Analysis of alkyl gallates and nordihydroguaiaretic acid using plastic capillary electrophoresis – microchips

Predicting Antioxidant Synergism via Artificial Intelligence and Benchtop Data

Lipid oxidation is a major issue affecting products containing unsaturated fatty acids as ingredients or components, leading to the formation of low molecular weight species with diverse functional groups that impart off-odors and off-flavors. Aiming to control this process, antioxidants are commonly added to these products, often deployed as combinations of two or more compounds, a strategy that allows for lowering the amount used while boosting the total antioxidant capacity of the formulation. While this approach allows for minimizing the potential organoleptic and toxic effects of these compounds, predicting how these mixtures of antioxidants will behave has traditionally been one of the most challenging tasks, often leading to simple additive, antagonistic, or synergistic effects. Approaches to understanding these interactions have been predominantly empirically driven but thus far, inefficient and unable to account for the complexity and multifaceted nature of antioxidant responses. To address this current gap in knowledge, we describe the use of an artificial intelligence model based on deep learning architecture to predict the type of interaction (synergistic, additive, and antagonistic) of antioxidant combinations. Here, each mixture was associated with a combination index value (CI) and used as input for our model, which was challenged against a test (n = 140) data set. Despite the encouraging preliminary results, this algorithm failed to provide accurate predictions of oxidation experiments performed in-house using binary mixtures of phenolic antioxidants and a lard sample. To overcome this problem, the AI algorithm was then enhanced with various amounts of experimental data (antioxidant power data assessed by the TBARS assay), demonstrating the importance of having chemically relevant experimental data to enhance the model's performance and provide suitable predictions with statistical relevance. We believe the proposed method could be used as an auxiliary tool in benchmark analysis routines, offering a novel strategy to enable broader and more rational predictions related to the behavior of antioxidant mixtures.

Research Spotlight: The next big thing is actually small

Recent developments in materials, surface modifications, separation schemes, detection systems and associated instrumentation have allowed significant advances in the performance of lab-on-a-chip devices. These devices, also referred to as micro total analysis systems (µTAS), offer great versatility, high throughput, short analysis time, low cost and, more importantly, performance that is comparable to standard bench-top instrumentation. To date, µTAS have demonstrated advantages in a significant number of fields including biochemical, pharmaceutical, military and environmental. Perhaps most importantly, µTAS represent excellent platforms to introduce students to microfabrication and nanotechnology, bridging chemistry with other fields, such as engineering and biology, enabling the integration of various skills and curricular concepts. Considering the advantages of the technology and the potential impact to society, our research program aims to address the need for simpler, more affordable, faster and portable devices to measure biologically active compounds. Specifically, the program is focused on the development and characterization of a series of novel strategies towards the realization of integrated microanalytical devices. One key aspect of our research projects is that the developed analytical strategies must be compatible with each other; therefore, enabling their use in integrated devices. The program combines spectroscopy, surface chemistry, capillary electrophoresis, electrochemical detection and nanomaterials. This article discusses some of the most recent results obtained in two main areas of emphasis: capillary electrophoresis, microchip-capillary electrophoresis, electrochemical detection and interaction of proteins with nanomaterials.

Application and potential of capillary electroseparation methods to determine antioxidant phenolic compounds from plant food material

Antioxidants are one of the most common active ingredients of nutritionally functional foods which can play an important role in the prevention of oxidation and cellular damage inhibiting or delaying the oxidative processes. In recent years there has been an increased interest in the application of antioxidants to medical treatment as information is constantly gathered linking the development of human diseases to oxidative stress. Within antioxidants, phenolic molecules are an important category of compounds, commonly present in a wide variety of plant food materials. Their correct determination is pivotal nowadays and involves their extraction from the sample, analytical separation, identification, quantification and interpretation of the data. The aim of this review is to provide an overview about all the necessary steps of any analytical procedure to achieve the determination of phenolic compounds from plant matrices, paying particular attention to the application and potential of capillary electroseparation methods. Since it is quite complicated to establish a classification of plant food material, and to structure the current review, we will group the different matrices as follows: fruits, vegetables, herbs, spices and medicinal plants, beverages, vegetable oils, cereals, legumes and nuts and other matrices (including cocoa beans and bee products). At the end of the overview, we include two sections to explain the usefulness of the data about phenols provided by capillary electrophoresis and the newest trends.

