Bruno Henrique Fumes

The role of graphene‐based sorbents in modern sample preparation techniques

The application of graphene-based sorbents in sample preparation techniques has increased significantly since 2011. These materials have good physicochemical properties to be used as sorbent and have shown excellent results in different sample preparation techniques. Graphene and its precursor graphene oxide have been considered to be good candidates to improve the extraction and concentration of different classes of target compounds (e.g., parabens, polycyclic aromatic hydrocarbon, pyrethroids, triazines, and so on) present in complex matrices. Its applications have been employed during the analysis of different matrices (e.g., environmental, biological and food). In this review, we highlight the most important characteristics of graphene-based material, their properties, synthesis routes, and the most important applications in both off-line and on-line sample preparation techniques. The discussion of the off-line approaches includes methods derived from conventional solid-phase extraction focusing on the miniaturized magnetic and dispersive modes. The modes of microextraction techniques called stir bar sorptive extraction, solid phase microextraction, and microextraction by packed sorbent are discussed. The on-line approaches focus on the use of graphene-based material mainly in on-line solid phase extraction, its variation called in-tube solid-phase microextraction, and on-line microdialysis systems.

Use of graphene supported on aminopropyl silica for microextraction of parabens from water samples

This paper describes the synthesis, characterization and use of graphene supported on aminopropyl silica through covalent bonds (Si-G) as a sorbent for microextraction by packed sorbent (MEPS). Five parabens (methyl, ethyl, propyl, butyl and benzyl) present in water matrices were used as model compounds for this evaluation. The Si-G phase was compared to other sorbents used in MEPS (C18 and Strata™-X) and also with graphene supported on primary-secondary amine (PSA) silica, where Si-G showed better results. After this, the MEPS experimental parameters were optimized using the Si-G sorbent. The following variables were optimized through univariate experiments: pH (4,7 and 10), desorption solvent (ACN:MeOH (50:50), ACN:H2O (40:60), MeOH and ACN) and ionic strength (0, 10 and 20% of NaCl). A factorial design 26-2 was then employed to evaluate other variables, such as the sample volume, desorption volume, sampling cycles, wash cycles and desorption cycles, as well as the influence of NaCl% on the extraction performance. The optimized method achieved a linear range of 0.2-20μg/L for most parabens; weighted calibration models were employed during the linearity evaluation to reduce the absolute sum of the residue values and improve R2, which ranged from 0.9753 to 0.9849. The methods accuracy was 82.3-119.2%; precision, evaluated as the coefficient of variance for intraday and interday analysis, ranged from 1.5 to 19.2%. After evaluation of the figures of merit, the method was applied to the determination of parabens in water samples.

Determination of pesticides in sugarcane juice employing microextraction by packed sorbent followed by gas chromatography and mass spectrometry

This paper describes the development of a method for the determination of six pesticides (tebuthiuron, carbofuran, atrazine, metribuzine, ametryn, and bifenthrin) in sugarcane juice using microextraction by packed sorbent as the extraction technique. The extraction steps were optimized by factorial design, being the variables pH, ionic strength, desorption solvent and solvent volume optimized for comparisons among sorbent materials. Among the evaluated materials C18-Chromabond(®) showed better extraction efficiency. A factorial design 2(3) with central point was used for the extraction cycles optimization. Draw/eject and washes cycles showed significant improvements in the extraction efficiency when the number of cycles increased. The method was validated and showed a limit of quantification in the range of 2.0-10.0 μg.L(-1) . The calibration curves were constructed by weighting models that reduced the sum of absolute residues values and improved determination coefficient. The matrix factor and extraction efficiency were 97.3-77.3% and 27.1-64.8%, respectively. The accuracy was 71.7-106.9%; precision evaluated as the coefficient of variance obtained in intra and inter day analysis was 4.5-15.9%. The method was applied to the determination of pesticide residues in four sugarcane juice samples commercially available in markets from different cities from São Paulo state, Brazil.

