Online thorium determination after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine by FI-spectrophotometry

A very sensitive and selective flow injection on-line determination method of thorium (IV) after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine is described. Thorium (IV) was selectively adsorbed from aqueous solution of pH 4.5 in a minicolumn at a flow rate of 13.6 mL min^?1, eluted with 3.6 mol dm^?3 HCl (5.6 mL min^?1), mixed with arsenazo-III (0.05% in 3.6 mol dm^?3 HCl stabilized with 1% Triton X-100, 5.6 mL min^?1) at confluence point and taken to the flow through cell of spectrophotometer where its absorbance was measured at 660 nm. Peak height was used for data analyses. The preconcentration factors obtained were 32 and 162, detection limits of 0.76 and 0.150 ??g L^?1, sample throughputs of 40 and 11 h^?1 for preconcentration times of 60 and 300 s, respectively. The tolerance levels for Zr(IV) and U(VI) metal ions is increased to 50-folds higher concentration to Th(IV). The proposed method was applied on different spiked tap water, sea water and biological sample and good recovery was obtained. The method was also applied on certified reference material IAEA-SL1 (Lake Sediment) for the determination of thorium and the results were in good agreement with the reported value.     

On-line spectrophotometric determination of scandium after preconcentration on XAD-4 resin impregnated with nalidixic acid

An on-line scandium preconcentration and determination method was developed with spectrophotometer associated with flow injection. Scandium from aqueous sample solution of pH 4.5 was selectively retained in the minicolumn containing XAD-4 resin impregnated with nalidixic acid at a flow rate of 11.8 mL min^?1 as scandium–nalidixic acid complex. The scandium complex was desorbed from the resin by 0.1 mol L^?1 HCl at a flow rate of 3.2 mL min^?1 and mixed with arsenazo-III solution (0.05 % solution in 0.1 mol L^?1 HCl, 3.2 mL min^?1) and taken to the flow through cell of spectrophotometer where its absorbance was measured at 640 nm. The preconcentration factors obtained were 35 and 155; detection limits of 1.4 and 0.32 μg L^?1 and sample throughputs of 40 and 11 were obtained for preconcentration time of 60 and 300 s, respectively. The tolerance limits of many interfering cations like Th(IV), U (VI), rare-earths and anions like tartrate, citrate, oxalate and fluoride were improved. The method was successfully applied to the determination of scandium from mock seawater samples and good recovery was obtained. The method was also validated on certified reference material IAEA-SL-1 (lake sediment) and the result was in good agreement with the reported value.     

Determination of Aluminum Traces in Hemodialysis and Tap Water Using Standard Method's Procedure Modified and Flow Injection Ionic Exchange Preconcentration

Abstract

A procedure for the spectrophotometric determination of aluminum traces in water using a flow injection (FI) preconcentration system has been proposed. The flow system was made up of a peristaltic pump, an injector‐commutator, and a minicolumn filled with 300.0 mg of Amberlite IR‐120 cationic exchange resin. After the preconcentration step, aluminum was eluted by a 4.0 mol l^?1 HCl solution. In a second stage, out of the flow system, the eluate was neutralized with a 4.0 mol l^?1 NaOH solution. The aluminum was submitted to the reaction with eriochrome cyanine to form a chelate in solution buffered to pH 5.85, according to the Standard Method's procedure with some modifications, and this was followed by spectrophotometric detection. Chemical and flow variables were studied in the preconcentration system. The precision of the proposed method was calculated for a solution containing 46.8 µg l^?1 of Al(III), when 40.0 ml of solution were preconcentrated (n=7), and their respective relative standard deviation (RSD) was 1.8%. The detection limit obtained was 1.7 µg l^?1 of Al(III) (sample volume=40.0 ml). The proposed method was successful in determining aluminum in water certified reference material.     

