Speciation of Cr(III) and Cr(VI) ions using a β-cyclodextrin-crosslinked polymer micro-column and graphite furnace atomic absorption spectrometry

A sensitive and selective method for the speciation of Cr(III) and Cr(VI) in water samples was developed. It is based on the selective binding of the complex formed between Cr(III) and 4-(2-pyridylazo)resorcinol adsorbed on a cross-linked polymer modified with β-cyclodextrin and placed in a micro-column. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify chromium. Cr(VI) ion is not adsorbed but remains in the aqueous sample phase. Thus, an in-situ separation of Cr(VI) and Cr(III) is accomplished. The concentration of Cr (VI) was calculated by subtracting the value for Cr(III) from that for total chromium. Under optimum conditions, the limit of detection of Cr(III) is 0.056 μg L^?1, and the linear range is from 2.0 to 160.0 μg L^?1. The relative standard deviation is 2.5% (n?=?3, at 30.0 μg L^?1). The preconcentration factor is 25. The method was applied to the speciation of chromium in water samples, and recoveries in spiked real samples range from 101.9% to 104.5%. A reference water sample (GBW(E)080642) also was analyzed, and the results were in good agreement with the certified values.

Speciation Analysis of Cr(III) and Cr(VI) after Solid Phase Extraction Using Modified Magnetite Nanoparticles

A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H₂O₂. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H₂O₂ concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL^?1, 0.1‐10.0 ng mL^?1 and 4.6% (for 5.0 ng mL^?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained.     

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.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Speciation Analysis of Chromium by Adsorptive Stripping Voltammetry in Tap and River Water Samples

An adsorptive stripping voltammetric method for speciation analysis of chromium in natural water samples has been developed. Ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents for Cr(III) present in the sample and formed as products of Cr(VI) reduction, respectively. Under optimum experimental conditions linear relations in the range from 1×10^?6 to 3×10^?5 mol L^?1 without accumulation and from 1×10^?9 to 1×10^?7 at 30 s accumulation time were obtained for Cr(III) and Cr(VI), respectively. For samples in which Cr(III) concentration is higher than 1×10^?6 mol L^?1 the Cr(III) and Cr(VI) were determined simultaneously in one voltammetric cell. For samples in which Cr(III) concentration is below 1×10^?6 mol L^?1 only Cr(VI) was selectively determined in the presence of Cr(III), which did not influence the Cr(VI) signal. The determination of Cr(III) and Cr(VI) was successful with the application of the proposed procedure in the presence of common foreign ions. The presented method was applied for the speciation of chromium in spiked tap and river water samples with satisfactory results.     

Comparative Study of Chromium Biosorption by Mesorhizobium amorphae Strain CCNWGS0123 in Single and Binary Mixtures

The appearance of chromium in the aqueous effluent is a major concern for the modern industry. In this work, Mesorhizobium amorphae strain CCNWGS0123 was investigated as a biosorbent to remove chromium from aqueous solutions. The optimum pH for Cr(III) and Cr(VI) biosorption were 4 and 2, respectively. This isolate showed an experimental maximum Cr(III) adsorption capacity of 53.52 mg?L^?1, while the result was 47.67 mg?L^?1 for Cr(VI), with an initial 100 mg?L^?1 Cr ions and 1.0 g?L^?1 biomass. In terms of time equilibrium, Cr(III) ion was more readily adsorbed than Cr(VI) by this isolate. The biosorption data of both ions fit the Langmuir isotherm better than that of Freundlich model. Meanwhile, this organism exhibited a good capability to release Cr ions, with desorption efficiency of 70 % for Cr(III) and 76 % for Cr(VI). Fourier transform infrared spectroscopy analysis showed that –OH, –COO, –NH, amide I, and C=O were involved in Cr(III) and Cr(VI) binding. The biosorbent was further characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry, which indicated an accumulation of chromium on the cellular level. In the binary mixtures, the removal ratio of total Cr and Cr(III) increased from pH?2 to 4. The highest removal ratio of the total Cr was observed in the 25/25 mg?L^?1 mixture at pH?4. In addition, the removal efficiency of Cr(VI) was closely influenced by Cr(III) in the mixture, decreasing to 23.57 mg?g^?1 in the 100/100 mg?L^?1 mixture system, due to the competition of Cr(III). The potential usage of the chromium-resistant rhizobium for the remediation of chromium-contaminated effluents has been demonstrated based on the above results.     

