviour and the determination of herbicide molinate were performed for the first time over the surface of solid amalgam electrode fabricated with silver nanoparticles using cyclic voltammetry and square-wave voltammetry techniques. The experimental and instrumental parameters were evaluated to reach the maximum analytical response for molinate. It was achieved when a medium composed of 0.04 mol L^?1 Britton–Robinson buffer at the pH value of 4.0 was used. Under these conditions, molinate showed one pronounced reduction peak at E_p = ?0.37 V (vs. Ag/AgCl 3 mol L^?1) that was characterised as an irreversible system. An analytical curve was constructed at the concentration range from 9.36 to 243.49 µg L^?1 and a limit of detection of 2.34 µg L^?1 was obtained. The amalgam electrode presented good stability during the measurements with relative standard deviation (RSD) values of 2.9% for the repeatability and 5.4% for the reproducibility. The voltammetric method developed here could be conveniently applied for the determination of molinate in river water and rice spiked samples at levels below those established on the legislations of European Union and Brazil with good accuracy (RSD of less than 5% for all samples). Comparison with HPLC technique was carried out and the results indicated satisfactory concordance. According to the results depicted here, the silver nanoparticles solid amalgam electrode showed itself highly sensitive and an interesting alternative for the routine analysis of molinate in water and food samples. Furthermore, it introduces an environmentally acceptable alternative to the mercury electrodes, most commonly used for determination of reducible pesticides.     

Solid Phase Extraction and High Performance Liquid Chromatography for Determination of Glyoxylic Acid in a Selective Oxidation Reaction

Currently, the development of a new method for the analysis of glyoxylic acid in selective oxidation of glyoxal system has become a key subject in its new industrial process development. Since solid phase extraction (SPE) could isolate and concentrate desired analytes from complex matrices, in this paper we tested the possibility of coupling SPE technique with HPLC for simultaneous determination of glyoxylic acid, formic acid, and oxalic acid in this complex chemical reaction system. Results demonstrated that the developed method could be successfully applied to this system, after samples were passed through SAX cartridges and yielded recoveries from 96.7% to 103%. The limits of detection were 2.6 × 10^?6, 3.6 × 10^?6, and 3.5 × 10^?7 mol L^?1, respectively; and their linear ranges between 1 × 10^?6 and 1 × 10^?2 mol L^?1.     

Simultaneous screening of homotaurine and taurine in marine macro-algae using liquid chromatography–fluorescence detection

Simultaneous analysis of homotaurine and its homologous, taurine, is a highly challenging issue, especially in matrices they exist simultaneously. A simple precolumn derivatization procedure combined with high-performance liquid chromatography–fluorescence detection was developed for simultaneous determination of homotaurine and taurine in marine macro-algae. The analytes were derivated with o-phthalaldehyde at an ambient temperature and alkaline medium. Calibration curves were linear in the ranges of 50–2500 µg L^?1 for homotaurine and 100–2500 µg L^?1 for taurine with the coefficients of determination higher than 0.998. Limits of detection of homotaurine and taurine were 15 and 30 µg L^?1, respectively. Intraday (n = 6) and inter-day (n = 4) precisions of the method were satisfactory with relative standard deviations less than 6.0%. Good recoveries (>94%) were acquired by the method for extraction of homotaurine and taurine from algae matrices. Liquid chromatography–mass spectrometry was also used to confirm detection of the analytes in algae samples. The data suggest that the method was successfully applied to simultaneous determination of homotaurine and taurine in algae samples.     

Speciation and determination of chromium ions by dispersive micro solid phase extraction using magnetic graphene oxide followed by flame atomic absorption spectrometry

A selective, simple and fast dispersive micro solid phase extraction method using magnetic graphene oxide (GO) as an efficient sorbent has been developed for the extraction, separation and speciation analysis of chromium ions. The method is based on different adsorption behaviour of Cr(VI) and Cr(III) species onto magnetic GO in aqueous solutions which allowed the selective separation and extraction of Cr(VI) in the pH range of 2.0–3.0. The retained Cr(VI) ions by the sorbent were eluted using 0.5 mL of 0.5 mol L^?1 nitric acid solution in methanol and determined by ?ame atomic absorption spectrometry. Total chromium content was determined after the oxidation of Cr(III) to Cr(VI) by potassium permanganate. All effective parameters on the performance of the extraction process were thoroughly investigated and optimised. Under the optimised conditions, the method exhibited a linear dynamic range of 0.5–50.0 µg L^?1 with a detection limit of 0.1 µg L^?1 and pre-concentration factor of 200. The relative standard deviations of 3.8% and 4.6% (n = 8) were obtained at 25.0 µg L^?1 level of Cr(VI) for intra- and inter-day analysis, respectively. The method was successfully applied to the speciation and determination of Cr(VI) and Cr(III) in environmental water samples.     

