Polyethylene Glycol Tert-octylphenyl Ether Research Articles

Quantification of arsenic in real samples using a spectrophotometric cloud point extraction of the formed ion pair with astrazon orange G

A novel cloud-point extraction (CPE) procedure for the determination of ultra-trace amounts of arsenic species in real samples, purchased from the local market by spectrophotometer was developed. Inorganic arsenic species analysis in water, beverages, and foods has become increasingly important in recent years, as arsenic species are considered carcinogenic and are assessed at significant levels in samples. The technique is established on a selective ternary complex of As(V) with astrazon orange G (AOG+) in the presence of tartaric acid and polyethylene glycol tertoctylphenyl ether (Triton X-114) at pH 4.0. The calibration curve developed within range 3.0–160 ng/mL with a correlation coefficient of 0.9988 for As(V) provided a preconcentration factor of 200 and a limit of detection (3S blank/m) of 0.88 ng/mL under optimum investigation conditions. The results of molar absorptivity and Sandell sensitivity are calculated and found to be 4.38 × 105 L/mol cm and 0.018 ng cm−2, respectively. The statistical treatment of data obtained from the proposed and GF-AAS procedures are compared in terms of Student’s t-tests and variance ratio F-tests has revealed no significant differences. The methodology has been effectively confirmed by assessing real samples and comparing it to the GF-AAS method statistically.

Quantification of arsenic in real samples using a spectrophotometric cloud point extraction of the formed ion pair with astrazon orange G

A novel cloud-point extraction (CPE) procedure for the determination of ultra-trace amounts of arsenic species in real samples, purchased from the local market by spectrophotometer was developed. Inorganic arsenic species analysis in water, beverages, and foods has become increasingly important in recent years, as arsenic species are considered carcinogenic and are assessed at significant levels in samples. The technique is established on a selective ternary complex of As(V) with astrazon orange G (AOG+) in the presence of tartaric acid and polyethylene glycol tertoctylphenyl ether (Triton X-114) at pH 4.0. The calibration curve developed within range 3.0–160 ng/mL with a correlation coefficient of 0.9988 for As(V) provided a preconcentration factor of 200 and a limit of detection (3S blank/m) of 0.88 ng/mL under optimum investigation conditions. The results of molar absorptivity and Sandell sensitivity are calculated and found to be 4.38 × 105 L/mol cm and 0.018 ng cm−2, respectively. The statistical treatment of data obtained from the proposed and GF-AAS procedures are compared in terms of Student’s t-tests and variance ratio F-tests has revealed no significant differences. The methodology has been effectively confirmed by assessing real samples and comparing it to the GF-AAS method statistically.

Formation of vesicles between negatively charged carbon quantum dots and cationic surfactant cetylpyridinium chloride (CPC) due to oxidative photo induced electron transfer

The tuning of photo physical properties of highly emissive carbon quantum dots which was synthesized from citric acid in DMF medium through solvothermal method is investigated inside micelles formed by different types of surfactants like cationic surfactant cetylpyridinium chloride (CPC), cetrimonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS) and neutral surfactant polyethylene glycol tert-octyl phenyl ether (TX100), polyoxoethylene lauryl ether (BRIJ-35). Interestingly, only CPC interacts with greater extent and formed co-assembly with negatively-charged carbon quantum dots (CQDs) whereas other surfactants like CTAB, SDS, TX100 and BRIJ-35 do not alter the fluorescence intensity extensively. This results in the formation of a non fluorescent vesicle. No phase separation was observed over the large concentration barrier of the CPC surfactant. However, no such vesicle formation takes place for another cationic surfactant CTAB excluding the role of only electrostatic interaction. The synthesized vesicle is characterized by various techniques including HRTEM, DLS. For the aqueous solution of CQDs having concentration of 0.5 mg/ml, addition of CPC leads to formation of different sized vesicles of size 40 nm to 100 nm. The driving force behind this formation of non-fluorescent vesicles is oxidative photo induced electron transfer which is revealed by the highest occupied molecular orbital (HOMO) –lowest unoccupied molecular orbital (LUMO) interaction between the donor (CQDs) and the acceptor (CPC). We trust such type vesicle can be a suitable alternative for drug carriers, biomarkers and other various applications also.

