Search for: calibration-curves
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    A horizontally oriented setup for liquid-liquid-liquid microextraction of estrogens

    , Article Analytical Methods ; Volume 5, Issue 22 , 2013 , Pages 6517-6522 ; 17599660 (ISSN) Bagheri, H ; Maleki, H ; Es'Haghi, A ; Sharif University of Technology
    A horizontally oriented liquid-liquid-liquid microextraction (HOLLLME) setup was developed and applied for the isolation of two major estrogens from aquatic media. In contrast to the conventional procedure, in this setup the extracting microdrop was suspended from a horizontally positioned needle in order to provide much higher stability to the extracting phase. The developed HOLLLME approach was applied to isolate two major selected estrogens from aquatic media followed by high performance liquid chromatography-ultraviolet (HPLC-UV) determination. Estrogens were, initially, extracted from water samples into hexane and subsequently, the back extraction stage was performed with 6 μL of sodium... 

    Sensor performance of nanostructured TiO2 thin films derived from particulate sol-gel route and polymeric fugitive agents

    , Article Sensors and Actuators, B: Chemical ; Volume 124, Issue 1 , 2007 , Pages 74-83 ; 09254005 (ISSN) Mohammadi, M. R ; Fray, D. J ; Cordero Cabrera, M. C ; Sharif University of Technology
    High specific surface area (SSA) nanocrystalline powders and dip-coated TiO2 thin films have been prepared by a particulate sol-gel route with added polymeric fugitive agents (PFAs), namely trehalose dihydrate (THD), polyethylene glycol (PEG6000) and hydroxypropyl cellulose (HPC). One of the highest SSA reported in the literature, obtained without PFA, was achieved (i.e., 181 m2/g), a value that could be increased up to 304 m2/g, 274 m2/g and 200 m2/g for PEG/TiO2, HPC/TiO2 and THD/TiO2 powders, respectively. Furthermore, the crystallite size varied from 1 nm for as-produced powders up to 4 nm for powders heat-treated at 600 °C. Thin films produced under optimised conditions showed excellent... 

    Design and Construction of a Densitometer Tool and Simulation of its Performance by the Mcnp Code and Comparison of the Obtained Data with Experimental Results

    , M.Sc. Thesis Sharif University of Technology Shabani, Ali (Author) ; Sohrabpour, Mostafa (Supervisor)
    In this Thesis, a nuclear borehole logging tool has been designed and constructed for measuring the bulk density of a formation by the use of gamma rays. One of the main applications of this tool is obtaining of porosity. It also is useful in the detection of formations containing oil and gas. This tool consists of: a gamma ray source 60Co, a single gamma ray detector NaI(Tl), lead shield and electronic modules. The cylindrical sond is entered into a borehole and the surrounding formation is subjected to the emitted gamma rays from the source. The formation density can be determined from the measurement of the scattered photons reaching the detector from the formation. The purpose of the... 

    Design and Construction of a Density Prob with Experimental Measurments

    , M.Sc. Thesis Sharif University of Technology Rafizade, Abolfazl (Author) ; Sohrabpour, Mostafa (Supervisor)
    In this project a dual density logging tool has been designed and constructed for measuring the bulk density of a formation using gamma rays. One of the main applications of this tool is obtaining porosity. It also is useful in the detection of formations containing oil and gas. In this work, MCNP Monte Carlo code was used to simulate the performance of the scattered gamma rays under various sond-formation parametric condition. The results coming from this code are applied to determine the fundamental parameters of gamma-gamma density tools like, Energy window, thickness of lead, optimum distance between each detectors. Furthermore, a novel method based on summation of back scatter and... 

