Sensitive Analysis of Malondialdehyde in Human Urine by Derivatization with Pentafluorophenylhydrazine then Headspace GC–MS

A sensitive method based on derivatization with pentafluorophenylhydrazine then headspace gas chromatography–mass spectrometry has been used for analysis of malondialdehyde in human urine. Preparation of urine sample by one-step derivatization/evaporation was performed by reaction of malondialdehyde with pentafluorophenylhydrazine in a headspace vial for 10 min; the derivatives were then injected in GC–MS analysis. The reaction was performed at pH 3, and total analysis time was 35 min. The method detection limit was 0.04 μg L^?1. For MDA concentrations of 2.0 and 10.0 μg L^?1 the relative standard deviation was less then 5%. The concentration of MDA in urine was measured to be 0.199 ± 0.252 μmol g^?1 creatinine (0.022 ± 0.028 μmol mmol^?1 creatinine).     

Preconcentration and spectrophotometric determination of trace amount of formaldehyde using hollow fiber liquid-phase microextraction based on derivatization by Hantzsch reaction

Formaldehyde is known as a highly toxic compound to humans and identified as a carcinogenic substance. In this study, Hantzsch reaction was utilized for the derivatization of trace amounts of formaldehyde in aqueous samples with acetylacetone in the presence of ammonia to form an extractable colored product named 3,5-diacetyl 1,4-dihydrolutidine (DDL) and its further extraction using two-phase hollow fiber liquid-phase microextraction. The main experimental variables affecting the extraction performance were investigated and optimized. Under the optimum conditions (sample volume 12 mL; reaction temperature 70 °C; ammonium acetate buffer solution 4 mL 0.1 mol L^?1; acetylacetone 5 mL 0.15 mol L^?1; solvent octanol, salt concentration 20% (w/v) NaCl; pH of donor phase 7.0; stirring speed 400 rpm and extraction time 30 min), the linear dynamic range, limit of detection (LOD as 3S _b/m) and relative standard deviation (RSD %) of the proposed method were obtained as 5–250 μg L^?1 (r ² = 0.9979), 3.6 μg L^?1 and 2.5%, respectively. Finally, the applicability of the proposed method was examined, and very good results were obtained. The results confirmed the applicability of the proposed method as a versatile, low-cost and sensitive preconcentration method for determination of low concentrations of formaldehyde in aqueous solutions.     

Spectrophotometric Determination of Bromate in Water Using Multisyringe Flow Injection Analysis

A multisyringe flow injection system for the spectrophotometric determination of bromate in water is proposed, based on the oxidation of phenothiazine compounds by bromate in acidic medium. Several phenothiazines were tested, including chlorpromazine, trifluoperazine, and thioridazine. Higher sensitivity and lower LOD were attained for chlorpromazine. Interference from nitrite, hypochlorite, and chlorite was eliminated in-line, without any changes in the manifold. The automatic methodology using chlorpromazine allowed the determination of bromate between 25 and 750 µg L^?1, with LOD of 6 µg L^?1, good precision (RSD < 1.6%, n = 10), and determination frequency of 35 h^?1.     

Determination of allura red using composites of water-dispersible reduced graphene oxide-loaded Au nanoparticles based on ionic liquid

A facile route for producing reduced graphene oxide (RGO)-loaded Au nanoparticles based on ionic liquids (IL) has been proposed, in which the as-prepared RGO can be dispersed stably in water. With the assistance of IL, Au nanoparticles were uniformly and densely absorbed on the surfaces of the IL functionalised reduced graphene oxide (IRGO), forming a new composite of IRGO/Au with high dispersibility. This IRGO/Au composite enhanced its electrochemical signal obviously in the measurement of allura red in foods and exhibited a wider linear response ranging from 0.297 (0.0006 μmol L^?1) to 99.3 μg L^?1 (0.2 μmol L^?1) with lower detection limit of 0.213 μg L^?1 (0.00043 μmol L^?1) at a signal-to-noise ratio of 3. To further study the practical applicability of the proposed sensor, the modified electrode was successfully applied to detect allura red in five kinds of common foods and the assay results were in a good agreement with the reference values detected by HPLC.     