Flow injection on-line spectrophotometric determination of thorium(IV) after preconcentration on XAD-4 resin impregnated with oxytetracycline

A very sensitive, selective and simple flow injection time-based method was developed for on-line preconcentration and determination of thorium(IV) at micro g L^–1 levels in environmental samples. The system operation was based on thorium(IV) ion retention at pH 4.0 in the minicolumn at a flow rate of 15.2 mL min^–1. The trapped complex was then eluted with 3.6 mol L^–1 HCl at a flow rate of 4.9 mL min^–1. The amount of thorium(IV) in the eluate was measured spectrophotometrically at 651 nm using arsenazo-III solution (0.05 % in 3.6 mol L^–1 HCl stabilized with 1 % triton X-100, 4.9 mL min^–1) as colorimetric reagent. All chemical, and flow injection variables were optimized for the quantitative preconcentration of metal and a study of interference level of various ions was also carried out. The system offered low backpressure and improved sensitivity and selectivity. At a preconcentration time of 60 s and a sample frequency of 40 h^–1, the enhancement factor was 97, the detection limit was 0.25 μg L^–1, and the precision expressed as relative standard deviation was 1.08 % (at 50 μg L^–1), whereas for 300 s of the preconcentration time and a sample frequency of 10 h^–1, the enhancement factor of 357, the detection limit (3σ) of 0.069 μg L^–1 and the precision of 1.32 % (at 10 μg L^–1) was reported. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference material IAEA-SL-1 (Lake Sediment) and spiked water samples.     

Ultrasensitive Assay of Gatifloxacin at Picogram Level Based on its Enhancing Effect on the Myoglobin‐Luminol Chemiluminescence Reaction

Abstract

Picogram‐level gatifloxacin was determined based on its significantly catalyzed effect on myoglobin‐luminol chemiluminescence (CL) reaction in the flow injection system. The enhanced chemiluminescence intensity was linear with gatifloxacin concentration in the range from 50 ngl^?1–10 µg l^?1 (r²=0.9995), and the detection limit was 20 ng l^?1 (3σ). At a flow rate of 2.0 ml min^?1 for each line, a complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 4.0% (n=7). The proposed method was applied successfully in the determination of gatifloxacin in tablets, human serum and urine samples with the recovery from 97.4–104.5%.     

Determination of uranium using a flow system with reagent injection. Application to the determination of uranium in ore leachates

The determination of uranium by a flow system with reagent injection is based on the reaction of U(IV) with Arsenazo III in 3.6 M HCl; U(IV) is generated by reduction of uranyl ion in a lead reductor minicolumn installed in the sample channel of the manifold. The interference effect caused by several ions is studied. The calibration graph is linear up to 1.0 × 10^?5 M (2.4 mg l^?1) and the detection limit is 2.8 × 10^?8 M (6.6 μg l^?1). The modification of the manifold by including a second valve to by-pass the reducing column allows the measurement of the difference in peak heights, which makes the method specific for uranium.     

Solid phase extraction using silica gel functionalized with Sulfasalazine for preconcentration of uranium(VI) ions from water samples

Silica gel surface was chemically functionalized by reaction the silanol from the silica surface with 3-chloropropyltrimethoxysilane followed by reaction with Sulfasalazine. This new sorbent has been used for the preconcentration of low levels of U(VI) ions from an aqueous phase. Parameters involved in extraction efficiency such as pH, weight of the sorbent, volume of sample and eluent were optimized in batch and column methods prior to determination by spectrophotometry using arsenazo(III) reagent. The results showed that U(VI) ions can be sorbed at pH range of 5.0–6.0 in a minicolumn and quantitative recovery of U(VI) (>98.0?±?1.6%) was achieved by stripping with 2.5 mL of 0.1 mol L^?1 HCl. The sorption capacity of the functionalized silica gel was 1.15 mmol g^?1 of U(VI). A linear calibration graph was obtained over the concentration range of 0.02–27.0 μg mL^?1 with a limit of detection of 1 μg L^?1 in treatment with 1000 mL of the U(VI) solution in which the preconcentration factor was as high as 400. The method was employed to the preconcentration of U(VI) ions from spiked ground water and synthetic sea water samples.     

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.     

