Kinetic Spectrophotometric Determination of Vanadium (V) Based on its Inhibitory Effect on the Thionine – Ascorbic Acid Reaction

ABSTRACT

A simple and sensitive kinetic method for the determination of vanadium(V) based on its inhibitory effect on the reduction of thionine by ascorbic acid at pH=5 is described. The reaction rate is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 598 nm after a fixed time (10 min). The calibration graph is linear in the range of 10 ? 120 ng ml^?1 of vanadium(V) and the detection limit is 6 ng ml^?1. The relative standard deviation (RSD) for 80 ng ml^?1 of V(V) was 0.96% (n=10). The method was successfully applied to the determination of vanadium in a certified reference sample.     

Application of β-cyclodextrin in polymeric solid phase for separation and determination of lead in different environmental matrices

Immobilization of β-cyclodextrin on Dowex resin as an insoluble polymeric matrix by covalent bond presents a new solid-phase medium for preconcentration of Pb (II) at trace level in environmental samples prior to its flame atomic absorption spectrometric determination. The method is based on the sorption of lead after passing on modified Dowex sorbent in a column. The effect of several parameters such as pH, flow rate of sample, eluent kind and volume was investigated. The sorption capacity of the matrix has been found to be 0.4996?mg?g^?1 of adsorbent with the preconcentration factor of 250 for Pb (II). Nitric acid (3 M) as an eluent was sufficient to obtain quantitative recovery (>95%) for Pb (II). The optimum flow rate was 10?ml?min ^?1. The calibration curve was linear in the range of (3–250?ng?mL^?1) with a correlation coefficient of 0.9995. The limit of detection (LOD) based on three times the standard deviation of the blank was 1.37?ng?mL^?1. The relative standard deviation (RSD) for determination of 10?ng?mL^?1 and 100?ngmL^?1 of Pb (II) was 3.00 % and 0.58 % (n?=?10), respectively. The method was successfully applied to determination of lead in some environmental samples such as tap water, river water, soil and rice.     

Comparative study of direct immersion and headspace single drop microextraction techniques for BTEX determination in water samples using GC-FID

In the present work the determination of benzene, toluene, ethylbenzene and o-xylene (BTEX) in environmental sample solutions using gas chromatography with flame ionisation detection (GC-FID) combined with three different sampling techniques, such as; direct single drop microextraction (DI-SDME), headspace single drop microextraction (HS-SDME) and ultrasonic assisted HS-SDME, were compared. In all of these techniques, for the determination of BTEX, the experimental parameters such as organic solvent effect, extraction time, agitation speed and salting effect were optimised. At their optimised conditions of operation the detection limits, times of extraction and precision for the three techniques are established. A detailed comparison of the analytical performance characteristics of these techniques for final GC-FID determination of BTEX in water samples was given. The technique provided a linear range of 50–20000?ng?mL^–1 for DI-SDME and 10–20000?ng?mL^–1 for HS-SDME methods, good repeatability (RSDs <4.72–7.74% for DI-SDME and 1.80–7.05% for HS-SDME (n?=?5), good linearity (r?≥?0.9978) and limits of detection (LODs) in the range of 0.006–10?ng?mL^?1 for DI-SDME, 0.1–3?ng?mL^–1 for HS-SDME methods (S/N?=?3). Then the optimised techniques were also applied to real samples (river and waste waters) containing BTEX and similar precision (RSD?<?8.2,?n?=?3) was obtained.     

Speciation analysis of inorganic vanadium (V(IV)/V(V)) by graphite furnace atomic absorption spectrometry following ion-exchange separation

A sensitive and simple method of ion-exchange resin separation and graphite-furnace atomic absorption spectrometry (GFAAS) detection was proposed for the determination of inorganic vanadium species. Methylene Blue (MB) was used as a chelating agent of V(V) for ion-exchange separation. The complex of V(V) and MB could be trapped by ion-exchange resin at pH 3.0 and eluted by 1.0?mol?L^?1 NaOH. The vanadium species was determined subsequently by GFAAS. The concentration of V(IV) was calculated by subtracting the V(V) concentration from the total concentration of vanadium. Under the optimized experimental conditions, the detection limit of V(V) is 0.48?µg?L^?1 with RSD of 2.6% (n?=?5, c?=?2.0?µg?L^?1). In order to verify the accuracy of the method, a certified reference soil sample was analyzed, and the results obtained were in good agreement with the certified values. The range of recovery for V(IV) and V(V) was 97.8–99.3% and 101.7–103.6%, respectively. The proposed method was applied to the speciation analysis of vanadium in lake-water samples.     

