Carlos Andrés Galán-Vidal

Simultaneous determination of tetracyclines in poultry muscle by capillary zone electrophoresis

A capillary zone electrophoresis method with UV detection was developed for the simultaneous detection and quantification of three tetracyclines in chicken meat samples: tetracycline (TC), oxytetracycline (OTC) and doxycycline (DOC). The separation conditions were: a running buffer containing 30 mM sodium phosphate, 2mM EDTA disodium salt and 2.5% 2-propanol, pH 12.0, a 5s hydrodynamic injection and a 14kV separation voltage. Two different clean-up methodologies were employed: solid-phase extraction with C(18) cartridges and ion exchange with Amberlite XAD7 resin. Analytes were detected at 360 nm in less than 12 min. LODs ranged from 61 microg kg(-1) for OTC to 68 microg kg(-1) for DOC with C(18) cartridges, and 81 microg kg(-1) for DOC to 89 microg kg(-1) for TC with Amberlite XAD7 resin. The recoveries for TC, OTC and DOC obtained by both methods were between 85 and 95%, and the peak area repeatability for all of the samples was below 5% in all cases. Twenty-four samples of commercial chicken drumsticks were examined with both clean-up methodologies. In nine cases (37.5%) TC was detected, in a range from 197.8 to 2564.3 microg kg(-1), and in seven cases (29.2%) OTC was detected in a range from 83.0 to 2049.3 microg kg(-1). DOC was not detected in any of the tested samples. This method would be useful for the routine monitoring of TCs residues in poultry muscle.

Nucleation and Growth Kinetics of Electrodeposited Sulfate-Doped Polypyrrole: Determination of the Diffusion Coefficient of SO42― in the Polymeric Membrane

A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO(4)(2-) ions is presented. Ppy films were electrochemically polymerized onto a graphite-epoxy resin electrode. Experimental current density transients (j-t) were obtained for three different potentiometric behaviors: anionic, cationic, and a combination. Theoretical models were used to fit the experimental j-t data to determine the nucleation and growth processes controlling the polymer synthesis. It was encountered that, in all cases, pyrrole electropolimerization involves two concomitant processes, namely, a Ppy diffusion limited multiple 3D nucleation and growth and pyrrole electro-oxidation on the growing surface of the Ppy nuclei. SEM analysis of the electrodes surfaces reveals that Ppy deposition occurred over most of the electrode surface by multiple nucleation of hemispheres, as the theoretical model used for the analysis of the current transients required. Hemispherical particles formed the polymeric film displaying different sizes. The order for the particle size was as follows: anionic > anionic-cationic > cationic. These results are congruent with those obtained by theoretical analysis of the corresponding current transients. Analysis of the impedance measurements recorded on the anionic Ppy film, immersed in an aqueous solution with different sulfate ion concentrations evidenced that SO(4)(2-) ions diffuse through the Ppy film provoking a decrease of its electrical resistance and an increase of its dielectric constant. From the Warburg impedance coefficient, the sulfate coefficient of diffusion in the Ppy film was 1.38 x 10(-9) cm(2) s(-1).

Effect of evaporation on C7 light hydrocarbon parameters

Abstract Light hydrocarbons are commonly used to evaluate crude oils to determine oil families, in-reservoir alteration processes such as evaporative fractionation, water washing, incipient biodegradation, maturity, and temperatures at which oil is expelled from source rocks. Light hydrocarbons in the C7 range will evaporate under ambient conditions, and losses can occur during sample collection, handling, or storage. However, the impact of partial evaporation on interpretation of light hydrocarbon data has not been reported previously. Laboratory evaporation experiments show that the rate of evaporation of each C7 hydrocarbon is different, and these differential rates will affect the measured concentrations of these compounds, certain ratios, and other calculations or plots using these data. The paraffinicity/aromaticity ratio of Thompson [Marine Pet. Geol. 5 (1988) 237], parameters utilized in the transformation and correlation star diagrams of Halpern [AAPG Bull. 79 (1995) 801], and the oil typing ternary plot of Jarvie [The Mountain Geologist 38 (2001) 19] are affected by evaporation. Other interpretive schemes such as P2 versus N2/P3 and the invariant ratio [Science 273 (1987) 514; Geochim. Cosmoschim. Acta 54 (1990) 1315] are not grossly affected by partial evaporation because these parameters are primarily controlled by the concentration of methylhexanes or by offsetting rates of evaporation in certain compounds. By careful evaluation of these parameters and various interpretive plots, the extent of evaporation can be qualitatively assessed and discrimination of oil types, alteration effects, and evaporative artifacts can still be reasonably ascertained. This study demonstrates that preservation of crude oils from evaporation is essential for accurate application of all light hydrocarbon parameters, although some parameters may still be utilized when partial evaporation has occurred.