    A sensitive and selective colorimetric method for detection of copper ions based on anti-aggregation of unmodified gold nanoparticles

    , Article Talanta ; Vol. 129, issue , 2014 , pp. 227-232 ; ISSN: 00399140 Hormozi-Nezhad, M. R ; Abbasi-Moayed, S ; Sharif University of Technology
    A highly sensitive and selective colorimetric method for detection of copper ions, based on anti-aggregation of D-penicillamine (D-PC) induced aggregated gold nanoparticles (AuNPs) was developed. Copper ions can hinder the aggregation of AuNPs induced by D-PC, through formation of mixed-valence complex with D-PC that is a selective copper chelator. In the presence of a fixed amount of D-PC, the aggregation of AuNPs decreases with increasing concentrations of Cu2+ along with a color change from blue to red in AuNPs solution and an increase in the absorption ratio (A520/A 650). Under the optimum experimental conditions (pH 7, [AuNPs] =3.0 nmol L-1 and [NaCl]=25 mmol L-1), a linear calibration... 

    Voltammetric monitoring of Cd (II) by nano-TiO2 modified carbon paste electrode sensitized using 1,2-bis-[o-aminophenyl thio] ethane as a new ion receptor

    , Article Sensors and Actuators, B: Chemical ; Vol. 192 , 2014 , pp. 648-657 ; ISSN: 09254005 Ramezani, S ; Ghobadi, M ; Bideh, B. N ; Sharif University of Technology
    The objective of the work ahead is presentation of a new carbon paste electrode (CPE) modified by TiO2 nanoparticles (TiO2NPs) and 1,2-bis-[o-aminophenyl thio] ethane (APTE) ligand as a selective cation receptor for determination of the Cd (II) ions using differential pulse anodic stripping voltammetry (DPASV). The electrode shows an excellent tendency to Cd (II) ions in presence of some interfering species. Under the optimum conditions, a linear calibration curve was obtained in the concentration range of 2.9 nM to 4.6 μM with a correlation coefficient of 0.9969 in the anodic potential of 0.54 (V vs. Ag/AgCl). The metal detection limit was 2.0 nM after 10 min preconcentration (S/N = 3). The... 

    Colorimetric detection of glutathione based on transverse overgrowth of high aspect ratio gold nanorods investigated by MCR-ALS

    , Article RSC Advances ; Volume 5, Issue 101 , 2015 , Pages 82906-82915 ; 20462069 (ISSN) Fahimi Kashani, N ; Shadabipour, P ; Hormozi-Nezhad, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2015
    In this paper, we present a simple platform for colorimetric detection of glutathione using gold nanorods (AR ∼ 6.5 ± 0.2) as a plasmonic sensor. The functional mechanism of the sensor is based on shifts of longitudinal plasmon resonance during selective transverse overgrowth induced by preferential binding of glutathione at the nanorod tips. Under the optimum conditions, a calibration curve showed two linear regimes at the range of 50 nM to 20 μM of glutathione with a detection limit as low as 40 nM. The nanosensor maintains relatively high selectivity for determination of glutathione in the presence of several other amino acids. However, cysteine at similar concentration levels strongly... 

    An ultrasensitive and selective turn-off fluorescent nanoprobe for the detection of copper ions

    , Article Analytical Methods ; Volume 7, Issue 12 , 2015 , Pages 5067-5073 ; 17599660 (ISSN) Hormozi Nezhad, M. R ; Taghipour, M ; Sharif University of Technology
    Royal Society of Chemistry  2015
    In this study, a novel approach for sensitive and extremely selective detection of copper ions has been developed based on fluorescence resonance energy transfer (FRET) between AuNPs as an acceptor and fluorescein isothiocyanate (FITC) as a donor. Initially, the fluorescence of the FITC molecule turns-off due to adsorption to the AuNPs surface. However, the fluorescence of the FITC-AuNPs system was switched to turn-on by adding d-Pencillamine (d-PC) to the solution mixtures as FITC molecules are released upon displacement by d-PC on the NPs surface. The higher affinity of d-PC toward the surface of AuNPs was further evidenced by controlling the fluorescence intensity enhancement of the... 