Multi‐Walled Carbon Nanotubes as Sorbent for Flow Injection On‐Line Microcolumn Preconcentration Coupled with Flame Atomic Absorption Spectrometry for Determination of Cadmium and Copper

Abstract

Multi‐walled carbon nanotubes (MWNTs) were used as sorbent for flow injection (FI) on‐line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace cadmium and copper in environmental and biological samples. Effective preconcentration of trace cadmium and copper was achieved in a pH range of 4.5–6.5 and 5.0–7.5, respectively. The retained cadmium and copper were efficiently eluted with 0.5 mol L^?1 HCl for on‐line FAAS determination. The MWNTs packed microcolumn exhibited fairly fast kinetics for the adsorption of cadmium and copper, permitting the use of high sample flow rates up to at least 7.8 mL min^?1 for the FI on‐line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 60 sec at a sample loading flow rate of 4.3 mL min^?1, the enhancement factor was 24 for cadmium and 25 for copper at a sample throughput of 45 h^?1. The detection limits (3σ) were 0.30 and 0.11 µg L^?1 for Cd and Cu, respectively. The precision (RSD) for 11 replicate measurements was 2.1% at the 10‐µg L^?1 Cd level and 2.4% at the 10‐µg L^?1 Cu level. The developed method was successfully applied to the determination of trace Cd and Cu in a variety of environmental and biological samples.     

Application of Ni(II)-imprinted cross-linked poly(methacrylic acid) synthesised through double-imprinting method for the on-line preconcentration of Ni(II) ions in aqueous media

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L^?1 HNO₃ at a flow rate of 7.0 mL min^?1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L^?1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min^?1, and sample throughput – 25 h^?1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L^?1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L^?1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions.     

Solvent extraction of Cu,Mo, V,and U from leach solutions of copper ore and flotation tailings

A micro-cloud point extraction method was discussed for preconcentration and spectrophotometric quantification of U(VI). The method depends on complex formation between U(VI) and 2-(4-sulphophenyloazo)-1,8-dihydroxy-3,6-naphtalenedisulphonic acid (SPADNS) at pH 7.0 and subsequent extraction of the complex in a mixed surfactant medium (cethyltrimethyl ammonium bromide and Triton X-114). The separation was carried out in the presence of 1% Na₂SO₄ at room temperature. The calibration curve was linear up to 3000 µg L^?1. The enrichment factor, detection limit and precision were 16.0, 1.05 µg L^?1, and 2.3%, respectively. The method was employed for the determination of U(VI) in real samples with different matrices.     

A combined spectroscopic and light scattering study of hydrolysis of uranium(VI) leading to colloid formation in aqueous solutions

This study mainly focuses hydrolysis reactions of uranium(VI) under an ambient atmosphere leading to colloid formation in near neutral solution using light scattering, UV–Vis and FTIR-ATR studies. UV–Vis and IR spectrum was recorded for uranyl solution at different pH range. U(VI) hydrolyzed colloids were detected and it was confirmed by the appearance of a band at 941 cm^?1 in the IR spectra. Light scattering measurements were performed on colloidal U(VI) solutions formed at pH range of 7–8. The average particle diameter was determined as 32–36 nm using dynamic light scattering. Well defined colloidal species are formed with no considerable change in particle size with increasing U(VI) concentration. The weight average molecular weight of colloidal species was predicted as 763 Da by Debye plot. The second virial coefficient (A₂) was found to be ?0.1139 ml g^?1 Da. The present study confirms that behaviour of U(VI) contradicts conventional Zr(IV), Th(IV) and Pu(IV) solution chemistry. U(VI) polymerization is less extensive and in neutral solutions it forms only oligomers with 2–3 uranyl units.     

Determination of Puerarin in Pharmaceutical Injection by Flow Injection Analysis with Acidic Potassium Permanganate–Glyoxal Chemiluminescence Detection

Abstract

A simple flow injection chemiluminescence method with synergistic enhancement has been investigated for the rapid and sensitive determination of puerarin. The method is based on the enhancing effect of puerarin on the chemiluminescence emission generated by the oxidation of glyoxal with potassium permanganate in a sulfuric acid medium. The optimization of chemical variables influencing the chemiluminescence response of the method has been carried out by applying experimental design, using the proposed flow?injection manifold. Under the optimal conditions, the enhanced chemiluminescence intensity was linear with the concentration of puerarin over the range from 10.0 ng · ml^?1 to 7.0 µg · ml^?1 (R²=0.9972) with a detection limit (3σ) of 3.0 ng · ml^?1. At a flow rate of 3.0 ml · min^?1, a complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0%. The proposed method was applied successfully in the assay of puerarin in pharmaceutical injection and human urine. The mechanism of chemiluminescence reaction was discussed briefly.     