Cloud point extraction coupled HPLC for a green downstream process and quantification of 1,9β,17,21-tetrahydoxy-4-methyl-19-nor-9β-pregna-1,3,5(10)-trien-11,20-dione and 1,9β,17,20β,21-pentahydoxy-4-methyl-19-nor-9β-pregna-1,3,5(10)-trien-11-one obtained by microbial biotransformation of cortisone

The widespread use of corticosteroids as molecules with high therapeutic potential has shown a gradual increase in recent years, but there is a need to progressively have molecules with high therapeutic effects but an increasingly low side effect profile. The chemical approach to the synthesis of new corticosteroids is often time-consuming, expensive, impacts the environment, difficult, and requires multiple manufacturing steps in contrast to new green approaches. In recent decades, microbial biotransformation has introduced an alternative to chemical synthesis of corticosteroids; however, although biotransformation seems to be a good alternative approach to traditional synthetic routes, the products often require difficult downstream purification processes. The purpose of this work was to identify an alternative process to liquid-liquid extraction for the isolation of two new steroids, 1,9β,17,21-tetrahydoxy-4-methyl-19-nor-9β-pregna-1,3,5(10)-trien-11,20-dione (SCA) and 1,9β,17,20β,21-pentahydoxy-4-methyl-19-nor-9β-pregna-1,3,5(10)-trien-11-one (SCB), obtained by biotransformation of cortisone with Rhodococus rhodnii. Cloud point extraction was chosen and applied for the first time as a “green” downstream method, as it is characterized by a profile of low cost, short extraction time, aqueous environment, moderate temperature, as well as performed with absolutely non-impactful and non-toxic extraction agents. Therefore, this study allowed the evaluation of the main factors affecting cloud point extraction, such as the concentration of polyethylene glycol tert-octylphenyl ether (TX-114), chosen as the extraction agent, of the electrolytes, such as NaCl, of the temperature and equilibration time at which the extraction is performed. Evaluation of extraction efficiencies was performed by RP-HPLC with values of 96% for SCA and 86% for SCB in real biotransformation samples. The analytical performances of the method were evaluated in terms of limits of detection (0.022 g L-1 for SCA and 0.016 g L-1 for SCB), limits of quantification (0.069 g L-1 for SCA and 0.050 g L-1 for SCB), linearity (0.072–3.82 g L−1). The relative standard deviations were calculated for the repeatability (0.54–0.91% for SCA and 0.70–3.80% for SCB) and stability (0.62–0.80% for SCA and 2.21–2.54% for SCB) of the proposed method. The accuracy was evaluated through recovery studies in relation to 50%, 100%, 150% excess analytes, allowing to obtain 99.69–99.77% recovery of SCA and 99.24–99.51% for SCB with RSD% less than 5%.

Surfactant mediated silver synthesis: Influence of surfactant molecular structure on the size and shape of silver particles

The current work employs non-ionic surfactants polyethylene glycol tert-octylphenyl ether (Triton X-114) and polyoxyethylene (20) sorbitan monolaurate (Tween 20) as capping agents for synthesizing silver particles. Formation of icosahedrons and Wulff polyhedrons are thermodynamically preferable for FCC silver, and anisotropic morphologies such as triangular/hexagonal platelets are less likely. Yet, with the use of Triton X-114, appreciable quantity of platelets is obtained. Beyond the molar ratio of 2.5 (Triton X-114: AgNO3), only anisotropic particles are identified. It is believed that preferential adsorption of the surfactant inhibits crystal growth along 〈111〉 direction. Instead, the particles grow along the edges of the hexagonal/triangular plates. In contrast, the use of Tween 20 yielded silver (nano)particles with spherical shape. The presence of multiple polymeric chains in the Tween 20 molecule exhibits strong interaction with the silver particles by restricting growth along multiple facets. These observations indicate the significant role of the molecular structure of capping agents in determining particle size and morphology.

