Application of an in-house packed octadecylsilica-functionalized graphene oxide column for capillary liquid chromatography analysis of hormones in urine samples.

Graphene oxide-based LC stationary phases were developed and applied for separating hormones from urine using capillaryLC-MS/MS. Using two analytical approaches - direct injection and column-switching arrangement - it was possible to evaluate the chromatographic parameters and perform tests on the raw biological fluid. Two stationary phases (SPs) were produced, varying the amino silica support particle diameter (Si, 5, and 10 µm). Graphene oxide was covalently bonded to the surface of Si particles, and this material was functionalized by the insertion of octadecylsilica groups, generating the SiGO-C18. Infra-red spectroscopy assays revealed that both steps were successful - supporting GO onto Si and further C18 customization. Scanning electron microscopy showed spherical geometries with minor irregularities and narrow particle size distribution for the produced SPs. The GO-coating rate was higher on the Si particles of 10 µm. As a result, the 10 µm produced column reported better resolution, efficiency, and peak capacity. Therefore, this SiGO-C18 capillary column (100 mm × 0.32 mm i.d., 10 µm dp) was applied successfully in a column-switching method to separate hormones in urine. Linearity (R2 above 0.99), quantification limits (between 1.0 and 5 µg/L), and other figures of merit of the method were determined. It is worth mentioning that the SiGO-C18 capillaryLC column performed adequately, separating the target compounds in less than 6 min. We hope this work could significantly contribute to shedding some light on graphene-based materials as a promising class of stationary phase for miniaturized liquid chromatography.

Multidimensional capillary liquid chromatography-tandem mass spectrometry for the determination of multiclass pesticides in "sugarcane spirits" (cachaças).

Cachaça or "sugarcane spirit" is a Brazilian beverage considered the third most consumed beverage worldwide. Sugarcane, its raw material, is one of the main crops developed in the country, placing Brazil as the largest producer of this commodity on a global scale. Considering the growth in sugarcane production, many farmers use pesticides in their crops. However, excess pesticides can be accumulated in products derived from sugarcane, creating an environmental and public health concern. In this context, the development of analytical methods capable of identifying residues of pesticides in cachaças and other sugarcane-derived products is essential to ensure the beverage's quality. This work presents a method to quantify multiclass pesticides in Brazilian sugarcane spirits (cachaças) through an automated multidimensional system. The first dimension consists of an extraction column packed with a graphene-silica phase, followed by a capillary liquid chromatography-tandem mass spectrometry system as the second dimension. The method was optimized by an experimental design, in which the influence of three variables was evaluated on the extraction process: percentage of acetonitrile, loading flow, and loading time. Afterward, twenty-two cachaças were analyzed to ascertain the applicability of the proposed method. The analyses reported five samples containing clomazone (a type of herbicide widely used in sugarcane production). The method showed good linearity under optimized conditions, with correlation coefficients greater than 0.981, and limits of detection and quantification of 5 µg L-1 and 10 µg L-1, respectively. The herein discussed results suggest that the proposed method could be a practical option for identifying pesticides in beverages. Graphical Abstract.

The Current Role of Graphene-Based Nanomaterials in the Sample Preparation Arena.

Since its discovery in 2004 by Novoselov et al., graphene has attracted increasing attention in the scientific community due to its excellent physical and chemical properties, such as thermal/mechanical resistance, electronic stability, high Young's modulus, and fast mobility of charged atoms. In addition, other remarkable characteristics support its use in analytical chemistry, especially as sorbent. For these reasons, graphene-based materials (GBMs) have been used as a promising material in sample preparation. Graphene and graphene oxide, owing to their excellent physical and chemical properties as a large surface area, good mechanical strength, thermal stability, and delocalized π-electrons, are ideal sorbents, especially for molecules containing aromatic rings. They have been used in several sample preparation techniques such as solid-phase extraction (SPE), stir bar sorptive extraction (SBSE), magnetic solid-phase extraction (MSPE), as well as in miniaturized modes as solid-phase microextraction (SPME) in their different configurations. However, the reduced size and weight of graphene sheets can limit their use since they commonly aggregate to each other, causing clogging in high-pressure extractive devices. One way to overcome it and other drawbacks consists of covalently attaching the graphene sheets to support materials (e.g., silica, polymers, and magnetically modified supports). Also, graphene-based materials can be further chemically modified to favor some interactions with specific analytes, resulting in more efficient hybrid sorbents with higher selectivity for specific chemical classes. As a result of this wide variety of graphene-based sorbents, several studies have shown the current potential of applying GBMs in different fields such as food, biological, pharmaceutical, and environmental applications. Within such a context, this review will focus on the last five years of achievements in graphene-based materials for sample preparation techniques highlighting their synthesis, chemical structure, and potential application for the extraction of target analytes in different complex matrices.

