Synthesis of natural deep eutectic solvents using a mixture design for extraction of animal and plant samples prior to ICP-MS analysis.

Solvents with both low density and viscosity have the advantage of higher extraction efficiency due to lower diffusivity and consequently higher mass transfer. In this study, a mixture design was performed for the synthesis of three different natural deep eutectic solvents (NADES) using citric acid, malic acid, and xylitol. The optimized proportion for each of the three solvents synthesized was selected based on density and viscosity values. The NADES were characterized by infrared spectroscopy analysis, that showed characteristic bands of the initial reagents and the presence of hydrogen bonds confirming the formation of each deep eutectic solvent. Then, the NADES were used as solvents in ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) of biological tissue and plant material samples for the determination of As, Cd, Hg, Pb, Se, and V by inductively coupled plasma mass spectrometry (ICP-MS). The results for the proposed methods were compared to microwave-assisted acid digestion (MW-AD). The extraction recoveries ranged from 80 to 120% for most of the elements determined. The use of NADES as carbon sources improved the sensitivity of the As and Cd analyses, due to charge transfer reactions between the analyte and C+ and/or other carbon species. In addition, the Analytical Eco-Scale was used to assess the greenness of the proposed analytical procedures (UAE and MAE). It showed that the UAE and MAE methods provided excellent green analyses, while the MW-AD method was rated as an acceptable green procedure.

Natural deep eutectic solvents for sample preparation prior to elemental analysis by plasma-based techniques.

Natural deep eutectic solvents (NADES) based on xylitol, citric acid, and malic acid were synthesized and were then characterized using infrared spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), also density and viscosity were measurements. The deep eutectic solvents were used as solvent in ultrasound-assisted extraction (DES-UAE) of plant samples prior to elemental analysis. Inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP OES) were employed for the determination of As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, and Zn in the extracts. The infrared analyses of the NADES revealed bands characteristic of the initial reagents, with the presence of hydrogen bonds, which confirmed the formation of a NADES. The thermal analyses showed decomposition temperatures of around 170 °C and endothermic events related to degradation of the NADES. The viscosity and density parameters were found to be related to the presence of hydrogen bonds. The extraction recoveries ranged from 80% to 120%, with some analytes presenting poor recoveries. There were no significant differences between the NADES, in terms of the concentrations of the analytes found in the extracts. However, there were differences between the analyte concentrations obtained using the NADES extraction method and the concentrations obtained using microwave-assisted acid digestion (MW-AD), possibly due to the different types of interactions between the solvents and the analytes. Plant tissues are complex matrices containing substantial amounts of silica, so some elements may be tightly bound and consequently difficult to release. The results indicated that UAE using NADES is a promising technique for the elemental extraction of plant samples.

Avaliação da interface adesiva em dentina sadia e afetada por cárie sob pressão pulpar simulada e após desafio em solventes / Evaluation of sound and caries-affected dentin interface under simulated pulpal pressure and aging in food-simulating solvents

O objetivo deste estudo foi avaliar a resistência de união (RU) e características da interface adesiva em dentina sadia e afetada por cárie, na presença de pressão pulpar simulada e após desafio em solventes. Setenta e dois molares humanos hígidos (SD) e outros trinta e seis molares humanos cariados (NCAD) foram seccionados para obtenção de 2 mm de espessura de dentina, a partir do corno pulpar mais alto. Dentre as amostras sadias, trinta e seis foram submetidas à formação artificial de dentina afetada por cárie pelo processo de ciclagem de pH (ACAD). Previamente ao procedimento restaurador, a análise química da superfície oclusal de cinco amostras de cada dentina foi avaliada em espectroscopia de infravermelho por Transformada de Fourier (FTIR) e microdureza de superfície (KHN). Todas as amostras foram tratadas, sob pressão pulpar simulada (20 cm H20), sequencialmente com: ácido fosfórico 37%, sistema adesivo (Scotchbond Universal, 3M/ESPE), fotopolimerização (10 s), confecção de um bloco de resina composta (Filtek Z350 XT; 3M/ESPE) e fotopolimerização (20 s). Após 48 h, palitos retangulares de resina-dentina (1mm2) foram obtidos e aleatoriamente divididos em grupos, de acordo com o tempo de envelhecimento (24 h e 30 dias) e solventes: água deionizada (A), etanol a 99% (E) e metiletilcetona (MEK). As amostras foram submetidas aos testes de resistência adesiva à microtração (0,5 mm/min; 10 kgf), e a interface adesiva avaliada em microscopia eletrônica de varredura (MEV). Os sistemas adesivos foram avaliados frente ao desafio dos solventes, por análise da resistência flexural (RF), módulo de elasticidade (ME), sorção (SO) e solubilidade (SL). Os resultados de RU foram submetidos aos testes ANOVA de medidas repetidas sob 3-fatores (dentina, solvente e tempo de armazenamento), seguido do teste de múltiplas comparações de Tukey (p<0,05). FTIR: diferenças químicas foram observadas entre os substratos, pela perda do conteúdo mineral na NCAD (maior) e ACAD (intermediário) em relação à SD. KHN: NCAD mostrou as menores médias, diferindo significantemente da SD. RU: dentina, tempos, interação dentina-tempo e interação dentina-tempo-solvente mostraram efeitos estatisticamente significantes: SD apresentou diferenças significativas quando armazenada 24 h em A; diferenças significantes foram observadas no grupo NCAD para o solvente E após 30 dias. MEV: as características da interface adesiva diferiram entre os substratos e solventes: A degradou a interface entre dentina e camada de sistema adesivo; E e MEK entre camada de adesivo e resina composta. RF/ME: solvente e tempo foram estatisticamente significantes, com as menores médias para E. SO/SL: A apresentou as menores médias, diferindo significantemente dos demais solventes. Pode-se concluir que o tipo de dentina, o solvente e o tempo de armazenamento interferiram negativamente nos valores de RU, com as menores médias para: NCAD, E em 30 dias; e, as propriedades físico-mecânicas do sistema adesivo foram diretamente afetadas pelo E.(AU)