Speciation of chromium in water samples using dispersive liquid–liquid microextraction and flame atomic absorption spectrometry

A novel method for preconcentration is described for chromium speciation at microgram per liter to sub-microgram per liter levels. It is based on selective complex formation of both Cr(VI) and Cr(III) followed by dispersive liquid–liquid microextraction and determination by microsample introduction-flame atomic absorption spectrometry. Effects influencing complex formation and extraction (such as pH, temperature, time, solvent, salinity and the amount of chelating agent) have been optimized. Enrichment factors up to 275 and 262 were obtained for Cr(VI) and total Cr, respectively. The calibration graph is linear from 0.3 to 20 µg L^?1, and detection limits are 0.07 and 0.08 µg L^?1 for Cr(VI) and total Cr, respectively. Relative standard deviations (RSDs) were obtained to be 2.0% for Cr(VI) and 2.6% for total Cr (n?=?7).     

Sorption of uranium using silica gel with benzoylthiourea derivatives

Benzoylthiourea derivatives (N,N-diphenyl-N′-(3-methylbenzoyl)thiourea and diphenyl-N′-(4-methylbenzoyl)thiourea) were impregnated onto silica gel. The preconcentration of uranium(VI) from aqueous solution was investigated. Extraction conditions were optimized in batch method prior to determination by uv–visible absorption spectrometry using arsenazo(III). The optimum pH for quantitative adsorption was found as 3–7. Quantitative recovery of uranium (VI) was achieved by stripping with 0.1 mol L^?1 HCl. Equilibration time was determined as 30 min for 99% sorption of U(VI). Under optimal conditions, dynamic linear range of for U(VI) was found as 0.25–10 μg mL^?1. The relative standard deviation as percentage and detection limit were 5.0% (n = 10) for 10 μg mL^?1 U(VI) solution and 8.7 ng mL^?1, respectively. The method was employed to the preconcentration of U(VI) ions in soil and tap water samples.     

Application of organo-nanoclay as a solid sorbent for rhodium complex separation and preconcentration

An organo-nanoclay is used as a new, easily accessible, and stable solid sorbent for the preconcentration of trace amounts of rhodium ions from aqueous solution, this followed by its determination by flame atomic absorption spectrometry (FAAS). Rh(III) ion was first complexed with 2,3,5,6-tetra(2-pyridyl) pyrazine (TPPZ) at pH values between 3.0 and 4.7, and then the complex was then adsorbed onto the nanoclay. The rhodium ions were eluted from the sorbent with HCl. The rhodium in the effluent was determined by FAAS. The linear analytical range is between 0.14 ng mL^?1 and 20.0 μg mL^?1 in the initial solution, the relative standard deviation at 2.0 μg mL^?1 of rhodium is 2.6% (n?=?8), the detection limit is 0.03 ng mL^?1, and the preconcentration factor is 140. Experimental parameters including the pH, eluent type, interference by other ions and breakthrough volume were optimized. The method was applied to the determination of rhodium in water, road dust and synthetic samples.     

Sensitive quantification of uranium using cloud point extraction coupled with inductively coupled plasma-optical emission spectrometry

This article reports the utilization of cloud point extraction as a preconcentration strategy prior to U(VI) determination by inductively coupled plasma-optical emission spectrometry. Complexes of U(VI) with Cyanex-301 were preconcentrated into mixed-micellar medium using Triton X-100 and Cetylpyridinium bromide at ambient temperature. Optimal values of parameters impacting the extraction efficiency were determined. The proposed technique has linearity range of 5–200 ng mL^?1 with r = 0.99 and detection and quantification limits of 0.57 and 0.85 ng mL^?1, respectively. The method has good selectivity for U(VI) over various cations and was successfully applied to U(VI) determination in water samples with satisfactory results.     

Determination of chromium(III) and total chromium in natural waters using a surface ion-imprinted silica gel as selective adsorbent

A sensitive and selective method has been developed to determine Cr(III) and total Cr in natural water samples by ICP-AES with a Cr(III)-imprinted aminopropyl-functionalised silica gel adsorbent. The Cr(III)-imprinted and non-imprinted adsorbent were prepared by an easy one-step reaction with a surface imprinting technique. Their maximum static adsorption capacities for Cr(III) were 11.12 mg g^?1 and 3.81 mg g^?1, respectively. The relative selectivity factors (α _r) for Cr(III)/Co(II), Cr(III)/Au(III), Cr(III)/Ni(II), Cr(III)/Cu(II), Cr(III)/Zn(II), and Cr(III)/Cr(VI), were 377, 21.4, 15.4, 27.7, 26.4, and 31.9, respectively. Under the optimal conditions, Cr(III) can be absorbed quantitatively, but Cr(VI) was not retained. Total chromium was obtained after reducing Cr(VI) to Cr(III) with hydroxyammonium chloride. The detection limit (3σ) for Cr(III) was 0.11 ng mL^?1. The relative standard deviation was 1.2%. The proposed method has been validated by analysing two certified reference materials and successfully applied to the determination and speciation of chromium in natural water samples with satisfactory results.     

