Marques Thiago L, Wiltsche Helmar, Nóbrega Joaquim A, Winkler Monika, Knapp Günter
Department of Chemistry, Federal University of São Carlos, Rodovia Washington Luiz, km 235, São Carlos, São Paulo, 13565-905, Brazil.
Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, Stremayrgasse 9, 8010, Graz, Styria, Austria.
Anal Bioanal Chem. 2017 Jul;409(18):4449-4458. doi: 10.1007/s00216-017-0388-5. Epub 2017 May 26.
Acid digestion is usually required for metal determination in food samples. However, this step is usually performed in batch mode which is time consuming, labor intensive, and may lead to sample contamination. Flow digestion can overcome these limitations. In this work, the performance of a high-pressure microwave-assisted flow digestion system with a large volume reactor was evaluated for liquid samples high in sugar and fat (fruit juice and milk). The digestions were carried out in a coiled perfluoroalkoxy (PFA) tube reactor (13.5 mL) installed inside an autoclave pressurized with 40 bar nitrogen. The system was operated at 500 W microwave power and 5.0 mL min carrier flow rate. Digestion conditions were optimized with phenylalanine, as this substance is known to be difficult to digest completely. The combinations of HCl or HO with HNO increased the digestion efficiency of phenylalanine, and the residual carbon content (RCC) was around 50% when 6.0% V/V HCl or HO was used in combination with 32% V/V HNO. Juice samples were digested with 3.7 mol L HNO and 0.3 mol L HCl, and the RCC was 16 and 29% for apple and mango juices, respectively. Concentrated HNO (10.5 mol L) was successfully applied for digesting milk samples, and the RCCs were 23 and 25% for partially skimmed and whole milk, respectively. Accuracy and precision of the flow digestion procedure were compared with reference digestions using batch mode closed vessel microwave-assisted digestion and no statistically significant differences were encountered at the 95% confidence level. Graphical abstract Application of a high-pressure microwave-assisted flow digestion system for fruit juice and milk sample preparation.
食品样品中的金属测定通常需要进行酸消解。然而，这一步骤通常以分批模式进行，既耗时又费力，还可能导致样品污染。流动消解可以克服这些局限性。在本研究中，对一种带有大体积反应器的高压微波辅助流动消解系统在高糖高脂肪液体样品（果汁和牛奶）方面的性能进行了评估。消解在一个安装在以40巴氮气加压的高压釜内的盘管全氟烷氧基（PFA）管反应器（13.5毫升）中进行。该系统以500瓦微波功率和5.0毫升/分钟的载气流速运行。以苯丙氨酸对消解条件进行了优化，因为已知该物质难以完全消解。HCl或H₂O与HNO₃的组合提高了苯丙氨酸的消解效率，当6.0%V/V的HCl或H₂O与32%V/V的HNO₃联合使用时残留碳含量（RCC）约为50%。果汁样品用3.7摩尔/升的HNO₃和0.3摩尔/升的HCl进行消解，苹果汁和芒果汁的RCC分别为16%和29%。浓HNO₃（10.5摩尔/升）成功用于消解牛奶样品，部分脱脂牛奶和全脂牛奶的RCC分别为23%和25%。将流动消解程序的准确度和精密度与使用分批模式密闭容器微波辅助消解的参考消解进行了比较，在95%置信水平下未发现统计学上的显著差异。图形摘要 高压微波辅助流动消解系统在果汁和牛奶样品制备中的应用。