The aim of this study was to evaluate the bond strength (BS) and adhesive interface characteristics of sound and caries-affected dentin under presence of simulated pulpal pressure (SPP) and after aging in solvents. Seventy-two sound human molars (SD) and thirty-six caries-affected human molars (NCAD) were sectioned to obtain 2-mm dentin thickness from the highest pulp horn. Among the sound dentin samples, thirtysix were submitted to artificial formation of caries by the pH cycling (ACAD). Prior to restorative procedures, chemical analysis of the dentin occlusal surface of five selected samples was performed in Fourier transform infrared spectroscopy (FTIR) and surface microhardness (KHN). All samples were treated, under simulated SPP (20 cm H20), sequentially with: 37% phosphoric acid, adhesive system (Scotchbond Universal, 3M/ESPE), light-cured (10 s), a composite resin build up (Filtek Z350 XT; 3M/ESPE) and light-cured (20 s). After 48 h, tooth-resin sticks (1mm2) were obtained and randomly divided into groups, according to storage time (24 h and 30 days) and solvents: deionized water (W), 99% ethanol (E) and methyl ethyl ketone (MEK). Samples were submitted to microtensile bond strength test (0.5 mm/min; 10 kgf), and the adhesive interface was evaluated by scanning electron microscopy (SEM). The adhesive system was evaluated, against the solvents challenge, by flexural strength (FS), modulus of elasticity (ME), sorption (SO) and solubility (SL). Data were submitted to 3-way ANOVA (dentin, solvent and storage times) followed by Tukey (p<0.05). FTIR: Chemical differences in dentin were observed through mineral content loss in NCAD (higher) and ACAD (intermediate) in relation to SD. KHN:NCAD showed the lowest mean, differing significantly from SD. BS: Dentin, time, interaction dentin-time and interaction dentin-time-solvent had a statistically significant effect: SD showed significant differences when storage 24h in W; statistically significant differences were observed in group NCAD storage 30 days in E. SEM: the characteristics of adhesive interface differs among substrates and aging solvents: W degradated the interface between dentin and adhesive; E and MEK between adhesive and composite resin. FS/ME: solvent and time were statistically significant, with the lowest mean for E. SO/SL: A showed lower means, differing significantly from the other solvents. It can be concluded that the type of dentin, aging solvents and storage time interfered negatively on BS values, with lowest values for: NCAD, E for 30 days; and the physico-mechanical adhesive properties were directly affected by E.(AU)

Enhanced electrochemical detection of quercetin by Natural Deep Eutectic Solvents.

New trends in analytical chemistry encourage the development of smart techniques and methods aligned with Green Chemistry. In this sense, Natural Deep Eutectic Solvents represents an excellent opportunity as a new generation of green solvents. In this work a new application for them has been proposed and demonstrated. These solvents were synthesized by combinations of inexpensive and natural components like, Glucose, Fructose, Citric acid and Lactic acid. The different natural solvents were easily prepared and added to buffer solution in different concentrations, allowing the enhancement of electrochemical detection of an important representative antioxidant like quercetin (QR) with improved signal up to 380%. QR is a ubiquitous flavonoid widespread in plants and food of plant origin. The proposed method using phosphate buffer with a eutectic mixture of Citric acid, Glucose and water in combination with carbon screen printed electrodes exhibited a good analytical performance. Detection and quantification limits were of 7.97 and 26.3 nM respectively; and repeatability with %RSDs of 1.41 and 7.49 for peak potential and intensity respectively. In addition, it has proved to be faster, greener and cheaper than other sensors and chromatographic methods available with the additional advantage of being completely portable. Furthermore, the obtained results demonstrated that the proposed method is able for the determination of QR in complex food samples.