Determination of Trace Amount of Lead(II) in Sweet Fruit‐Flavored Powder Drinks by Differential Pulse Adsorptive Stripping Voltammetry at Carbon Paste Electrode

A new method is described for the determination of lead based on the cathodic adsorptive stripping of the lead–nuclear fast red (NFR) at a carbon paste electrode (CPE). The differential pulse voltammograms of the adsorbed complex of lead–NFR are recorded from ?0.10 to ?0.60 V (versus Ag/AgCl electrode). Optimal conditions were found to be an electrode containing 25% paraffin oil and 75% high purity graphite powder, 4.0×10^?5 mol L^?1 NFR; buffer solution (pH of 3.0), accumulation potential and time, ?0.20 V, 60 and 120 s (for high and low concentration of lead), respectively. The results show that the complex can be adsorbed on the surface of the CPE, yielding one peak at ?0.34 V, corresponding to reduction of NFR in the complex at the electrode. The detection limit was found to be 0.2 ng mL^?1 with a 120s accumulation time. The linear ranges are from 0.5 to 50 (t_acc=120 s) and 50 to 200 ng mL^?1 (t_acc=60 s). Application of the procedure to the determination of lead in lake water, bottled mineral water, synthetic samples and sweet fruit‐flavored powder drinks samples gave good results.     

Solid-phase extraction of Hg(II) on creatine modified activated carbon and determination by ICP-OES in water samples

A new sorbent was successfully prepared by immobilizing creatine on activated carbon and then used for separation/preconcentration of trace Hg(II) prior to detection by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions including pH, sample flow rate and volume, eluting variables and tolerance limit of interfering ions were evaluated and established. At pH 1.0 and flow rate of 2.5?mL?min^?1, Hg(II) was adsorbed quantitatively on the column, then quantitatively eluted by 2.0?mL 0.1?mol?L^?1 nitric acid solution; other transition metal ions did not interfere with the determination of Hg(II). An enrichment factor of 100 was obtained for Hg(II). The maximum adsorption capacity was 49.5?mg?g^?1. Under the optimal conditions, the value of the detection limit (3σ) was 0.06?ng?mL^?1, and the relative standard deviation (RSD) calculated was lower than 3.0% (n?=?8). The methodology was validated by analyzing certified reference materials and successfully applied to the determination of trace Hg(II) in natural water samples with satisfactory results.     

A selective modified nanoporous silica as sorbent for separation and preconcentration of dysprosium in water samples prior to ICP-OES determination

In this research a new physically functionalized nanoporous silica (SBA-15) using N′-[(2-hydroxy phenyl) methylene] benzohydrazide (BBH) was utilized as a selective sorbent for the separation, preconcentration and determination of dysprosium (Dy) in natural water by inductively coupled plasma optical emission spectrometry (ICP-OES). The selectivity of BBH to Dy (III) ion was previously tested by conductometric and spectroscopic methods. Conditions for effective adsorption of Dy were optimized with respect to experimental parameters in batch process. The extraction recovery was 96.5, analytical curve was linear in the range 0.2–1000?µgL^?1, and the detection limit was 0.05?ng?mL^?1. The relative standard deviation (RSD) under optimal conditions was 3.2% (n?=?10). The sorbent exhibited high adsorption capacity and fast rate of equilibrium for sorption of Dy ions. The method was applied for recovery and determination of dysprosium in different environmental water samples.     

Simultaneous determination of carbazole-based explosives in environmental waters by dispersive liquid—liquid microextraction coupled to HPLC with UV-Vis detection

Dispersive liquid-liquid microextraction as a rapid, simple and efficient method coupled with high performance liquid chromatography-UV-Vis detection was used for sample preparation and subsequent determination of carbazole, tri nitro carbazole (TrNC) and tetra nitro carbazole in water samples. The influence of several important variables on the extraction efficiency has been evaluated. The methods works best with chloroform as an extractant and acetonitrile as the dispersive solvent. Under optimum conditions, the calibration curve is linear in the range from 0.007 to 1.75?μg?mL^?1 for TNC, 0.006 to 1.52?μg?mL^?1 for TrNC, and 0.008–2.10?μg?mL^?1 for carbazole. The limits of detection (LODs; at a signal-to-noise ratio of 3), range from 1.7 to 1.1?ng?mL^?1, for TNC, TrNC and carbazole. Also, the relative standard deviations (RSD, n?=?6) for the extraction of TNC (at 174?ng?mL^?1), TrNC (at 151?ng?mL^?1) and carbazole (at 84?ng?mL^?1) vary between 4.1 and 5.2%. The enrichment factors range from 179 to 186. The method was successfully applied to the determination of TNC, TrNC and carbazole in environmental samples.

