Solid-Phase Microextraction of Phthalate Esters from Aqueous Media by Functionalized Carbon Nanotubes (Graphene Oxide Nanoribbons) and Determination by GC–FID

Multiwalled carbon nanotubes were exposed to hydrothermal treatment for obtaining graphene oxide nanoribbons (GONRs). The fabricated graphene oxide nanoribbons have been morphologically and compositionally characterized via FE-SEM, XRD, and FT-IR techniques. The as-synthesized GONRs have been used as sorbent phase for headspace solid-phase microextraction of phthalate esters (PEs) from aqueous solutions. In this regard, the GC–FID analysis route has been used for quantification of PEs. The new SPME fiber shows remarkable analytical figures of merit including broad dynamic linear ranges, low limits of detection, as well as good stability and reasonable relative standard deviations for evaluation of PEs. The linearity of the method for analysis of PEs including DnBP, DnPP, DEHP, DEHA, BBP, and DMP was between the range of 0.05–100, 0.05–100, 0.1–100, 0.1–100, 0.2–100, and 0.5–100 μg L^?1, respectively. The limits of detection (based on S/N?=?3) and correlation coefficients were found to be in the range of 0.02–0.2 μg L^?1 and 0.9907–0.9952, correspondingly. The prepared GONR-coated SPME fiber shows larger extraction yield in comparison to pristine MWNTs and commercial PDMS SPME fibers. Furthermore, real sample analysis showed that there is no significant matrix effect for evaluation of PEs from environmental water samples and proposed method could be used for evaluation and determination of PEs from aqueous samples in a precise and accurate manner. The existence of functional groups, π–π interactions, as well as hydrogen bonding between adsorbent phase and PE analytes could be the reason for observing such a high extraction yield.

     

Spectrophotometric and thermodynamic study on the dimerization equilibrium of ionic dyes in water by chemometrics method

The monomer-dimer equilibrium and thermodynamic of several ionic dyes (Neutral Red, Nile Blue A, Safranine T and Thionine) has been investigated by means of spectrophotometric and chemometrics methods. The dimerization constants of these ionic dyes have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-75 degrees C at concentrations of Neutral Red (1.73 x 10(-5) M), Nile Blue A (3.94 x 10(-5) M), Safranine (6.59 x 10(-5) M) and Thionine (6.60 x 10(-5) M). The monomer-dimer equilibrium of these dyes has been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed. The processing of the data carried out for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants to the temperature (van't Hoff equation).     

Spectrophotometric determination of acidity constants of alizarine red S in water, water-Brij-35 and water-SDS micellar media solutions

The acidity constants of Alizarine Red S in water, water-Brij-35 and water-SDS micellar media solutions at 25 degrees C and an ionic strength of 0.1 M have been determined spectrophotometrically. To evaluate the pH-absorbance data, a resolution method based on the combination of soft- and hard-modeling is applied. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. DATAN program applied for determination of acidity constants. Results show that the pKa values of Alizarine Red S are influenced as the percentages of a neutral and an anionic surfactant such as Brij-35 and SDS, respectively, added to the solution of this reagent. Effect of surfactant on acidity constants and pure spectrum of each component are also discussed.     

Multiwavelength spectrophotometric determination of acidity constants of 1-（2-thiazolylazo）-2-naphthol in methanol-water mixtures

The acid-base properties of 1-(2-thiazolylazo)-2-naphthol (TAN) in mixtures of methanol-water at 25℃and an ionic strength of 0.1 mol/L are studied by a multi-wavelength spectrophotometric method.The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model DATAN program was used for determination of acidity constants.The corresponding pK_a values in methanol-water mixtures were determined.There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures.     