    MoS2 quantum-dots as a label-free fluorescent nanoprobe for the highly selective detection of methyl parathion pesticide

    , Article Analytical Methods ; Volume 9, Issue 4 , 2017 , Pages 716-723 ; 17599660 (ISSN) Fahimi Kashani, N ; Rashti, A ; Hormozi Nezhad, M. R ; Mahdavi, V ; Sharif University of Technology
    Royal Society of Chemistry  2017
    A reliable, simple, and sensitive fluorescence method was developed for the determination of methyl parathion (MP) in rice using MoS2 quantum dots (QDs). Rapid hydrolysis of MP under alkaline conditions, and thus the formation of p-nitrophenol (p-NP) can be used for MP detection. The functional mechanism of the nanoprobe relies on p-nitrophenol-induced photoluminescence quenching of MoS2 QDs. The high probability of resonance energy transfer (RET) stems from the spectral overlap of MoS2 QD emission spectra and the absorption spectra of p-NP. The high value of the Stern-Volmer constant (KSV = 3.73 × 104 M-1) suggests the efficient quenching of MoS2 QDs by MP in the course of the ET process.... 

    Development of multi-response optimization and quadratic calibration curve for determination of ten pesticides in complex sample matrices using QuEChERS dispersive liquid–liquid microextraction followed by gas chromatography

    , Article Journal of Separation Science ; Volume 42, Issue 23 , 2019 , Pages 3553-3562 ; 16159306 (ISSN) Balsini, P ; Parastar, H ; Sharif University of Technology
    Wiley-VCH Verlag  2019
    In this study, QuEChERS combined with dispersive liquid-liquid microextraction is developed for extraction of ten pesticides in complex sample matrices of water and milk. In this regard, effective factors of proposed extraction technique combined with gas chromatography with flame ionization detector were designed, modeled, and optimized using central composite design, multiple linear regression, and Nelder–Mead simplex optimization. Later, univariate calibration model for ten pesticides was developed in concentration range of 0.5–100 ng/mL. Surprisingly, quadratic calibration behavior was observed for some of the pesticides. In this regard, Mandel's test was used for evaluating linearity... 

    Using three different optical fiber designs to study humidity effect on the air refractive index

    , Article Optics and Lasers in Engineering ; Volume 50, Issue 11 , November , 2012 , Pages 1495-1500 ; 01438166 (ISSN) Golnabi, H ; Sharif University of Technology
    Design and operation of three different optical designs based on the light intensity modulation for investigation of the humidity effects on the air index of refraction are described. The measurement variable is the transmitted power, which depends on the refractive index of the medium in the path of a fiber-to-fiber optical design. Three different probes (probe #1, #2, and #3) are tested in which probe #1 and probe #2 can also check the presence of water or any other transparent liquid in the gap between the two axial fibers. Performances of the new systems are tested as a refractive index monitoring mean and experimental results are given. The variations of the modulated powers as... 

    Spectrophotometric determination of glutathione and cysteine based on aggregation of colloidal gold nanoparticles

    , Article Scientia Iranica ; Volume 19, Issue 3 , June , 2012 , Pages 958-963 ; 10263098 (ISSN) Hormozi Nezhad, M. R ; Seyedhosseini, E ; Robatjazi, H ; Sharif University of Technology
    We report herein the development of a highly sensitive colorimetric method for the determination of cysteine and glutathione, based on aggregation of the citrate capped gold nanoparticles (Au NPs). This was exploited from high affinity of low-molecular-weight aminothiols towards the Au NPs surface, which could induce displacement of the citrate shell by the thiolate shell of target molecules, resulting in aggregation of the NPs through intermolecular electrostatic interaction or hydrogen-bonding. As a result of aggregation, which can be affected by the ionic strength, pH and concentration of Au NPs, the plasmon band at around 521 nm decreases gradually, along with formation of a new red... 