Evaluation of Two Fully Automated Setups for Mycotoxin Analysis Based on Online Extraction-Liquid Chromatography-Tandem Mass Spectrometry.

Mycotoxins are secondary metabolites of fungi species widely known for their potentially toxic effects on human health. Considering their frequent presence in crops and their processed food, monitoring them on food-based matrices is now an important topic. Within such a context, the sample preparation step is usually mandatory before the chromatographic analysis, due to the complexity of matrices such as nuts, cereals, beverages, and others. For these reasons, we herein present the evaluation of two greener setups, based on the automation and miniaturization of the sample preparation step for mycotoxin analysis in different beverages. Firstly, we describe an analytical method based on a multidimensional assembly, coupling a lab-made microextraction column (508 µm i.d. × 100 mm) to a UPLC-MS/MS for the analysis of ochratoxin A in beverages. This configuration used a synthesized sorbent phase containing C18-functionalized graphene-silica particles, which exhibited excellent extraction performance, as well as being reusable and cheaper than commercially available extractive phases. Sequentially, a second setup, based on a multidimensional capillary LC coupled to MS/MS, was assessed for the same purpose. In this case, a graphene oxide-based capillary extraction column (254 µm i.d. × 200 mm) was used as the first dimension, while a C18 analytical capillary column performed the mycotoxin separation in beverages. Although this second one has similarities with the first, we focused mainly on the benefits related to the link between a miniaturized/automated sample preparation device with a capillary LC-MS/MS system, which made our analysis greener. Additionally, the chromatographic efficiency could even be enhanced.

Modified graphene-silica as a sorbent for in-tube solid-phase microextraction coupled to liquid chromatography-tandem mass spectrometry. Determination of xanthines in coffee beverages.

Given the increasing need for analyzing natural or contaminating compounds in complex food matrices in a simple and automated way, coupling miniaturized sample preparation techniques with chromatographic systems have become a growing field of research. In this regard, given the low extraction efficiency of conventional sorbent phases, the development of materials with enhanced extraction capabilities is of particular interest. Here we present several synthesized graphene-based materials supported on aminopropyl silica as sorbents for the extraction of xanthines. The synthesized materials were characterized by infrared spectroscopy and scanning electron microscopy. Aminopropyl silica coated with graphene oxide and functionalized with octadecylsilane/end-capped (SiGOC18ecap) showed the best performance for xanthines extraction. Hence, this material was employed as an in-tube solid phase microextraction (in-tube SPME) device coupled online with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and applied for the analysis of xanthines in roasted coffee samples. Extraction parameters and detection conditions were optimized. The method showed low limits of quantification (0.3-1.0 µg L-1), precision as relative standard deviation (RSD) values lower than 10%, recoveries between 73 and 109%, and pre-concentration factors from 5.6 to 7.2. Caffeine was determined in all ground roasted and instant coffee samples, in a wide range (0.9 to 36.8 mg g-1), and small amounts of theobromine and theophylline were also detected in some samples. This work demonstrated that functionalized graphene-based materials represent a promising new sorbent class for in-tube SPME, showing improved extraction capacity. The method was efficient, simple, and fast for the analysis of xanthines, demonstrating an excellent potential to be applied in other matrices.

Miniaturized liquid chromatography applied to the analysis of residues and contaminants in food: A review.

The humankind is pretty dependent on food to control several biological processes into the organism. As the world population increases, the demand for foodstuffs follows the same trend claiming for a high food production situation. For this reason, a substantial amount of chemicals is used in agriculture and livestock husbandries every year, enhancing the likelihood of contaminated foodstuffs being commercialized. This outlook becomes a public health concern; thus, the governmental regulatory agencies impose laws to control the residues and contaminants in food matrices. Currently, one of the most important analytical techniques to perform it is LC. Despite its already recognized effectiveness, it is often time consuming and requires significant volumes of reagents, which are transformed into toxic waste. In this context, miniaturized LC modes emerge as a greener and more effective analytical technique. They have remarkable advantages, including higher sensitivity, lower sample amount, solvent and stationary phase requirements, and more natural coupling to MS. In this review, most of the critical characteristics of them are discussed, focusing on the benchtop instruments and their related analytical columns. Additionally, a discussion regarding the last 10 years of publications reporting miniaturized LC application for the analysis of natural and industrial food samples is categorized. The main chemical classes as applied in the crops are highlighted, including pesticides, veterinary drugs, and mycotoxins.