Marieta L.C. Passos

Estimation of postmortem interval by hypoxanthine and potassium evaluation in vitreous humor with a sequential injection system.

The estimation of the time since death known as postmortem interval (PMI) is a main issue in the field of forensic science and legal medicine. In this work it is proposed a sequential injection system for the determination of hypoxanthine and potassium in the same sample of vitreous humor since the concentrations of both parameters change with PMI and the vitreous humor has been regarded as the ideal extracellular fluid for these kinds of determinations. By measuring both parameters the accuracy of estimation of PMI can be increased, and the effects of factors which influence the values in postmortem chemistry minimized. Hypoxanthine determination is based on its oxidation to uric acid (290 nm), catalyzed by immobilized xanthine oxidase, and the quantification of potassium levels in vitreous humor was performed using a tubular potassium ion-selective electrode. With a unique analytical cycle both analytes were evaluated being potassium levels determined during the degradation of hypoxanthine in the enzymatic reactor. Working concentration ranges between 6.04-40.00 micromol L(-1) and 7.00 x 10(-5) to 1.00 x 10(-1)mmol L(-1) were obtained, for hypoxanthine and potassium, respectively. The method proved to be reproducible with R.S.D. <5% for hypoxanthine and <3% for potassium. Sampling rate was approximately 30 per hour for the sequential determination of both parameters being 15 and 60 determinations per hour if hypoxanthine or potassium, where evaluated independently. Statistical evaluation at the 95% confidence level showed good agreement between the results obtained, for the vitreous humor samples, with both the SIA system and the comparison batch procedures. Moreover the methodology has low environmental impact in agreement with the demands of green analytical chemistry as only 2.7 mL of chemical waste is produced during both determinations.

Evaluation of digestion procedures for simultaneous determination of Ca, P, Mg, K and Na in biodiesel by inductively coupled plasma optical emission spectrometry

In the present work, the efficiency of two procedures for the digestion of biodiesel was investigated for the simultaneous determination of Ca, P, Mg, K and Na by axial view ICP OES. In the open system with conventional heating, concentrated nitric and sulfuric acids were added to the samples, and the addition of hydrogen peroxide completed the digestion. In the microwave-assisted closed system, complete digestion was performed using concentrated nitric acid and hydrogen peroxide. The analytical performances were evaluated through limits of quantification, precision of the overall procedures, final acidity of the digests, and residual carbon contents. The contents of residual carbon for the biodiesel samples digested were 0.358 ± 0.012% using the open system with conventional heating and 0.614 ± 0.023% using the microwave-assisted closed vessel system, demonstrating the high efficiency of both proposed procedures. The optimized microwave-assisted decomposition procedure produced the fastest, safest and most accurate analytical results with recoveries of 89.0-103.0% and deviations lower than 5% in most cases. Low limits of detection were obtained (< 0.40 µg g-1), adequate for the established limits set out in Brazilian legislation for these analytes. Three biodiesel samples produced from different oil sources were analyzed. In comparison with other procedures proposed in the literature, the developed procedure using the microwave-assisted closed system is advantageous because it neither require organic standard solutions for calibrations nor use toxic organic solvents.

Nanoparticle-based assays in automated flow systems: A review.

Nanoparticles (NPs) exhibit a number of distinctive and entrancing properties that explain their ever increasing application in analytical chemistry, mainly as chemosensors, signaling tags, catalysts, analytical signal enhancers, reactive species generators, analyte recognition and scavenging/separation entities. The prospect of associating NPs with automated flow-based analytical is undoubtedly a challenging perspective as it would permit confined, cost-effective and reliable analysis, within a shorter timeframe, while exploiting the features of NPs. This article aims at examining state-of-the-art on continuous flow analysis and microfluidic approaches involving NPs such as noble metals (gold and silver), magnetic materials, carbon, silica or quantum dots. Emphasis is devoted to NP format, main practical achievements and fields of application. In this context, the functionalization of NPs with distinct chemical species and ligands is debated in what concerns the motivations and strengths of developed approaches. The utilization of NPs to improve detectors performance in electrochemical application is out of the scope of this review. The works discussed in this review were published in the period of time comprised between the years 2000 and 2013.

Determination of metoprolol, acebutolol and propranolol in pharmaceutical formulations using the same SIA system

A mechanized system for the determination of b-blockers in pharmaceutical formulations is presented. Using the Sequential Injection Analysis (SIA) technique it was achieved a simple, economical and versatile methodology adaptable to any pharmaceutical control involving these substances. It does not require any pre-treatment for the samples, as they must only be dissolved in acid before analysis. Linear calibration plots were obtained for metoprolol (40.52 - 250 mg L-1), acebutolol (32.85 - 140 mg L-1) and propranolol (16.58 - 120 mg L-1). A R.S.D. lower than 5% was attained. The methodology was used in tablets, injections and prolonged-release capsules. Common excipients used in pharmaceuticals do not interfere. Statistical comparison of the results obtained with the proposed methodology and with the official methods showed good agreement (95% confidence level). SIA system produces only 2.50 mL of effluents per determination whereas the reference methodologies consume around 140 mL.

A soft strategy for covalent immobilization of glutathione and cysteine capped quantum dots onto amino functionalized surfaces

A novel strategy for immobilization of CdTe quantum dots (QDs) onto amino functionalized solid supports was developed. QDs capped with compounds holding an amino group were covalently bonded to the substrate under mild reaction conditions, exhibiting great stability and strong luminescence.

