Haroldo Silveira Dórea

Simultaneous determination of eight pesticide residues in coconut using MSPD and GC/MS

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine dimethoate, malathion, lufenuron, carbofuran, 3-hydroxycarbofuran, thiabendazole, difenoconazole and trichlorfon in coconut pulp using gas chromatography-mass spectrometry with selected ion monitoring (GC/MS, SIM). Different parameters of the method were evaluated, such as type of solid-phase (C(18), alumina, silica-gel and Florisil), the amount of solid-phase and eluent (dichloromethane, acetone, ethyl acetate, acetonitrile, n-hexane and n-hexane:ethyl acetate (1:1, v/v)). The best results were obtained using 0.5 g of coconut pulp, 1.0 g of C(18) as dispersant sorbent, 1.0 g of Florisil as clean-up sorbent and acetonitrile saturated with n-hexane as eluting solvent. The method was validated using coconut pulp samples fortified with pesticides at different concentration levels (0.25-1.0 mg kg(-1)). Average recoveries (four replicates) ranged from 70.1% to 98.7%, with relative standard deviations between 2.7% and 14.7%, except for lufenuron and difenoconazole, for which recoveries were 47.2% and 48.2%, respectively. Detection and quantification limits for coconut pulp ranged from 0.02 to 0.17 mg kg(-1) and from 0.15 to 0.25 mg kg(-1), respectively.

Validation of an analytical method for analysis of cannabinoids in hair by headspace solid-phase microextraction and gas chromatography-ion trap tandem mass spectrometry.

The development of an analytical method for the determination of Delta(9)-tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) in samples of human hair is described. Samples were subjected to a procedure based on the combination of headspace solid-phase microextraction (HS-SPME) with gas chromatography linked with mass spectrometry operating in tandem mode (GC-MS/MS). A 10 mg aliquot of sample was firstly decontaminated using petroleum ether, deionized water and dichloromethane (2 mL of each solvent), for 10 min under sonication, and then digested in alkaline solution (1 mol L(-1) NaOH). The method variables evaluated were pH, mass of hair, fiber type, extraction temperature, desorption time, ionic strength, pre-equilibrium time and extraction time. Parameters concerning operation of the tandem mode MS/MS were also assessed and optimized. Validation of the method demonstrated excellent linearity in the range 0.1-8.0 ng mg(-1), with regression coefficients better than 0.994. Precision was determined using two different concentrations (upper and lower limits of the linear range), and RSD values were between 6.6 and 16.4%. Absolute recoveries (measured in triplicate) were in the range 1.1-8.7%, and limits of detection and quantification were 0.007-0.031 ng mg(-1) and 0.012-0.062 ng mg(-1), respectively. The LOQ for THC (0.062 ng mg(-1)) was below the cut-off value (LOQ < or = 0.1 ng mg(-1)) established by the Society of Hair Testing (SOHT), the Society of Toxicological and Forensic Chemistry (STFCh) and the Société Française de Toxicologie Analytique (SFTA). The optimized SPME method was applied in analysis of hair samples from Cannabis drug users, showing that CBN and CBD were present in all samples analyzed.

Multivariate optimization of a solid phase microextraction-headspace procedure for the determination of benzene, toluene, ethylbenzene and xylenes in effluent samples from a waste treatment plant

A method based on solid-phase microextraction (SPME) and gas chromatography with flame ionization detection (GC-FID) has been optimized for the determination of benzene, toluene, ethylbenzene and xylenes (BTEX) in water released from a waste treatment plant. The extraction step was optimized using fractional factorial and central composite designs including the following experimental factors: saline concentration; extraction time; desorption time; agitation velocity; headspace volume. A multiple function was used to describe the experimental conditions for simultaneous extraction of the compounds. The procedure, based on direct SPME at 50 degrees C, using a polydimethylsiloxane fiber, showed good linearity (r>0.997 over a concentration range 2-200 microg L(-1)) and repeatability (relative standard deviation (RSD)<4.23%) for all compounds, with limits of detection ranging from 0.05 to 0.28 microg L(-1), and limits of quantification ranging from 0.14 to 0.84 microg L(-1). Concentrations of the target compounds in these samples were between 145.8 and 1891 microg L(-1).

