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Amino-functional silica-coated N-doped carbon dots (NH 2 -SiO 2 -CDs) were covalently modified by l-tryptophan (chiral selector) by producing an amide bond between carboxyl groups of L-try and amino groups of NH 2 -SiO 2 -CDs to develop a novel high throughput chiral nanoprobes (L-try-CONH-SiO 2 -CDs) for highly sensitive and enantioselective quantification of S-/R-mandelic acid (S-/R-Man). The method showed a great difference between S- and R-isomers (enantioselectivity coefficient = 4.17) due to the ultra-stability of the Meisenheimer complex that was formed between S-isomer and nanoprobe (K S-Man /K R-man  = 2122.7, where K is the binding-constant). At optimal experimental conditions, two linear ranges of 0.5-25.0 (LOD of 0.05 μM) and 0.5-22.0 μM (LOD of 0.27 μM) for S- and R-Man, respectively, along with an enhanced sensitivity toward S-isomer (about 5.7-fold higher than R-isomer) were attained. High selectivity for the determination of mandelic acid was achieved compared to metal ions, amino acids, and sugars that commonly coexist with it. Intra-day as well as inter-day assays, respectively, showed RSD values of about 3.2 and 3.9%. The mechanistic studies were performed for proving the enantioselective behavior of the developed nanoprobe. The method was then used for S-/R-mandelic acid determination in bio-samples. The figures of merit for the method were found to be better than those already reported for enantioselective detection of R-/S-Man., Competing Interests: Declaration of competing interest The Authors declare that there are no known conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A sensitive and selective novel multinanozyme colorimetric method for glutathione (GSH) detection was developed. MnO 2 -nanozymes can catalyze the oxidation reaction of 3, 3՛-diaminobenzidine (DAB) and produce a brown indamine polymer. In the presence of GSH, this reaction slowly proceeds. When Au-nanozymes was used as peroxidase mimic along with MnO 2 -nanozymes, the analytical signal and selectivity (particularly, over Cys and AA) were significantly improved for GSH detection. Therefore, this novel multinanozyme system was further developed through optimization for the colorimetric detection of GSH. The calibration curve presented two wide linear range from 0.05 to 0.19 and 0.19-11.35 mg L ̶ 1 with a very low detection limit of 0.02 mg L ̶ 1 (5 nM) for GSH. The developed method was employed for human serum analysis without any dilution and any deproteinization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Modified micellar liquid chromatography (MLC) with a natural deep eutectic solvent (NADES), produced from choline chloride (ChCl) and ethylene glycol (EG), was employed for melamine (MEL) monitoring in milk matrix. This sustainable mobile phase was attained through chemometrical optimization of crucial variables including concentration of sodium dodecyl sulphate ([SDS]) along with volume percentages of both NADES and glacial acetic acid (GAC). The desirability function and central composite design were utilized as chemometrical tools. Retention time (t R - MEL ), and chromatographic peak width of MEL at 50% of its height (W 50% - MEL ) were considered for finding the best possible arrangement of the influential factors in the configuration of the mobile phase. Under the optimal experimental conditions of 0.10 mol L -1 SDS, 4% (v/v) NADES, and 4% (v/v) GAC, the results showed that both t R - MEL and W 50% - MEL drastically decreased when NADES was a part of the mobile phase composition. This indicated that ChCl-EG-based NADES had a significant impact on improving the chromatographic behaviour of an ionizable polar compound, MEL. At the optimal point, MEL was eluted in approximately 10 min without being interfered by coexisting proteins and endogenous species in milk. The practical performance of the mobile phase was established through direct injection of milk samples into the MLC system. The eligibility criteria of the United State-Food and Drug Administration (US-FDA) were considered for validation of the introduced methodology., (Copyright © 2019. Published by Elsevier B.V.)