Speciation of Cr(III) and Cr(VI) using solid phase extraction and determination of total As inductively coupled plasma atomic emission spectrometry

An inductively coupled plasma atomic emission spectrometric (ICP-AES) method was developed for speciation and simultaneous determination of Cr and As, since these two analytes are commonly determined in various water samples in order to assess their toxicity. The objective of this research was to study the speciation of Cr(III), Cr(VI) in the presence of As(III) and/or As(V) using solid phase extraction (SPE) and ICP-AES. For these measurements, four spectral lines were used for each analyte with the purpose of selecting the most appropriate for each element. Finally with the use for first time of a cation-exchange column filled with benzosulfonic acid and elution with HCl, the speciation in solutions which contained [Cr(III)?+?Cr(VI)?+?As(V)] and [Cr(III)?+?Cr(VI)?+?As(III)] was examined. It was demonstrated that the separation of the two chromium species is almost quantitative and the simultaneous determination of chromium species and total arsenic analytes is possible, with very good performance characteristics. The estimated limits of detection for Cr(III), Cr(VI), As(III) and/or As(V) were 0.9?µg?L^?1, 1.1 µg?L^?1, 4.7 µg?L^?1 and 4.5 µg?L^?1 respectively, the calculated relative standard deviations (RSDs) were 3.8%, 4.1%, 5.2% and 5.1% respectively, and finally the accuracy of the methods was estimated using a certified aqueous reference material and found to be 5.6% and 4.8% for Cr(III) and Cr(VI) respectively. The method was applied to the routine analysis of various water samples.     

Preconcentration and Determination of Chromium Species Using Octadecyl Silica Membrane Disks and Flame Atomic Absorption Spectrometry

A novel and selective method for the fast determination of trace amounts of chromium species in water samples has been developed. The procedure is based on the selective formation of chromium diethyldithiocarbamate complexes at different pH in the presence of Mn(II) as an enhancement agent of chromium signals followed by elution with organic eluents and determination by atomic flame absorption spectrometry. The maximum capacity of the employed disks was found to be (396±3) µg and (376±2) µg for Cr(III) and Cr(VI), respectively. The detection limit of the proposed method is 49 and 43 ng·L^?1 for Cr(III) and Cr(VI), respectively. The proposed method was successfully applied for determination of chromium species Cr(III) and Cr(VI) in different water samples.     

On line pre-reduction of Se(VI) by nano-TiO2 controlled volatilization for speciation analysis of inorganic selenium using HPLC-AFS

An on-line nano-TiO₂ controlled volatilization system was developed for inorganic selenium speciation based on the irradiation of thiourea with ultraviolet light. It provides an effective hyphenation unit for atomic fluorescence spectrometry. The effects of several factors such as the acidity, the concentration of thiourea, the amounts of TiO₂, the concentration of KBH₄ and the flow rates of carrier gas were investigated. Under optimal conditions, the limit detections for Se(IV) and Se(VI) were 2.38 and 3.39 ng mL^?1 (100?µL injection, 3 times of the baseline noise), respectively. The relative standard for deviations of 50 ng mL^?1 Se(IV) and Se(VI) were 3.7% and 2.7%, respectively. The method has been applied for determination of inorganic selenium species in real samples and the recoveries were between 93% and 98%.     

Determination of Pantoprazole, Rabeprazole, Esomeprazole, Domperidone and Itopride in Pharmaceutical Products by Reversed Phase Liquid Chromatography Using Single Mobile Phase

A simple, sensitive, and precise high performance liquid chromatographic method for the analysis of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride, with ultraviolet detection at 210 nm, has been developed, validated, and used for the determination of compounds in commercial pharmaceutical products. The compounds were well separated on a Hypersil BDS C18 reversed-phase column by use of a mobile phase consisting of 0.05 M, 4.70 pH, potassium dihydrogen phosphate buffer - acetonitrile (720:280 v/v) at a flow rate of 1.0 mL min^?1. The linearity ranges were 400–4,000 ng mL^?1 for pantoprazole, 200–2,000 ng mL^?1 for rabeprazole, 400–4,000 ng mL^?1 for esomeprazole, 300–3,000 ng mL^?1 for domperidone and 500–5,000 ng mL^?1 for itopride. Limits of detection (LOD) obtained were: pantoprazole 147.51 ng mL^?1, rabeprazole 65.65 ng mL^?1, esomeprazole 131.27 ng mL^?1, domperidone 98.33 ng mL^?1 and itopride 162.35 ng mL^?1. The study showed that reversed-phase liquid chromatography is sensitive and selective for the determination of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride using single mobile phase.     

