Fernando Antonio Simas Vaz

New multilayer coating using quaternary ammonium chitosan and κ-carrageenan in capillary electrophoresis: Application in fast analysis of betaine and methionine

The aim of this study was to develop a new multilayer coating with crosslinked quaternary ammonium chitosan (hydroxypropyltrimethyl ammonium chloride chitosan; HACC) and κ-carrageenan for use in capillary electrophoresis. A new semi-permanent multilayer coating was formed using the procedure developed and the method does not require the presence of polymers in the background electrolyte (BGE). The new capillary multilayer coating showed a cathodic electroosmotic flow (EOF) of around 30×10(-9) m(2) V(-1) s(-1) which is pH-independent in the range of pH 2 to 10. The enhanced EOF at low pH obtained contributed significantly to the development of a fast method of separation. The multilayer coating was then applied in the development of a fast separation method to determine betaine and methionine in pharmaceutical formulations by capillary zone electrophoresis (CZE). The BGE used to determine the betaine and methionine concentrations was composed of 10 mmol L(-1) tris(hydroxymethyl) aminomethane, 40 mmol L(-1) phosphoric acid and 10% (v/v) ethanol, at pH 2.1. A fused-silica capillary of 32 cm (50 µm ID×375 µm OD) was used in the experiments and samples and standards were analyzed employing the short-end injection procedure (8.5 cm effective length). The instrumental analysis time of the optimized method was 1.53 min (approx. 39 runs per hour). The validation of the proposed method for the determination of betaine and methionine showed good linearity (R(2)>0.999), adequate limit of detection (LOD <8 mg L(-1)) for the concentration in the samples and inter-day precision values lower than 3.5% (peak area and time migration). The results for the quantification of the amino acids in the samples determined by the CZE-UV method developed were statistically equal to those obtained with the comparative LC-MS/MS method according to the paired t-test with a confidence level of 95%.

Optimisation of a Capillary Zone Electrophoresis Methodology for Simultaneous Analysis of Organic Aliphatic Acids in Extracts of Brachiaria brizantha

INTRODUCTION Aluminum toxicity is commonly verified in acidic soils, and poses a severe limitation to plant growth and development. Therefore, Al complexation by the root system mucilage, Al complexation by organic compounds that are exuded by the roots and internal metabolic processes must be monitored by organic acids (OA), since they play a central role in these aluminum tolerance mechanisms. OBJECTIVE To optimise a capillary zone electrophoresis method able to perform simultaneous separation of acetic, citric, formic, lactic, malic, oxalic, pyruvic, succinic, tartaric and aspartic acid in plant extract solutions. METHODOLOGY Method optimisation was achieved by a chemometric approach through experimental designs. The optimal condition found was: 20 mmol/L phthalic acid buffer; 0.8 mmol/L cetyltrimethyl-ammonium bromide; pH 3.4 adjusted with tris(hydroxymethyl)aminomethane (around 16 mmol/L); -15 kV of voltage; 25 °C of cartridge temperature; indirect ultraviolet detection at 240 nm; and 25 mbar injection for 2 s, within an analysis time of 4 min. RESULTS As a repeatability test of the optimal condition, 30 replicates were carried out with the same working electrolyte, where the relative standard deviation of each peak ranged from 0.081 to 0.36% (for migration time) and from 2.4 to 4.6% (for peak area). CONCLUSION The methodology was successfully applied to simultaneously determine citric, malic and aspartic acid in roots and leaves extract solutions of Brachiaria brizantha, demonstrating its usefulness to study aluminum tolerance.

Analysis of amino acids, proteins, carbohydrates and lipids in food by capillary electromigration methods: a review

A review of the literature covering the evolution of amino acid, protein, lipid and carbohydrate analysis in food samples by electromigration techniques over the last 20 years is presented. The manuscript summarizes different modes, including capillary zone electrophoresis, micellar electrokinetic chromatography, capillary electrochromatography, capillary gel electrophoresis, capillary isotachophoresis, non-aqueous (or nonaqueous) capillary electrophoresis, capillary isoelectric focusing and microfluidic chip electrophoresis, employing different detection systems, such as ultraviolet-visible absorption, laser-induced fluorescence, mass spectrometry, amperometric detection, and capacitively coupled contactless conductivity detection. Briefly, the present review evidences that CE is a very interesting analytical separation technique for food analysis, offering short analysis times and versatility in a simple sample preparation step as inherent advantages compared to classical chromatographic methodologies, which make it a separation technique that is very attractive for quality control in industry and government agencies.