Synthesis and characterisation of novel chelating resin for selective preconcentration and trace determination of Pb(II) ions in aqueous samples by innovative microsample injection system coupled flame atomic absorption spectrometry

Expanded polystyrene (EPS) foam waste (white pollutant) was utilised for the synthesis of novel chelating resin i.e. EPS-N = N-α-Benzoin oxime (EPS-N = N-Box). The synthesised resin was characterised by FT-IR spectroscopy, elemental analysis, and thermogravimetric analysis. A selective method for the preconcentration of Pb(II) ions on EPS-N = N-Box resin packed in mini-column was developed. The sorbed Pb(II) ions were eluted with 5.0 mL of 2.0 mol L^?1 HCl and determined by microsample injection system coupled flame atomic absorption spectrometry (MIS-FAAS). The average recovery of Pb(II) ions was achieved 95.5% at optimum parameters such as pH 7, resin amount 400 mg, flow rates 1.0 mL min^?1 (of eluent) and3.0 mL min^?1 (of sample solution). The total saturation capacity of the resin, limit of detection (LOD) and limit of quantification (LOQ) of Pb(II) ions were found to be 30 mg g^?1, 0.033 μg L^?1 and 0.107 μg L^?1, respectively with preconcentration factor of 300. The accuracy, selectivity and validation of the method was checked by analysis of sea water (BCR-403), wastewater (BCR-715) and Tibet soil (NCS DC-78302) as certified reference materials (CRMs). The proposed method was applied successfully for the trace determination of Pb(II) ions in aqueous samples.     

Schiff base-functionalised styrofoam resin for preconcentration of metal ions in wastewater and wastewater-irrigated vegetables samples

Polystyrene (PS) was extracted from styrofoam waste and functionalised with schiff base, N,N-bis(salicylidene)cyclohexanediamine (SCHD) through an azo spacer. The resin was characterised and used for preconcentration of Pb(II), Ni(II) and Cd(II) ions prior to their trace determinations by microsample injection system–coupled flame atomic absorption spectrometry (MIS-FAAS). The recoveries of studied metal ions were achieved ≥96.0% with relative standard deviation (RSD) ≤4.5 at optimum parameters: pH 8; resin amount 300 mg; flow rates 3.0 mL min^?1 of sample solution; and 2.0 mL min^?1 of eluent (2.0 mol L^?1 HNO₃). The limits of detection (LODs) and limits of quantification (LOQs) were found to be 0.32, 0.23 and 0.21 and 1.10, 0.78 and 0.69 μg L^?1, respectively, with preconcentration factors (PFs) of 500, 800 and 1000, respectively. The linear ranges of the method were 1–40, 1–25 and 1–20 μg L^?1 for Pb(II), Ni(II) and Cd(II) ions, respectively. The accuracy and validation of the method were evaluated by analysis of certified reference materials (CRMs). The method was successfully applied for preconcentration of studied metal ions in wastewater and wastewater-irrigated vegetable samples.     

In Situ Biphasic Extractive Fermentation for Hexanoic Acid Production from Sucrose by Megasphaera elsdenii NCIMB 702410

Hexanoic acid production by a bacterium using sucrose as an economic carbon source was studied under conditions in which hexanoic acid was continuously extracted by liquid–liquid extraction. Megasphaera elsdenii NCIMB 702410, selected from five M. elsdenii strains, produced 4.69 g l^?1 hexanoic acid in a basal medium containing sucrose. Production increased to 8.19 g l^?1 when the medium was supplemented by 5 g l^?1 sodium butyrate. A biphasic liquid–liquid extraction system with 10 % (v/v) alamine 336 in oleyl alcohol as a solvent was evaluated in a continuous stirred-tank reactor held at pH 6. Over 90 % (w/w) of the hexanoic acid in a 0.5 M aqueous solution was transferred to the extraction solvent within 10 h. Cell growth was not significantly inhibited by direct contact of the fermentation broth with the extraction solvent. The system produced 28.42 g l^?1 of hexanoic acid from 54.85 g l^?1 of sucrose during 144 h of culture, and 26.52 and 1.90 g l^?1 of hexanoic acid was accumulated in the extraction solvent and the aqueous fermentation broth, respectively. The productivity and yield of hexanoic acid were 0.20 g l^?1 h^?1 and 0.50 g g^?1 sucrose, respectively.     

