Fernanda Midori de Oliveira

Hybrid molecularly imprinted poly(methacrylic acid-TRIM)-silica chemically modified with (3-glycidyloxypropyl)trimethoxysilane for the extraction of folic acid in aqueous medium

In the present study a hybrid molecularly imprinted poly(methacrylic acid-trimethylolpropane trimethacrylate)-silica (MIP) was synthesized and modified with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) with posterior opening of epoxy ring to provide hydrophilic properties of material in the extraction of folic acid from aqueous medium. The chemical and structural aggregates of hybrid material were characterized by means of Fourier Transform Infrared (FT-IR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Thermogravimetric analysis (TGA) and textural data. Selectivity data of MIP were compared to non-imprinted polymer (NIP) through competitive sorption studies in the presence of caffeine, paracetamol or 4-aminobenzamide yielding relative selectivity coefficients (k′) higher than one unit, thus confirming the selective character of MIP even in the presence of structurally smaller compounds than the folic acid. The lower hydrophobic sorption by bovine serum albumin (BSA) in the MIP as compared to unmodified MIP proves the hydrophilicity of polymer surface by using GPTMS with opening ring. Under acid medium(pH 1.5) the sorption of folic acid onto MIP from batch experiments was higher than the one achieved for NIP. Equilibrium sorption of folic acid was reached at 120 min for MIP, NIP and MIP without GPTMS and kinetic sorption data were well described by pseudo-second-order, Elovich and intraparticle diffusion models. Thus, these results indicate the existence of different binding energy sites in the polymers and a complex mechanism consisting of both surface sorption and intraparticle transport of folic acid within the pores of polymers.

Surfactant effect on electrochemical-induced synthesis of α-Ni(OH)2

Nickel hydroxide films were electrosynthesized in the presence of different diluted surfactant solutions by galvanostatic electroprecipitation. Lamellar α-Ni(OH)2 films are obtained using cationic surfactant cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS), and also neutral surfactant Tween® 80. The films were structurally and morphologically characterized by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy, and electrochemically by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The results evidenced that SDS remains intercalated between the lamellae of α-Ni(OH)2. Albeit the presence of CTAB and Tween® 80, it was noticed in FTIR spectra that the surfactants did not intercalate. The morphology was affected by the presence of different surfactants. All studied surfactants displaced the oxidation potential (EO) of Ni2+/Ni3+ process to less positive values. Also, the presence of surfactants improved the electrode charge efficiency and the charge response for the same number of moles of nickel ions deposited. The ratio of the charge and frequency change is 4.4 times bigger for films deposited with SDS when compared with pure α-Ni(OH)2 films.

Preparation of a new restricted access molecularly imprinted hybrid adsorbent for the extraction of folic acid from milk powder samples

A new hybrid molecularly imprinted polymer (MIP) combined with restricted access (RAM) has been synthesized based on random free-radical polymerization and a sol–gel process. From competitive adsorption studies by using the RAM-MIP and RAM-NIP with folic acid and structurally similar molecules (caffeine, 4-aminobenzamide or paracetamol), relative selectivity coefficients (k) higher than one unit were achieved, indicating good recognition selectivity for folic acid. The percentage of BSA protein exclusion was higher for the RAM-MIP (55.3 ± 2.0) as compared to the MIP (35.9 ± 2.5%). The solid phase extraction (SPE) procedure was performed by loading the acid extract from milk powder samples previously submitted to saponification and acidification with 10% trichloroacetic acid (TCA) until pH 1.5, through 100 mg of RAM-MIP packed into SPE cartridge. The elution step was carried out by using a mixture of acetonitrile : 0.266 mol L−1 acetate buffer at pH 5.7 (15 : 85, v/v), the same composition of the mobile phase of HPLC. The intra-day precision (n = 10) of the procedure assessed as relative standard deviation (RSD) was 4.7 and 4.1% for the respective concentrations of 20.0 and 150.0 μg L−1. The applicability of the method was attested by analysis of different brands of milk powder samples fortified with folic acid, as well as by high recovery percentages 95.0–108.4% obtained upon addition and recovery tests. The cleanup process accomplished by RAM-MIP was so efficient that very few remaining matrix components were detected in the eluate by high performance liquid chromatography.