Fast and selective microfluidic chips for electrochemical antioxidant sensing in complex samples

In this work, capillary electrophoresis chips with electrochemical detection have been assessed as creative and selective microfluidic platforms to integrate and simplify on a microscale the traditional methods for complex natural antioxidants determination. Depending on the acid-base properties of the analytes, two approaches (class-selective electrochemical index determination (CSEID) and individual antioxidant determination (IAD)) were investigated for the analysis of nine antioxidants ((+)-catechin, rutin, quercetin, chlorogenic, ferulic, caffeic, protocatechuic, vanillic, and gallic acids) in food samples. First, the novel concept of a class-selective electrochemical index is proposed allowing a fast and reliable determination of the main antioxidant classes (flavonoids and phenolic acids) in less than 100 s. In addition, an impressive separation of nine antioxidants is also offered in less than 260 s with the individual antioxidant determination approach. Qualitative and quantitative performances of both approaches were studied. The analytical figures of merit (i.e., electroosmotic flow (EOF) precision as relative standard deviation (RSD), resolution, signal precision as RSD, limit of detection, limit of quantification, and accuracy as recovery) of both approaches were <4%, approximately 1, < or = 5%, <8 microM, 30 microM, between 91% and 104%, and <4%, < or = 2%, <9%, < or = 6 microM, < or = 20 microM (with the exception of protocatechuic acid, which shows values of 40 and 130 microM, respectively), between 80% and 107% for the CSEID and IAD concepts, respectively, which are excellent for food samples analysis. A set of representative samples was analyzed including apple and pear skins and pulps, red and white wines, and green tea tablets. High agreement was observed between the results of the sample analyses from the two microchip-based approaches, and good correlation was observed with results obtained from traditional methods. Although the prominent phenolic antioxidant classes and compounds were successfully determined, some nonprominent peaks were not detected in the samples when applying the IAD approach. Different integration strategies on microchip platforms were further explored, looking for a simplification of the overall analytical process without losing the excellent analytical characteristics obtained in both approaches. The results are promising and indicative of the progress of analytical microfluidics toward the "plateau of productivity" and the routine laboratory application.

Electrophoretic Effects of the Adsorption of Anionic Surfactants to Poly(dimethylsiloxane)-Coated Capillaries

Poly(dimethylsiloxane) (PDMS) is one of the most convenient materials to construct capillary electrophoresis microchips. Even though PDMS has many advantages, its use is often limited by its hydrophobicity. Although it is well-known that the surface properties of PDMS can be modified by anionic surfactants, very little is known regarding the driving forces or the electrophoretic consequences of the adsorption of anionic surfactants. In this work, the adsorption of alkyl surfactants on PDMS was studied by performing electroosmotic flow (microEOF) measurements. In order to mimic the behavior of PDMS microchannels, fused-silica capillaries were coated with PDMS and used for the microEOF measurements. This approach allowed using standard CE instrumentation and provided significant advantages over similar experiments performed on microchips. The change in the microEOF in the presence of surfactants was correlated to the surfactant adsorbed amount which, plotted versus surfactant concentration, gives an adsorption isotherm. The adsorption isotherms were obtained using alkyl surfactants with different chain lengths and head groups. According to our results, the interaction of alkyl surfactants with the PDMS surface is determined by a combination of hydrophobic and electrostatic interactions, where the former is more significant than the latter. The affinity of each surfactant for the PDMS surface was calculated by fitting the adsorption profiles with a Langmuir equation and, in the case of single-charged surfactants, correlated to the corresponding cmc value.

Electrophoretic separation of environmentally important phenolic compounds using montomorillonite-coated fused-silica capillaries

This paper reports a simple procedure for coating fused-silica capillaries with poly(diallyldimethyl ammonium chloride) and montmorillonite. The coated capillaries were characterized by performing EOF measurements as a function of buffer pH, number of layers of coating, and number of runs (stability). The coated capillaries showed a highly stable mu(EOF) (run-to-run RSD less than 1.5%, n = 20), allowing continuous use for several days without conditioning. The coated capillaries were then used for the effective separation of nine environmentally important phenolic compounds showing a significant improvement in the resolution, when compared to bare fused-silica capillaries. The EOF of the coated capillaries was constant in alkaline solutions (pH > or = 7), allowing the optimization of the separation conditions of phenolic compounds without significantly affecting the mu(EOF).

