Preparation of Molecularly Imprinted Magnetic Graphene Oxide-Gold Nanocomposite and Its Application to the Design of Electrochemical Sensor for Determination of Epinephrine.

In this study, a new molecularly imprinted polymer (MIP) based nanocomposite was synthesized then used to determine epinephrine (EPN) by the use of an electrochemical sensor modified by it. Typical techniques for the synthesis of MIP have disadvantages, such as weak binding sites, low mass transfer and low selectivity. One of the ways to improve electrochemical properties is the use of graphene oxide (GR-Ox) and modification of its surface. For this purpose, GR-Ox was initially magnetized (MGR-Ox), then its surface was coated with a silica layer, and gold nanoparticles (AuNPs) were coated on its surface. Subsequently, copolymerization of methacrylic acid (MAA) and N,N'-methylene-bis-acrylamide (MBA) in the presence of EPN was performed on the MGO-AuNPs surface. Afterwards, a selective carbon paste electrode (CPE) with synthetic nanocomposite was fabricated to detect EPN. Under optimal conditions, a linear range from 10-8 to 5.0 × 10-7 M was obtained for the measurement of EPN in urine and blood with a detection limit of 5 × 10-9 M (S/N = 3).

Potassium permanganate-glutaraldehyde chemiluminescence system catalyzed by gold nanoprisms toward selective determination of fluoride.

Gold and silver nanoparticles (NPs) are shown to exert a positive effect on the chemiluminescence (CL) reaction of permanganate aldehydes. Interestingly, between various shapes examined, Au nanoprisms have the highest beneficial effect. This effect is even more notable in the presence of sodium dodecyl sulfate (SDS) surfactant. UV-vis spectra and transmission electron microscopy were used to characterize the NP shapes and sizes. Furthermore, it was observed that iron(III) ions can slightly increase CL emission of this system. This intensification is very effective in the presence of fluoride ions (F(-)). These observations form the basis of the method for the high sensitive determination of F(-) in the 6-1200 nmol L(-1) concentration range, with a detection limit of 2.1 nmol L(-1). The proposed method has good precision and was satisfactorily used in the selective determination of low concentrations of fluoride ion in real samples.

Determination of Hg(II) ions in sea food samples after extraction and preconcentration by novel Fe3O 4@SiO 2@polythiophene magnetic nanocomposite.

This work describes a novel Fe3O4@SiO2@polythiophene magnetic nanocomposite and its application in the preconcentration of Hg(II) ions. The parameters affecting the preconcentration procedure were opted by a Box-Behnken design through response surface methodology. Three factors (uptake time, magnetic nanosorbent amount, and pH of sample) were selected as the main factors affecting the sorption step, while four variables (type, volume and concentration of the eluent as well as the elution time) were selected as main factors in the optimization study of the elution step. Following the sorption and elution of Hg(II), it was quantified by cold vapor atomic absorption spectrometry. Under the optimum condition, the limit of detection was 0.02 ng mL(-1) and all the relative standard deviations were less than 9.2 %. The obtained sorption capacity of this new sorbent was 59 mg g(-1). Finally, this nanocomposite was successfully applied to the rapid extraction of trace quantities of Hg(II) ions in sea food samples and satisfactory results were obtained.

Highly Sensitive Determination of Ethylenediaminetetraacetic Acid Using a Permanganate Chemiluminescence System Catalyzed by Gold Nanoparticles.

A sensitive and selective chemiluminescence method was developed to determine ethylenediaminetetraacetic acid (EDTA) in water samples. It was observed that gold nanoparticles (AuNPs) catalyzed chemiluminescence (CL) reactions of permanganate-aldehydes which underwent an enhancement effect in the presence of iron(III) ions (Fe(3+)). This effect is more remarkable in the presence of EDTA, and a highly intensive CL emission is created in proportion to the EDTA concentration. These observations form the basis of the method for the high sensitive determination of EDTA in the 0.83 - 167 nmol L(-1) concentration range, with a detection limit of 0.25 nmol L(-1). The relative standard deviations for five repeated measurements of 5, 40 and 140 nmol L(-1) EDTA were 1.14, 2.48 and 0.65%, respectively. The method has good selectivity toward EDTA, and there are no interferences from other ions. The offered method has good precision, and was satisfactorily used for the sensitive determination of EDTA in water samples.

Determination of mercury(II) ions in seafood samples after extraction and preconcentration by a novel functionalized magnetic metal-organic framework nanocomposite.

