Heberth Juliano Vieira

Flow injection spectrophotometric method for chloride determination in natural waters using Hg(SCN)(2) immobilized in epoxy resin.

A flow injection (FI) spectrophotometric method was proposed for the determination of chloride ion in natural waters. The determination of chloride was carried out by reaction with Hg(SCN)(2) immobilized in an epoxy resin bead in a solid-phase reactor (SPR) and the thiocyanate ions released were determined spectrophotometrically at 480nm after complexing reaction with Fe(III). The analytical curve for chloride was linear in the concentration range from 5.6 x 10(-5) to 2.2 x 10(-4)moll(-1) with a detection limit of 1.4 x 10(-5)moll(-1). The relative standard deviation (R.S.D.) was 2.2% for a solution containing 2.2 x 10(-4)moll(-1) (n = 10). The simple manifold allows a routine analytical frequency of 100 determinations per hour. The main advantage of the developed method is the 400% reduction of the Hg waste solution generated when compared to conventional methods for chloride determination based on the same spectrophotometric reaction.

Flow injection turbidimetric determination of acetylcysteine in pharmaceutical formulations using silver nitrate as precipitant reagent

A simple, accurate and precise flow-injection turbidimetric procedure is reported for the determination of acetylcysteine in pharmaceutical formulations. The procedure is based on the precipitation of acetylcysteine with silver nitrate solution in acid medium and the insoluble salt produced was monitored at 410 nm. The analytical curve for acetylcysteine was linear in the concentration range from 1.0 × 10-4 to 1.0 × 10-3 mol L-1 with a detection limit of 5.0 × 10-5 mol L-1. The sampling rate was 60 h-1 and the relative standard deviations (RSDs) were less than 2.0% for 1.0 × 10-4 and 5.0 × 10-4 mol L-1 acetylcysteine solutions (n=10). The recovery of this analyte in four samples ranged from 97.6 to 103 %. A paired t-test showed that all results obtained for acetylcysteine in pharmaceutical products using the proposed flow-injection procedure and the official procedure agreed at the 95% confidence level.

Electroregenerable anion-exchange resin with triiodide carbon paste electrode for the voltammetric determination of adrenaline

An electroregenerable carbon paste electrode modified with triiodide ions immobilized in an anion-exchange resin (Lewatit M500) is proposed for the determination of adrenaline in pharmaceutical products by differential-pulse voltammetry (DPV). Adrenaline was chemically converted into adrenochrome by the I3- ions at the electrode surface. The electrochemical reduction back to adrenaline was obtained at a potential of -0.16 V vs. Ag/AgCl (3 mol l(-1) KCl). A 20% decrease of the initial analytical signal was observed after 350-400 determinations; the carbon paste electrode was 100% electroregenerated at a fixed potential of +0.65 V vs. Ag/AgCl (3 mol l(-1) KCl) in 0.1 mol l(-1) KI solution for 20 min. The differential-pulse voltammograms were obtained by applying a sweep potential between 0.0 and -0.34 V, following the adrenochrome reduction at -0.16 V. Under the optimum conditions established, such as pH 6.0; scan rate 20 mV s(-1) and pulse amplitude 50 mV, the calibration curve was linear from 2.0 x 10(-5) to 3.1 x 10(-4) mol l(-1) adrenaline with a detection limit of 3.9 x 10(-6) mol l(-1). The recovery of adrenaline ranged from 99.8 to 103.1% and the RSD was 2.6% for the solution containing 1.0 x 10(-4) mol l(-1) adrenaline (n = 10). The results obtained for adrenaline in pharmaceutical samples using the proposed carbon paste electrode are in agreement with those obtained using a pharmacopoeial procedure at the 95% confidence level.

Adsorption of L-amino Acids on Sea Sand

A study of adsorption of L-alanine, L-tyrosine, L-glutamic acid, and L-lysine on sea sand was carried out. Only L-lysine showed adsorption on sea sand, probably due to the presence of the positively charged R group. Our results raise some doubts as to whether sand was important for the pre-concentration of amino acids prior to peptide condensation on the Pre-Biotic Earth.

Determinação indireta de N-acetil-L-cisteína por injeção em fluxo empregando Ce(IV) e ferroína

An indirect flow injection spectrophotometric procedure is proposed for the determination of N-acetyl-L-cysteine in pharmaceutical formulations. In this system, ferroin ([Fe(II)-(fen)2]2+) in excess, with a strong absorption at 500 nm, is oxidized by cerium(IV) yielding cerium(III) and [Fe(III)-(fen)2]3+ (colorless), thus producing a baseline. When N-acetyl-L-cysteine solution is introduced into the flow injection system, it reacts with cerium(IV) increasing the analytical signal in proportion to the drug concentration. Under optimal experimental conditions, the linearity of the analytical curve for N-acetyl-L-cysteine ranged from 6.5x10-6 to 1.3x10-4 mol L-1. The detection limit was 5.0x10-6 mol L-1and recoveries between 98.0 and 106% were obtained. The sampling frequency was 60 determinations per hour and the RSD was smaller than 1.4% for 2.2x10-5 mol L-1 N-acetyl-L-cysteine.