A simple and informative quantitative structure-retention relationship (QSRR) model has been introduced for prediction of retention times in some anthraquinone derivatives using reversed-phase micellar liquid chromatography (MLC) technique. In the developed multiple linear regression model, the structural descriptors of analytes as well as the empirical parameters of organic modifiers in the applied MLC systems have been considered. Retention times of 77 chromatographic samples (16 anthraquinones were evaluated by using 6 different organic modifiers) were experimentally determined and utilized as the independent variables of the QSRR model. Five small-chain alcohols (methanol, ethanol, propanol, butanol, and pentanol) as well as acetonitrile were used as the eluent modifiers. A five-parametric model was attained for the logarithm of the retention time values which covered about 96 and 95% variance of the chromatographic data in training and cross-validation, respectively. The presence of an excellent correlation coefficient for external validation test (= 0.94) and a well-applicable domain proved the prediction ability of the constructed model. Both validity and reliability of the formulated model were examined through its application on diverse random-selected training and test sets. Moreover, quantum chemical calculations were performed in the framework of density functional theory to simulate the interactions between AQs and modifiers and gain mechanistic details about the retention behavior in the MLC system., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A sensitive and reliable ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) procedure was developed and validated for extraction and analysis of malondialdehyde (MDA) as an important lipids-peroxidation biomarker in human plasma. In this methodology, to achieve an applicable extraction procedure, the whole optimization processes were performed in human plasma. To convert MDA into readily extractable species, it was derivatized to hydrazone structure-base by 2,4-dinitrophenylhydrazine (DNPH) at 40 °C within 60 min. Influences of experimental variables on the extraction process including type and volume of extraction and disperser solvents, amount of derivatization agent, temperature, pH, ionic strength, sonication and centrifugation times were evaluated. Under the optimal experimental conditions, the enhancement factor and extraction recovery were 79.8 and 95.8%, respectively. The analytical signal linearly (R 2  = 0.9988) responded over a concentration range of 5.00-4000 ng mL -1 with a limit of detection of 0.75 ng mL -1 (S/N = 3) in the plasma sample. To validate the developed procedure, the recommend guidelines of Food and Drug Administration for bioanalytical analysis have been employed., (Copyright © 2018. Published by Elsevier B.V.)

Bilayer pseudo-stationary phase micellar liquid chromatography (MLC) was developed for simultaneous isocratic isolation of hydrochlorothiazide, as a basic-polar (hydrophilic) cardiovascular drug, as well as triamterene and losartan potassium, as acidic-nonpolar (hydrophobic) cardiovascular drugs. Utilizing a deep eutectic solvent (DES), as a novel green mobile phase additive in combination with acetonitrile (ACN) and acetic acid (ACA), drastically improved the chromatographic behavior of the drugs. Concentration of sodium dodecyl sulphate (SDS), as well as volume percentages of ACN, DES, and ACA were optimized by using a central composite design. The optimal composition of the mobile phase (0.12 mol L -1 SDS, 5% ACN, 4% DES, and 2% ACA) was chosen through the desirability function. The chromatographic peaks of both hydrophilic and hydrophobic drugs, respectively, emerged at high and low retention time values in the shortest total analysis time of 20 min (at a flow rate of 2 mL min -1 ). Analytical characterization of the developed approach was investigated through Food and Drug Administration (FDA) guidelines. Applicability of the method was evaluated by analysing of human plasma samples which were directly injected into the system., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A new, fast and inexpensive colorimetric sensor was developed for chiral recognition of tryptophan enantiomers using chitosan-capped silver nanoparticles. The function of the sensor was based on scanometry and spectrophotometry of the colored product of a reaction solution containing a mixture of chitosan-capped silver nanoparticles, phosphate buffer and tryptophan enantiomers. The image of the colored solution was taken using the scanometer and the corresponding color values were obtained using Photoshop software which subsequently were used for optimization of the experimental parameters as the analytical signal. Two types of color values system were investigated: RGB (red, green and blue values) and CMYK (cyan, magenta, yellow and black values). The color values indicated that L-tryptophan had better interaction than D-tryptophan with chitosan-capped silver nanoparticles. A linear relationship between the analytical signal and the concentration of L-tryptophan was obtained in the concentration range of 1.3 × 10 -5 -4.6 × 10 -4 molL -1 . Detection limits, were obtained to be 2.1 × 10 -6 , 2.4 × 10 -6 and 3.8 × 10 -6 molL -1 for L-tryptophan based on R (red), G (green) and B (blue) values, respectively., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Amino-functionalized magnetic nanoparticles (Fe 3 O 4 ) have been investigated as a