Extraction of natural colorants using supramolecular solvents composed of Triton X-114 and ionic liquids

The interest for natural colorants from microbial sources has increased in the last few years. However, the extraction of these compounds from complex biomasses/matrices is still a challenge for industrial applications, mainly due to the requirements of biocompatibility, sustainability, and efficiency. With this aim, supramolecular solvents (SUPRAS) composed of nonionic polyethylene glycol tert-octylphenyl ether (TX-114) and various cationic surfactants (n-alkyl-3-methyl imidazolium bromide ([Cnmim]Br, n = 10, 12, 14, 16), and tributyl-tetradecylphosphonium chloride ([P4,4,4,14]Cl) ionic liquids (ILs) and cetyltrimethylammonium bromide (CTAB)) were here studied for the extraction of red polyketides colorants from the fermented broth of Talaromyces amestolkiae. Firstly, the influence of ILs on the SUPRAS phase behavior was determined by measuring the cloud point temperature (TCP) and coarse-grained molecular dynamic (CG-MD) simulations. The results of extraction showed that for all SUPRAS the red colorant preferentially partitioned into the surfactant-rich (bottom) phase (partition coefficients, K > 10) with the highest partition using [C14mim]Br as a co-surfactant (K = 14.69 ± 0.15). The systems studied also allowed high recovery efficiency of all mixed surfactant-based SUPRAS (>70 % of red colorant recovered in a single extraction step) with selective for the separation of the red colorant from the yellow (1.52 ± 0.04) and orange (1.62 ± 0.08) counterparts present in the fermented broth. The novel SUPRAS have demonstrated remarkable potential in extracting red colorants from fermented broth, without requiring harsh operating conditions. As such, these platforms offer an effective means of concentrating and pre-purifying the red colorants, and hold promise for application to other molecules with similar chemical properties.

Nonionic Surfactant-Assisted In Situ Generation of Stable Passivation Protective Layer for Highly Stable Aqueous Zn Metal Anodes.

A highly stable interface for aqueous rechargeable Zn batteries is of importance to inhibit the growth of Zn dendrites and suppress the side reactions. In this work, we have developed a stable honeycomb-like ZnO passivation protective layer on the Zn surface, which is in situ generated with the assistance of a nonionic surfactant additive (polyethylene glycol tert-octylphenyl ether, denoted as PEGTE). The ZnO passivation layer can facilitate the uniform distribution of the electric field, guiding the uniform deposition of Zn2+ and inhibit the generation of dendrites. As a result, the symmetric cell using the electrolyte with PEGTE shows an excellent performance at high areal capacity, reflected by stable cycling for over 2400 h at 5 mAh/cm2 and 1300 h at 10 mAh/cm2. The full cell paired with V2O5 demonstrates a long lifespan for more than 600 cycles at a low negative/positive capacity ratio.

Determination of Naphthol Yellow S and Chromotrope 2B at trace levels by spectrophotometry after mixed micellar cloud point extraction using TX-114 and TBAB

A method for the determination of two anionic dyes, Naphthol Yellow S (NYS) and Chromotrope 2B (CTB) in the presence of TBAB (Tetra butyl ammonium bromide) and Triton X-114 (Polyethylene glycol tert-octylphenyl ether) mixed micelles was developed by cloud point extraction pre-concentration technique. Good extraction efficiency was achieved for both NYS and CTB(85-92)% from their aqueous solutions by the optimization of pH of the solution, concentration of surfactants and salting out agent. Linearity was found to be in the range 1.5 – 30.0 μg mL-1for NYS and 1.86 – 27.2 μg mL-1 for CTB. The limit of detection was found to be in ngmL-1 range. Langmuir adsorption model was successfully applied to the phase separation process. The enthalpy, entropy and free energy change for solubilization of these dyes in surfactant phase were also determined. This method was then used to determine the dye concentration in the tap and sea water samples.

