Aplicação do ultra-som em sistemas eletroquímicos: considerações teóricas e experimentais

The aim of this review is to present and discuss the applications of ultrasound in electrochemical systems such as in sonoelectroanalysis and sonoelectrolysis for the electrochemical combustion of organic compounds. Initially, theoretical and experimental aspects are discussed, particularly those related to the enhancement of mass transport and the surface cleaning effects. Some results are included to illustrate alternative geometries for the experimental measurements and the working electrodes used in these systems. In the sequence, the available publications are presented and discussed to demonstrate that ultrasound combined with electrochemical techniques is a powerful set-up for the detection of analytes such as metals and/or organic compounds in hostile media and for the effective destruction of toxic organic substances. At the end, a table summarizes the results already published in the literature.

Determination of Cd and Pb in fuel ethanol by filter furnace electrothermal atomic absorption spectrometry

A method was developed for quantification of Cd and Pb in ethanol fuel by filter furnace atomic absorption spectrometry. Filter furnace was used to eliminate the need for chemical modification, to stabilize volatile analytes and to allow the application of short pyrolysis step. The determinations in samples were carried out against calibration solutions prepared in ethanol. Recovery tests were made in seven commercial ethanol fuel samples with values between 90 and 120%. Limits of detection were 0.1 µg L-1 for Cd and 0.3 µg L-1 for Pb. Certified water samples (APS 1071, APS 1033, NIST 1643d, NIST 1640) were also used to evaluate accuracy and recoveries from 86.8% to115% were obtained.

Eletrocromatografia capilar: contextualização, estado da arte e perspectivas

Capillary electrochromatography (CEC) is a separation technique in which the mobile phase flow is based on the application of a voltage across a packed capillary, which generates an electroosmotic flow that transports the analytes along the capillary toward the detector. As it combines the separation mechanisms of high-performance liquid chromatography (HPLC) and of capillary electrophoresis (CE), CEC can be considered a hybrid of HPLC and CE. This review presents some fundamental aspects of CEC and is focused on the instrumental advances of the technique, such as column technology, operation modes and detection systems, presenting recent papers on these topics and some applications and perspectives about CEC.

Validation of an analytical methodology for the quantitative analysis of petroleum hydrocarbons in marine sediment samples

This work describes a validation of an analytical procedure for the analysis of petroleum hydrocarbons in marine sediment samples. The proposed protocol is able to measure n-alkanes and polycyclic aromatic hydrocarbons (PAH) in samples at concentrations as low as 30 ng/g, with a precision better than 15% for most of analytes. The extraction efficiency of fortified sediments varied from 65.1 to 105.6% and 59.7 to 97.8%, for n-alkanes and PAH in the ranges: C16 - C32 and fluoranthene - benzo(a)pyrene, respectively. The analytical protocol was applied to determine petroleum hydrocarbons in sediments collected from a marine coastal zone.

Otimização e validação de métodos analíticos para determinação de BTEX em água utilizando extração por headspace e microextração em fase sólida

Three analytical methods for the determination of BTEX in water were optimized and validated. With the best method the analytes were extracted of 10 mL of sample with 2.50 g of NaCl in headspace vial of 20 mL by HS and SPME to 40 ºC for 30 min for adsorption and to 250 ºC for 4 min for desorption and were analyzed by GC-MS. The recovery was between 97.9% and 104.3%, and the limit of detection was 2.4 ng L-1 for o-xylene. This method was using to analyze BTEX in water supply and surface water in Ouro Preto city. No sample had concentrations of BTEX above the legislation.

Estratégias de pré-concentração em eletroforese capilar: parte 2. Manipulação da velocidade da fase dispersa/secundária

This work describes CE preconcentration strategies based on the effect of manipulation of the disperse/secondary velocity. Introduced by Terabe et al. in 1984, micellar electrokinetic chromatography is a powerful separation approach that increases the usage of electrokinetic phenomena for the separation of nonionic compounds. The main disadvantage of MEKC is the low concentration sensitivity associated with the limited optical path length for on-capillary photometric detection and the limited volume of sample solution that can be injected. This paper compiles on-line concentration strategies for neutral analytes by sample stacking and sweeping in micellar electrokinetic chromatography.

Desenvolvimento de métodos analíticos para determinação de agrotóxicos em sedimentos por cromatografia gasosa monodimensional e bidimensional abrangente com micro detector de captura de elétrons

The development of analytical methods for determination of eight pesticides of different chemical classes (trichlorfon, propanil, fipronil, propiconazole, trifloxystrobin, permethrin, difenoconazole and azoxystrobin) in sediments with gas chromatography-micro-electron capture detector (GC/µECD) and comprehensive two-dimensional gas chromatography with micro-electron capture detector (GCxGC/µECD) is described. These methods were applied to real sediment samples, and the best results were obtained using a 5% diphenyl-methylpolysiloxane column for 1D-GC. For GCxGC the same column was employed in the first dimension and a 50%-phenyl-methylpolysiloxane stationary phase was placed in the second dimension. Due to the superior peak capacity and selectivity of GCxGC, interfering matrix peaks were separated from analytes, showing a better performance of GCxGC.