support for covalent immobilization of lipase. The nanoparticles were prepared by chemical coprecipitation method and subsequently were coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. With glutaraldehyde, as the coupling agent, the lipase from Rhizopus oryzae was successfully immobilized onto the amino-functionalized magnetic nanoparticles. The synthesized support was characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The results showed that the load of immobilized protein could reach as high as 7mg protein g -1 support. The optimum pH for maximal catalytic activity of the immobilized enzyme was 8.0 at 40°C. The K m values were found as 0.66 and 0.57mgmL -1 for the free and immobilized enzymes, respectively. The V max values for the free and immobilized enzymes were calculated as 0.14 and 0.47μmolmg -1 min -1 , in turn, when p-nitrophenyl butyrate (pNPB) was used as the substrate. A quick separation of lipase from the reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 10 cycles while retaining 64% of its initial activity., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A simple, fast and green method for chiral recognition of S- and R-naproxen has been introduced. The method was based on quenching of the fluorescence intensity of bovine serum albumin-stabilized gold nanoclusters in the presence of naproxen enantiomers. The quenching intensity in the presence of S-naproxen was higher than R-naproxen when phosphate buffer solution at pH7.0 was used. The chiral recognition occurred due to steric effect between bovine serum albumin conformation and naproxen enantiomers. Two linear determination range were established as 7.4×10 -7 -9.1×10 -6 and 9.1×10 -6 -3.1×10 -5 molL -1 for both enantiomers and detection limits of 7.4×10 -8 molL -1 and 9.5×10 -8 molL -1 were obtained for S- and R-naproxen, respectively. The developed method showed good repeatability and reproducibility for the analysis of a synthetic sample. To make the procedure applicable to biological samples, the removal of heavy metals from the sample is suggested before any analytical attempt., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Gas-assisted dispersive liquid-phase microextraction (GA-DLPME) has been developed for preconcentration and spectrophotometric determination of copper ion in different water samples. The ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate and argon gas, respectively, were used as the extracting solvent and disperser. The procedure was based on direct reduction of Cu(II) to Cu(I) by hydroxylamine hydrochloride, followed by extracting Cu(I) into ionic liquid phase by using neocuproine as the chelating agent. Several experimental variables that affected the GA-DLPME efficiency were investigated and optimized. Under the optimum experimental conditions (IL volume, 50µL; pH, 6.0; acetate buffer, 1.5molL(-1); reducing agent concentration, 0.2molL(-1); NC concentration, 120µgmL(-1); Ar gas bubbling time, 6min; argon flow rate, 1Lmin(-1); NaCl concentration, 6% w/w; and centrifugation time, 3min), the calibration graph was linear over the concentration range of 0.30-2.00µgmL(-1) copper ion with a limit of detection of 0.07µgmL(-1). Relative standard deviation for five replicate determinations of 1.0µgmL(-1) copper ion was found to be 3.9%. The developed method was successfully applied to determination of both Cu(I) and Cu(II) species in water samples., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A rapid, simple and inexpensive spectrofluorimetric sensor for determination of doxycycline based on its interaction with thioglycolic acid-capped cadmium telluride quantum dots (TGA/CdTe QDs) has been developed. Under the optimum experimental conditions, the sensor exhibited a fast response time of <10s. The results revealed that doxycycline could quench the fluorescence of TGA/CdTe QDs via electron transfer from the QDs to doxycycline through a dynamic quenching mechanism. The sensor permitted determination of doxycycline in a concentration range of 1.9×10(-6)-6.1×10(-5)molL(-1) with a detection limit of 1.1×10(-7)molL(-1). The sensor was applied for determination of doxycycline in honey and human serum samples., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel, simple and highly sensitive colorimetric method is developed for determination of Amoxicillin (AMX). The system is based on aggregation of citrate-capped gold nanoparticles (AuNP) in acetate buffer (pH=4.5) in the presence of the degradation product of Amoxicillin (DPAMX). It was found that the color of gold nanoparticles changed from red to purple and the intensity of surface plasmon resonance (SPR) peak of AuNPs decreased. A new absorption band was appeared in the wavelength range of 600-700nm upon addition of DPAMX. The absorbance ratio at the wavelength of 660 and 525nm (A660/A525) was chosen as the analytical signal indirectly related to AMX concentration. The linearity of the calibration graph was found over the concentration range of 0.3-4.5μM AMX with a correlation coefficient of 0.9967. Under the optimum experimental conditions, the detection limit was found to be 0.15μM. The applicability of the method was successfully demonstrated by analysis of AMX in pharmaceutical formulations including capsules and oral suspensions., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The nanoparticles of Fe(3)O(4) as well as the binary nanoparticles of ionic liquid and Fe(3)O(4) (IL-Fe(3)O(4)) were synthesized for removal of reactive red 120 (RR-120) and 4-(2-pyridylazo) resorcinol (PAR) as model azo dyes from aqueous solutions. The mean size and the surface morphology of the nanoparticles were characterized by TEM, DLS, XRD, FTIR and TGA techniques. Adsorption of RR-120 and PAR was studied in a batch reactor at different experimental conditions such as nanoparticle dosage, dye concentration, pH of the solution, ionic strength, and contact time. Experimental results indicated that the IL-Fe(3)O(4) nanoparticles had removed more than 98% of both dyes under the optimum operational conditions of a dosage of 60mg, a pH of 2.5, and a contact time of 2min when initial dyes concentrations of 10-200mg L(-1) were used. The maximum adsorption capacity of IL-Fe(3)O(4) was 166.67 and 49.26mg g(-1) for RR-120 and PAR, respectively. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The Langmuir adsorption constants were 5.99 and 3.62L mg(-1) for adsorptions of RR-120 and PAR, respectively. Both adsorption processes were endothermic and dyes could be desorbed from IL-Fe(3)O(4) by using a mixed NaCl-acetone solution and adsorbent was reusable., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this article, the ability of a new and efficient hard-soft method, previously proposed by our research group, is reported for modeling of the complex formation equilibria in the presence of interferences. This method is based on the net analyte signal (NAS) concept, which is a part of total signal that is directly related to the concentration of the component of interest. It monitors the concentration changes of any chemical species involved in the evolutionary process without requiring any pure spectra or having previous knowledge about the presence of the interferences. The proposed hard-soft method based on net analyte signal (HS-NAS) only needs a chemical model for one of the species involved in the reaction under study. The reliability of the method was examined by applying it to the measured data and spectrum of the known real systems of Fe(2+)-azithromycin and Ca(2+)-tetracycline., (Copyright © 2010 Elsevier B.V. All rights reserved.)

In this paper, imidazolium-based ionic liquids [C(4)mim][PF(6)], [C(6)mim][PF(6)], [C(8)mim][PF(6)], [C(6)mim][BF(4)] and [C(8)mim][BF(4)] were tested as extracting solvents for removal of 3-indole butyric acid (IBA) from aqueous media with subsequent determination using HPLC. Percent extraction of IBA was strongly affected by pH of aqueous phases and the chemical structures of ionic liquids (ILs). Extraction of IBA was quantitative in the pH values lower than pK(a) of IBA. Considering both extraction and stripping efficiencies of IBA, [C(4)mim][PF(6)] was found to act more efficient than other studied ILs. Capacity of [C(4)mim][PF(6)] was 17.6x10(-4)mmol IBA per 1.0 mL of IL. Ionic strength of aqueous phase and temperature had shown no serious effects on extraction efficiency of IBA. A preconcentration factor of 100 and a relative standard deviation of 1.16% were obtained. It was found that ionic liquid phase was reusable almost five times for extraction/stripping purposes. 3-Indole acetic acid showed interferential effect in the extraction step. In order to assess the applicability of the method, extraction and stripping of IBA from pea plants and some other samples were studied.

In this work the catalytic role of unsupported gold nanoparticles on the luminol-hydrazine reaction is investigated. Gold nanoparticles catalyze the reaction of hydrazine and dissolved oxygen to generate hydrogen peroxide and also catalyze the oxidation of luminol by the produced hydrogen peroxide. The result is an intense chemiluminescence (CL) due to the excited 3-aminophthalate anion. In the absence of gold nanoparticles no detectable CL was observed by the reaction of luminol and hydrazine unless an external oxidant is present in the system. The size effect of gold nanoparticles on the CL intensity was investigated. The most intensive CL signals were obtained with 15-nm gold nanoparticles. UV-vis spectra and transmission electron microscopy studies were used to investigate the CL mechanism. The luminol and hydroxide ion concentration, gold nanoparticles size and flow rate were optimized. The proposed method was successfully applied to the determination of hydrazine in boiler feed water samples. Between 0.1 and 30 microM of hydrazine could be determined with a detection limit of 30 nM.

In situ mercury film electrode produced in the presence of thiocyanate has been shown extremely useful for highly sensitive adsorptive stripping voltammetric measurements of atrazine down to sub-microg L(-1) level. Operational parameters have been optimized and the stripping voltammetric performance has been investigated using square wave scans. The adsorptive stripping response is linear over the range of 0.5-60 microg L(-1) atrazine, with a detection limit of 0.024 microg L(-1). The method has been applied to the determination of atrazine in soil and water samples.

Artificial neural networks (ANNs) are among the most popular techniques for nonlinear multivariate calibration in complicated mixtures using spectrophotometric data. In this study we propose a computer-based method for removing Te(IV) interference in the determination of Se(IV) using artificial neural networks. In this way, an artificial neural network consisting of three layers of nodes was trained by applying a back-propagation learning rule. The resulting RMSE of prediction for selenium was obtained as 0.108.