Evaluation of poly(vinylpyridine)-supported protoporphyrin resin for the sampling/separation of manganese(II) using a hyphenated FIA-FAAS system

The present study describes the development of a preconcentration method for manganese determination by FAAS using poly(protoporphyrin-co-vinylpyridine) as a sorbent. To synthesize this material, 4-vinylpyridine and protoporphyrin were copolymerized in the presence of ethylene glycol dimethacrylate as a cross-linker and 2,2-azobisisobutyronitrile as an initiator. The factors affecting the flow injection preconcentration system were optimized by employing 25 fractional factorial and Doehlert matrix designs. The proposed on-line preconcentration method was performed by percolating 18.0 mL aliquots of Mn(II) solutions (pH 8.3) at a flow rate of 6.0 mL min−1 through a mini-column, packed with 100 mg of poly(protoporphyrin-co-vinylpyridine); the Mn(II) ions were then on-line eluted with 1.5 mol L−1 HNO3 into the FAAS nebulizer. Under these conditions, it was possible to yield a linear curve in the concentration range of 0.0–120.0 μg L−1, with a correlation coefficient of 0.997. Besides, the following system parameters were obtained: sampling frequency of 15 h−1, preconcentration factor of 53, consumptive index of 0.34 mL, concentration efficiency of 17.6 min−1, detection limit of 0.34 μg L−1, and quantification limit of 1.13 μg L−1. The method precision (repeatability) estimated for ten measurements of 1.0 and 50.0 μg L−1 Mn(II) standard solutions was found to be 5.2 and 4.9%, respectively. Moreover, the protoporphyrin incorporation into the poly(vinylpyridine) network caused a remarkable 323% increase in the methods sensitivity. Finally, the proposed procedure was not affected by potentially interfering ions. Thus, it was successfully applied to the Mn(II) determination in water, food and sediment samples.

Preconcentration of Nickel(II) by a Mini-Flow System with a Novel Ternary Oxide Solid Phase and Flame Atomic Absorption Spectrometry

ABSTRACT A SiO2/Al2O3/Sb2O5 mixed oxide was synthesized via a sol-gel method and applied to the on-line preconcentration of Ni(II) with determination by flame atomic absorption spectrometry. The mixed oxide was characterized by infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray fluorescence, thermogravimetric analysis, and the specific surface area. Analysis was performed by percolating 20.0 mL of sample at pH 7.1 through 100 mg of SiO2/Al2O3/Sb2O5 packed into a mini-column at 9.5 mL min−1. Under the optimum conditions, a preconcentration factor of 77.5-fold, linear dynamic range from 5.0 to 270.0 µg L−1, and limits of detection and quantification of 0.48 and 1.61 µg L−1 were obtained. The effects of several concomitant ions were evaluated and no interferences were observed. The method was employed for the analysis of water with good recoveries (92.9–100.6%) and the accuracy was verified by using a marine sediment certified reference material (MESS-3).

Solid Phase Extraction to On-Line Preconcentrate Trace Cadmium Using Chemically Modified Nano-Carbon Black with 3-Mercaptopropyltrimethoxysilane

Carbon black (CB) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was used as solid phase extractor for Cd2+ in a flow injection system coupled to flame atomic absorption spectrometry (FAAS). The influence of pH, buffer concentration, preconcentration flow rate and eluent concentration on preconcentration of Cd2+ were investigated by means of chemometric tools. The characterization of the adsorbent chemically modified was performed by Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Raman spectroscopy and textural analysis. To perform the on-line preconcentration, 20.0 mL of a pH 7.0 Cd2+ solution at a flow rate of 4.0 mL min−1 was loaded through 30.0 mg of modified CB and then eluted with 1.0 mol L−1 HCl toward the FAAS instrument. The limits of detection and quantification were found to be 0.20 and 0.66 µg L−1, respectively. Addition and recovery tests carried out in real samples (mineral, tap and saline waters, and cigarette sample) and the analysis of certified reference material (TORT-2, lobster hepatopancreas reference) attested the applicability of proposed method.

Application of Ni(II)-imprinted cross-linked poly(methacrylic acid) synthesised through double-imprinting method for the on-line preconcentration of Ni(II) ions in aqueous media

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L−1 HNO3 at a flow rate of 7.0 mL min−1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L−1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min−1, and sample throughput – 25 h−1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L−1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L−1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions.