    Investigation of humidity effect on the air refractive index using an optical fiber design

    , Article Journal of Applied Sciences ; Volume 11, Issue 16 , 2011 , Pages 3022-3027 ; 18125654 (ISSN) Mehrabani, A ; Golnabi, H ; Sharif University of Technology
    In this study operation of an optical design based on the intensity modulation for the refractive index change has been described. The reported instrument measures the transmitted output power depending up on the medium refractive index in the light path of a fiber-to-fiber design. A liquid cell is located between the fibers in the light path and power variations for different cold and hot water levels in the cell are measured. By using a reference humidity meter the calibration curve representing the relative humidity (%RH) as a function of the transmitted output power is obtained. For the hot water with the final temperature of T = 32.7°C the output power range of 255.0 -313.OnW is... 

    Simultaneously synthesis and encapsulation of metallic nanoparticles using linear-dendritic block copolymers of poly (ethylene glycol)-poly (citric acid)

    , Article Key Engineering Materials, 8 July 2010 through 9 July 2010 ; Volume 478 , July , 2011 , Pages 7-12 ; 10139826 (ISSN) ; 9783037851357 (ISBN) Naeini, A. T ; Vossoughi, M ; Adeli, M ; Sharif University of Technology
    Linear-dendritic triblock copolymers of linear poly(ethylene glycol) and hyperbranched poly(citric acid) (PCA-PEG-PCA) were used as the reducing and capping agents to encapsulate gold and silver nanoparticles (AuNPs and AgNPs). PCA-PEG-PCA copolymers in four different molecular weights were synthesized using 2, 5, 10 and 20 citric acid/PEG molar ratios and were called A 1, A 2, A 3 and A 4, respectively. Nanoparticles were encapsulated simultaneously during the preparation process. AuNPs were simply synthesized and encapsulated by addition a boiling aqueous solution of HAuCl 4 to aqueous solutions of A 1, A 2, A 3 and A 4. In the case of silver, an aqueous solution of AgNO 3 was reduced... 

    A sensitive colorimetric detection of ascorbic acid in pharmaceutical products based on formation of anisotropic silver nanoparticles

    , Article Scientia Iranica ; Volume 17, Issue 2 F , 2010 , Pages 148-153 ; 10263098 (ISSN) Hormozi Nezhad, M. R ; Karimi, M. A ; Shahheydari, F ; Sharif University of Technology
    A sensitive colorimetric method for the detection of ascorbic acid was proposed in this research based on the reduction of silver ions by ascorbic acid in the presence of citrate-stabilized silver seeds, additional trisodium citrate and a polymer such as polyvinylpyrrolidone. The color of the stable sol is controlled by varying the concentration of trisodium citrate (TSC), polyvinylpyrrolidone, silver nitrate and silver seeds. The reduction of Ag + to triangle silver nanoparticles (Ag-NPs) by ascorbic acid in the presence of trisodium citrate (TSC) and silver seeds produced two very intense surface plasmon resonance peaks of Ag-NPs. The plasmon absorbance of Ag-NPs allows the quantitative... 

    Silver nanoparticles modified carbon nanotube paste electrode for simultaneous determination of dopamine and ascorbic acid

    , Article Journal of Electroanalytical Chemistry ; Volume 633, Issue 1 , 2009 , Pages 85-91 ; 15726657 (ISSN) Tashkhourian, J ; Hormozi Nezhad, M. R ; Khodavesi, J ; Javadi, S ; Sharif University of Technology
    Elsevier  2009
    A novel modified carbon-paste electrode was employed for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) with good selectivity and high sensitivity. Silver nanoparticle and carbon nanotube modified carbon-paste electrode (Ag/CNT-CPE) displayed excellent electrochemical catalytic activities towards dopamine (DA) and ascorbic acid (AA). The oxidation overpotentials of DA and AA were decreased significantly compared with those obtained at the bare CPE. Differential pulse voltammetry was used for the simultaneous determination of DA and AA. The peak separation between DA and AA was 67 mV. The calibration curves for DA and AA were obtained in the range of 8.0 × 10-7-6.4 ×... 