Flow Injection Spectrophotometric System for Ranitidine Determination in Pharmaceuticals Using Cerium(IV) and Ferroin

An indirect flow injection spectrophotometric procedure for the determination of ranitidine in pharmaceutical formulations is proposed. The method was based on the oxidation of the ranitidine with cerium(IV) in acidic medium and subsequent determination of cerium(IV) excess by reaction with ferroin which was monitored spectrophotometrically at 500 nm. The linearity of the analytical curve for ranitidine ranged from 2.5 x 10 -4 to 1.25 x 10 -3 mol L -1 . The detection limit of 1.6 x 10 -6 mol L -1 and recoveries between 96.6 and 103 % were obtained. The sampling rate of 60 determinations per hour and the RSD smaller than 0.3% for 7.1 x 10 -4 mol L -1 ranitidine were also obtained. The method was applied with success in the determination of ranitidine in several commercial formulations.

A multicommuted flow-based system for hydrogen peroxide determination by chemiluminescence detection using a photodiode

Abstract A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III). The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l−1 H2O2 with a LD of 1.8 µmol l−1 H2O2 and coefficient of variations smaller than 0.8% for 1.0×10−5 mol l−1 and 6.8×10−5 mol l−1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.

Flow‐Injection Turbidimetric Determination of Tannins in Tea Samples Using Copper(II)/Acetate as Precipitant Reagent

Abstract A flow‐injection (FI) turbidimetric method for determination of tannins content in tea samples based on the precipitation reaction with copper(II) in acetate medium is proposed. In this method, 350 µL of 0.05 mol L−1 copper(II) and 350 µL of sample were injected simultaneously in two water carrier streams of a merging zones system. After mixing at a 50 cm coiled reactor, the mixture converged with a flow stream of 0.10 mol L−1 ammonium acetate solution producing a precipitate in a 100 cm coiled reactor that was monitored at 500 nm. Under the optimized experimental conditions, the calibration graph for tannic acid was linear in the concentration range from 18.0 to 725 mg L−1 with a detection limit of 6.49 mg L−1. The relative standard deviations (RSD) were smaller than 1.2% (n = 10) for solutions containing 110 and 365 mg L−1 of tannic acid, and the analytical frequency was 90 determinations per hour. The results obtained in the analysis of tea samples (green, black, and brown) were compared with those provided by the Folin–Ciocalteu method. #Financial support from FAPESP, PADCT/CNPq, and also the scholarships granted by CAPES to E. Piccin and H.J. Vieira are gratefully acknowledged.

Determinação de paracetamol em produtos farmacêuticos empregando um sistema de análise por injeção em fluxo com geração de ácido nitroso

The use of nitrous acid (HNO2) for determination of paracetamol (acetoaminophen) in liquid and solid formulations employing flow injection system is described. The determination of this drug was carried out by reacting paracetamol with nitrous acid generated in-line and the product yielded was measured at 430 nm in alkaline medium. The analytical curve ranged from 9.7x10-5 to 6.2x10-3 mol L-1 of paracetamol, with a detection limit of 2.5x10-5 mol L-1. The relative standard deviations (RSDs) were smaller than 2% for solutions containing 1.2x10-4 and 2.8x10-4 mol L-1 of paracetamol (n=10) and 60 determinations per hour were obtained. The results of determination of paracetamol in pharmaceutical formulations obtained by the proposed FI procedure were in good agreement with those obtained using theUSP procedure at a confidence level of 95% and within an acceptable range of error.

Flow injection spectrophotometric determination of adrenaline using a solid-phase reactor containing triiodide ions immobilized in an anion-exchange resin

A flow injection spectrophotometric procedure with on-line solid-phase reactor containing ion triiodide immobilized in an anion-exchange resin is proposed for the determination of adrenaline (epinephrine) in pharmaceutical products. Adrenaline is oxidized by triiodide ion immobilized in an anionic-exchange resin yielding adrenochrome which is transported by the carrier solution and detected at a wavelength of 488 nm. Adrenaline was determined in three pharmaceutical products in the 6.4 x 10-6 to 3.0 x 10-4 mol L-1 concentration range with a detection limit of 4.8 x 10-7 mol L-1. The recovery of this analyte in three samples ranged from 96.0 to 105 %. The analytical frequency was 80 determinations per hour and the RSDs were less than 1 % for adrenaline concentrations of 6.4 x 10-5 and 2.0 x 10-4 mol L-1 (n=10). A paired t-test showed that all results obtained for adrenaline in commercial formulations using the proposed flow injection procedure and a spectrophotometric batch procedure agree at the 95% confidence level.