Sequential injection technique as a tool for the automatic synthesis of silver nanoparticles in a greener way

This paper presents a new way to the synthesis of uniform and size-controlled silver nanoparticles by means of microreaction technology. It complies with the philosophy of green chemistry by developing a process that prevents pollution at source-by automation of the manipulations using microtubes manifolds and with the use of benign reagents and photochemistry to enhance the reaction of synthesis of Ag nanoparticles. Effect of hydrodynamic parameters (reagent volumes and volume flow rate) and concentrations (reducer and stabilizer), temperature, pH and UV irradiation time on morphology and size of nanoparticles was studied. The silver nanoparticles has been characterized by transmission electronic microscopy (TEM), electron diffraction X-ray spectroscopy (EDS), UV-vis spectra analysis, dynamic light scattering (DLS) and zeta potential measurements. Particles are mostly spherical in shape and have average sizes between 7 and 20 nm. The particle size can be controlled by changing not only the flow rate and UV light time exposition but also the reducer/AgNO3 concentration ratio. This is a sustainable and cost-saving methodology that guarantees not only reproducible synthesis, but also the changing of NPs characteristics at time by simple control of the fluid transport.

Improved activity of α-chymotrypsin in mixed micelles of cetyltrimethylammonium bromide (CTAB) and ionic liquids: A kinetic study resorting to sequential injection analysis

In the present work an automatic methodology, based on sequential injection analysis, (SIA) for the kinetic evaluation of α-chymotrypsin (α-CT) activity in cetyltrimethylammonium bromide (CTAB)/ionic liquid (IL) mixed micelles, was developed. The α-CT-catalysed hydrolysis of N-succinyl-l-phenylalanine-p-nitroanilide (SPpNA) was monitored by following the change in absorbance at 410nm brought about by the formation of p-nitroaniline (pNA). The influence of parameters such as reagents concentration, flow rate, as well as reaction coil length, on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions were subsequently selected. The effect of CTAB/IL micelles on the catalytic constant Kcat and apparent Michaelis-Menten constant (KM) for SPpNA hydrolysis was then studied. The kinetic assays evidence that CTAB/ILs mixed micellar systems can induce α-CT superactivity. In order to perform a critical evaluation of the obtained results, CMC and average micellar size of CTAB/hmim[Cl], CTAB/bmim[Cl], CTAB/bmpyr[Cl] and CTAB/bmpy[Cl] mixed micelles were evaluated by fluorescence and dynamic light scattering, respectively. The SIA methodology showed to be an interesting tool for evaluation of α-CT activity in mixed micelles as it proved to be robust and exhibited good repeatability in all the assay conditions leading also to a reduction of the consumption of solvents as well as of effluent production.

A reagent-free method based on a photo-induced fluorimetry in a sequential injection system

According to the current demands of environmentally friendly analytical chemistry and with a view to achieving lower reagent consumption with improved analytical performance, an automatic methodology composed of a photoreactor and fluorimetric detection (λ(exc)=287 nm, λ(em)=378 nm) was developed. To this end, a sequential injection analysis (SIA) system was developed for indomethacin determination using ultra-violet (UV) light which promotes an increase in the fluorescence of indomethacin. This increase in sensitivity makes it possible to apply this methodology to a dissolution test and to determine indomethacin in pharmaceutical formulations. The calibration graph for indomethacin was linear between 4.10 × 10(-6) and 9.00 × 10(-5) mol L(-1)and the detection limit was 1.23 × 10(-6) mol L(-1). The method was proven to be reproducible with a R.S.D.<5% and sampling rate of approximately 20 per hour. The potential effect of several compounds commonly used as excipients on analytical signals was studied and no interfering effect was observed. Statistical evaluation at the 95% confidence level showed good agreement between the results obtained for the pharmaceutical samples with both the SIA system and comparison batch procedures.

Automated evaluation of the inhibition of glutathione reductase activity: application to the prediction of ionic liquids' toxicity

This work is based on the automated evaluation of the influence of several ionic liquids (ILs) on the activity of immobilized glutathione reductase (GR), as an indicator of their toxicity. The reactions involved are the reduction of oxidized glutathione (GSSG) by GR, followed by the oxidation of the formed product (reduced glutathione – GSH) by the sulfhydryl reagent 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB) to form a yellow derivate 2-nitro-5-thiobenzoic acid (TNB), measurable at 412 nm. The bioassay was performed in a SIA system where the ILs were submitted to a simple and precise on-line dilution strategy before evaluation of their toxicity. The activity assays were implemented in strictly aqueous media and in the presence of increasing concentrations of seven commercially available ILs. EC50 values between 0.24 and 2.55 M were obtained for the tested compounds, revealing distinct inhibitory effects. The least and most toxic ILs found in this study were emim[Ms] and emim[BF4], respectively. The automated methodology is an interesting analytical tool for the evaluation of GR activity in ILs proving to be robust while presenting good repeatability, with RSD less than 5%, in all the assay conditions, leading also to a reduction of the consumption of solvents as well as of effluent production (2 mL per cycle).

Immobilization of Distinctly Capped CdTe Quantum Dots onto Porous Aminated Solid Supports

Immobilization of quantum dots (QDs) onto solid supports could improve their applicability in the development of sensing platforms and solid-phase reactors by allowing the implementation of reusable surfaces and the execution of repetitive procedures. As the reactivity of QDs relies mostly on their surface chemistry, immobilization could also limit the disruption of solution stability that could prevent stable measurements. Herein, distinct strategies to immobilize QDs onto porous aminated supports, such as physical adsorption and the establishment of chemical linking, were evaluated. This work explores the influence of QD capping and size, concentration, pH, and contact time between the support and the QDs. Maximum QD retention was obtained for physical adsorption assays. Freundlich and Langmuir isotherms were used to analyze the equilibrium data. Gibbs free energy, enthalpy, and entropy were calculated and the stability of immobilized QDs was confirmed.