New materials for sample preparation techniques in bioanalysis

The analysis of biological samples is a complex and difficult task owing to two basic and complementary issues: the high complexity of most biological matrices and the need to determine minute quantities of active substances and contaminants in such complex sample. To succeed in this endeavor samples are usually subject to three steps of a comprehensive analytical methodological approach: sample preparation, analytes isolation (usually utilizing a chromatographic technique) and qualitative/quantitative analysis (usually with the aid of mass spectrometric tools). Owing to the complex nature of bio-samples, and the very low concentration of the target analytes to be determined, selective sample preparation techniques is mandatory in order to overcome the difficulties imposed by these two constraints. During the last decade new chemical synthesis approaches has been developed and optimized, such as sol-gel and molecularly imprinting technologies, allowing the preparation of novel materials for sample preparation including graphene and derivatives, magnetic materials, ionic liquids, molecularly imprinted polymers, and much more. In this contribution we will review these novel techniques and materials, as well as their application to the bioanalysis niche.

An overview of multidimensional liquid phase separations in food analysis

Food safety is a priority public health concern that demands analytical methods capable to detect low concentration level of contaminants (e.g. pesticides and antibiotics) in different food matrices. Due to the high complexity of these matrices, a sample preparation step is in most cases mandatory to achieve satisfactory results being usually tedious, lengthy, and prone to the introduction of errors. For this reason, many research groups have focused efforts on the development of online systems capable to do the cleanup, concentration, and separation steps at once through multidimensional separation techniques (MDS). Among several possible setups, the most popular are the multidimensional chromatographic techniques (MDC) that consist in combining more than one mobile and/or stationary phase to provide a satisfactory separation. In the present review, we selected a variety of multidimensional separation systems used for food contaminant analysis in order to discuss the instrumentation aspects, the concept of orthogonality, column approaches used in these systems, and new materials that can be used in these columns. Selected classes of contaminants present in food matrices are introduced and discussed as example of the potential applications of multidimensional liquid phase separation techniques in food safety.

Unified chromatography: Fundamentals, instrumentation and applications†

The concept of unified chromatography has been in existence for 50 years after the work of Giddings proposing that all modes of chromatography (gas chromatography, liquid chromatography, supercritical fluid chromatography and so on) may be treated together under a single unified theory. His idea was partially fulfilled 23 years later by Ishii, Takeuchi and colleagues, who demonstrated for the first time the possibility to analyze a complex sample containing substances with a wide range of boiling points and polarities in the same instrument and column, just by varying the mobile phase pressure and temperature to change from one chromatographic mode to another. This approach has been demonstrated through application to the separation of complex mixtures in several areas including crude oil, edible oils and polymers. Still, unified chromatography has not yet been fully developed. In the present work, we will review the fundamentals, instrumentation and several applications of the technique. Also discussed are the drawbacks that still hinder development, as well as the recent developments and trends in instrumentation and columns that suggest the most feasible ways forward to the full development of unified chromatography.

Graphene particles supported on silica as sorbent for residue analysis of tetracyclines in milk employing microextraction by packed sorbent

This paper describes the use of graphene‐based sorbents for determination of four tetracyclines in milk. The synthesized materials were combined with microextraction by packed sorbent (MEPS) to act as the sample preparation step. The extraction performance of these sorbents was compared to commercial phases, and graphene supported on silica provided the best results. The analytical method optimization was carried out by employing experimental design. Firstly, an evaluation of the experimental variables (elution solvent, use of EDTA, ionic force, and pH of the washing solution) was made by a 24‐1 factorial experimental design. The variables sampling, washing and elution cycles of MEPS were further optimized under a full 23 experimental design. The validation parameters were determined under optimized conditions resulting in a linearity ranging from 15 to 110 μg/L with R2 values above 0.98, and LOQs ranging from 0.05 to 0.9 μg/L. The accuracy ranged from 87.9 to 118.4% and intra/inter‐day precision reported by the RSDs were lower than 19%. The proposed and validated method was successfully applied to the analysis of 11 milk samples from different animals, revealing traces of tetracyclines in only two of them. This study focused on the evaluation of graphene‐based sorbents combined with MEPS for tetracycline analysis provided equivalent or even better results than other proposed methods, suggesting being a sensitive, fast and reliable alternative method for the determination of tetracyclines in milk samples.