Evaluation of Histidine Functionalized Multiwalled Carbon Nanotubes for Improvement in the Sensitivity of Cadmium Ions Determination in Flow Analysis

The determination of heavy metal ions in environmental, clinical and food samples has been a common concern for several researchers and in special case of aquatic environment, there has been a more stringent regulation standards pertaining to the discharge of heavy metals. Some efforts have been carried out to develop many treatment processes to reduce the disposal of heavy metal ions mainly in water bodies. The different treatment processes include precipitation, membrane filtration, ion exchange and adsorption (Tokalioglu et al. 2009), however, the levels of heavy metals disposal into water bodies are still rising, mainly in aqueous effluents discharged into aquatic bodies (Mello et al. 2005). As example, lead is considered as the major environmental pollutant and has become the most widely scattered toxic heavy metal in the world as a result of anthropogenic action. It is very well known that lead enters the environment through several industrial activities, such as industrial ammunition, paper board mill, battery manufacturing and coal burning and pigments (Zhan & Zhao, 2003). Lead can cause several effects on central nervous system, blood pressure, kidneys and reproductive system (Needleman, 2004). Similarly to lead, cadmium is also considered as toxic for animals and humans, and it is classified by the International Agency for Research on Cancer as a human carcinogen (IARC, 1993). The National Council for the Environment in Brazil (CONAMA, 2005) established 0.2 mg L-1 as the maximum level of cadmium for effluent discharge in aquatic bodies, while 5.0 and 3.0 μg L-1 are the maximum contaminant levels in potable water allowed by EPA(EPA, 2003) and ANVISA (ANVISA, 2004), respectively. Even at low concentration levels (≤ g L-1), there is bioaccumulation of heavy metals in aquatic organisms, so there is a growing need for their monitoring in different types of water samples. In addition, the heavy metal ions monitoring can provide both important aspects in water quality and controlling the industrial processes (Martinotti et al. 1995). Thus, the development of analytical methods based on preconcentration systems has commonly been the aim of choice for the determination of trace metals in water and

EXTRAÇÃO/PRÉ-CONCENTRAÇÃO DE ÍONS COBRE NO PONTO NUVEM EXPLORANDO A FORMAÇÃO DE COMPLEXOS COM DMIT (4,5-DIMERCAPTO-1,3-DITIOL-2-TIONATO)

The present study proposes a method for cloud point preconcentration of copper ions at pH 2.0 based on complexes formed with [4,5-dimercapto-1,3-dithyol-2-thionate] and subsequent determination by flame atomic absorption spectrometry (FAAS). Under optimal analytical conditions, the method provided limits of detection of 0.84 and 0.45 µg L-1, by preconcentrating 12.0 and 24.0 mL of sample, respectively. The method was applied for copper determination in water samples, synthetic saliva, guarana powder, tea samples and soft drinks and the accuracy was assessed by analyzing the certified reference materials Dogfish Liver (DOLT-4) and Lobster Hepatopancreas (TORT-2).

Development of HPLC Method for Quantification of Orphenadrine, Paracetamol, and Caffeine in Pharmaceutical Formulations

A method for the determination of orphenadrine (ORPH), paracetamol (PAR) and caffeine (CAF) using HPLC was developed. The proposed method provides an easy sample preparation and low cost using a mobile phase consisting of 80% of water with direct determination of the active principles present in pharmaceutical formulations. The separation of ORPH, PAR and CAF was accomplished on a C18 colu at 5 ̊C at a flo ate of . L i -1 using acetonitrile/water (pH 2.5) as mobile phase (20:80, v/v). The method exhibits linear responses for ORPH, PAR and CAF in the concentration ranges of 0 – 150 mg L, 0 – 200 mg L and 0 – 200 mg L, respectively. The detection limits and quantification determined according to IUPAC recommendation were found to be 1.14 and 3.79 mg L -1 for ORPH, 0.05 and 0.17 mg L -1 for PAR and 0.02 and 0.07 mg L -1 for CAF. Recoveries varying from 98.02 up to 101.81% for two pharmaceutical formulations spiked with these analytes were achieved assuring the accuracy of the proposed method.