Cloud-point extraction,preconcentration, and spectrophotometric determination of palladium in water samples

The possibility of using Thio-Michler's Ketone (TMK), 4,4′-bis(dimethylamino) thiobenzophenone, for palladium(II) concentrated by micellar extraction at the cloud-point temperature, and later spectrophotometric determination, was investigated. Under the optimum conditions, preconcentration of 50?mL of water samples in the presence of 0.1% (w/v) octylphenoxy polyethoxy ethanol (Triton X-114), 2?×?10^?6?mol?L^?1?TMK and 1?×?10^–3?mol?L^?1 buffer solution (pH?=?3.0) gave the limit of detection of 0.47?ng?mL^?1, and the calibration graph was linear in the range of 2–50?ng?mL^–1. The recovery under optimum working conditions was higher than 97%. The proposed method has been applied to the spectrophotometric determination of palladium(II) in natural water samples after cloud-point extraction with satisfactory results.     

Chemical modification of alumina surface by immobilization of 1-((5-nitrofuran-2-yl)methylene)thiosemicarbazide for extractive concentration of silver ions

A column, solid phase extraction (SPE), preconcentration method was developed for determination of silver by using alumina coated with 1-((5-nitrofuran-2-yl)methylene)thiosemicarbazide and determination by flame atomic absorption spectrometry. The separation/preconcentration conditions for the quantitative recovery were investigated. At pH 2, the maximum sorption capacity of Ag⁺ was 7.5?mg?g^?1. The linearity was maintained in the concentration range of 0.02–11.0?µg?mL^?1 in the final solution or 0.14–1.10?×?10^4?ng?mL^?1 in the original solution for silver. The preconcentration factor of 140 and relative standard deviation of ±1.4% was obtained, under optimum conditions. The limit of detection (LOD) was calculated as 0.112?ng?mL^?1, based on 3σ_bl/m (n?=?8) in the original solutions. The proposed method was successfully applied to the determination trace amounts of silver in the environmental samples such as tea, rice and wheat flour, mint, and real water samples.     

Miniaturized flow-injection-analysis (μFIA) system with on-line chemiluminescence detection based on the luminol-hypochlorite reaction for the determination of ammonium in river water

A miniaturized flow-injection-analysis system constructed from glass and polydimethylsiloxane was employed for the determination of ammonium in river water. The sample was filtered and delivered to the reactor chip electro-osmotically using a disposable fritted capillary, while reagents were delivered to the system by gravity. Ammonia was mixed with the hypochlorite, to form a monochloramine. Once the alkaline luminol (3-aminophthalhydrazide) was delivered to the system, it was oxidized by the unconsumed hypochlorite emitting a bright blue light (λ _max?～?440?nm) that was detected using a miniaturized photomultiplier tube (PMT) located directly under the chip. The calibration model for ammonium standards was linear up to 0.1?µg?mL^?1 (y?=??8.96x?+?1.02; correlation coefficient, r ²?=?0.9715) over a working range of 0.0–0.5?µg?mL^?1. A detection limit of 10?±?6?µg?mL^?1 was achieved with a precision value of (RSD ≤ 6.4%), for n?=?5. A direct and standard addition method were used to determine the concentration of ammonium in a river-water sample (from the Humber Estuary, UK) which was found to be 0.075?±?0.005?µg?mL^?1, with a precision value of (RSD?≤?3.7%), for n?=?9. The results obtained showed good agreement with the average concentration 0.065?µg?mL^?1 (provided by the local environmental agency), for the analysis of ammonia at different sample points on the estuary.     