Determinação simultânea de trialometanos e agrotóxicos em água por cromatografia gasosa

A method for simultaneous analysis of trihalomethanes and organochloride and pyrethroid pesticides in water utilizing SPME-HS and GC-ECD was developed. In the optimized method 25 mL of water containing 2% (w/v) Na2HPO4 were heated to 60 °C for 50 min. The fiber (PDMS - 100 μm) was exposed to a headspace for the same period. For all analytes it was found that LOQ < MCL (Maximum Contaminant Level), CV < 20% and r > 0.9. The method was applied to potable and surface water samples. Some trihalomethanes were encountered in potable waters, at levels below the MCL.

Aplicação da cromatografia gasosa bidimensional abrangente com microdetector de captura de elétrons para determinação de agrotóxicos em sedimentos

Analysis of seven pesticides in sediments was successfully achieved using comprehensive two-dimensional gas chromatography with micro-electron capture detection, as it provided higher sensitivity and less matrix interference. Repeatability and intermediate precision of peak areas and heights were less than 4% and the recovery percentage for the analytes ranged from 52 to 115%. Instrumental LOD and LOQ were in the range of 0.60 to 2.31 μg L-1 and 1.83 to 5.62 μg L-1, respectively. Concentrations of 3.34 μg kg-1 (dry basis) for trifloxystrobin and azoxystrobin (below the LOQ) were found in a sediment sample.

Desenvolvimento e validação de método analítico para determinação de benzoato, sorbato, metil e propilparabenos em produtos alimentícios utilizando a eletroforese capilar

In this work, a rapid and simple method using capillary electrophoresis (CE) was developed for the determination of the benzoate, sorbate, methyl and propylparaben in foodstuffs. A running buffer consisting of 20 mmol L-1 (pH = 9.3) tetraborate enabled separation of the analytes in less than 5 min. The detector wavelength was set at 220 nm. The method was successfully applied to the analysis of sodas, sweeteners, sauces and juices. The range of preservatives found were from 478.5-466.6 mg kg-1 for methylparaben , 83.7-231.3 mg kg-1 for sorbate and 336.7-428.3 mg kg-1 for benzoate.

Sistema de análises em fluxo polivalente para a determinação espectrofotométrica de fármacos

A flow system based on the sandwich technique is proposed for the sequential determination of ascorbic acid, dipyrone, acetylcysteine, captopril and paracetamol. The procedure is based on the reduction of Cu(II) by the analytes followed by the spectrophotometric measurement of the complex of Cu(I) with 2,2'-biquinoline 4,4'-dicarboxylic acid. Linear responses were achieved in the µmol L-1 range, with coefficients of variation better than 1.7%. Sampling rate was estimated as 60 determinations per hour, consuming 230 µg of BQA and generating 2.5 mL of waste per determination. Results for commercial samples agreed with those obtained by procedures recommended by the American and European pharmacopeias at the 95% confidence level.

Principais técnicas de preparo de amostra para a determinação de resíduos de agrotóxicos em água por cromatografia líquida com detecção por arranjo de diodos e por espectrometria de massas

The determination of pesticide residues in water samples by Liquid Chromatography require sample preparation for extraction and enrichment of the analytes with the minimization of interferences to achieve adequate detection limits. The Solid Phase Extraction (SPE), Solid Phase Microextraction (SPME), Stir Bar Sorptive Extraction (SBSE) and Dispersive Liquid-Liquid Microextraction (DLLME) techniques have been widely used for extraction of pesticides in water. In this review, the principles of these sample preparation techniques associated with the analysis by Liquid Chromatography with Diode Array Detection (LC-DAD) or Mass Spectrometry (LC-MS) are described and an overview of several applications were presented and discussed.

Análise por injeção em fluxo com detecção amperométrica de múltiplos pulsos: potencialidades e aplicações

The potentialities and applications of the Multiple Pulse Amperometric detection (MPA) coupled with Flow Injection Analysis (FIA) are evaluated. Important aspects as cleaning and activation of electrode surface, indirect and simultaneous analysis of electroactive compounds and the use of the internal standard method for quantifications utilizing FIA-MPA are presented. The main parameters concerning the detection of electroactive analytes by multiple pulse amperometric detection in flowing solutions were also discussed. In addition, aspects such as flow rate, sample volume, application time of the potential pulses and instrumentation necessary for implementing of the method were also addressed.

Evaluation of pesticide adsorption in gas chromatographic injector and column

Components in complex matrices can cause variations in chromatographic response during analysis of pesticides by gas chromatography. These variations are related to the competition between analytes and matrix components for adsorption sites in the chromatographic system. The capacity of the pesticides chlorpyrifos and deltamethrin to be adsorbed in the injector and chromatographic column was evaluated by constructing three isotherms and changing the column heating rate to 10 and 30 ºC min-1. By using ANCOVA to compare the slope of calibration graphs, results showed that the higher the injector temperature (310 ºC) the lower the pesticide adsorption. Also, deltamethrin influenced the adsorption of chlorpyrifos on the column chromatographic.

Chlorophenols in tap water from wells and surface sources in Rio de Janeiro, Brazil: method validation and analysis

Two analytical methods were validated for determination of trichlorophenols, tetrachlorophenols and pentachlorophenol in drinking water. Limits of quantification were at least ten times lower than maximum permissible levels set by the Brazilian legislation, which are 200 ng mL-1 for 2,4,6-trichlorophenol and 9 ng mL-1 for pentachlorophenol. Chlorophenol levels were determined in tap water collected in the Municipality of Rio de Janeiro. 2,4,6-Trichlorophenol residues were detected in 36% of the samples, varying from 0.008 to 0.238 ng mL-1. All other analytes were below the limit of quantification. The validated methods showed to be suitable for application in routine quality control.