R. Salghi

Selective extraction and determination of catecholamines in urine samples by using a dopamine magnetic molecularly imprinted polymer and capillary electrophoresis

A rapid and selective method for the extraction and determination of catecholamines (CLs) from urine samples has been successfully developed using a magnetic molecularly imprinted polymer (MMIP) as a sorbent material. The MMIP has been prepared using dopamine hydrochloride (DA) as template molecule, methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EDMA) as cross-linking agent and Fe(3)O(4) magnetite as magnetic component. The extraction was carried out by stirring urine samples with the magnetic polymer. When the extraction was completed, the MMIP, together with the captured analytes, was easily separated from the sample matrix by an adscititious magnet. The analytes desorbed from the MMIP were determined by capillary electrophoresis (CE). It was shown that the MMIP had high affinity and selectivity toward DA and other structurally related CLs such as 3-methoxytyramine hydrochloride (MT), DL-normetanephrine hydrochloride (NME), DL-norephinephrine hydrochloride (NE) and (±) epinephrine (E). Different parameters affecting the extraction efficiency were evaluated in order to achieve the optimal pre-concentration of the analytes and to reduce non-specific interactions. Under the optimal conditions, the CL limits of detection were at the 0.04-0.06 μM range. The relative standard deviations of migration time and response ranged from 0.7% to 1.4% and from 2.9% to 5.5%, respectively. The proposed method was successfully applied to determine CLs, including MT, NME, DA, NE and E in human urine samples.

Triazolic compounds as corrosion inhibitors for copper in hydrochloric acid

Purpose – To correlate the inhibitory effect of triazole compounds on the corrosion of copper in HCl at various temperatures by semi‐empirical molecular orbital theory.Design/methodology/approach – Two triazoles were selected as the best inhibitors among the triazole compounds tested. Gravimetric and electrochemical measurements were conducted.Findings – Correlation between inhibition efficiency and calculation of molecular orbital of triazole compounds was obtained. Cu(I)‐triazole complex formation was confirmed by UV spectroscopy.Research limitations/implications – The calculation of energetic levels of molecular orbital may be a tool to explain the classification of inhibitor efficiency.Practical implications – The theoretical calculation is a complementary mean to selecting an efficient inhibitor among a given series. Good agreement between the experimental methods explored and theoretical calculations was observed.Originality/value – The originality of this work was the finding of the correlation bet...

A study of tetrazoles derivatives as corrosion inhibitors of copper in nitric acid

Purpose – To evaluate the effect of some tetrazole compounds as corrosion inhibitors of copper in HNO3 at various temperatures.Design/methodology/approach – 1‐phenyl‐5‐mercapto‐1,2,3,4‐tetrazole (PMT) was selected as the best inhibitor among the tetrazole compounds tested. Gravimetric and electrochemical techniques were conducted.Findings – PMT was an excellent inhibitor for copper in acid. Its efficiency attained 97.5 per cent and decreased slightly with temperature.Research limitations/implications – The inhibition efficiency increased with the concentration of PMT to reach 97.5 per cent at 10−3 M. Good agreement between the various methods explored was observed. Polarisation measurements also showed that PMT acted as a mixed inhibitor.Practical implications – The efficiency of PMT increased with the concentration but decreased with rise of temperature in the 298‐333 K range. As such, PMT could be used in chemical cleaning and pickling processes.Originality/value – The originality of this work was the f...

Detection of argan oil adulteration with vegetable oils by high-performance liquid chromatography-evaporative light scattering detection.

Triacylglycerol profiles were selected as indicator of adulteration of argan oils to carry out a rapid screening of samples for the evaluation of authenticity. Triacylglycerols were separated by high-performance liquid chromatography-evaporative light scattering detection. Different peak area ratios were defined to sensitively detect adulteration of argan oil with vegetable oils such as sunflower, soy bean, and olive oil up to the level of 5%. Based on four reference argan oils, mean limits of detection and quantitation were calculated to approximately 0.4% and 1.3%, respectively. Additionally, 19 more argan oil reference samples were analysed by high-performance liquid chromatography-refractive index detection, resulting in highly comparative results. The overall strategy demonstrated a good applicability in practise, and hence a high potential to be transferred to routine laboratories.

Corrosion inhibition of steel in sulfuric acidic solution by the Chenopodium Ambrosioides Extracts

Abstract The influence of natural occurring extract of Chenopodium Ambrosioides (CAE) on the corrosion inhibition of carbon steel in sulfuric acid solution is studied by the weight loss method, potentiodynamic polarization and impedance spectroscopy (EIS) measurements. The experimental results reveal that extract has a good inhibiting effect on the metal tested in 0.5 M H2SO4 solution. The protection efficiency increases with increasing inhibitor concentration to attain 94% at 4 g/l. Potentiodynamic polarization studies clearly reveal that it acts essentially as a cathodic inhibitor. EIS results show that the change in the impedance parameters (Rt and Cdl) with concentration of extract of Chenopodium Ambrosioides is indicative of the adsorption of molecules leading to the formation of a protective layer on the surface of carbon steel. The efficiency decreases with temperature. The adsorption of Chenopodium Ambrosioides extract is found to obey the Langmuir adsorption isotherm. The activation energies and enthalpies of the corrosion process of carbon steel in acidic medium were determined.

