Performance evaluation of a high-pressure microwave-assisted flow digestion system for juice and milk sample preparation

Thiago L. Marques*, Helmar Wiltsche, Joaquim A. Nóbrega, Monika Winkler, Günter Knapp

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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−1 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 H2O2 with HNO3 increased the digestion efficiency of phenylalanine, and the residual carbon content (RCC) was around 50% when 6.0% V/V HCl or H2O2 was used in combination with 32% V/V HNO3. Juice samples were digested with 3.7 mol L−1 HNO3 and 0.3 mol L−1 HCl, and the RCC was 16 and 29% for apple and mango juices, respectively. Concentrated HNO3 (10.5 mol L−1) 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. [Figure not available: see fulltext.].

Original languageEnglish
Pages (from-to)4449-4458
Number of pages10
JournalAnalytical and Bioanalytical Chemistry
Issue number18
Publication statusPublished - 1 Jul 2017


  • Flow digestion system
  • Fruit juice
  • Milk
  • Multielement analysis
  • Sample preparation

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry

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