Simultaneous spectrophotometric determination of nitroaniline isomers after cloud point extraction by using least-squares support vector machines

Cloud point extraction has been used for the preconcentration of m-nitroaniline, o-nitroaniline and p-nitroaniline and later simultaneous spectrophotometric determination using polyethylene glycol tert-octylphenyl ether (Triton X-100) as surfactant. The resolution of a ternary mixture of the nitroaniline isomers (after extraction by cloud point) by the application of least-squares support vector machines (LS-SVM) was performed. The chemical parameters affecting the separation phase and detection process were studied and optimized. Under the optimum experimental conditions (i.e. pH 7.0, Triton X-100=0.6%, equilibrium time 20 min and cloud point 75 degrees C), calibration graphs were linear in the range of 0.2-20.0, 0.1-15.0 and 0.1-17.0 microg ml(-1) with detection limits of 0.08, 0.05 and 0.06 microg ml(-1) for m-nitroaniline, o-nitroaniline and p-nitroaniline, respectively. The experimental calibration matrix was designed with 21 mixtures of these chemicals. The concentrations were varied between calibration graphs concentrations of nitroaniline isomers. The root mean square error of prediction (RMSEP) for m-nitroaniline, o-nitroaniline and p-nitroaniline were 0.0146, 0.0308 and 0.0304, respectively. This procedure allows the simultaneous determination of nitroaniline isomers in synthetic and real matrix samples good reliability of the determination was proved.     

Determination of trace amounts of morphine in human plasma by anodic adsorptive stripping differential pulse voltammetry

New adsorptive anodic differential pulse stripping voltammetry method for the direct determination of morphine at trace levels in human plasma of addicts is proposed.The procedure involves an adsorptive accumulation of morphine on a HMDE,followed by oxidation of adsorbed morphine by voltammetry scan using differential pulse modulation.The optimum conditions for the analysis of morphine are pH 10.5,Eacc of -100 mV（vs.Ag/AgCl）,and tacc of 120 s.The peak current is proportional to the concentration of morphine,and a Linear calibration graph is obtained at 0.01-3.10μg mL^-1.A relative standard deviation of 1.06%（n=5）was obtained,and the limit of detection was 3 ng mL^-1.The capabiLity of the method for the analysis of real samples was evaluated by the determination of morphine in spiked human plasma and addicts human plasma with satisfactory results.     

Simultaneous spectrophotometric determination of cobalt,copper and nickel using 1-（2-thiazolylazo）-2-naphthol by chemometrics methods

The simultaneous determination of cobalt, copper and nickel using 1-（2-thiazolylazo）-2-naphthol （first figure of this article） by spectrophotometric method is a difficult problem in analytical chemistry, due to spectral interferences. By multivariate calibration methods, such as partial least squares （PLS） regression, it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction （OSC） is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 550-750-nm range for 21 different mixtures of cobalt, copper and nickel. Calibration matrices were formed from samples containing 0.05-1.05, 0.05-1.30 and 0.05-0.80 μg·mL^-1 for cobalt, copper and nickel, respectively. The root mean square error of prediction （RMSEP） for cobalt, copper and nickel with OSC and without OSC were 0.007, 0.008, 0.011 and 0.031,0.037, 0.032 μg· mL^-1, respectively. This procedure allows the simultaneous determination of cobalt, copper and nickel in synthetic and real samples and good reliability of the determination was proved.     

Determination of Riboflavin in Human Plasma by Excitation‐Emission Matrix Fluorescence and Multi‐Way Analysis

Direct determination of riboflavin (Fig. 1), a vitamin, in human plasma was accomplished based on excitation‐emission matrix (EEM) fluorescence measurements and multi‐way chemometrics method based on parallel factor analysis (PARAFAC). The PARAFAC trilinear model, without restrictions and using one factor was used in the data analysis. The excitation wavelength range was from 380 to 460 nm and the emission was recorded from 480 to 600 nm. The calibration set was constructed with sixteen standard solutions in a concentration range of 0.02–0.38 μg mL^?1 for riboflavin. The capabilities of the method for the analysis were evaluated by determination of riboflavin in synthetic and real samples with satisfactory results. The accuracy of the methods, evaluated through the root mean square error of prediction (RMSEP), was 0.0059 for riboflavin by the PARAFAC model. Also, partial least squares (PLS) model was built at one excitation wavelength and used to determine a set of synthetic and real samples. The best model was obtained with PARAFAC. This result shows that molecular fluorescence spectroscopy can be used for the development of robust analytical methods for the direct determination of riboflavin in complex backgrounds such as human plasma.