Vagner Bezerra dos Santos

Determination of biogenic amines in beer and wine by capillary electrophoresis-tandem mass spectrometry

A capillary electrophoresis-tandem mass spectrometry (CE-MS/MS) method for the simultaneous assessment of nine biogenic amines (spermine, spermidine, putrescine, cadaverine, histamine, phenylethylamine, tryptamine, tyramine, and urocanic acid) in commercial samples of beer and wine is introduced. The samples were submitted to a simple clean-up step with poly(vinylpolypyrrolidone) followed by filtration. Electrophoretic separation in a polyvinyl alcohol (PVA)-coated capillary using 0.5 mol L(-1) acetic acid (pH 2.5) as background electrolyte and detection by electrospray-tandem mass spectrometry was employed. The range of the correlation coefficients of the calibration curves of the analyzed compounds was 0.996-0.999, and the limits of detection and limits of quantification were in the range of 1-2 μg L(-1) and 3-8 μg L(-1), respectively. The recovery values for samples spiked at three concentration levels (0.2, 0.5, and 1.0 mg L(-1)) ranged from 87 to 113% with standard deviation not greater than 5.8%. The use of a PVA-coated silica capillary allows suppressing the electroosmotic flow and, consequently, increasing of the separation efficiency. The method was successfully used to determine biogenic amines in commercial samples of beer and wine.

Determination of halosulfuron-methyl herbicide in sugarcane juice and tomato by capillary electrophoresis–tandem mass spectrometry

A capillary electrophoresis-tandem mass spectrometry (CE-MS/MS) method for the determination of halosulfuron-methyl (HSU) residue in samples of sugarcane juice and tomato is introduced and validated. The samples were submitted to a QuEChERS extraction procedure followed by electrophoretic separation in NH4HCO3 electrolyte (adjusted to pH 8.5) and detection by electrospray-tandem mass spectrometry. The total HSU migration took place in less than 3.5 min, and the detection was accomplished by monitoring three fragmentation processes of this anion: m/z 435-182, 139, and 83. The R(2) values for concentrations up to 100 ppb (μg kg(-1)) were, respectively, 0.992, 0.992, and 0.978. Recovery values for samples spiked at three concentration levels (10, 20 and 50 ppb) were in the range of 96-104% with standard deviation not greater than 5.0%. The limit of detection for HSU in sugarcane juice and tomato was 2 ppb for both samples.

A simple paper-strip colorimetric method utilizing dehydrogenase enzymes for analysis of food components

In this study, we present a simple chromatographic paper-based colorimetric assay for the analysis of selected food compounds. The biochemical principle utilises enzymes from the dehydrogenase family coupled with diaphorase in the presence of a tetrazolium dye, MTT, and NAD+. The colored reaction product that developed on the surface of the chromatography paper could either be qualitatively analysed by the naked eye, that is, it could be used for screening analysis, or it could be recorded by using a smartphone camera and evaluated in freeware ImageJ in order to obtain data for quantitative analysis. The general concept was demonstrated and optimised using (L)-glutamate dehydrogenase and the versatility of the proposed method was illustrated by using other enzymes from the dehydrogenase family. The linear range for (L)-glutamate was found to be 0.5–5.0 mmol L−1 using the digital image method. The limit of detection found by the naked eye was 0.05 mmol L−1 and 0.028 mmol L−1 by digital imaging. The paper assay stored in a freezer provided a reproducible response for at least 6 weeks. This research presents the successful modification of an MTT-cell viability test principle and its use in the fabrication of an inexpensive, easy to prepare, simple to use, portable and rapid-responding paper-based assay.

A simple approach to compensate the suction caused by the electrospray ionization source in capillary electrophoresis-mass spectrometry systems.