Preparation and characterization of ionic and non-ionic surfactants impregnated κ-carrageenan hydrogel beads for investigation of the adsorptive mechanism of cationic dye to develop for biomedical applications

In this work, the κ-carrageenan (CRG) hydrogel beads were impregnated by polyethylene glycol tert-octylphenyl ether (Triton X-100, TTX), as a non-ionic surfactant, and sodium dodecylbenzene sulfonate (SDBS), as an ionic surfactant, in the presence of crosslinking agents of potassium chloride and aluminum chloride. The prepared hydrogel beads were examined by FTIR, XRD, SEM, BET, and TGA analysis, which well confirmed their successful impregnation by the surfactants. The results revealed that the spherical/cubic CRG-TTX hydrogels have a higher crystal structure and thermal resistance than spherical CRG-SDBS. It was demonstrated that the impregnation of CRG hydrogel beads with TXX and SDBS surfactants improves their adsorption behavior toward methylene blue (MB) from aqueous media. The surfactant amount significantly effects on adsorbent performance, whereas the best surfactant concentration was found to be half of the critical micellar concentration. The optimum concentration of adsorbents was obtained 1 g L−1, and the best removal efficiencies were achieved in the pH range of 4 to 8. The maximum adsorption capacity was obtained 482.15 mg g−1 and 469.57 at 45 °C for CRG-TTX and CRG-SDBS, respectively. The dye adsorption kinetics followed the pseudo-second-order kinetic model and the obtained adsorption experimental data were in good agreement with the Langmuir isotherm equation. Thermodynamic study indicated that the process was spontaneous in nature and endothermic. The polymeric microspheres can be employed to deliver drugs in a rate-controlled and sometimes targeted manner.

Hydrolysis of Peptide Bonds in Protein Micelles Promoted by a Zirconium(IV)-Substituted Polyoxometalate as an Artificial Protease.

The development of artificial proteases is challenging, but important for many applications in modern proteomics and biotechnology. The hydrolysis of hydrophobic or unstructured proteins is particularly difficult due to their poor solubility, which often requires the presence of surfactants. Herein, it is shown that a zirconium(IV)-substituted Keggin polyoxometalate (POM), (Et2 NH2 )10 [Zr(α-PW11 O39 )2 ] (1), is able to selectively hydrolyze β-casein, which is an intrinsically unstructured protein at pH 7.4 and 60 °C. Four surfactants (sodium dodecyl sulfate (SDS), N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12), 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), and polyethylene glycol tert-octylphenyl ether (TX-100)), which differ in the nature of their polar groups, were investigated for their role in influencing the selectivity and efficiency of protein hydrolysis. Under experimental conditions, β-casein forms micellar structures in which the hydrophilic part of the protein is water accessible and able to interact with 1. Identical fragmentation patterns of β-casein in the presence of 1 were observed through SDS poly(acrylamide) gel electrophoresis both in the presence and absence of surfactants, but the rate of hydrolysis varied, depending on the nature of surfactant. Whereas TX-100 surfactant, which has a neutral polar head, caused only a slight decrease in the hydrolysis rate, stronger inhibition was observed in the presence surfactants with charges in their polar heads (CHAPS, ZW3-12, SDS). These results were consistent with those of tryptophan fluorescencequenching studies, which showed that the binding between β-casein and 1 decreased with increasing repulsion between the POM and the polar heads of the surfactants. In all cases, the micellar structure of β-casein was not significantly affected by the presence of POM or surfactants, as indicated by circular dichroism spectroscopy.

The effects of surfactants on the heterogeneous uptake of sulfur dioxide on hematite

Surfactants are often found to be associated with atmospheric particles. They can change the physicochemical properties of these particles, and thereby impact their chemical reactivity. However, their influences on heterogeneous reactions of atmospheric trace gases have not been paid much attention. In this study, the impacts of different surfactants on the heterogeneous conversion of SO2 on hematite were investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), including cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS) and nonionic polyethylene glycol tert-octylphenyl ether (Triton X-100). Results indicated that heterogeneous reactivities of hematite-surfactant mixtures were significantly different due to the presence of different surfactants. Under dry conditions, heterogeneous reactivities decreased with the increase of their concentrations, but the higher reactivities were observed at an appropriate concentration range of CTAB and SDS when compared to pure hematite, showing their promoting effects at this concentration range. Under the condition of 58% relative humidity, the heterogeneous reactivities increased first and then decreased with the increasing mass fractions of CTAB and SDS, but pure hematite showed the highest reactivity. While the mixtures containing Triton X-100 had stronger ability to suppress sulfate formation under 58% RH than under dry condition, though these mixtures under 58% RH presented same trend as under dry condition. Water molecules can renew surface reactive sites and promote sulfate formation at an appropriate mass fraction of CTAB or SDS, water molecules can also promote the adsorption mode transition of Triton X-100 from adsorption through terminal OH groups to adsorption through ethoxyl groups, resulting in more surface active sites being covered and a drastically decrease in the reactivity. A possible mechanism for the impact of surfactants on the heterogeneous conversion of SO2 on hematite is proposed, and atmospheric implications based on these results are discussed.