Silica Microspheres for SPE and Determination of Fungicides in Water by LC

A new method has been developed for the determination of metalaxyl, myclobutanil, and tebuconazole in environmental water samples with preconcentration by cartridges packed with SiO₂ microspheres prior to LC. Several parameters such as the volume and composition of eluent, sample flow rate, sample pH, and sample volume were optimized. Under the optimal conditions, excellent detection limits (S/N = 3) and precision (RSD, n = 6) were 0.02 ng mL^?1, 1.3% for metalaxyl, 0.02 ng mL^?1, and 2.4% for myclobutanil and 0.08 ng mL^?1 and 4.3% for tebuconazole, respectively. The method was applied to the analysis of real-water samples, and satisfactory results were obtained. The average spiked recoveries were in the range of 86.3–97.5%. These results indicate that SiO₂ microspheres have great potential to be used as a novel solid phase extraction adsorbent that could have wide applications in the environmental field.     

Determination of Meserine,a new candidate for Alzheimer’s disease in mice brain by liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic and tissue distribution study

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Meserine ((?)-meptazinol phenylcarbamate), a novel potent inhibitor of acetylcholinesterase (AChE), was developed, validated, and applied to a pharmacokinetic study in mice brain. The lower limit of quantification (LLOQ) was 1 ng mL^?1 and the linear range was 1–1,000 ng mL^?1. The analyte was eluted on a Zorbax SB-Aq column (2.1?×?100 mm, 3.5 μm) with the mobile phase composed of methanol and water (70:30, v/v, aqueous phase contained 10 mM ammonium formate and 0.3 % formic acid) using isocratic elution, and monitored by positive electrospray ionization in multiple reaction monitoring (MRM) mode. The flow rate was 0.25 mL min^?1. The injection volume was 5 μL and total run time was 4 min. The relative standard deviation (RSD) of intraday and interday variation was 2.49–7.81 and 3.01–7.67 %, respectively. All analytes were stable after 4 h at room temperature and 6 h in autosampler. The extraction recoveries of Meserine in brain homogenate were over 90 %. The main brain pharmacokinetic parameters obtained after intranasal administration were T _max?=?0.05 h, C _max?=?462.0?±?39.7 ng g^?1, T _1/2?=?0.4 h, and AUC_(0-∞)?=?283.1?±?9.1 ng h g^?1. Moreover, Meserine was distributed rapidly and widely into brain, heart, liver, spleen, lung, and kidney tissue. The method is validated and could be applied to the pharmacokinetic and tissue distribution study of Meserine in mice.     

Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

Determination of Total Chromium in Biological Samples by Automated Reagent Injection Chemiluminescence Analysis

A sensitive method for the determination of total chromium in real samples by flow injection–chemiluminescence (FI–CL) analysis was proposed. It was found that the CL intensity from luminol–lysozyme reaction could be markedly quenched, and the decrease of CL intensity was linear with the logarithm of Cr(III) concentrations over the range of 5.0 to 4000 pg mL^?1 with a detection limit of 2.0 pg mL^?1 (3σ) and relative standard deviations (RSDs) of 3.0, 2.6, and 2.0% for 10, 100, and 1000 pg mL^?1 Cr(III) (n = 7), respectively. At a flow rate of 2.0 mL min^?1, the whole process including sampling and washing could be accomplished within 36 s. The proposed CL method was successfully applied to the determination of total chromium in pharmaceutical capsules, a dietary supplement, and spiked human serum samples, with recoveries from 92.2 to 108.4% and RSDs of less than 4.0%. Using the homemade FI–CL model, the binding constant (K = 4.38 × 10⁶ L mol^?1) and the binding sites (n ≈ 1) of Cr(III) to lysozyme were given.     

Surfactant-assisted dispersive liquid–liquid micro-extraction combined with magnetic solid-phase extraction for analysis of polyphenols in tobacco samples

A novel and simple two-step micro-extraction technique combining surfactant-assisted dispersive liquid–liquid micro-extraction and magnetic solid-phase extraction prior to high-performance liquid chromatography was established for analysis of polyphenols including chlorogenic acid, caffeic acid, and scopoletin in tobacco samples. In the developed system, Fe₃O₄ nanoparticles were synthesized by a one-step chemical co-precipitation method and used to remove hydrophobic substances in tobacco samples by physical adsorption. Low-density solvent (1-heptanol) and cationic surfactant cethyltrimethyl ammonium bromide were employed as extraction solvent and disperser agent, respectively. Under the optimized experimental conditions, a good linearity of the method was obtained over the concentration range from 0.1 to 1000 ng mL^?1 for target analytes. The limits of detection (S/N?=?3) were 0.05 ng mL^?1 for CGA, 0.10 ng mL^?1 for CFA, and 0.12 ng mL^?1 for SP, respectively. Finally, the applicability of the developed method was evaluated by extraction and determination of these three phenolic compounds in tobacco samples and satisfactory average recoveries of spiked samples were between 96.6 and 102.7%.