Molecularly imprinted stir bar sorptive extraction coupled with high-performance liquid chromatography for trace analysis of naphthalene sulfonates in seawater

In this paper, a novel molecularly imprinted polymer coated stir bar has been used to selectively extract naphthalene sulfonates (NS_s) directly from seawater sample. 1-Naphthalene sulfonic acid (1-NS) was used as template molecule. The effects of different parameters were optimized on the extraction efficiency and the optimum conditions were established as: the absorption and desorption times were fixed, respectively, at 10 and 15 min, stirring speed was 700 rpm, pH was adjusted to 4.1, amount of NaCl was 1 mol L^?1 and extraction process was performed at a temperature of 50 °C. The linear ranges were 2–250 µg L^?1 for 3,6-NDS-1-OH (1-naphthol-3,6-disulfonic acid), 4–250 µg L^?1 for 2-NS (2-naphthalene sulfonate) and 3–250 µg L^?1 for 1-NS. The detection limits were within the range of 0.32–0.95 µg L^?1. Under optimum conditions, the detection limits of the NSs were 0.84, 0.95 and 0.32 µg L^?1 with the enrichment factor of 117-, 41- and 77-fold for 2-NS, 1-NS, and 6-NDS-1-OH, respectively. The repeatability of the method was satisfactory (0.53 ≤ RSD ≤6.0 %, n = 10). The method has been successfully applied for the analysis of trace amounts of three naphthalene sulfonates in seawater of Chabahar Bay.     

Highly sensitive electrocatalytic determination of pyrazinamide using a modified poly(glycine) glassy carbon electrode by square-wave voltammetry

A new voltammetric sensor based on electropolymerization of glycine at glassy carbon electrode (GCE) was developed and applied to determine of pyrazinamide (PZA) by square-wave voltammetry (SWV). The initial cyclic voltammetric studies showed an electrocatalytic activity of poly(Gly)/GCE on redox system of pyrazinamide in 0.1 mol L^?1 phosphate buffer solution pH 7.5, with E _Pc and E _Pa in ?0.85 and ?0.8 V (versus E _Ag/AgCl), respectively. Studies at different scan rates suggest that the redox system of pyrazinamide at poly(Gly)/GCE is a process controlled by diffusion in the interval from 10 to 100 mV s^?1. Square-wave voltammetry-optimized conditions showed a linear response of PZA concentrations in the range from 0.47 to 6.15 μmol L^?1 (R?=?0.998) with a limit of detection (LOD) of 0.035 μmol L^?1 and a limit of quantification (LOQ) of 0.12 μmol L^?1. The developed SWV-poly(Gly)/GCE method provided a good intra-day (RSD?=?3.75 %) and inter-day repeatability (RSD?=?4.96 %) at 4.06 μmol L^?1 PZA (n?=?10). No interference of matrix of real samples was observed in the voltammetric response of PZA, and the method was considered to be highly selective for the compound. In the accuracy test, the recovery was found in the range of 98.2 and 104.0 % for human urine samples and pharmaceutical formulation (tablets). The PZA quantification results in pharmaceutical tablets obtained by the proposed SWV-poly(Gly)/GCE method were comparable to those found by official analytical protocols.     

Use of Capillary Zone Electrophoresis and Micellar Electrokinetic Chromatography for Separations of Anthraquinone Derivatives