External polyacrylate-coating as alternative material for preparation of photopolymerized sol-gel monolithic column

Photopolymerized sol-gel monolithic columns for use in capillary electrochromatography were prepared in 125 microm i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (approximately 370 nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370 nm for 20 min inside the capillaries to prepare the columns through sol-gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene.

Flow injection analysis of ethambutol in synthetic urine using a graphite-polyurethane composite electrode as an amperometric detector

AbstractEthambutol (ETB) is a first-line antitubercular drug effective against actively growing Mycobacterium tuberculosis. Resistance of the mycobacterium to ethambutol among tuberculosis (TB) patients results from inadequate or inappropriate dosing of treatment or using low quality medication. It is therefore necessary to develop reliable methods for determining ethambutol metabolic profiles of patients at point of care for proper dosing. Herein an efficient ETB sensor device is illustrated. It consists of a graphite-polyurethane composite electrode.In order to characterise the electrochemical behaviour of ethambutol at pH = 8.0 voltammetric studies were performed. The detector was assembled in a flow injection apparatus and operated at +1.2 V (vs. Ag/AgCl(NaCl sat.)). The influence of sample volume and flow rate was studied. The linear response for the method was extended up to a 1.1 mmol L−1 ethambutol solution with a detection limit of 0.0634 mmol L−1. The reproducibility of current responses for injections of 0.7 mmol L−1 ethambutol solution was evaluated to be 5.1% (n = 30) and the analytical frequency was 161 determinations h−1. Two different samples were successfully analysed and the results were in good agreement with those obtained using capillary zone electrophoresis (CZE).

Fundamentos de eletroforese capilar: uma abordagem por animações

Among the analytical separation techniques, capillary electrophoresis (CE) has attracted attention in both academic and industrial fields, mainly owing to its efficiency, short analysis times, low reagent consumption and residue generation. This is also the case in Chemistry courses, books and papers, demonstrating CE´s well-established status. However, despite the range of available bibliographic material, there is a lack of animations showing the CE dynamic process. Therefore, the aim of this work was to show the development of a group of animations available for public access, where electrolyte and analytes movements under different CE modes; electropherogram formation; and online ultraviolet-visible spectra can be viewed. The normal or reverse electroosmotic flow generation in the vicinity of the silica capillary wall and the partition motion of neutral compounds between micellar and aqueous phases are also shown. Capillary zone electrophoresis, micellar electrokinetic chromatography, capillary electrochromatography, capillary isoelectric focusing, capillary isotachophoresis and capillary gel electrophoresis, are included in this package. This animation approach can be highly didactic and can complement the theoretical study of CE techniques, which may aid researchers, teachers and students interested in understanding the dynamism and potential of different CE modes.

A Rapid Method for Total Β‐Escin Analysis in Dry, Hydroalcoholic and Hydroglycolic Extracts of Aesculus hippocastanum L. by Capillary Zone Electrophoresis

INTRODUCTION Seeds of Aesculus hippocastanum L. are used in European phytotherapy to treat inflammatory and vascular problems, and also to help in the regulation of the microcirculation. Thus, the quality control of herbal medicines using this species is important. OBJECTIVE To develop and to optimise a capillary zone electrophoresis method to determine total β-escin in different extracts of A. hippocastanum L. METHODS The optimal condition found through chemometric approach was: 25 mmol/L of bicarbonate-carbonate buffer, pH 10.3; +20 kV of voltage; 20°C of cartridge temperature; direct ultraviolet detection at 226 nm; 13 mbar injection for 5 s and analysis time within 6 min. RESULTS Repeatability, coefficient of variation (CV; %) = 3.19, 3.07 and 1.89 (n = 12), and intermediate precision, CV (%) = 3.05, 3.53 and 2.99 (n = 24) for dry, hydroalcoholic and hydroglycolic extracts, respectively were achieved. The accuracy was evaluated through recovery tests in concentration levels of 100, 150 and 200 g/L, ranging from 98.17 to 104.68%. The proposed method exhibited linearity (r = 0.9983) in the concentration range from 101.4 to 907.2 g/L and limits of detection and quantification equal to 11.63 and 38.76 g/L respectively. CONCLUSION A fast and reliable methodology for determination of total β-escin was successfully validated and applied on extracts of A. hippocastanum L. demonstrating its usefulness to quality control of medicines containing this plant species.