Use of 2-Hydrazinobenzothiazole-Modified Copolymer(s) as Potential Chelating Agent for Sensitive and Selective Determination of Low Levels of Mercury in Seafood by Ultrasound-Assisted Cloud-Point Extraction Combined with Spectrophotometry.

In this study, a new method was developed for the pre-concentration of trace mercury from seafood samples prior to analysis by spectrophotometry. The method is based on the complexation between 2-hydrazinobenzothiazole (2-HBT)-modified copolymer(s) and Hg(II) in the presence of an ionic surfactant, cetyltrimethylammonium bromide (CTAB), as sensitivity enhancer at pH4.5 and the extraction of the complex into the surfactant-rich phase of polyethylene glycol tert-octylphenyl ether (Triton X-114) as the extractant. The variables affecting extraction efficiency were evaluated and optimized. Due to the observation that the modified copolymers are 2.5-fold more sensitive and selective to the Hg2+ ions than the CH3Hg+, the amounts of free Hg2+ and total Hg were determined at 325nm by spectrophotometric detection of free Hg2+ and total Hg in the pre-treated and extracted fish samples using dilute acid mixture containing Triton X-114 and K2Cr2O7, before and after oxidation of CH3Hg+ to Hg2+ with mixture of KBr and KBrO3 in the acidic media. The amount of CH3Hg+ was calculated from the difference between total Hg and free Hg2+ amounts. The accuracy was tested by analysis of two certified samples. The results were statistically in good agreement with the certified values, and the precision was lower than 6.4%. The limits of detection were 1.40 (1.58) and 1.91 (2.11)μgL-1 for Hg2+ from the two calibration solutions spiked before the pre-treatment, respectively. It has been observed that there is no significant matrix effect by comparison of slopes of the calibration curves. The method was applied to seafood samples for speciation analysis of free Hg2+ and CH3Hg+. In terms of speciation, while total Hg is detected in the range of 12.6-143.8μgkg-1, the distribution of mercury in seafood was in the range of 7.4-53.3μgkg-1 for CH3Hg+ and in 8.3-90.5μgkg-1 for free Hg2+.

Effect of [Zr(α-PW11O39)2]10− Polyoxometalate on the Self-Assembly of Surfactant Molecules in Water Studied by Fluorescence and DOSY NMR Spectroscopy

The catalytic fragmentation of hydrophobic proteins by polyoxometalates (POMs) requires the presence of surfactants in order to increase the solubility of the protein. Depending on the nature of the surfactant, different effects on the kinetics of protein hydrolysis are observed. As the molecular interactions between the POMs and surfactants in solutions have been scarcely explored, in this study, the interaction between the catalytically active Keggin polyoxometalate [Zr(α-PW11O39)2]10− and four different surfactants—sodium dodecyl sulfate (SDS), dodecyldimethyl(3-sulfopropyl)ammonium (Zw3-12), dodecyldimethyl(3-sulfopropyl) ammonium (CHAPS), and polyethylene glycol tert-octylphenyl ether (TX-100)—have been studied in aqueous media. The effect of polyoxometalate on the self-assembly of surfactant molecules into micelles and on the critical micellar concentration (CMC) has been examined by fluorescence spectroscopy and diffusion ordered NMR spectroscopy (DOSY).