ESI sources continuously consume the liquid at the tip of the capillary, which causes the dragging of the BGE. The laminar nature of this flow causes the broadening of the peaks and loss of separation efficiency. The usual solution for this problem is to compensate this phenomenon by reducing the pressure at the inlet vial by either leveling of this vial or pumping off the air that is over it. However, one must know the pressure to be applied in order to prevent under‐ or over‐compensation. The procedure herein introduced allows the easy calculation of this pressure by obtaining two electropherograms at two different values of separation voltage. The migration times of the peaks allow the calculation of the apparent mobilities even in the presence of the laminar flow. Therefore, one can calculate the contributions from both electrophoresis and hydrodynamic flow, and finally the pressure associated with the undesirable flow. This pressure is then applied as a negative pressure at the inlet vial in the following experiments. Increase of up to 192% in the number of plates was obtained in a simple experiment. In addition, the bubble forming caused by the ESI suction during injection was prevented by turning off the nebulizer gas during the changes of inlet vials.

Amphetamine and derivatives in natural weight loss pills and dietary supplements by capillary electrophoresis-tandem mass spectrometry

A capillary electrophoresis-tandem mass spectrometry (CE-MS/MS) method for amphetamine (AM), phentermine (PTM), methamphetamine (MAM), methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA), and methylenedioxyethylamphetamine (MDEA) in commercial samples of homeopathic and phytotherapic medicines and dietary supplements is presented. The samples were submitted to a modified QuEChERS extraction procedure (at apparent pH 13) followed by electrophoretic separation in 0.1molL-1 formic acid electrolyte (pH 2.4) and detection by ESI-MS/MS. A polyvinyl alcohol coated capillary was employed to prevent the adsorption of the analytes to the capillary wall. The limits of detection and quantitation were from 0.02 to 0.06μgL-1 and from 0.06 to 0.21μgL-1, respectively, with recovery ranging from 85 to 123% and the standard deviations were not greater than 6.1%. In addition, the separation occurs in less than six minutes.

A capillary electrophoresis/tandem mass spectrometry approach for the determination of monoalkyl carbonates

The hemiesters of carbonic acid, which include the monoalkyl carbonates (MACs), are a poorly-known class of species with potential interest for biological processes. Capillary electrophoresis (CE) with tandem mass spectrometry is herein introduced as a complementary technique to CE with capacitively coupled contactless conductivity detection (C4D) for the study of MACs. Multiple reactions monitoring mode was used to improve sensitivity and selectivity, the loss of CO2 (44 u) at low collisional energy being the key feature of the MACs. To improve the control over the temperature – and consequently over the hydrolysis of the MACs during the electrophoretic migration – a thermostating case for the silica capillary was developed. Quantitation was possible by using the estimated concentration of MAC from the initial concentrations of the reagents and the equilibrium constant in the calibration procedure. The LOD for monoethyl carbonate was 0.2 μmol L−1, which is ca. two orders of magnitude lower than the LOD obtained by CE-C4D. Using a modified BGE for the separation of MACs, the LODs for mono-3-pentyl, mono-1-butyl, mono-2-propyl, and monoethyl carbonates were 0.2, 0.5, 2, and 1.3 μmol L−1, respectively.

Formation of isomers of anionic hemiesters of sugars and carbonic acid in aqueous medium

Hemiesters of carbonic acid can be freely formed in aqueous media containing HCO3(-)/CO2 and mono- or poly-hydroxy compounds. Herein, (13)C NMR spectroscopy was used to identify isomers formed in aqueous solutions of glycerol (a prototype compound) and seven carbohydrates, as well as to estimate the equilibrium constant of formation (Keq). Although both isomers are formed, glycerol 1-carbonate corresponds to 90% of the product. While fructose and ribose form an indistinct mixture of isomers, the anomers of d-glucopyranose 6-carbonate correspond to 74% of the eight isomers of glucose carbonate that were detected. The values of Keq for the disaccharides sucrose (4.3) and maltose (4.2) are about twice the values for the monosaccharides glucose (2.0) and fructose (2.3). Ribose (Kequ2009=u20090.89)-the only sugar without a significant concentration of a species containing a -CH2OH group in an aqueous solution-resulted in the smallest Keq. On the basis of the Keq value and the concentrations of HCO3(-) and glucose in blood, one can anticipate a concentration of 2-4 µmol L(-1) for glucose 6-carbonate, which corresponds to ca. of 10% of its phosphate counterpart (glucose 6-phosphate).