Determination of Olive Oil Acidity

Publisher Summary The best olive oils are the ones that present up to 1% degree of acidity. Those with more than 3.3% acidity need to be submitted to refining processes before they are commercialized. As market value and health benefits are directly related to olive oil acidity level, the development and optimization of analytical methodologies aimed at determining the degree of acidity of the product is relevant. AVT is the standard methodology to determine oil acidity, in which the sample dissolved in alcohol or ether is neutralized with KOH or NaOH, using phenolphthalein as an indicator. Alternatively, other methods have been proposed in order to replace the conventional titration such as FIA in automated systems, methods based on voltammetric reduction of quinones, FT-Raman, FT-IR, NIR, NMR, HPLC, GC, and CE. This chapter presents further information as regards the application of analytical methodologies for determining olive oil acidity as found in the literature. The scenario reported in the literature presents analytical methodologies as simple as volumetric titration up to the more sophisticated techniques such as spectroscopic and separation methods. Researchers, students, and professionals interested in olive oil determinations have a wide variety of analytical methods available from which they can choose, taking into account necessity, cost, accessibility, analysis time (number of samples analyzed per hour), sample preparation mode (with or without previous treatment), and sensitivity.

Chromophoreasy, an Excel-Based Program for Detection and Integration of Peaks from Chromatographic and Electromigration Techniques

This paper describes the development, evaluation, features and applications of Chromophoreasy, an alternative Excel-based program for recognition and integration of chromatographic and electrophoretic peaks. The proposed recognition is made according to parameters adjustable by the analyst, such as time range, noise smoothing window size and slope/curvature sensitivity. During integration, retention/migration time, area, height, half-height width, plate numbers, asymmetry factor, US Pharmacopeia tailing factor, resolution and statistical moments are determined. A chromatogram/electropherogram is plotted along with the found baselines. The effect of peak shape (heights and symmetries) and baseline slope over accuracy was evaluated and the precision of recognition/integration was investigated under several simulated conditions, with varied signal-to-noise levels, smoothing modes and smoothing window sizes. Data from liquid and gas chromatography, capillary electrophoresis and electrochromatography techniques with refractive index, flame ionization, capacitively coupled contactless conductivity (lab-made) and ultraviolet absorbance detections, respectively, were treated, illustrating the broad applicability of the proposed program for standard and sample analysis. Statistically similar results were obtained, when compared with other commercial software, showing it to be a simple, practical and reliable tool for general use in the separation area.

Optimized Separation Method for Estriol, 17-β-Estradiol and Progesterone by Capillary Electrochromatography with Monolithic Column and its Application to a Transdermal Emulsion

A monolithic stationary phase based on 3-(methacryloxypropyl)trimethoxysilane monomer, prepared within a fused silica capillary externally coated with a UV-transparent fluoropolymer was employed for separation of estriol, 17-b-estradiol and progesterone by capillary electrochromatography in a standard mixture. A 23 factorial design was used to optimize the separation system. The optimized condition containing 30% (v/v) of acetonitrile and 10 mmol L-1 aqueous ammonium acetate presented a total run time less than 10 min by applying 25 kV. The resolution between adjacent peaks ranged from 1.8 up to 2.9 and the plate numbers per column meter in this condition was 1873, 3631 and 3886 for the estriol, 17-b-estradiol and progesterone peaks, respectively. The optimized method was employed in the quantitative analysis of a commercial transdermal emulsion formulation.