Extraction, Preconcentration, and Quantification of Low Levels of Free Formaldehyde from Some Beverage Matrices by Combination of Ultrasound-Assisted-Cloud Point Extraction with Spectrophotometry

In the present study, due to use of formaldehyde (FA) as a food additive as well as its endogenous and natural occurrence in aquatic products, a new preconcentration method for the quantification of free formaldehyde (FA) in beverages was developed before analysis by spectrophotometry at 538 nm. The method is based on spontaneously Cannizzaro disproportionation of FA with Variamine blue (VBH2) in the presence of ionic surfactant, sodium dodecylsulfate (SDS) as both sensitivity enhancer and counter ion at pH 7.0, and then extraction of the formed ion-pairing complex into the nonionic surfactant, polyethylene glycol tert-octylphenyl ether (Triton X-114). The effect of analytical variables was evaluated in detail, and the optimal working conditions were established. There was a rectilinear relationship in the range of 2–400 μg L−1 with changing sensitivity. The limits of detection and quantification of the method with a sensitivity enhancement of 65 after preconcentration were 0.53 and 1.76 μg L−1, respectively. The accuracy was validated by using two spiked quality control samples in linear working range and by comparing the results obtained from the samples with those of independent method, which is known as a slight modified acetylacetone method. It has been observed that the results obtained by both methods are statistically compatible with a t value ranging from 0.09 to 0.65 (t critical 2.31). The intra-day and inter-day precisions as a result of stabilization of mixed micellar system were lower than 4.9% (as RSD%, n 5), and the recoveries were quantitatively higher than 95% for the two quality control samples spiked with 10, 25, and 50 μg L−1 with satisfactory results. The method was successfully applied to the quantification of low levels of free FA in selected beverage matrices.

Cloud point extraction of rare earths and zinc using 1,10-phenanthroline and Triton X-114 coupled with microwave plasma torch-atomic emission spectrometry

In the present work, cloud point extraction (CPE) of rare earths and zinc coupled with microwave plasma torch-atomic emission spectrometry (MPT-AES) was studied with 1,10-phenanthroline as the chelating agent and polyethylene glycoltert-octylphenyl ether (Triton X-114) as the surfactant.

Application of multivariate designs in the development of a method for vanadium determination in natural waters by HR-CS GF AAS after cloud-point extraction

A method for trace vanadium determination in natural waters was developed using multivariate approaches (two-level fractional factorial, Doehlert and constrained mixture designs). The preconcentration method was based on the cloud point extraction of vanadium after its complexation with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), separation of a micellar phase on the cloud point of the non-ionic surfactant polyethylene glycol tert-octylphenyl ether (Triton X-114) and subsequent determination using high resolution continuous source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The developed method presented limits of detection and quantification of 0.13 and 0.42μgL−1 respectively, an enrichment factor of 13.3-fold and precision expressed as a repeatability (% RSD, n=10, 2μgL−1) of 2.5%. Analysis of a certified reference material (Trace elements water, NIST 1643e) and spike tests with recoveries between 84% and 123% showed that the proposed method presents adequate accuracy. The proposed method was applied in the analysis of natural waters collected in an area with naturally occurring vanadium (Maracás, Bahia, Brazil) and groundwater collected from artesian wells located at gas stations.

An evaluation of the bioaccessibility of arsenic in corn and rice samples based on cloud point extraction and hydride generation coupled to atomic fluorescence spectrometry

A simple, inexpensive and rapid method was proposed for the determination of bioaccessible arsenic in corn and rice samples using an in vitro bioaccessibility assay. The method was based on the preconcentration of arsenic by cloud point extraction (CPE) using o,o-diethyldithiophosphate (DDTP) complex, which was generated from an in vitro extract using polyethylene glycol tert-octylphenyl ether (Triton X-114) as a surfactant prior to its detection by atomic fluorescence spectrometry with a hydride generation system (HG-AFS). The CPE method was optimized by a multivariate approach (two-level full factorial and Doehlert designs). A photo-oxidation step of the organic species prior to HG-AFS detection was included for the accurate quantification of the total As. The limit of detection was 1.34μgkg−1 and 1.90μgkg−1 for rice and corn samples, respectively. The accuracy of the method was confirmed by analyzing certified reference material ERM BC-211 (rice powder). The corn and rice samples that were analyzed showed a high bioaccessible arsenic content (72–88% and 54–96%, respectively), indicating a potential human health risk.

