Antonio Luiz Pires Valente

Screening of Brazilian fruit aromas using solid-phase microextraction–gas chromatography–mass spectrometry

Manual headspace solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) was used for the qualitative analysis of the aromas of four native Brazilian fruits: cupuassu (Theobroma grandiflorum, Spreng.), cajá (Spondias lutea. L.), siriguela (Spondias purpurea, L.) and graviola (Anona reticulata, L). Industrialized pulps of these fruits were used as samples, and extractions with SPME fibers coated with polydimethylsiloxane, polyacrylate, Carbowax and Carboxen were carried out. The analytes identified included several alcohols, esters, carbonyl compounds and terpernoids. The highest amounts extracted, evaluated from the sum of peak areas, were achieved using the Carboxen fiber.

Applications of solid-phase microextraction to chemical analysis of live biological samples

This work reviews some recent applications of solid-phase microextraction (SPME) for the chemical analysis of live biological samples. Application of SPME to microbiological analysis, organic volatile compounds emitted by vegetables and insect semiochemicals will be discussed. A short discussion on the principles and the basic parameters of SPME is also included.

Microextração por fase sólida

Fundamental aspects of Solid Phase Micro-Extraction (SPME) are discussed in the present paper. The application of SPME as a microtechnique of sample preparation for gas chromatographic analysis is considered and related to existing theoretical models. Both research prototypes and commercial SPME devices are considered.

A Headspace Solid Phase Microextraction (HS-SPME) method for the chromatographic determination of alkylpyrazines in cocoa samples

A Headspace Solid Phase Microextraction (HS-SPME) procedure for isolation and determination of alkylpyrazines in cocoa liquor, using Gas Chromatography with Flame Ionization Detection (GCFID) for the separation and detection of the analytes, is presented here. The HS-SPME operational conditions were optimized using extractions of samples spiked with known amounts of alkylpyrazines typically found on cocoa products. The maximum extraction efficiency was obtained using SPME fibers coated with 65 µm Carbowax/divinylbenzene. Additionally, the best results were achieved with extraction temperature of 60 oC, 15 min of sample/headspace equilibration time and 45 min extraction time. It was also observed that suspending the samples in saturated aqueous NaCl solution during extractions resulted in a significant increment on the peak areas. This procedure was found to be effective to determine the so-called pyrazinic ratios (quotient between peak areas of alkylpyrazines), which are useful as quality parameters for cocoa liquor.

Aplicação de SPME (Solid Phase Micro-Extraction) na análise de águas potáveis de três localidades do estado de São Paulo

The technique of solid phase microextraction (SPME) was used for the extraction of halogenated contaminants of water samples from three cities of the State of Sao Paulo and the extracts were submitted to gas chromatographic analysis with electron capture detection (GC-ECD). In the samples of water collected at the city of Sao Paulo the detected level of trihalomethanes (THM) expressed as the sum of chloroform, dibromochloromethane and dichlorobromomethane, were higher than the permissible limit established by the Brazilian regulation. In the samples collected at the two other cities the level of any of the three THM remained below the sensitivity of the ECD.

Compound retention dependence of the response in a gas chromatography-atomic emission detection system

Abstract The relationship between the response of a laboratory-made GC–microwave-induced helium plasma atomic emission detection (MIP) system prototype and compound nature was studied by monitoring the carbon 247.9 nm atomic emission line. The test samples for this study were solutions of alkanes, arenes and haloarenes prepared at two concentration levels; varied plasma generation conditions (microwave input powers and helium support plasma gas flows) were evaluated. The statistical examination of the data pointed to a dependence between MIP signal and compound retention – less retained compounds tend to show reduced MIP signals.

Use of a Computer Controlled Hand-scanner for Quantitative Thin Layer Chromatographic Analysis

A microcomputer controlled hand-scanner was used as a densitometer for the quantitation of analytes after separation by TLC (thin layer chromatography). This densitometric process is based on measuring light intensity and counting the number of pixels covering the spots obtained for the analytes after TLC separation. The combination of the aforementioned process with the internal standardization method (ISM) of quantification enabled reliable quantitative data to be obtained for TLC. This methodology, which is simple and relatively inexpensive, has been successfully applied in the TLC analysis of ionic dyes, with less than 2% levels of precision and accuracy.

Extração e pré-concentração de compostos orgânicos voláteis por permeação em membrana para análise cromatográfica

This work discusses sample preparation processes for gas chromatography (GC) based on the technique of extraction through membrane permeation (MPE). The MPE technique may be easily coupled to GC via a relatively simple device, which is a module that holds the membrane and is directly connected to the GC column. The possibility of operational errors due to sample handling is substantially reduced in an MPE-GC system because the sample preparation and the chemical analysis are accomplished as a one-step process. The MPE technique is of relatively wide application as it can be used for aqueous samples, solid samples and gaseous samples. Depending on the type of sample the extraction is performed with the membrane in direct contact with the sample or in contact with its headspace. The MPE-GC technique is very useful in trace analysis, due to the time-dependent enrichment of the analyte. A typical application of MPE-GC is the analysis of VOCs present in water that may be accomplished with detection limits at the low ppb (mgL-1) level.

Feasibility of Use of the Microwave Induced Plasma Atomic Emission Detector as a Compound Independent Detector for Quantitative Chromatographic Analysis

The independence of the response of a Microwave Induced Plasma Atomic Emission Detector (GC-MIP) for Gas Chromatography with the chemical structure of the analyte has been exploited using as teste samples nine organochlorine compounds. With signal monitoring at the chlorine 479.5 nm emission line and after proper adjustment of the operational conditions of the GC-MIP the agreement of the detector response for the nine compounds was of 8.5% or less, which is adequate for the use of the compound-independent calibration method. It is proposed that the reliability of the quantitation after applying the compound-independent calibration methodology may be enhanced if a set of calibration compounds is used instead of a single calibration compound.

Modificação de um micro-extrator de vidro para pré-enriquecimento de traços de pesticidas organoclorados de água para análise por cromatografia gasosa

Two models of a glass micro-extractor were constructed after modification of a model proposed in the literature. The two models were used for the simultaneous extraction and enrichment of organochlorinated pesticides from aqueous matrixes to an organic solution appropriate for the gas chromatographic analysis of the pesticide. It was established that the performance of one of the modified micro-extractors permits the pre-concentration of the pesticides to a level that allow their quantitation at the trace level with electron capture detection. It is thus concluded that the glass micro-extractor is a suitable tool for the sample preparation step in the gas chromatographic analysis of environmental pollutants of the class of pesticides.