Determination of Gallic Acid by Flow Injection Analysis Based on Luminol‐AgNO3‐Ag NPs Chemiluminescence System

A novel flow injection procedure has been developed for the determination of gallic acid based on the enhancement function for luminol‐AgNO₃‐Ag NPs chemiluminescence (CL) system by gallic acid. The enhancement mechanism was proposed for the reinforcing effect of the gallic acid on the CL system. The UV‐vis absorption spectrum and CL emission spectrum were applied to confirm the mechanism. The method is simple, rapid and sensitive with a detection limit of 5×10^?10 g·mL^?1 and a linear range of 8.0×10^?10–1.0×10^?7 g·mL^?1. The relative standard deviation (RSD) is 1.3% for eleven measurements of 5×10^?8 g·mL^?1 gallic acid. The method has been successfully applied to the determination of gallic acid in Chinese proprietary medicine–Jianmin Yanhou tablets and synthesized samples.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.     

Solid phase extraction of trace amounts of Pb(II) in opium, heroin, lipstick, plants and water samples using modified magnetite nanoparticles prior to its atomic absorption determination

A new, simple, fast and reliable solid-phase extraction method has been developed for separation/preconcentration of trace amounts of Pb(II) using dithizone/sodium dodecyl sulfate-immobilized on alumina-coated magnetite nanoparticles, and its determination by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) after eluting with 4.0?mol?L^?1 HNO₃. Optimal experimental conditions including pH, sample volume, eluent concentration and volume, and co-existing ions have been studied and established. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation of Pb(II) using FAAS technique were 280 (for 560?mL of sample solution), 0.28?ng?mL^?1, 1.4?C70?ng?mL^?1 and 4.6% (for 10?ng?mL^?1, n?=?10), respectively. These analytical parameters using GFAAS technique were 300 (for 600?mL of sample solution), 0.002?ng?mL^?1, 0.006?C13.2?ng?mL^?1 and 3.1% (for 5?ng?mL^?1, n?=?10), respectively. The presented procedure was successfully applied for determination of Pb(II) content in opium, heroin, lipstick, plants and water samples.     

Determination of Rifampicin by Peroxomonosulfate‐Cobalt(II) Chemiluminescence System

Rifampicin can enhance the chemiluminescence (CL) of peroxomonosulfate‐cobalt(II) system, and the CL intensity is strongly dependent on the rifampicin concentrations. Based on this phenomenon, a rapid and sensitive flow injection CL method was developed for the determination of rifampicin. The relative CL intensity was linear with the rifampicin concentration over the range of 5×10^?8 to 1×10^?6 g·mL^?1 (r=0.9991), the detection limit was 7×10^?9 g·mL^?1 (S/N=3), and the relative standard deviation was 2.7% for 6×10^?7 g·mL^?1 rifampicin (n=11). Furthermore, this method was successfully applied to the determination of rifampicin in real eye drop and capsules sample.     

On-Line Monitoring of Formaldehyde In Water and Air Using Chemiluminescence Detection

A rapid and sensitive chemiluminescence flow sensor for the determination of formaldehyde was proposed in this article. The analytical reagents involved in chemiluminescence (CL) reaction, luminol and KIO₄, were both immobilized on an anion-exchange column. The CL signal produced by the reaction between luminol and KIO₄, which were eluted from the column through water injection, was decreased in the presence of formaldehyde. Formaldehyde was sensed by measuring the decrement of CL intensity, which was observed linear over the logarithm of formaldehyde concentration range of 5.0-1000.0 ng mL^?1, and the limit of detection is 1.8 ng mL^?1 (3σ). At a flow rate of 2.0 mL min^?1, including sampling and washing, could be performed in 0.5 min with a relative standard deviation of less than 3.0%. The flow sensor offered reagentless procedures and remarkable stability in determination of formaldehyde, and could be easily re-used over 80 h. The proposed flow microsensor was applied successfully in the determination of formaldehyde in artificial water samples and air.     

2-(5-Nitro-2-Pyridylazo)-5-(N-Propyl-N-Sulfopropylamino)Phenol as a new analytical reagent for flow-injection spectrophotometric determination of trace vanadium(V)