Flow-Injection Analysis Based on Extraction and Spectrophotometric Determination of Penicillins with Thiazine Dyes

Abstract

A new method for flow-injection analysis (FIA) for the determination of penicillins based on the extraction and spectrophotometric determination of ion associates with selected thiazine dyes (methylene blue, azure A, and azure B) is proposed. The reaction conditions (c_dye = 2 × 10^?4 mol l^?1, c_KCl = 1 mol l^?1, pH ? 6, λ = 635 nm) were found. The factorial design has been carried out to determine the optimum flow conditions. A wide linear dynamic range of calibration curves (5.1–700 µg ml^?1 for penicillin V with all dyes, R = 0.9985) and good repeatability (e.g., relative standard deviation [RSD] = 4.6–0.6% in this concentration range for the reaction with azure B) were found. The detection limit for penicillin V is 1.5 µg ml^?1, and the determination limit is 5.1 µg ml^?1. The maximum analysis rate is 35 samples per h. The practical samples of pharmaceutics were tested. There are no interferences from the additives in pharmaceutics.     

Quantitative Determination of Hyponitrite and Hyponitrate by Ion Chromatography

A simple, sensitive and reliable method for the rapid determination of hyponitrite and hyponitrate (Angeli’s salt) in alkaline media, is presented where both species are relatively stable. The method is based on the separation of the two anions by an anion exchange column and thereafter UV spectrophotometric detection at 248 nm. The calibration curves were linear over the concentration range of 0.4–100 mg L^?1, whereas the detection limit was found to be 50 μg L^?1 for hyponitrite and 100 μg L^?1 for hyponitrate. Under these conditions, the determination of nitrate and nitrite is also possible.     

Determination of trace amounts of plutonium in low-active liquid wastes from spent nuclear-fuel reprocessing plants by flow injection-based solid-phase extraction/electrochemical detection system

A flow injection-based electrochemical detection system coupled to a solid-phase extraction column was developed for the determination of trace amounts of plutonium in low-active liquid wastes from spent nuclear-fuel reprocessing plants. The oxidation state of plutonium in a sample solution was adjusted to Pu(VI) by the addition of silver(II) oxide. A sample solution was made up in 3 mol L^?1 HNO₃ and loaded onto a column packed with UTEVA^® with 3 mol L^?1 HNO₃ as the carrier. Plutonium(VI) was adsorbed onto the resin, and interfering elements were removed by rinsing the column with 3 mol L^?1 HNO₃. Subsequently, the adsorbed Pu(VI) was eluted with 0.01 mol L^?1 HNO₃, and then introduced directly into the flow-through electrolysis cell with boron-doped diamond electrode. The eluted Pu(VI) was detected by an electrochemical amperometric method at a working potential of 0.1 V (vs. Ag/AgCl). The current produced on reduction of Pu(VI) was continuously monitored and recorded. The plutonium concentration was calculated from the relationship between the peak area and concentration of plutonium. The relative standard deviation of ten analyses was 1.1% for a plutonium solution of 25 μg L^?1 containing 50 ng of Pu. The detection limit calculated from three-times the standard deviation was 0.82 μg L^?1 (1.6 ng of Pu).     

Multivariate optimisation of a rapid and simple automated method for bismuth determination in well water samples exploiting long path length spectrophotometry

