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A Sample Preparation Method for Fluoride Detection by Potentiometry with Ion-selective Electrode in Medicinal Plants
Journal of Fluorine Chemistry ( IF 1.9 ) Pub Date : 2020-01-17 , DOI: 10.1016/j.jfluchem.2020.109459
Ana Luiza G. Mendes , Mariele S. Nascimento , Rochele S. Picoloto , Erico M.M. Flores , Paola A. Mello

In this study, the fluoride concentration in medicinal plants was determined in a range from 0.25 to 250 µg g-1. Fluoride was determined using potentiometry with ion-selective electrode (ISE) after sample preparation. Sample masses ranging from 0.1 to 1.0 g were pressed into pellets and burned using the microwave-induced combustion (MIC) method. After combustion, fluoride was absorbed in diluted ammonia for further determination by using ISE. Recoveries close to 100% were obtained with a low relative standard deviation (5%), using 20 bar of oxygen and 5 min of reflux. Solutions obtained using the MIC method presented low carbon content (< 25 mg L-1) and avoided additional dilution prior to analysis. Up to 1.0 g of medicinal plant was efficiently digested, facilitating fluoride determination at low levels (limit of quantification was 2.5 µg g-1). No statistical difference (t-test, 95% of confidence level) was observed between the values obtained using ISE after MIC digestion and the values of certified reference materials (CRMs) of aquatic plant (BCR 60) and olive leaves (BCR 62). In addition, results presented no statistical difference compared to those acquired using the AOAC’s recommended Method 975.04 (Fluoride in plants). A microwave-assisted extraction (MAE) method was also evaluated using the optimized conditions for MIC (1 g, 6 mL of 25 mmol L-1 ammonia solution and 5 min of reflux). However, MAE digests presented high carbon content in final solutions (around 5 g L-1) and interference was observed during fluoride determination using ISE. Therefore, the MIC method allowed to efficiently digest up to 1.0 g of sample, and the analyte was absorbed in a suitable alkaline solution. Using this method, fluoride detection by ISE was possible even for samples at low concentration being considered a rather attractive quality control method for fluoride levels in medicinal plants.



中文翻译:

离子选择性电极电位法检测药用植物中氟的样品制备方法

在这项研究中,确定药用植物中的氟化物浓度范围为0.25至250 µg g -1。样品制备后,使用带有离子选择电极(ISE)的电位计测定氟化物。将质量范围从0.1到1.0 g的样品压成颗粒,并使用微波诱导燃烧(MIC)方法进行燃烧。燃烧后,氟化物吸收在稀释的氨中,以使用ISE进行进一步测定。使用20 bar的氧气和5分钟的回流,可以得到相对低的标准偏差(5%)的接近100%的回收率。使用MIC方法获得的溶液碳含量低(<25 mg L -1),并避免在分析前进行额外稀释。可以有效地消化多达1.0 g的药用植物,从而有助于以低水平测定氟化物(定量限为2.5 µg g -1)。在MIC消化后使用ISE获得的值与水生植物(BCR 60)和橄榄叶(BCR 62)的认证参考物质(CRM)的值之间未观察到统计学差异(t检验,置信度的95%)。此外,与使用AOAC推荐的方法975.04(植物中的氟化物)获得的结果相比,结果没有统计学差异。还使用针对MIC(1 g,6 mL的25 mmol L -1的MIC)的优化条件评估了微波辅助萃取(MAE)方法氨溶液,回流5分钟)。但是,MAE消化液在最终溶液中的碳含量较高(约5 g L -1),并且在使用ISE测定氟化物的过程中观察到干扰。因此,MIC方法可以有效地消化多达1.0 g的样品,并且分析物被吸收在合适的碱性溶液中。使用此方法,即使对于低浓度的样品,也可以通过ISE检测氟化物,这被认为是药用植物中氟化物含量的一种颇具吸引力的质量控制方法。

更新日期:2020-01-17
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