Retention profile of Fe,Mn and Cu onto chemically treated polyurethane with carbon disulfide

Dithiocarbamate modified polyurethane foam (DTC-PUF) was synthesized as a new solid-phase extraction sorbent for the preconcentration and determination of Fe(II), Mn(II) and Cu(II) in environmental samples using flame atomic absorption spectrometry. Maximum extraction of the elements was achieved at pH 5–7 and flow rate 3 mL min^?1. Quantitative desorption was achieved by 10 mL from 1.0 mol L^?1 HCl solution. The capacity of the sorbent was 149.2 ± 0.5, 237.5 ± 0.2, 200.2 ± 0.1 μg g^?1 and the limit of detection was of 0.015, 0.015 and 0.012 μg mL^?1for Fe(II), Mn(II) and Cu(II), respectively. A preconcentration factor of 100 was obtained for all elements. The developed method was successfully applied to the determination of the tested elements in water (tap and lake) and plant (spinach and parsley leaves) samples and showed good recovery values from 98 to 111% with corresponding RSD values ranged from 0.6 to 8.6%.     

On-Line SPE Coupled with LC for Analysis of Traces of Sudan Dyes in Foods

We report a sensitive and simple method for analysis of traces of Sudan dyes in foods in which solid-phase extraction on activated silica gel for preconcentration was combined, on-line, with high-performance liquid chromatography. With a loading flow rate of 1.7 mL min^?1 for sampling 50 mL Sudan I–IV at pH 6.7, enrichment factors ranging from 196 to 991 were achieved. Detection limits (S/N = 3) of Sudan I–IV were in the range 1.4–7.0 ng L^?1, and the relative standard deviation for repeatability of peak areas in five replicate analyses of 0.01 μg L^?1 Sudan I–IV was 2.2–4.5%. When blank food samples (chilli powder, chilli sauce, and duck eggs) were spiked with Sudan III at two levels (0.25 and 0.50 μg L^?1) then analyzed by this method recovery ranged from 70.3 to 95.2%.     

On-line preconcentration and determination of Au(III) in various environmental/industrial samples by flame atomic absorption spectrometry

A rapid and simple on-line method is described for the determination of Au(III) in various samples. The method is based on the sorption of gold(III) on Lewatit MonoPlus TP207 chelating resin including the iminodiacetate group, which is used as sorbent material and packed in a minicolumn. The chemical variables such as the pH of the sample solution, eluent type, interfering ions and concentrations of reagents, and instrumental variables such as sample loading volume, reagents flow rates, and tubing length, which affect the efficiency of the method were studied and optimised. Au(III) was sorbed on the chelating resin, from which it could be eluted with 3 mol L^?1 HCl, and then introduced directly to the nebuliser-burner system of FAAS. The limit of detection of the method was 0.2 µg L^?1 while the relative standard deviation was <4.0% for 20 µg L^?1 Au(III) concentration. The preconcentration factor was found to be 106 while the optimised sample volume was 15.3 mL. The accuracy of the method was verified by analysing the certified reference material. The developed method was applied successfully for the determination of gold in different samples with satisfactory results.     

Comparative solid phase extraction study on the U(VI) preconcentration by using immobilized thermotolerant <Emphasis Type="Italic">Bacillus vallismortis</Emphasis> and <Emphasis Type="Italic">Bacillus mojavensis</Emphasis>

Bacillus vallismortis and Bacillus mojavensis were loaded onto Amberlite XAD-4 resin and used for solid phase extraction (SPE) of uranium(VI). A quick and simple UV–Vis spectrophotometric method was used to determine U(VI) ion. The best experimental conditions were determined as being a pH of 5.0; a sample flow rate of 2.0 mL min^?1; 200.0 mg of biosorbent; 800 mg of Amberlite XAD-4, and 5.0 mL of 1 mol L^?1 HCl as desorption solution for both immobilized bacteria. The preconcentration factors were achieved as 80 for both solid phase extractor. The developed methods were validated by applying to reference water and tea samples.