A flow injection method using 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol-(Nitro-PAPS) as a new chromogenic reagent is presented for sensitive and rapid determination of vanadium. Nitro-PAPS reacts with vanadium(V) in weakly acidic medium to form a water soluble complex of molar absorptivity of 8.0 × 10⁴L mol^–1 cm^–1 at 592 nm (maximum absorption wavelength), which permits the straightforward application of a flow injection system to the sensitive determination of vanadium. Under the optimum conditions established, a linear calibration graph was obtained in the range 1–120 ng mL^–1. The relative standard deviation for 60 ng mL^–1 vanadium was 2.2% (n = 5) and the limit of detection was 1 ng mL^–1. The sample throughput is about 40 h^–1. Most inorganic and organic anions examined did not interfere even at concentrations of 3000–6000 times of vanadium. Interference from cobalt(II), copper(II) and nickel(II) at 200ng mL^–1 levels can be overcome by the addition of N-(dithio-carboxy)sarcosine. The recoveries for each 20 and 10 ng mL^–1 vanadium added to the river water were 98 and 97%, respectively.The authors express their thanks to Miss Miho Suzuki and Miss Hiroyo Yamada for their experimental assistance in part.     

Adsorptive Cathodic Stripping Voltammetric Determination of Uranium(VI) in Presence of N‐Phenylanthranilic Acid

N‐Phenylanthranilic acid was used as a complexing agent for determination of uranium(VI) by adsorptive cathodic stripping voltammetry. Under the optimal experimental conditions of the experimental parameters, the peak current was proportional to the concentration of U(VI) in the range 0.75–30 ng mL^?1 and the detection limit was 0.036 ng mL^?1. The influence of possible interferences was investigated. The method was applied for determination of uranium in waste water from uranium conversion facility and natural water samples. Application of the method for simultaneous determination of U(VI) and Cu(II) showed that these ions could be simultaneously determined in a single scan at relatively wide concentration range.     

Monitoring chlorophenols in industrial effluents by solid-phase microextraction–gas chromatography–mass spectrometry

A method for the determination of 19 chlorophenols in industrial effluents samples using solid-phase microextraction (SPME) coupled to gas chromatography–mass spectrometry has been developed. Four kinds of different SPME fibres have been studied. Among them, the polyacrylate and carbowax®-divinylbenzene fibres were the most adequate. The extraction process was optimized by means of the experimental design, which allows the study of a large number of factors with a reasonable number of experiments. The optimized method allows the determination of the studied chlorophenols in complex matrices with a high organic content with detection limits down to 0.07?ng?mL^?1 and RSD ranging from 4.4% to 13.8%. The recovery studies with spiked real effluent samples at low levels of chlorophenols ranged from 59.8% to 142.1% for the lowest level (0.5?ng?mL^?1) and from 79.6% to 115.8% for the highest spiked level (2?ng?mL^?1). These results show the suitability of the proposed method to monitor chlorophenols in complex samples. 2,4,5-TCP was detected at concentrations close to its limits of detection in effluents coming from an oil refinery.     

A miniaturized flow-injection analysis ( μ FIA) system with on-line chemiluminescence detection for the determination of iron in estuarine water

A miniaturized flow-injection analysis system constructed from a glass base plate and polydimethylsiloxane (PDMS) top plate was employed for the determination of iron in river water. Two designs were investigated, one utilizing a syringe pump and the other utilizing EOF pumping with a mini-filtration system incorporated. The syringe pump system was used to optimize the analytical method on chip, where the pump was used to deliver both the analyte and the reagents to the reactor chip. The highly sensitive chemiluminescence reaction between alkaline luminol (3-aminophthalhydrazide) and 0.1?M of hydrogen peroxide (H₂O₂) in the presence of iron(II) was utilized. The bright blue light (λ _max?～?440?nm) emitted was detected using a miniaturized photomultiplier tube interfaced directly under the chip. The light intensity signals were recorded, and the corresponding concentration of iron(II) concentration was determined. The calibration for iron(II) standards was linear up to 0.75?µg?mL^?1 (y?=?5.7839x?+?0.0378, r² ?=?0.9939) with a precision value of up to 3.72% RSD, for n?=?3. The limits of detection (blank?+?3s _y/x) were found to be 28?ng?mL^?1. The system which utilized EOF pumping and incorporated a minifiltration unit provided a linear calibration for 0–5?µg?mL^?1 (y?=?3.316x?+?0.1831; correlation coefficient, r ²?=?0.9996) over a working range of 0.0–0.5?µg?mL^?1. This system provided lower limits of detection 5.1?ng?mL^?1 and better repeatability (%RSD less than 0.5% for n?=?4), but problems occurred with the mini-filtration system at higher iron(II) concentrations. The EOF pumping system provided slightly higher results for the concentration of iron(II) in the Humber estuary (0.058?µg?mL^?1), but these results were in line with the results expected by the Environment Agency.