A novel approach to size separation of gold nanoparticles by capillary electrophoresis–evaporative light scattering detection

A simple and rapid methodology to separate and characterize gold nanoparticles (AuNPs) in aqueous medium by capillary electrophoresis–evaporative light scattering detection (CE–ELSD) is presented. First, a controlled synthesis procedure to obtain water-soluble AuNPs, by varying the trisodium citrate concentration was described. These free AuNPs were separated by capillary zone electrophoresis (CZE) based on the differences in the charge-to-mass ratio of the AuNPs–citrate in a mixed buffer of ammonium acetate (20 mM), containing tris(hydroxymethyl)-aminomethane (Tris, 20 mM) and 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS; 10 mM) at pH 8.5. Under optimal working conditions, three small different-sized AuNPs were successfully separated whose average sizes were 3.5, 6.5 and 10.5 nm. The average diameter was lower than 1.2 nm for all of them (calculated by high-resolution transmission electron microscopy, TEM). Thus, this CE-based method was able to separate AuNPs that differ by only 3 nm in diameter. It can be a valuable methodology for the rapid and cost-effective characterization of other nanomaterials in the future in aqueous solutions.

Inhibition de la corrosion du cuivre en milieu HCl 0,5 M par les composes organiques de type triazole

Abstract Some triazole-type organic compounds were tested as corrosion inhibitors for copper in 0.5 M HCl solution at 20°C. Electrochemical (potentiodynamic polarization and polarization resistance measurements) and gravimetric methods were used for this study. The obtained results showed that 3-amino-1,2,4 triazole (ATA) and 3,5 diamino-1,2,4 triazole (DTA) effectively reduce the corrosion rate of copper. The inhibition efficiency (E%) of these compounds increases with their concentrations and attains maximum values at 10−3M and 10−4 for ATA and DTA, respectively. The variation of efficiency with logC shows that these inhibitors are adsorbed on the metallic surface according to the Frumkin adsorption isotherm model.

Supercritical fluid extraction as an on-line clean-up technique for rapid amperometric screening and alternative liquid chromatography for confirmation of paraquat and diquat in olive oil samples

A rapid and simple method for the direct screening of paraquat (PQ) and diquat (DQ) in olive oil samples is proposed. The sample screening method involves supercritical fluid extraction (SFE) (clean-up followed by the extraction of the analytes) followed by continuous flow electrochemical detection. Those samples for which the total concentration is close to or above the threshold limit established by the Columbian Society for Social Protection (0.05 microg g(-1)) are subsequently analyzed by liquid chromatography (LC) with diode array detection (DAD). This confirmation method allows the determination of PQ and DQ in the range between 0.04 and 1.0 microg g(-1), with average relative standard deviations lower than 3.5%, and 0.003 and 0.002 microg g(-1) detection limits for PQ and DQ, respectively. The proposed arrangement opens up interesting prospects for the direct determination of polar pesticides in complex samples with a good throughput and a high level of automation.

Étude électrochimique de l'inhibition de la corrosion de l'alliage d'aluminium 3003 en milieu bicarbonate par les composés triazolique

Abstract Some triazole — type organic compounds have been tested as corrosion inhibitors for aluminium 3003 alloy in 0.1 M HCO3− + 0.1 M Cl− by electrochemical polarization methods. All tests were conducted at pH = 8 and 12. The obtained results showed that 3,5-diamino-1,2,4-triazole (DTA) was the best inhibitor. The inhibition efficiency (E%) of the DTA was higher at pH 8 than at pH = 12. DTA was probably adsorbed on the aluminium surface according to a Langmuir isotherm for both pH values. The effect of the temperature indicated that inhibition by DTA decreases with increasing temperature.

Inhibition of carbon steel corrosion in 1 M HCl medium by potassium thiocyanate

Abstract The effect of potassium thiocyanate (KSCN) on the corrosion of carbon steel (C-steel) in 1 M HCl has been investigated in relation to the concentration of the inhibitor by polarization curves, electrochemical impedance spectroscopy and weight loss measurement. The results obtained revealed that this compound is a good mixed type inhibitor with predominant cathodic effectiveness. The effect of temperature on the corrosion behavior with the addition of optimal concentration of KSCN was studied in the temperature range 298–328 K. The value of inhibition efficiency decreases slightly with the increase in temperature. Changes in impedance parameters (charge transfer resistance, Rct, and double layer capacitance, Cdl) were indicative of adsorption of KSCN on the metal surface, leading to the formation of a protective film. Adsorption of KSCN on the C-steel surface was found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined and discussed.