Ma. Elena Páez-Hernández

Determination of quinolones in milk samples using a combination of magnetic solid-phase extraction and capillary electrophoresis

A magnetic solid‐phase extraction (MSPE) method combined with capillary electrophoresis for the simultaneous determination of seven quinolones (QNs) (danofloxacin, ciprofloxacin, marbofloxacin, enrofloxacin, difloxacin, oxolinic acid, and flumequine), using (S)‐(+)‐6‐methoxy‐α‐methyl‐2‐naphthaleneacetic acid as internal standard, in milk samples was developed. The variables involved in the preconcentration magnetic procedure were: the composition of the magnetic support composition, the sample pH, and the weight of magnetic adsorbent used. The variables were optimized using a simplex‐lattice design. Different magnetite covered with octyl‐phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and octyltrimethoxysilane; the solids were evaluated for QN preconcentration. Under optimal conditions, a linear range was obtained from 27 to 1000 μg L−1 with limits of detection ranging from 9 to 12 μg L−1 for the seven QNs. The absolute recoveries of the seven QNs at three different spiked levels (40, 150, and 400 μg L−1) ranged from 74% to 98% with a relative standard deviation less than 10% in all cases. The proposed method was applied to analyze 20 whole milk samples of different brands. All samples were positive for the presence of QN residues; in some cases, extract dilution was required. The concentrations found are in the range from 31.1 to 5047.3 μg L−1. Marbofloxacin was the most frequently found. The method proposed offers advantages in terms of simplicity, sensitivity, efficiency, cost, and analysis time making it an alternative for the analysis of QNs in whole milk samples.

Determination of oxytetracycline in milk samples by polymer inclusion membrane separation coupled to high performance liquid chromatography

The determination of oxytetracycline in milk samples using a polymer inclusion membrane concept with high performance liquid chromatography (HPLC) was studied. The membranes developed are composed by cellulose acetate as polymer base, Cyanex 923 as carrier and o-nitrophenyl octyl ether as plasticizer. In the optimal conditions, the method exhibits good linearity in the range 0.03-0.20 mg L(-1) with a limit of detection and quantification of 8.2 and 27.3 μg L(-1) respectively. The method was successfully applied to the analysis of milk samples with high selectivity.

Application of an Activated Carbon-Based Support for Magnetic Solid Phase Extraction Followed by Spectrophotometric Determination of Tartrazine in Commercial Beverages

A method is presented for magnetic solid phase extraction of tartrazine from nonalcoholic beverages. The method involves the extraction and clean-up by activated carbon covered with magnetite dispersed in the sample, followed by the magnetic isolation and desorption of the analyte by basified methanol. The tartrazine eluted from the magnetic support was determined by spectrophotometry. Under optimal conditions, the linear range of the calibration curve ranges from 3 to 30 mg L−1, with a limit of detection of 1 mg L−1. The method was validated by comparing the results with those obtained by HPLC. A precision of <5.0% was obtained in all cases and no significant differences were observed (P < 0.05).

Purification of Anthocyanins with o-Dihydroxy Arrangement by Sorption in Cationic Resins Charged with Fe(III)

In the present work, a new purification method of anthocyanins with o-dihydroxy arrangement is proposed. This method is based on a ligand-exchange mechanism, using a cationic exchange resin loaded with metallic ions in order to increase the affinity of the resin to the anthocyanin(s) with o-dihydroxy arrangement. This method was used to purify the main anthocyanin (cyanidin-3-glucoside; Cy-3-glc) from the anthocyanic methanolic extract of blue corn. The best sorption result was using Fe(III) in its ion form. The purification procedure begins with the formation of a metal-anthocyanin complex (Cy-3-glc-Fe) which was optimal at pH 5, followed by a NaOH 0.1 M elution process in order to eliminate anthocyanins without o-dihydroxy arrangement, sugars, and organic acids. Finally, the pure anthocyanin is obtained by adding HCl 0.1 M which breaks the metal-anthocyanin complex.

Evaluacion del contenido de metales y su efecto en la estabilidad de antocianinas Metal content evaluation and its effect on the stability of anthocyanins

Anthocyanins are natural pigments interesting in the area of food due to the large color range they exhibit and their beneficial effects on health as a result of their antioxidant properties. Their use in food is limited by the low stability of the compounds contained in the antioxidant extracts.  Stabilization by metal complexation is one of the most important mechanisms for anthocyanin stability. In this work, the main metals contained in blue creole corn are quantified by inductively coupled plasma atomic emission spectroscopy followed by the evaluation of the stability constant of the selected ion metals with the main anthocyanidin (cyanidin); finally the effect of metal ion addition on the color stability is presented. The results obtained demonstrate that the main found metals are capable of complexing and stabilizing the cyanidin according to stability constants estimated by capillary electrophoresis (log β1 = 5.3, 5.0, 5.5 and 4.0 for Ca (II), Cu (II), Fe (II) and Fe (III), respectively).