Magnetic Solid Phase Extraction Applied to Food Analysis

Magnetic solid phase extraction has been used as pretreatment technique for the analysis of several compounds because of its advantages when it is compared with classic methods. This methodology is based on the use of magnetic solids as adsorbents for preconcentration of different analytes from complex matrices. Magnetic solid phase extraction minimizes the use of additional steps such as precipitation, centrifugation, and filtration which decreases the manipulation of the sample. In this review, we describe the main procedures used for synthesis, characterization, and application of this pretreatment technique which were applied in food analysis.

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.

Presence and antimicrobial resistance of Escherichia coli isolated from foodstuffs in Hidalgo State (Mexico)

The presence of Escherichia coli in foods taken from the grocery stores and the supermarkets in Hidalgo State (Mexico) was determined for 73 samples of poultry meat, 60 samples of pork, 86 samples of beef, and 66 samples of vegetables. A total of 352 E. coli strains were isolated, identified, and analyzed by an agar disk diffusion assay for their resistance to 10 antimicrobials. Poultry meat and vegetables taken from groceries showed significantly higher counts (P = 0.0002 and P = 0.0461, respectively) when compared with the samples taken from supermarkets. Compared with the isolates recovered from other foods, E. coli isolated from chicken meat had higher levels of antimicrobial resistance against all antimicrobials tested, with the exceptions of nitrofurantoin resistance of isolates from pork and streptomycin resistance in isolates from pork and beef. In addition, the E. coli isolates from samples taken from the groceries showed higher resistance rates than the isolates from samples taken from the supermarkets for the cases of pork isolates resistance to ampicillin (P = 0.0497), chloramphenicol (P = 0.0075), doxycycline (P = 0.002), and streptomycin (P = 0.0094) and beef isolates resistance against ampicillin (P = 0.0048), streptomycin (P = 0.002), and sulfisoxazole (P = 0.003). The present study revealed that the observed resistance rates correlated well with those reported in the national surveillance programmes of developed countries, with the exception of isolates from chicken meat, which have higher resistance rates. Also, from a microbiological safety point of view, samples taken from supermarkets were in a much better conditions than those obtained from the groceries.

Flow based determination of Cr(VI) by adsorptive cathodic stripping voltammetry on an immobilized magnetic poly(ionic liquid) modified electrode

In this work an electrochemical procedure for Cr(VI) flow based determination in tap water is presented. An AdCSV method was developed using a screen printed electrode modified with magnetic poly(1-allyl-3-methylimidazolium) chloride and the procedure does not require the addition of complexing agents in the solution unlike the methodologies reported so far for Cr(VI) determination. The flow based system is described and the control variables were studied in detail and optimized using a Taguchi parameters design. Under optimal conditions, the electrochemical sensor offered an excellent response to Cr(VI) and the limit of detection estimated from 3σ was 0.5 µg L-1 (n = 3) allowing the analysis of tap water samples. The effect of interfering ions was also investigated below the maximum permissible limits for tap water according to Mexican standards. The presence of the magnetic particles on the sorbent allowed its easy modification on the electrode surface between each determination when removing the magnetic field placed in the wall-jet cell. Finally, the precision of the method was tested with tap water samples using standard addition method for Cr(VI) quantification and the accuracy was evaluated comparing the results with the dyphenylcarbazide method and by analyzing a certified water sample. The method shows good repeatability and reproducibility (%RSD less than 5%) making it feasible for Cr(VI) flow based determination and no significant difference is observed in the results obtained by both methods.

DEVELOPMENT OF A SECOND TYPE ELECTRODE BASED ON THE SILVER/SILVER IBUPROFENATE PAIR FOR IBUPROFEN QUANTIFICATION IN PHARMACEUTICAL SAMPLES

Ibuprofen is a widely used pharmaceutical because of its therapeutic properties; it is considered a safe medicament, thus it does not require medical prescription to be sold. However, in order to ensure consumers health it is indispensable that the pharmaceutical industry relies on analytic methods for its quantification. Potentiometry has proven to be a successful technique using second type electrodes, which in agreement with Nernsts equation can detect anions activity. On consideration of this, this research work presents the development of a second type electrode based on the silver/silver ibuprofenate pair. This involved modifying a pure silver wire using a sodium ibuprofenate solution, to obtain the redox pair. The following analytic parameters were obtained with the aid of the modified electrode: a sensitivity of -0.049 V decade [ibuprofenate]-1, 8 µmol L-1 for the detection limit and a quantification limit of 1.2 µmol L-1. The repeatability value in terms of the relative standard deviation was 5.9%. After performing an interferences analysis using some ions and excipients, it was corroborated that there were none, thus allowing appropriate quantification on a real sample.