An automated spectrophotometric system is proposed for the determination of bismuth in well water samples, using multi-syringe flow injection analysis (MSFIA) and exploiting a liquid waveguide capillary cell (LWCC). This method is based on the colorimetric reaction of bismuth and methylthymol blue (MTB) in the presence of polyvinylpyrrolidone (PVP) in acid medium (0.1 mol L^?1 HNO₃). The Bi(III)–MTB complex was measured at 600 nm. The method was optimised by multivariate techniques. Some figures of merit of the proposed system are worth being highlighted, such as its wide linear working range (between 4.9 and 600 μg L^?1), its low detection limit (1.5 μg L^?1 of bismuth) and its high intra-day precision and inter-day precision (0.7% (n = 12) and 1.4% (n = 5), respectively, both expressed as RSD). Moreover, a high injection frequency of 30 h^?1 is achieved, as the proposed analyser is a powerful tool for fast Bi(III) determination. The method developed was successfully validated by analysing reference samples (pharmaceutical samples) by comparing the results with those obtained by ICP-OES and it was satisfactorily applied to well water samples. Besides, the present system is miniaturised allowing in situ measurements in control processes and field analysis.     

Determination of Zn(II) in rock and vegetable samples after acidic digestion followed by ultrasound-assisted solid-phase extraction with reduced graphene oxide as novel sorbent,in combination with flame atomic absorption spectrometry

Graphene, a novel class of carbon nanostructures, has great promise for use as sorbent materials because of its ultrahigh specific surface area. A new method using reduced graphene oxide (RGO) as sorbent was developed for the preconcentration of trace amounts of zinc (Zn) to its determination by flame atomic absorption spectrometry. Zinc could be adsorbed quantitatively on RGO in the pH range of 1–9, and then eluted completely with 0.5 mL of 0.1 mol L^?1 HCl. Some effective parameters on the extraction were selected and optimized. Under optimum conditions, the calibration graph was linear in the concentration range of 0.2–15 μg L^?1 with a detection limit of 0.14 μg L^?1 with an enrichment factor of 100.12. The relative standard deviation for ten replicate measurements of 10 μg L^?1 of Zn was 0.58 %, respectively. The proposed method was successfully applied in the analysis of rock and vegetable samples. Good spiked recoveries over the range of 99.9–100 % were obtained. This work not only proposes a useful method for sample preconcentration, but also reveals the great potential of graphene as an excellent sorbent material in analytical processes.     

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.     

Determination of Copper in Human Urine by RP-LC After Pre-column Derivatization with Neocuproine and Use of Monolithic Column

A selective sensitive RP-LC–UV/VIS method with pre-column derivatization was developed for the determination of copper in human urine at a trace level. This method is based on the selective reaction of 2,9-dimethyl-1,10-phenanthroline (neocuproine) with copper(I) to produce a yellow-orange hydrophobic complex in a neutral or slightly acidic buffer solution (adjusted to pH 5.9). Copper(II) was reduced to copper(I) ions by ascorbic acid as a weak reducer, which was added both to urine sample and mobile phase, respectively. A hydrophobic copper(I)–neocuproine chelate was determined by RP-LC–UV/VIS using a monolithic column Chromolith Performance RP-8e (100 × 4 mm I.D.) at 30.0 ± 0.1 °C with a methanol: aqueous buffer (pH 5.9, ammonium acetate and ascorbic acid 2.8 mmol L^?1) mobile phase at flow rate of 2.00 mL min^?1. Sample injection volume was 20 μL and detection was done at 453 nm. The method was validated over a concentration range of 0.09–11.50 μmol L^?1. The LOD of copper in human urine was found to be 0.07 μmol L^?1 concentration level, suitable for clinical analysis. The precision of the results, reported as the RSD, was below 4.6 % for copper concentration within range 0.5–5.0 μmol L^?1 in the spiked human urine samples.     

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.     

Fabrication of a nanostructured TiO2/carbon nanotube composite electrode for voltammetric and impedimetric determination of NTO explosive in the water and soil samples

An electrochemical oxidation route was developed for sensitive and selective assay of nitrotriazolone (NTO) explosive in some environmental samples on a multi-walled carbon nanotube (MWCNTs)/TiO₂ nanocomposite paste electrode, for prevention of the analytical interference of conventional reducible energetic compounds. Detailed evaluations were made for the electrochemical behaviour of NTO on the modified electrode by adsorptive stripping voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques in the pH range of 2.0–10.0. Parameters such as diffusion coefficient constant of NTO were calculated, and various experimental conditions were also optimised. Under optimal conditions the calibration curve had two linear dynamic ranges of 130.0–3251.5 μg L^?1 and 6.5–26.0 mg L^?1 with a detection limit of 26.0 μg L^?1 (0.2 μmol L^?1) and precision of <3%. This electrochemical sensor was further applied to determine NTO in real soil and water samples with satisfactory results.     

