Ultrasound-assisted treatment of coconut water samples for potentiometric stripping determination of zinc

Abstract

Este trabalho descreve a utilização da análise por redissolução potenciométrica (PSA) sobre eletrodos de filme de mercúrio para a determinação de zinco em água de coco. Foi desenvolvida metodologia para o tratamento de tais amostras por ultra-som, otimizada para a determinação de zinco total por PSA. Um mililitro de amostra foi tratado com 2 mL da mistura 1:1 (v/v) de HCl concentrado e H 2 O 2 (30% m/v) dentro de frascos fechados (4 mL) em um banho ultrassônico seguido de uma etapa de aquecimento em banho-maria por 15 min. Esta metodologia foi otimizada para a determinação de zinco total e foi validada através de análise direta das amostras por espectrometria de absorção atômica com forno de grafite (GFAAS). O limite de detecção obtido pelo método proposto por PSA foi de 1.35 μg L -1 (aplicando 45 s de pré-concentração). Tentativas para quantificar cobre nas mesmas amostras mostraram que o conteúdo deste metal é menor que o limite de detecção de ambas as técnicas, GFAAS e PSA (0.030 μg L -1 depois de 600 s de pré-concentração) com eletrodos de ouro.This work describes the application of potentiometric stripping analysis (PSA) at mercury film electrodes for zinc determination in coconut water. A sample ultrasound-assisted treatment was developed and optimised for the total zinc determination by PSA. One milliliter of sample was treated with 2 mL of 1:1 (v/v) concentrated HCl and H 2 O 2 (30% m/v) mixture in closed (4 mL) vessels under sonication (in ultrasonic bath), followed by a thermal step (in a boiling bath, for 15 min). This methodology was optimised for total zinc determination and was validated by graphite furnace atomic absorption spectrometry (GFAAS) analysis utilizing the sample without any treatment. The limit of detection obtained by the proposed PSA method was 1.35 μg L -1 (applying 45 s of preconcentration). Attempts to evaluate the amount of copper in the same sample show that the content of this metal is lower than the detection limits of both techniques, GFAAS and PSA (0.030 μg L -1 after 600 s of preconcentration) at gold film electrodes.Keywords: potentiometric stripping analysis, zinc, copper, coconut water, ultrasound-assisted treatment, ultrasonic bath IntroductionCoconut water is a common refreshing drink and has been used as an excellent isotonic in Brazil and other tropical countries.1 Extracted from the coconut endosperm (Cocos nucifera), coconut water has several applications, such as the preservation of sheep preantral follicles in situ, 2 the replacement of the high cost total parenteral nutrition solutions 3 and oral rehydration fluid for gastric and intestinal diseases. Due to this increasing interest on applications of coconut water, more recent contribution for the better understanding of its composition has been reported. 5,6 Santoso et al. 6 described the presence of vitamins, sugar, organic acids, fatty acids, amino acids, fibers, and minerals in coconut (Cocos nucifera). Cytokinins were identified and determined using micellar electrokinetic capillary chromatography after pre...

Wavelet-Based determination of Cu and Pb in water samples using potentiometric stripping analysis with a Lab-Made potentiostat

“…1 PSA is particularly useful for determination of trace and ultra-trace concentration levels of heavy metals in a variety of matrices such as food, sediments and water, as well as in biological samples. [2][3][4] As compared to voltammetric stripping analysis (VSA), PSA has several advantages, such as smaller dependence on the electrode surface reproducibility, robustness with respect to the presence of some electroactive organic species, applicability to the analysis of solutions with low ionic strength, no need for deoxygenation of the sample, lower background contributions. 5,6 In addition, PSA can be carried out with a simple and inexpensive instrumentation, which can be easily automated.…”

Direct Determination of Copper in Biodiesel Using Stripping Analysis

“…A commercial (Metrohm) glassy-carbon electrode (2-mm diameter) coated with a thin mercury film was used as working electrode for copper determinations after ultrasound-assisted extraction. The coating was carried out by applying À0.7 V for 5 minutes in a solution containing 1 mmol L À1 mercury(II) and 0.1 mol L À1 HCl [8,17].…”

“…Analytical methodologies for trace metal determination in fuel (oil samples) generally needs a sample treatment step in order to release the metals from the organic matrix and eventually to eliminate residual organic matter which may interfere on the detection system [7,8]. Ultrasound-assisted sample treatment has been successfully applied for the preparation of biological [9][10][11], environmental [12][13][14][15] and food samples [16,17]. Otherwise, stripping chronopotentiometry (SCP) has been applied for the direct measurement of metals in biological fluids [18,19] such as human plasma, urine, and blood samples.…”

Disposable Graphite Foil Based Electrodes and Their Application in Pharmaceutical Analysis

“…Consequently, a sample treatment procedure was required for zinc determination in such a sample. Based on our previous experience with the application of ultrasonic baths to accelerate decomposition and/or extraction of metals from complex samples such as lubricating oil [26], urine [27] and coconut water [28], we optimized the procedure to treat the ophthalmic collyrium sample. After ultrasonic treatment in an oxidant medium, the sample was analyzed by SW-ASV.…”