Hollow fiber-based liquid phase microextraction with factorial design optimization and gas chromatography–tandem mass spectrometry for determination of cannabinoids in human hair

A new method, based on hollow fiber liquid-phase microextraction (HF-LPME) and gas chromatography-tandem mass spectrometry (GC-MSMS), was developed for determination of Delta(9)-tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) in samples of human hair. Since hair is a solid matrix, the samples were subjected to alkaline digestion using NaOH. The aqueous solutions obtained were extracted using a 6cm polypropylene fiber (600microm i.d., 200microm wall thickness, 0.2microm pore size) for each extraction. A 2(5-1) fractional factorial design for screening, and a central composite design for optimization of significant variables, was applied during development of the extraction method. The variables evaluated were the type of extraction solvent, pH, stirring speed, extraction time, and acceptor phase volume. The optimized conditions for the proposed extraction procedure were 10mg of hair sample; 20microL of butyl acetate; aqueous (pH 14) donor phase containing 6.8% NaCl; 600rpm stirring speed; 20min extraction time. A linear response was obtained in the ranges 1-500pgmg(-1) (CBD and CBN) and 20-500pgmg(-1) (THC), with regression coefficients >0.99. Precision, determined as the relative standard deviation, was 3.3-8.9% (intra-day) and 4.4-13.7% (inter-day). Absolute recoveries varied in the ranges 4.4-4.8% (CBD), 7.6-8.9% (THC) and 7.7-8.2% (CBN). Limits of detection (LOD, S/N=3) and quantification (LOQ, S/N=10) were 0.5-15pgmg(-1) and 1-20pgmg(-1), respectively. The method was successfully used to determine CBD, THC and CBN in hair samples from patients in a drug dependency rehabilitation center. Concentrations varied in the ranges 1-18pgmg(-1) (CBD), 20-232pgmg(-1) (THC) and 9-107pgmg(-1) (CBN), confirming the suitability of the method for monitoring studies.

Determination of ethyl carbamate in cachaça produced from copper stills by HPLC

Ethyl carbamate (EC) is a common substance in fermented foods and drinks, and its quantification is important because of its carcinogenic nature and its usually presence in alcoholic beverages. The present work involved the development and validation of an analytical method for the evaluation of EC in cachaça by HPLC-FLD after previous derivatization with xanthydrol. The method presented a mean recovery of 94.88%, an intra-day precision of 4.19% (30.0 μgL(-1)) and 3.32% (75.0 μgL(-1)), a coefficient of determination (r(2)) equal to 0.9985, and limits of detection and quantification equal to 6.39 and 21.32 μgL(-1), respectively. The results show that the analytical method is accurate, reproducible and linear over the concentration range from 5.0 to 160 μg of EC per litre. The method was applied to the analysis of EC in cachaça, the analyses being rapid and efficient.

Development of MSPD method for the determination of pesticide residues in tomato by GC-MS

A simple and effective extraction method based on matrix solid-phase dispersion was developed to determine dimethoate, methyl-parathion, malathion, tebuconazole and cypermethrin in tomato using gas chromatography-mass spectrometry and selected ion monitoring (GC-MS, SIM). Different parameters of the method were evaluated, such as type of solid phase (C18, alumina, silica-gel and Florisil), the amount of solid phase and eluent [dichloromethane, ethyl acetate, n-hexane and n-hexane:ethyl acetate (1:1 and 1:3, v/v)]. The best results were obtained using 2.0 g of tomato, 0.5 g of alumina as dispersant sorbent, 0.5 g of Florisil as clean-up sorbent and dichloromethane as eluting solvent. The method was validated by fortified tomato samples at different concentration levels (0.05 to 4.0 mg kg-1). Average recoveries (7 replicates) ranged from 77% to 100% with relative standard deviation between 3.7% and 12.9%. Detection and quantification limits ranged from 0.01 to 0.02 mg kg-1 and 0.03 to 0.06 mg kg-1 for the whole fruit of tomato, respectively. The proposed method was applied to analyze of these compounds in commercial tomato samples and residues of methyl-parathion, dimethoate and malathion were detected on the tomato samples at concentrations below the maximum residue levels (MRLs) established by Brazilian legislation and Codex Alimentarius.