Optimized solid phase extraction based on diethyldithiocarbamate-coated Fe3O4 magnetic nanoparticles followed by ICP-OES for determination of Cd(II) and Ni(II) in rice and water samples

In the present study, application of Fe₃O₄ magnetic nanoparticles (MNPs) coated with diethyldithiocarbamate as a solid-phase sorbent for extraction of trace amounts of cadmium (Cd²⁺) and nickel (Ni²⁺) ions by the aid of ultrasound was investigated. The analytes were determined by inductively coupled plasma-optical emission spectroscopy. Fe₃O₄ MNPs were prepared by solvothermal method and characterized with dynamic light scattering, scanning electron microscope and X-ray diffraction. Response surface methodology was used for optimization of the extraction process and modeling the data. The optimal conditions obtained were as follows: chelating agent, 1.2 g L^?1; pH, 6.13; sonication time, 13 min and Fe₃O₄ MNPs, 10.3 mg. The calibration curves were linear over the concentration range of 1–1,000 μg L^?1 for Cd²⁺ and 2.5–1,000 for Ni²⁺ with the determination coefficients (R ²) of 0.9997 and 0.9995, respectively. The limits of detection were 0.27 μg L^?1 for Cd²⁺ and 0.76 μg L^?1 for Ni²⁺. The relative standard deviations (n = 7, C = 200 μg L^?1) for determination of Cd²⁺ and Ni²⁺ were 2.0 and 2.7 %, respectively. The relative recoveries of the analytes from tap, river and lagoon waters and rice samples at the spiking level of 10 μg L^?1 were obtained in the range of 95–105 %.     

Simultaneous Determination of Acetaminophen, Caffeine, and Chlorphenamine Maleate in Paracetamol and Chlorphenamine Maleate Granules

A simple and rapid HPLC method using phenacetin (PHN) as internal standard has been developed for simultaneous determination of acetaminophen, caffeine, and chlorphenamine maleate in the product compound paracetamol and chlorphenamine maleate granules. Separation and quantitation were achieved on a 250 mm × 4.6 mm, 5 μm particle, C₁₈ column. The mobile phase was methanol 0.05 mol L^?1 aqueous KH₂PO₄ solution, 45:55 (v/v), containing 0.1% triethylamine and adjusted to pH 3.6 by addition of phosphoric acid; the flow rate was 1.0 mL min^?1. Detection of all compounds was by UV absorbance at 260 nm and elution of the analytes was achieved in less than 12 min. The linearity, accuracy, and precision of the method were acceptable to good over the concentration ranges 6.4–153.6 μg mL^?1 for acetaminophen, 5.0–120.0 μg mL^?1 for caffeine, and 9.6–230.4 μg mL^?1 for chlorphenamine maleate.     