Nitroprusside as a Novel Reagent for Flow Injection Spectrophotometric Determination of Captopril

ABSTRACT A novel flow injection system for the determination of captopril in pharmaceutical formulations is described. Nitroprusside was employed as a new, nontoxic reagent. Captopril reacted with nitroprusside in basic solution to yield a red chromophore with maximum absorbance at 521 nm. The calibration relationship was linear for concentrations from 3.0 × 10−6 to 1.0 × 10−3 mol L−1 with a limit of detection of 1.0 × 10−6 mol L−1. The recoveries from captopril tablets were between 99.7 and 102.3%. The sampling frequency was 50 h−1 and the relative standard deviation was estimated to be 1.0% for 5.0 × 10−4 mol L−1 captopril. A paired t-test showed that analysis of tablets by the flow procedure and a potentiometry provided similar results at the 95% confidence level.

Phytochemical characterization of the Vochysia rufa (Vochysiaceae) extract and its effects on oxidative stress in the pancreata of streptozotocin-induced diabetic rats

Aqueous extract of macerated Vochysia rufa stem bark has been commonly used in the treatment of diabetes. Therefore, we evaluated the antihyperglycemic and antioxidant effects of an extract of V. rufa on the pancreata of streptozotocin (STZ)-induced diabetic rats. Animals received one of the following treatments daily by oral gavage: water (diabetic-control), V. rufa extract (diabetic-V. rufa), or glibenclamide (diabetic-GBD). Total antioxidant capacity; levels of thiobarbituric acid reactive substances, reduced glutathione, and sulfhydryls; and superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities were measured in the pancreas. Biochemical analysis of serum total cholesterol and fractions, triglycerides, creatinine, urea, acid uric, ALP, γ-GT, AST, and ALT was performed, and pancreatic β-cells positive for insulin were evaluated by immunohistochemistry. Rats treated with extract exhibited a decrease in fasting blood glucose compared with levels in diabetic control rats. GPx activity and sulfhydryl levels were significantly lower in diabetic-V. rufa rats compared with those of diabetic-control rats. V. rufa extract acted to normalize the biochemical alterations found in diabetic rats (diabetic-controls), as demonstrated by increases in urea, HDL, ALP, AST, and ALT. Reduction in blood glucose was independent of an increase in insulin. The V. rufa extract was found to be composed of free sugars (inositol, galactose, glucose, mannose, sucrose, arabinose, and ribose) as the main metabolites. Thus, aqueous extract of the stem bark of V. rufa is capable of reducing blood glucose, resulting in an antioxidant effect on the pancreatic tissue of STZ-diabetic rats.

A Compact Microcontrolled Microfluidic System for Photometric Determination of Phosphate in Natural Water Samples

A compact environmentally friendly microcontrolled microfluidic device ideal for in situ phosphate determination was developed based on a microsystem based on low-temperature co-fired ceramics (LTCC) coupled to a light-emitting diode (LED)–photometer with a multicommutation flow analysis (MCFA) approach. The experimental parameters of the MCFA analyzer were optimized by chemometric studies. Under the best experimental conditions, limits of detection and quantification of 0.02u2009mgu2009Pu2009L–1 and 0.07u2009mgu2009Pu2009L–1, respectively, and a sampling frequency of 67u2009h–1 were estimated. Moreover, a low sample consumption of only 60u2009μL per determination was the other advantage that fully meets the requirements of sustainable research and green chemistry purposes.