Browsing by Author "Jose Trivino, Juan"

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    Determination of a natural (17β-estradiol) and a synthetic (17α-ethinylestradiol) hormones in pharmaceutical formulations and urine by adsorptive stripping voltammetry
    (2019) Jose Trivino, Juan; Gomez, Marisol; Valenzuela, Javiera; Vera, Ariesny; Arancibia, Veronica
    An efficient, fast and sensitive method for the determination of 17 beta-estradiol, (E2) and 17 alpha-ethinylestradiol (EE2) in pharmaceutical formulations and in urine was developed and validated using a hanging mercury drop electrode (HMDE), screen printed carbon electrodes (SPCE), and screen printed carbon nanotube electrodes (SPCNTE). Both analyzes are adsorbed on the working electrodes. To obtain sensitive and selective methods, the effects of various parameters such as pH, adsorption potential, and time (E-ads, t(ads)) were optimized. The optimum experimental conditions chosen for the two analyzes were pH: 10.0; E-ads: - 0.60 and t(ads): 30 s, when HMDE was used. Under these conditions, one reduction signal was found at -1.31 V for E2 and two reduction signals at - 0.23 V and -1.20 V for EE2. The detection limits (DLs) were found to be 0.3 mu g L-1 for E2, 14.8 mu g L-1 for EE2 at - 0.23 V, and 9.7 mu g L-1 for EE2 at -1.20 V. On the other hand, in screen printed electrodes E2 and EE2 present oxidation of the phenolic hydroxyl groups at 0.30, 0.31, 0.32, and 0.33 V (pH:10) with DLs of 242, 277; 182, and 191 mu g L-1 for SPCE and SPCNTE, respectively. The method was successfully applied to the determination of these analyzes in Primaquin (R) (E2), Gynera (R) (EE2), spiked urine (with EE2), and urine samples of women who used Tinelle (R) (EE2) as contraceptive drug.
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    Development of a fast and sensitive method for the determination of As(III) at trace levels in urine by differential pulse anodic voltammetry using a simple graphene screen-printed electrode
    (2020) Nunez, Claudia; Jose Trivino, Juan; Segura, Rodrigo; Arancibia, Veronica
    A simple and fast anodic voltammetric method was employed to determine traces of As(III) in urine samples using commercial screen-printed graphene electrodes without subsequent modification. To obtain a sensitive and selective method for As(III) determination, the effects of various parameters such as pH, supporting electrolyte concentration, accumulation potential (E-acc), accumulation time (t(acc)), and potential scan conditions were studied. The optimum experimental conditions were chosen to be as follows: pH of 2.8 (0.01 mol L-1 phosphate buffer), scan increment of 4 mV, pulse width of 80 ms, pulse period of 0.5 s, and pulse amplitude of 200 mV. Differential pulse voltammograms were obtained by scanning from -0.80 V to 0.80 V without applying an accumulation step. Under these conditions, one peak was observed at 0.27 V due to As-0 oxidation. After optimizing the experimental conditions, the anodic peak current for As was found to be linearly related to its concentration up to ca. 5.0 mu g L-1, with detection and quantitation limits (DLs, QLs) of 0.28 mu g L-1 and 0.92 mu g L-1, respectively. The developed method was validated by the determination of As(III) in spiked tap water from our laboratory, which showed an As(III) concentration of 50.64 +/- 0.10 mu g L-1 (spiked with 50.0 mu g L-1); two urine samples (where As was not detected) spiked with As(III) 0.73 mu g L-1 and 0.91 mu g L-1 (in the cell) showed an As(III) concentration of 0.70 mu g L-1 and 0.91 mu g L-1, respectively. The method was successfully applied to the determination of As-total in 16 urine samples obtained from workers occupationally exposed to inorganic arsenic compounds without previous treatment. The results obtained for As-total were compared with measurements made by an external analytical laboratory, which used HG-AAS. To determine As-total, As(V) was reduced in the presence of thiosulfate in an acid medium. The electrode showed good stability and repeatability.
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    The effect of aged microglia on synaptic impairment and its relevance in neurodegenerative diseases
    (2021) Jose Trivino, Juan; von Bernhardi, Rommy
    Microglia serve key functions in the central nervous system (CNS), participating in the establishment and regulation of synapses and the neuronal network, and regulating activity-dependent plastic changes. As the neuroimmune system, they respond to endogenous and exogenous signals to protect the CNS. In aging, one of the main changes is the establishment of inflamm-aging, a mild chronic inflammation that reduces microglial response to stressors. Neuroinflammation depends mainly on the increased activation of microglia. Microglia over-activation may result in a reduced capacity for performing normal functions related to migration, clearance, and the adoption of an anti-inflammatory state, contributing to an increased susceptibility for neurodegeneration. Oxidative stress contributes both to aging and to the progression of neurodegenerative diseases. Increased production of reactive oxygen species (ROS) and neuroinflammation associated with age-and disease dependent mechanisms affect synaptic activity and neurotransmission, leading to cognitive dysfunction. Astrocytes prevent microglial cell cytotoxicity by mechanisms mediated by transforming growth factor 131 (TGF131). However, TGF131-Smad3 pathway is impaired in aging, and the age-related impairment of TGF13 signaling can reduce protective activation while facilitating cytotoxic activation of microglia. A critical analysis on the effect of aging microglia on neuronal function is relevant for the understanding of age-related changes on neuronal function. Here, we present evidence in the context of the ?microglial dysregulation hypothesis?, which leads to the reduction of the protective functions and increased cytotoxicity of microglia, to discuss the mechanisms involved in neurodegenerative changes and Alzheimer?s disease.
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    Voltammetric method for the determination of Pb2+ and Cd2+ in water samples using a nafion-guanine-coated mercury film electrode
    (2022) Jose Trivino, Juan; Nunez, Claudia; Merino-San Martin, Ignacio; Zuniga, Manuel; Arancibia, Veronica
    A sensitive voltammetric method is reported for the simultaneous determination of Pb2+ and Cd2+ using a nafion-guanine-coated mercury film glassy carbon electrode. This modified electrode exhibited well-developed signals for the reduction of the adsorbed complexes Pb-Guanine and Cd-Guanine, at -0.59 and -0.76 V respectively. The effects of parameters such as pH, accumulation potential and time (E-acc, t(acc)) were optimized. These studies were done using metallic ions on their own and also mixed together. The best pH for the individual analysis of Pb2+ or Cd2+ were 2.2 and 6.1 respectively, whereas a pH of 5.0 (acetate buffer 0.01 mol L-1) was chosen for simultaneous determination. Under the optimized conditions (pH = 5.0; t(acc) = 60 s; E-acc = -1.0 V) reduction signal was found to be proportional to the concentration of Pb2+ and Cd2+ over the 6.6-35.0 mu g L-1 range, with 36 detection limits (DL) of 2.2 and 4.6 mu g L-1. However, for lower concentrations, a time of 120 s was applied, yielding a linear range from 0.5 to 12.0 mu g L-1 with DLs of 0.26 and 0.25 mu g L-1 for Pb2+ and Cd2+, respectively. If the guanine (G) is in the solution, the signals are much lower than in the modified electrode. The method was validated by determining Pb2+ and Cd2+ in certified reference material (GBW08607) and synthetic sea water (ASTM D665), spiked with 22 metal ions, with satisfactory results. Subsequently, the method was applied in bottled mineral waters and sea water samples without previous treatment.