Study of the Mode of Inclusion for 7-Hydroxyflavone in β-Cyclodextrin Complexes

This paper aimed to study the mode of inclusion for 7-hydroxyflavone (7HF) in β-cyclodextrin (β-CD) complex in basic (pH 12) and acid (pH 4.5) media. The thermodynamic parameters of the complexation of 7HF with β-CD were evaluated by means of steady-state fluorescence and solubility measurements at several temperatures. The 7HF–β-CD inclusion complex was spontaneously formed at 1:1 stoichiometry in both basic and acid media. The high number of hydrogen bonds formed between the host and the guest molecules favored complexation in the basic medium, with a ground-state equilibrium constant (K) of 990 ± 130 mol −1 L, at 25 o C. The quantum-mechanics calculations showed that complexation of 7HF (neutral or anionic form) with β-CD occurred mainly via the phenyl group of the flavonoid. This result agreed with the induced circular dichroism signal of 7HF complexed with β-CD.

Miniaturized Column Liquid Chromatography

Abstract Miniaturization in liquid chromatography (LC) has received considerable attention from analysts since the demonstration of its advantageous applicability in diverse fields including the OMICS arena (proteomics, metabolomics, foodomics, lipodomics, etc.) as well as several other niches such as environmental, biological, foodstuff, and pharmaceutical analysis. Although the first attempts to miniaturize modern LC systems started around 1967, these efforts have not yet been completed, with several practical problems still to be solved. Therefore, this is still an open and exciting area for research involving new instrumentation, columns improvement, novel sorbent materials, smaller volume detectors, lower dead volume connections, multidimensional systems, and so on. Among the main difficulties still hindering the wide implementation of miniaturized LC, particularly in routine labs, a major one relates to the absence of appropriate and robust commercial instrumentation designed and dedicated to mini-LC, instead of rough adaptation from conventional high-performance LC instrumentation. Removing this obstacle will facilitate the expansion of this exciting research area involving new instrumentation, columns improvement, novel sorbent materials, smaller volume detectors, lower dead volume connections, multidimensional systems, and robust miniaturized columns available with a large range of stationary phases prepared with distinct chemical (sorbents) and physical (length, internal diameter, and film thickness) characteristics. In this chapter, the main topics related to the recent advances and prospects for miniaturization of LC are discussed including the following: (1) instrumentation (pumps, column heater, tubing and connectors, sample introduction, and detectors); (2) column technology, including both filled (monolithic and packed capillary/nano-LC columns) and open-tubular columns (wall-coated open-tubular and porous layer open-tubular columns); and (3) simplified theory of micro- and nano-LC. Furthermore, the recent development of nanomaterials fully compatible with the principles of micro- and nano-LC are presented and discussed, including monoPLOT columns and molecularly imprinted polymer monolithic columns. Selected applications of miniaturized LC as well as the coupling of capillary and nano-LC columns with mass spectrometry are also addressed.

Packed in-tube solid phase microextraction with graphene oxide supported on aminopropyl silica: Determination of target triazines in water samples

ABSTRACT On-line in-tube solid phase microextraction (in-tube SPME) coupled to high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) was successfully applied to the determination of selected triazines in water samples. The method based on the employment of a packed column containing graphene oxide (GO) supported on aminopropyl silica (Si) showed that the extraction phase has a high potential for triazines extraction aiming to its physical-chemical properties including ultrahigh specific surface area, good mechanical and thermal stability and high fracture strength. Injection volume and loading time were both investigated and optimized. The method validation using Si-GO to extract and concentrate the analytes showed satisfactory results, good sensitivity, good linearity (0.2–4.0 µg L−1) and low detection limits (1.1–2.9 ng L−1). The high extraction efficiency was determined with enrichment factors ranging from 1.2–2.9 for the lowest level, 1.3–4.9 intermediate level and 1.2–3.0 highest level (n = 3). Although the analytes were not detected in the real samples evaluated, the method has demonstrated to be efficient through its application in the analysis of spiked triazines in ground and mineral water samples.