In the present work, a fast, easy and efficient analytical method was developed and validated for the determination of phenolic compounds (4-hydroxybenzoic, vanillic, caffeic, p-coumaric, sinapic, ferulic and ellagic acids, and naringenin) in red sweet pepper. Extraction of phenolic compounds was carried out using the quick, easy, cheap, effective, rugged and safe (QuEChERS) method, followed by separation and detection using ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). When the acetate version of the QuEChERS method was used, higher amounts of the phenolic compounds were extracted. In the dispersive solid phase extraction (d-SPE) clean-up step, combination of 50 mg of octadecylsilane (C18) and 7.5 mg of graphitized carbon black (GCB), resulted in the greatest removal of interferents, especially carotenoids, without significant retention of phenolic compounds. The recoveries for the proposed method were 82-103%, the limits of quantification were 2-150 µg kg-1, and the precision values expressed in terms of relative standard deviation (RSD) were ≤ 15%. The method developed was successfully applied to the analysis of different red sweet pepper cultivars.

Liquid chromatography is often used for the determination of pesticide multiresidues in foods. In Brazil, the strawberry crop is an example of a food with high levels of irregularities because of the application of pesticides. This is a major concern from the perspective of food safety, environmental protection, and certification for food export. The purpose of this study is to evaluate and compare chromatographic separation and detection methods in relation to a newly developed and validated method using ultra high performance liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) for the analytical determination of pesticides in strawberries. The comparisons were based on evaluations of the analysis time, consumption of the solvent in the mobile phase, injection volume, detectability, matrix effect, and recovery. The results showed that the LC–MS/MS and UHPLC–MS/MS techniques were both extremely efficient at analyzing pesticide residues with different physico-chemical parameters that were present at low concentrations in a complex matrix. The UHPLC separation method provided better chromatographic performance and productivity, which contributed favorably to routine analytical determinations. Detection by MS/MS had better detectability and selectivity compared with the diode array detector.

The constant evolution of science and the growing demand for new technologies have led to new techniques in instrumentation that can improve detection, separation, resolution, and peak capacity. Comprehensive two-dimensional liquid chromatography (LC×LC) is presented as a powerful tool in complex sample analyses. During an analysis, a sample is subjected to two independent separation mechanisms that are combined, resulting in increased resolving power. For appropriate application of LC×LC, understanding the influence of parameters that require optimization is necessary. The main purpose of optimization is to predict the combination of stationary phases, separation conditions, and instrumental requirements to obtain the best separation performance. This review discusses theoretical, intrumental, and chemometric aspects of LC×LC and focuses on its applications in foods. It aims to provide a clear understanding of the aspects that can be used as strategies in the optimization of this analytical method.

This review first discusses the limitations of many of the supports and stationary phases used in reversed phase high performance liquid chromatography and then describes those, developed more recently, that present better stabilities and more versatile selectivities. Emphases will be given to stationary phases that use higher purity silicas, hybrid silicas, monolithic silicas, metallic oxides and mixed oxides as supports and those that have embedded polar groups or contain phenyl or fluoro groups as the stationary phase as well as the phases used for mixed mode or hydrophilic interaction separations. These modern stationary phases facilitate the analysis of complex mixtures.

O aumento da estabilidade química e a redução da alta atividade de grupos residuais têm sido, nas últimas quatro décadas, os principais focos de pesquisas na preparação de fases estacionárias para cromatografia líquida de alta eficiência na modalidade de fase reversa (CLAE-FR). Novas e eficientes estratégias de modificação da superfície da sílica e a introdução de novos materiais como suportes cromatográficos têm minimizado estas limitações e possibilitado uma crescente popularização da CLAE-FR. Neste trabalho será apresentada uma visão geral do estado da arte de uma das estratégias de preparo de fases estacionárias que vem contornando tais limitações da CLAE-FR; as fases estacionárias baseadas na imobilização de polímeros orgânicos pré-sintetizados sobre partículas de sílica e sílica metalizada (zirconizada e titanizada). Uma consideração especial será dada ao desenvolvimento destas fases estacionárias ocorrido no Brasil nos últimos 15 anos.

Increasing stability and reducing the high activity of residual groups from stationary phases have been the main focuses of research on the preparation of reversed-phase high-performance liquid chromatography (RP-HPLC) phases over the last four decades. New and more efficient strategies for modifying the silica surface as well as the introduction of new chromatographic supports have minimized these effects and have enabled the increasing popularization of RP-HPLC. In this paper, an overview will be given of the state-of-the-art in stationary phases for RP-HPLC based on immobilization of pre-synthesized organic polymers on both silica and metalized-silica supports. Special consideration is given to the development of HPLC stationary phases in Brazil in the past 15 years.