Analysis of Pesticide Residues in Rice Using Matrix Solid-Phase Dispersion (MSPD)

This work reports a multi-residue extraction method based on matrix solid-phase dispersion (MSPD) and capillary gas chromatography - electron capture detection for quantification of two widely used organophosphorus insecticides (malathion and parathion-methyl) and an organochlorine pesticide (b-endosulfan) in rice. A set of experiments was done with a spiked matrix with a standard mix, varying sample and solid phase amounts, solid phase and eluting solvent. Analyses of fortified rice samples were performed at different levels (0.5-10.0 mg kg-1). Mean recoveries from three replicates ranged from 75.5% to 116.0%, with coefficients of variation from 0.5% to 10.9%. The limit of detection was in the range of 20 to 105 pg for the pesticides. Commercial rice was analyzed for method application.

Evolution of the concentration of phenolic compounds in cachaça during aging in an oak (Quercus sp.) barrel

A cachaca, tradicional e popular bebida brasileira, e obtida por meio da destilacao do mosto fermentado de cana de acucar. Dentre as etapas do processo de producao da bebida, o envelhecimento natural consiste em armazena-la em recipientes de madeira apropriados por um tempo determinado, onde ocorrem alteracoes na composicao quimica, aroma, sabor e cor da bebida. Este trabalho teve como objetivo realizar um acompanhamento da composicao fenolica em diferentes periodos de envelhecimento da cachaca em tonel de carvalho (Quercus sp.). Foram realizadas coletas periodicas durante o periodo de envelhecimento da cachaca em tonel de carvalho e realizaram-se analise de treze compostos fenolicos utilizando a tecnica de cromatografia liquida de alta eficiencia com detector de arranjo de diodos (HPLC-DAD). Foi constatado um aumento progressivo na concentracao dos compostos analisados ao longo do periodo analisado, sendo que os compostos encontrados em maior concentracao foram siringaldeido e acido galico.

Distribution and sources of aliphatic hydrocarbons in surface sediments of Sergipe River estuarine system

The assessment of aliphatic hydrocarbons was performed in the Sergipe River estuarine system, northeastern Brazil. Aliphatic hydrocarbons concentration ranged from 9.9 ug g⁻¹ up to 30.8 ug g⁻¹ of dry sediment. The carbon preference index (CPI, based on nC₂₄ to nC₃₄ range), indicated predominance of petrogenic input in two of the sites analyzed (P4 and P5). The unresolved complex mixture (UCM) was found to be present in seven of the nine sites sampled (except for P4 and P5). Overall, the results of this work suggest that there is a mix of organic matter sources to the sediment. Although the coast of Sergipe has an intense off shore petroleum exploration and the Sergipe River crosses the entire city of Aracaju, the capital city of Sergipe, non-significant anthropogenic fingerprint was assessed.

APLICAÇÃO DA TÉCNICA DE DISPERSÃO DA MATRIZ EM FASE SÓLIDA (DMFS) NA ANÁLISE DE PESTICIDAS EM QUIABO POR CG-EM

A matrix solid phase dispersion and gas chromatography-mass selective detection method for the simultaneous determination of monocrotophos, methyl parathion, cypermethrin and deltamethrin in okra is described. Analyses of 2 g of fortified okra (0.05-0.75 mg kg-1) showed an average recovery of 96.2% (71.4-128.4%) and average relative standard deviation of 11.7% (1.4-37.1%). The cypermethrin recovery at the lower level was above 130%. The limit of detection ranged from 0.02 to 0.15 mg kg-1. The procedure was applied to the okra samples and has found 0.56 mg kg-1 of cypermethrin-cis, 0.75 mg kg-1 of cypermethrin-trans and 2.71 mg kg-1 of deltamethrin.