This work describes a novel functionalized magnetic metal-organic framework nanocomposite [(Fe3O4-2,5-dimercapto-1,3,4-thiadiazole)/metal-organic framework] and its application in the preconcentration of Hg(II) ions. The parameters affecting the preconcentration procedure were optimized by a Box-Behnken design through response surface methodology. Three variables (uptake time, magnetic nanosorbent amount, and pH value) were selected as the main factors affecting the sorption step, while four variables (type, volume, and concentration of the eluent; and elution time) were selected as main factors in the optimization study of the elution step. Following the sorption and elution of analytes, the ions were quantified by cold vapor atomic absorption spectrometry. Under the optimum conditions, the limit of detection was 0.01 ng/mL and all the relative standard deviations were less than 10%. The obtained sorption capacity (in mg/g) of this new sorbent was 124. Ultimately, this nanocomposite was successfully applied to the rapid extraction of trace quantities of Hg(II) ions in seafood samples and satisfactory results were obtained.

Determination of heavy metal ions in vegetable samples using a magnetic metal-organic framework nanocomposite sorbent.

This paper describes the synthesis and application of a novel magnetic metal-organic framework (MOF) [(Fe3O4-benzoyl isothiocyanate)/Cu3(benzene-1,3,5-tricarboxylate)2] to pre-concentrate trace amounts of Cd(II), Pb(II), Zn(II) and Cr(III) ions and their determination by flame atomic absorption spectrometry. A Box-Behnken design was used to find the parameters affecting the pre-concentration procedure through response surface methodology. Three factors including uptake time, amount of the magnetic sorbent and pH of the sample were selected as affecting factors in the sorption step, and four factors including type, volume and concentration of the eluent as well as the elution time were selected in the elution step for the optimisation study. The opted values were 30 mg, 10.1 min, 5.9, EDTA, 4.0 ml, 0.57 mol l(-1) EDTA solution and 13.0 min for the amount of the magnetic sorbent, uptake time, pH of the sample, type, volume, concentration of the eluent, and elution time, respectively. The limits of detection (LODs) were 0.12, 0.7, 0.16, and 0.4 ng ml(-1) for Cd(II), Pb(II), Zn(II) and Cr(III) ions, respectively. The relative standard deviations (RSDs) of the method were less than 7.2% for five separate batch experiments for the determination of 30 µg l(-1) of Cd(II), Pb(II), Zn(II) and Cr(III) ions. The sorption capacity of the [(Fe3O4-benzoyl isothiocyanate)/MOF] was 175 mg g(-1) for Cd(II), 168 mg g(-1) for Pb(II), 210 mg g(-1) for Zn(II) and 196 mg g(-1) for Cr(III). It was found that the magnetic MOF nanocomposite demonstrated a higher capacity compared with Fe3O4-benzoyl isothiocyanate. Finally, the magnetic MOF nanocomposite was successfully applied to the rapid extraction of trace amounts of the heavy metal ions from vegetable samples.

Simultaneous spectrophotometric determination of benzoic acid, sorbic acid, and ascorbic acid using a net analyte signal-based method.

The net analyte preprocessing/classical least-squares (NAP/CLS) method is a simple chemometric method that has been used for the simultaneous spectrophotometric determination of benzoic acid, sorbic acid, and ascorbic acid. The obtained results indicated that the performances of the NAP/CLS and partial least-squares methods were almost identical. The net analyte signal (NAS) concept was also used to calculate multivariate analytical figures of merit, such as LOD, selectivity, and sensitivity. Wavelength selection was applied based on the concept of NAS regression, and improved the method performance in samples containing nonmodeled interferences. The method afforded recoveries in the range of 98-105%. The proposed method was successfully applied to determination of the analytes in an Iranian soft drink.

Simultaneous spectrofluorimetric and spectrophotometric determination of melatonin and pyridoxine in pharmaceutical preparations by multivariate calibration methods.

Partial least-squares (PLS) calibration and principal component regression (PCR) methods were utilized for the simultaneous spectrofluorimetric and spectrophotometric determination of pyridoxine (PY) and melatonin (MT). Since emission and adsorption spectra of these drugs overlap, PY and MT cannot be directly determined by fluorimetric nor by spectrophotometric methods. Full-spectrum multivariate calibration PLS and PCR methods were developed for both fluorimetry and spectrophotometry. The conditions were optimized for fluorimetric as well as for spectrophotometric determination of both drugs. The simultaneous determination of PY and MT was carried out in mixtures by recording the emission fluorescence spectrum between 324 and 500 nm (lambda(ex) 285 nm) for fluorimetry, and by recording the absorption spectrum between 250 and 350 nm for spectrophotometry (lambda(max(PY)) 310 nm, lambda(max(MT)) 278 nm). The experimental calibration matrixes were designed orthogonally. At the optimum conditions, dynamic ranges were 0.04-1.3 and 0.1-4 microg ml(-1) for fluorimetry and 1-22 and 1-24 microg ml(-1) for spectrophotometry for MT and PY, respectively. The calibration concentrations were prepared in the dynamic ranges. The parameters of the chemometrics procedure for the simultaneous determination of MT and PY were optimized, and the proposed methods were validated with prediction set. Finally the procedures were successfully applied to simultaneous spectrofluorimetric and spectrophotometric determination of PY and MT in synthetic mixtures and in a pharmaceutical formulation.