Electrochemical detection of phenolic compounds using cylindrical carbon-ink electrodes and microchip capillary electrophoresis

A simple method to fabricate cylindrical carbon electrodes for use in capillary electrophoresis (CE) microchips is described. The electrodes were fabricated using a metallic wire coated with carbon ink. Several experimental variables were studied in order to establish the best conditions to fabricate the electrode. Finally, the electrodes were integrated in a poly(dimethylsiloxane) microchip and used for the analysis of phenolic compounds. Using the optimum conditions, the analysis of a mixture of dopamine, epinephrine, catechol, and 4-aminophenol was achieved in less than 240 s, showing good linear responses (R(2)=0.999) in the 0.1-190 microM range, and limits of detection (without the use of stacking or a decoupler) of 140 and 105 nM for dopamine and epinephrine, respectively.

The effects of alkyl sulfates on the analysis of phenolic compounds by microchip capillary electrophoresis with pulsed amperometric detection

The effects of different surfactants (sodium 2-ethylhexyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium tetradecyl sulfate) on the analysis of phenolic compounds by microchip-CE with pulsed amperometric detection were investigated. Using sodium decyl sulfate as a model surfactant, the effects of concentration and pH were examined. Under the optimized conditions, the analysis of six phenolic compounds was performed and compared with control runs performed without surfactant. When these surfactants were present in the run buffer, decreases in the migration time and increases in the run-to-run reproducibility were observed. Systematic improvements in the electrochemical response for the phenolic compounds were also obtained. According to the results presented, surfactants enhance the analyte-electrode interaction and facilitate the electron transfer process. These results should allow a more rational selection of the surfactants based on their electrophoretic and electrochemical effects.

Capillary Electrophoresis-Amperometric Determination of Antioxidant Propyl Gallate and Butylated Hydroxyanisole in Foods

Capillary electrophoretic separation coupled with end-column amperometric detection for the simultaneous quantification of butylated hydroxyanisole (BHA) and propyl gallate (PG) in food was developed. Important factors affecting separation and detection, such as the running buffer, separation voltage, and detection potential, were investigated in detail. An improved working electrode preparation method was used, where a carbon disk of 33 microm in diameter was sealed in a tip and positioned opposite the outlet of a capillary. The experiments indicated that the preparation method was simple, and the obtained electrode exhibited good flexibility and stability for the determination of phenolic antioxidants. The separation was carried out within 5 min using a 50 cm length capillary, with a solution containing 5 mM phosphate and 5 mM borax of pH 8.84 as a separation buffer, and a separation potential of 20 kV. Amperometric detection was achieved with an applied potential of 0.70 V versus Ag|AgCl| saturated KCl. There was excellent linearity between the peak current and the concentrations of the analytes in the range of 1.8 - 180.2 microg/mL for BHA and 10.6 - 212.2 microg/mL for PG, respectively. Relative standard deviations of 4.92% for BHA and 5.27% for PG were obtained, respectively. The developed method was successfully applied for the determination of antioxidants in several commercial foods.

Application of microchip-CE electrophoresis to follow the degradation of phenolic acids by aquatic plants

In this paper, we describe the separation and detection of six phenolic acids using an electrophoretic microchip with pulsed amperometric detection (PAD). The selected phenolic acids are particularly important because of their biological activity. The analysis of these compounds is typically performed by chromatography or standard CE coupled with a wide variety of detection modes. However, these methods are slow, labor intensive, involve a multistep solvent extraction, require skilled personnel, or use bulky and expensive instrumentation. In contrast, microchip CE offers the possibility of performing simpler, less expensive, and faster analysis. In addition, integrated devices can be custom-fabricated and incorporated with portable computers to perform on-site analysis. In the present report, the effect of the separation potential, buffer pH and composition, injection time and PAD parameters were studied in an effort to optimize both the separation and detection of these phenolic acids. Using the optimized conditions, the analysis can be performed in less than 3 min, with detection limits ranging from 0.73 microM (0.10 microg/mL) for 4-hydroxyphenylacetic acid to 2.12 microM (0.29 microg/mL) for salicylic acid. In order to demonstrate the capabilities of the device, the degradation of a mixture of these acids by two aquatic plants was followed using the optimized conditions.