Determination of Copper in Human Urine by Cloud Point Extraction and Flame Atomic Absorption Spectrometry

ABSTRACTThis work reports novel cloud point extraction and preconcentration for the determination of copper in human urine by flame atomic absorption spectrometry. The method is based on the selective reaction of 2,9-dimethyl-1,10-phenanthroline (neocuproine) with Cu(I) to produce highly hydrophobic chelate that is extracted and preconcentrated using polyethylene glycol tert-octylphenyl ether (Triton X-114) as nonionic surfactant. Before the derivatization reaction, Cu(II) was reduced to Cu(I) by ascorbic acid. The effect of pH, concentration of the chelating agent and surfactant, equilibration temperature, and incubation time were investigated. Under optimum conditions, preconcentration of copper from 10 mL of urine sample in the presence of 0.10% (w/v) Triton X-114 and 0.1 mmol/L neocuproine at pH 5.9 permitted a limit of detection of 0.01 µg/L for copper in urine. The relative standard deviation was less than 3.5% for copper concentrations from 0.5 to 100.0 µg/L following cloud point extraction. The correlation coefficients of the calibration curves were higher than 0.999. The effects of matrix ions (cations and anions) on the recovery of copper were studied systematically. The use of flame atomic absorption spectrometry with certified reference material for the determination of copper in human urine yielded satisfactory results.

Enhanced electrogenerated chemiluminescence of Ru(bpy)32+/TPrA (bpy=2,2׳-bipyridine; TPrA=tri-n-propylamine) via oxygen quenching using melatonin

The effect on the electrogenerated chemiluminescence (ECL) of the Ru(bpy)32+/TPrA (bpy=2,2׳-bipyridine; TPra=tri-n-propylamine) system when melatonin (N-acetyl-5-methoxytryptamine; MLT) and structurally related compounds (e.g., d- and l-Tryptophan (TRY), 7-Azatryptophan (7-AZA) and Serotonin (SER)) are present in aqueous buffered solution is reported. MLT, d- and l-TRY, SER and 7-AZA display weak intrinsic ECL when TPrA is used as an oxidative–reductive coreactant. However, micromolar concentrations of melatonin result in up to 2.5-fold enhancement of Ru(bpy)32+/TPrA ECL while the other analytes attenuate ECL between 2- and 1000-fold. Photoluminescence (PL) emission efficiencies do not change in the presence of melatonin unless the melatonin solution has undergone electrochemical bulk oxidation, at which point PL and ECL are nearly indistinguishable. Spectroscopic, electrochemical and spectroelectrochemical studies indicate that the mechanism involves oxygen scavenging by melatonin oxidation products. This scavenging prevents the quenching of the *Ru(bpy)32+ excited states by dissolved oxygen in solution. Melatonin can be coupled with 30% by volume 2,2,2-trifluorethanol (TFE) or with the nonionic surfactant Triton X-100 (polyethylene glycol tert-octylphenyl ether) for even greater enhancement of Ru(bpy)32+/TPrA ECL.

Determination and speciation of Se(IV), Se(VI), and selenomethionine in iranian walnut samples by spectrophotometry after cloud point extraction

A sensitive and selective micelle-mediated speciation and preconcentration method has been developed for trace amount of inorganic and organic selenium prior to UV-Vis spectrophotometry determination. The method is based on cloud point extraction of Se(IV) ions with polyethylene glycol tert-octylphenyl ether (Triton X-114) in presence of 2,3-diaminonaphthalene (DAN) as a chelating agent. Se(IV) ions react with DAN in a surfactant solution yielding a hydrophobic complex at pH 3. The phase separation was accelerated by a 20 min centrifugation at 3500 rpm. The calibration graph obtained from Se(IV)-DAN complexes was linear in the concentration range of 5.0–400.0 ng/mL and detection limit was 9 ng/mL. The relative standard deviation was 1.6% in the determination of 80 ng/mL Se(IV). The proposed method was successfully applied to the speciation and determination of selenium species-Se(IV), Se(VI), selenomethionine—in walnut samples with satisfactory results.