The behavior of seven hydroxy anthraquinone derivatives was studied by capillary zone electrophoresis and micellar electrokinetic chromatography. The effects of buffer pH (6.5–10.8) and sodium dodecyl sulfate concentration (10–20 mmol L^?1) on the effective mobilities of the analytes and their separation were tested. A comparison of the two optimized separation systems showed that micellar electrokinetic chromatography was superior as it permits separation of all the seven analytes within 15 min, using 15 mmol L^?1 sodium dodecyl sulfate in 10 mmol L^?1 tetraborate buffer, pH 8.5, at a voltage of 20 kV. The calibration curves were linear in the concentration range from 5.0 · 10^?7 to 5.0 · 10^?4 mol L^?1 for most of the analytes, at a detection wavelength of 254 nm. LOD and LOQ values of the analytes were in the ranges of 2.10 · 10^?7–1.28 · 10^?6 mol L^?1and 6.99 · 10^?7–4.25 · 10^?6 mol L^?1, respectively. The proposed separation conditions were applied to determination of 1,2-dihydroxy anthraquinone (alizarin) and 1,2,4-trihydroxy anthraquinone (purpurin) in Rubia tinctorum aglycone and of the recently described 1-acetyl-2,4,5,7-tetrahydroxy-9,10-anthraquinone and 1-acetyl-2,4,5,7,8-pentahydroxy-9,10-anthraquinone in the mycelium of fungi Geosmithia lavendula.     

Highly Sensitive Flow-Injection Chemiluminescence Detection of Carbonyl Compounds in Wine Samples

A modified Trautz–Schorigin reaction, by using tannic acid-H₂O₂ system for the oxidation and determination of two kinds of carbonyl compounds was developed in this paper. It was found that formaldehyde and acetaldehyde could effectively enhance the chemiluminescence signals of tannic acid–H₂O₂ system in alkaline medium. Under optimized conditions, the proposed method has a linear range of 7 × 10^?9–1 × 10^?4 mol L^?1 for formaldehyde and 1 × 10^?8–1 × 10^?4 mol L^?1 for acetaldehyde with detection limits of 9 × 10^?11 and 3 × 10^?10 mol L^?1, respectively. The relative standard deviations for 15 repeated measurements of 1 × 10^?6 mol L^?1 HCHO and CH₃CHO are 1.13% and 1.65%, respectively. Analysis time per sample is 35 seconds. A comparison of results found by the proposed method with those obtained by a standard reference method provided good agreement. The proposed method is simple, rapid, convenient, and sensitive.     

Determination of Triazine Herbicides and Metabolites by Solid Phase Extraction with HPLC Analysis

An efficient solid phase extractive preconcentration/separation method was developed for the trace determination of herbicides in aqueous samples using Amberlite XAD-4 resin as the adsorbent. The retained herbicides were eluted with methanol at a flow rate of 1.0 mL min^?1 and determined by HPLC-DAD (wavelength of 220 nm) using water (pH:4.7, phosphoric acid) and methanol (ratio 35:65) as the mobile phase with a flow rate of 1.0 mL min^?1. Quantitative recoveries of simazine, atrazine and its metabolities were achieved at optimized analysis conditions that included 0.75 g of resin; a pH of 3.0; an eluent volume of 3.0 mL; an eluent flow rate of 1.0 mL min^?1; and a sample flow rate of 4.0 mL min^?1. The limits of detection, preconcentration factor, and linear ranges for the herbicides were 0.084–0.121 µgL^?1, 1000, and 0.5–20 mg L^?1, respectively. The performance of the method was evaluated by analysis of spiked water samples. The recoveries of simazine, atrazine and their metabolities were found to be quantitative (99.6–104.8%) with RSDs of 2.2–4.8% and 2.8–4.7% for intra-day and inter-day precision, respectively. The proposed method was successfully applied for trace determination of studied analytes in waste water, apple juice, and red wine samples.     

Simultaneous Electrochemical Determination of Hydroquinone and Catechol at MWNTs and Cobalt(II) Tetrakisphenylporphyrin Modified Electrode

A multi-wall carbon nanotubes (MWNTs) and cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) modified glassy carbon electrode (MWNTs/Co(II)TPP/GCE) has been prepared. It can be used for individual or simultaneous determination of hydroquinone (HQ) and catechol (CC). The anodic peaks of HQ and CC can be separated well. Owing to the unique properties of MWNTs and special synergistic effect of MWNTs and Co(II)TPP, the modified electrode exhibited a remarkable and stable current response for CC and HQ. The linear ranges for CC and HQ were 1.0–450.0 µmol L^?1 and 0.8–400.0 µmol L^?1 with detection limits of 0.8 µmol L^?1 and 0.5 µmol L^?1, respectively. Furthermore, Co(II)TPP, MWNTs, and Co(II)TPP/MWNTs composite were also used to construct modified electrodes and the electrochemical performances were studied.