    Experimental investigation of factors affecting miscible two-phase flow in fractured and non-fractured micromodels

    , Article Proceedings of the 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, 23 June 2008 through 25 June 2008, Darmstadt ; Issue PART B , 2008 , Pages 1027-1034 ; 0791848345 (ISBN); 9780791848340 (ISBN) Farzaneh, A ; Kharrat, R ; Ghazanfari, M. H ; ASME ; Sharif University of Technology
    Micromodel is small-scale artificial model of porous medium which is known as a novel approach for simulating flow and transport in porous media. For better understanding the effect of fracture geometrical properties on oil recovery efficiency, a series of first contact miscible solvent injection process were conducted on horizontal glass micromodels at several fixed flow rate conditions. The micromodels were initially saturated with the heavy crude oil. The produced oil as a function of injected volume of solvents was measured using image analysis of the provided pictures. The concentration calibration curves of solvents in heavy crude oil were used for evaluating the solvents... 

    Electrochemical determinations of 6-mercaptopurine on the surface of a carbon nanotube-paste electrode modified with a cobalt salophen complex

    , Article Journal of Solid State Electrochemistry ; Volume 16, Issue 4 , April , 2012 , Pages 1643-1650 ; 14328488 (ISSN) Shahrokhian, S ; Ghorbani Bidkorbeh, F ; Mohammadi, A ; Dinarvand, R ; Sharif University of Technology
    A mixture of multi-walled carbon nanotube/graphite paste electrode modified with a salophen complex of cobalt was prepared and was applied for the study of the electrochemical behavior of 6-mercaptopurine (MP) using cyclic and differential pulse voltammetry (DPV). An excellent electrocatalytic activity toward the oxidation of MP was achieved, which led to a considerable lowering in the anodic overpotential and remarkable increase in the response sensitivity in comparison with unmodified electrode. Utilizing DPV method, a linear dynamic range of 1-100 μM with detection limit of 0.1 μM was obtained in phosphate buffer of pH 3.0. The electrochemical detection system was very stable, and the... 

    Resolution and quantification of complex mixtures of polycyclic aromatic hydrocarbons in heavy fuel oil sample by means of GC × GC-TOFMS combined to multivariate curve resolution

    , Article Analytical Chemistry ; Volume 83, Issue 24 , 2011 , Pages 9289-9297 ; 00032700 (ISSN) Parastar, H ; Radović, J. R ; Jalali-Heravi, M ; Diez, S ; Bayona, J. M ; Tauler, R ; Sharif University of Technology
    Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) combined to multivariate curve resolution-alternating least-squares (MCR-ALS) is proposed for the resolution and quantification of very complex mixtures of compounds such as polycyclic aromatic hydrocarbons (PAHs) in heavy fuel oil (HFO). Different GC × GC-TOFMS data slices acquired during the analysis of HFO samples and PAH standards were simultaneously analyzed using the MCR-ALS method to resolve the pure component elution profiles in the two chromatographic dimensions as well as their pure mass spectra. Outstandingly, retention time shifts within and between GC × GC runs were not affecting... 

    Experimental investigation of constant and concentration-dependent diffusivity of a hydrocarbon solvents-heavy oil system: A comparative study

    , Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects ; Volume 34, Issue 3 , 2011 , Pages 235-245 ; 15567036 (ISSN) Nasirahmadi, E ; Kharrat, R ; Ghazanfari, M. H ; Rashtchian, D ; Sharif University of Technology
    This work is concerned with the experimental investigation of mass transfer, which occurs during diffusion of hydrocarbon solvents in heavy oil based on constant and concentration-dependent diffusion coefficient. Here, a series of free fall diffusion experiments have been conducted in sealed test tubes at fixed temperatures. Pentane, hexane, and octane were used as solvents and were placed on heavy oil in tubes. The diffusivity of heavy oil into solvents was monitored by a digital camera. The image analysis technique was applied to extract concentration profiles in diffusion zones of solvents by means of calibration curves. Fick's second law was used to obtain both constant and...