Chromatography combined with several different detection systems is one of the more used and better performing analytical tools. Chromatography with tandem mass spectrometric detection gives highly selective and sensitive analyses and permits obtaining structural information about the analites and about their molar masses. Due to these characteristics, this analytical technique is very efficient when used to detect substances at trace levels in complex matrices. In this paper we review instrumental and technical aspects of chromatography-tandem mass spectrometry and the state of the art of the technique as it is applied to analysis of toxic substances in food.

Sílica organicamente modificada e molecularmente impressa foi preparada através de um procedimento sol-gel simples, e avaliada como sorvente específico para extração em fase sólida (Solid Phase Extraction, SPE) de fenobarbital em amostras aquosas e forenses. As propriedades analíticas dessa sílica molecularmente impressa (MIS, molecularly imprinted silica) foram inicialmente avaliadas e o material determinado como específico para as espécies-alvo: o fator de impressão IF, medido como a razão entre o pico do fenobarbital em cromatogramas de MIS e NIS (sílica não-impressa) foi estimado como 58. Este valor é consideravelmente maior que aquele apresentado normalmente para sorventes de impressão convencional baseados em metacrilatos e sugere que interações não-específicas analito/sorvente são insignificantes no MIS. O material foi aplicado no isolamento de fenobarbital de amostras aquosas e plasma; limites de detecção de 10 e 62 µg mL-1, respectivamente, foram encontrados para essas amostras.

A molecularly imprinted organically modified silica was prepared through a simple sol-gel procedure, and evaluated as specific sorbent for solid-phase extraction (SPE) of phenobarbital from aqueous and forensic samples. The analytical properties of the molecularly imprinted silica (MIS, non-imprinted sílica) were initially evaluated and the MIS was found to be specific towards the target species: the imprinting factor IF, measured as the ratio between phenobarbital peak areas in the MIS and NIS chromatograms, was estimated as 58. This value is considerably higher than those usually found for conventional methacrylate-based molecularly imprinted sorbents and suggests that non-specific analyte/sorbent interactions are insignificant in the MIS. This material is applied to the isolation of phenobarbital from aqueous samples and plasma; detection limit of 10 and 62 µg mL-1 was achieved for the former samples, respectively.

This paper presents an easy and practical procedure to obtain silica-based C-8 type sorbents for use in solid-phase extraction. The materials are prepared by depositing poly(methyloctylsiloxane), PMOS, on the silica support. Two different treatments for immobilization were used: thermal treatment or gamma irradiation. Suitable recoveries were obtained after pre-concentration of dilute solutions, at the ng/L level, of a mixture of pesticides, indicating the good performance of the materials.

Monolithic stationary phases represent a new generation of chromatographic separation media. These phases consist of a continuous separation bed prepared by in situ polymerization or consolidation inside the column tubing. In recent years, their simple preparation procedure, unique properties and excellent performance have attracted quite remarkable attention in liquid chromatography and capillary electrochromatography. This review summarizes the preparation, characterization and applications of monolithic stationary phases. The analytical potential of these columns is demonstrated with separations involving various families of compounds in different separation modes.

The present work reviews recent advances in the preparation of new reversed phase packing materials such as sterically protected, bidentate, hybrid organic-inorganic and monolithic phases and phases containing embedded polar groups. The bonding chemistry involved in the preparation of these phases as well as their advantages over conventional C8 and C18 reversed phases are discussed. Understanding the reasons behind the development of these newer column packings helps analysts select the best stationary phase for a given application.

Particles of porous silica or other solvent resistent inorganic oxides can be functionalized by aliphatic (e.g., C-8 or C-18) or other groups to give stationary phases for use in reversed phase HPLC. The functionalization can be done by bonding of individual groups to the surface of the support particles, by producing an organic polymeric film from pre-polymers, or by adsorbing/immobilizing pre-formed polymers on the surfaces. These three types of functionalization are reviewed.

When organic compounds present in biological fluids are analysed by chromatographic methods, it is generally necessary to carry out a prior sample preparation due the high complexity of this type of sample, especially when the compounds to be determinated are found in very low concentrations. This article describes some of the principal methods for sample preparation in analyses of substances present in biological fluids. The methods include liquid-liquid extraction, solid phase extraction, supercritical fluid extraction and extraction using solid and liquid membranes. The advantages and disadvantages of these methods are discussed.