Selective Liquid-Liquid Extraction of Mercury(II) from Aqueous Solution by N-Alkyldithiophosphate Compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4)

The extraction of mercury(II) from nitric acid solutions by the dithiophosphate compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4) has been examined. The best extracting properties were displayed by the liquid compound containing the longest alkyl chain CH3(CH2)4S2P(OC6H4)2 (Pen-DTP) in acidic media. The results indicate the stability of Pen-DTPA in nitric and sulphuric media. Pen-DTP selectively extracted Hg(II) in the presence of some interfering ions such as Cd(II), Pb(II) and Bi(III). The Hg(II) recovery from back-extraction experiments with chloridric acid is higher than 70%. Mostly, this extractant shows a remarkable selectivity in the extraction of mercury (76.6%) in the presence of Ag(I) (9.2%) without using a masking agent.

Size exclusion chromatography (SEC-HPLC) as an alternative to study thrombin inhibition

In vitro analysis of anticoagulant compounds with a potential use as antithrombotic drugs, has been traditionally performed using techniques like spectrophotometry, turbidimetry, as well as electrochemical and clinical assays. Although, these techniques have some disadvantages such as: the inability to measure the total biological activity of thrombin, interferences and, sometimes, the quantitative determination of the inhibition ratio is not accurate. In the present work, the conversion of fibrinogen to fibrin was monitored by molecular exclusion chromatography (SEC-HPLC) in three different reaction systems. An inhibition percentage of 43.19±2.02% was obtained using heparin as an anticoagulant, in addition to the determination of the percentage of heparin bonded to thrombin. This methodology has not been previously described and has high potential for the determination of anticoagulant capacity with higher precision, the determination of thrombins total biological activity and the quantitative determination of the inhibition ratio.

Development of Cellulose Acetate Microcapsules with Cyanex 923 for Phenol Removal from Aqueous Media

Microcapsules of cellulose acetate with Cyanex 923 were prepared and used in this study for phenol removal from water and synthetic textile wastewater. The influence of several factors on the microcapsules extraction efficiency was studied, as well as characterization and phenol adsorption isotherm. Microcapsules characterization demonstrated the extractant reagent encapsulation, while in a batch mode procedure, good adsorption of phenol (ca. 5.5 × 10−3 mol Kg−1) has been reached. A slight decrease in phenol extraction percentage was obtained when synthetic textile wastewater was used (ca. 4.955 × 10−3 mol Kg−1), although a decrease in color was observed due to dye microcapsule extraction. Results indicate that this method is a promising alternative to conventional phenol removal technologies for aqueous samples of low phenol concentrations or in textile effluents.

Evaluation of activated composite membranes for the facilitated transport of phenol

Abstract In this work the results on the first use of an activated composite membrane (ACM) containing Cyanex 923 for the extraction and transport of phenol are presented. A new dense layer-ACM configuration constituted by piperazine showed better stability than that prepared with 1,3-phenylenediamine. The effects of several parameters on the transport of phenol such as feed phase pH, carrier concentration and stripping phase composition were evaluated. The performance of the membrane was also evaluated during continuous additions of phenol and for a long period of time, observing the same rate of extraction and reextraction. Moreover, phenol transport was evaluated starting from synthetic wastewater of resin production plants type. The results exhibit the potential use of ACMs in the elimination and transport of organic species, even when analyte is initially found in complex solutions.

Earliest Results in the Use of Activated Composite Membranes for the Transport of Silver Ions from Aqueous Solutions

This paper presents the results concerning the first use of activated composite membranes (ACMs) for the facilitated transport of silver ions containing di-(2-ethylhexyl)-dithiophosphoric acid (DTPA) as the carrier. DTPA was immobilized by interfacial polymerization in a dense layer that was deposited in a porous layer, which was prepared on a nonwoven fabric support by phase inversion. The influence of fundamental parameters affecting the transport of silver ion as the carrier concentration in the membrane phase and stripping agent variation of the stripping solution have been studied. In the optimal conditions, the amount of silver transported across the ACMs was greater than 50%, whereas if the content of the carrier is modified, more than the 90% of the initial silver is removed from the feed phase.