Biomethane Production in an AnSBBR Treating Wastewater from Biohydrogen Process

An anaerobic sequencing batch reactor containing immobilized biomass (AnSBBR) was used to produce biomethane by treating the effluent from another AnSBBR used to produce biohydrogen from glucose- (AR-EPHG) and sucrose-based (AR-EPHS) wastewater. In addition, biomethane was also produced from sucrose-based synthetic wastewater (AR-S) in a single AnSBBR to compare the performance of biomethane production in two steps (acidogenic and methanogenic) in relation to a one-step operation. The system was operated at 30 °C and at a fixed stirring rate of 300 rpm. For AR-EPHS treatment, concentrations were 1,000, 2,000, 3,000, and 4,000 mg chemical oxygen demand?(COD)?L^?1 and cycle lengths were 6 and 8 h. The applied volumetric organic loads were 2.15, 4.74, 5.44, and 8.22 g COD L^?1 day^?1. For AR-EPHG treatment, concentration of 4,000 mg COD L^?1 and 4-h cycle length (7.21 g COD L^?1 day^?1) were used. For AR-S treatment, concentration was 4,000 mg COD L^?1 day^?1 and cycle lengths were 8 (7.04 g COD L^?1 day^?1) and 12 h (4.76 g COD L^?1 day^?1). The condition of 8.22 g COD L^?1 day^?1 (AR-EPHS) showed the best performance with respect to the following parameters: applied volumetric organic load of 7.56 g COD L^?1 day^?1, yield between produced methane and removed organic material of 0.016 mol CH₄?g COD^?1, CH₄ content in the produced biogas of 85 %, and molar methane productivity of 127.9 mol CH₄?m^?3 day^?1. In addition, a kinetic study of the process confirmed the trend that, depending on the biodegradability characteristics of the wastewaters used, the two-step treatment (acidogenic for biohydrogen production and methanogenic for biomethane production) has potential advantages over the single-step process.     

Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes

Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at ?1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L^?1 (1 μg L^?1 for Mn) to 20 μg L^?1 (30 μg L^?1 for Zn, Pb and 80 μg L^?1 for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L^?1 (5 μg L^?1 for Cd) to 100 μg L^?1 (200 μg L^?1 for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol^?1, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb  nA L μmol^?1. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments.      

Simultaneous Determination of Dopamine and Uric Acid by Electrocatalytic Oxidation on a Carbon Paste Electrode Using Pyrogallol Red as a Mediator

A sensitive and selective electrochemical method for the simultaneous determination of dopamine (DA) and uric acid (UA) was developed using a pyrogallol red modified carbon paste electrode. Under the optimized conditions, the peak current was linearly dependent on 1.0–700.0 μmol L^?1 DA and 50.0–1000.0 μmol L^?1 UA. The detection limits for DA and UA were 0.78 μmol L^?1 and 35 μmol L^?1, respectively. Finally, this method was also examined for the determination of DA and uric acid in real samples such as drugs and urine.     

Indirect quantification of trace levels cyanide in environmental waters through flame atomic absorption spectrometry coupled with cloud point extraction

Cloud point extraction (CPE) has been used for the preconcentration and indirect quantification of cyanide after the formation of a ion-associate complex with 3-amino-7-diethylamino-8,9-benzo-2-phenoxazine chloride (Nile blue, NB⁺) in the presence of copper (II) ions, and later analysis by flame atomic absorption spectrometry (FAAS) using polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) as extracting surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. At pH 5.5, preconcentration of only 50 mL of sample in the presence of 0.04 % (w/v) PONPE 7.5 and 5.64 × 10^?5 mol L^?1 Nile blue permitted the detection of 3.75 μg L^?1 cyanide. The enhancement factor was 64.7 for cyanide. The proposed method was successfully applied to the determination of free cyanide in environmental water samples. The method was compared with the pyridine–barbituric acid method and the paired t test was used to determine whether the results obtained by the two methods differ significantly.     

Determination of Six Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC-NPD

A single-drop microextraction (SDME) procedure with a modified microsyringe was developed for the analysis of six organophosphorus pesticides (OPPs) in water. Microsyringe was modified by attaching a 2-mm cone onto the needle tip end. The conditions affecting SDME performance including microextraction solvent, stirring speed, extraction time, ionic strength and sample pH were optimized. Under the optimized conditions, the linear ranges of the SDME with ethion as internal standard were 0.05–50 μg L^?1 (except for dimethoate 5–5,000 μg L^?1) and limits of detection (LOD) were 0.012–0.020 μg L^?1 (except for dimethoate 0.45 μg L^?1). Recoveries of six pesticides were in the range of 70.6–107.5 % with relative standard deviation lower than 6.0 %. The modified method is simple, rapid and sensitive, and acceptable in the analysis of OPPs pesticides in water samples.