Digiprep jr block digestion system

The acid digestions took place employing a DigiPREP Jr block digestion system acquired from SCP Science (Montreal, Quebec, Canada). That instrument is equipped with 24 positions for 50 mL polypropylene (PE) digestion tubes (DigiTubes; SCP Science; Montreal, Quebec, Canada). The acid digestion procedure here employed has already been described in previous studies by the research group [37 (link),38 (link)]. Firstly, the samples (0.25 g) were placed into digestion tubes. Then, 2 mL nanopure water, 2 mL HCl, and 5 mL HNO₃ were added, and the samples were digested by applying a stepwise temperature increase procedure for 20 min up to 65 °C and maintaining this temperature for a total of 30 min. After a cooling step, 3 mL of H₂O₂ was added to carry out a second digestion by increasing the temperature gradually over 30 min to 110 °C, and maintaining it for a total of 60 min. To finish the procedure, the digested samples were filtered using a 0.45 μm filter and a −600 mbar vacuum port and then transferred to a 50 mL volumetric DigiTube, filling it to 50 mL with nanopure water. All samples were prepared in triplicate.

Acid digestions were performed in a DigiPREP Jr block digestion system from SCP Science (Montreal, Quebec, Canada) equipped with a 24-position graphite heating block for 50 mL polypropylene (PE) digestion tubes (DigiTubes; SCP Science; Montreal, Quebec, Canada). The digestion procedure employed here was based on the conditions established in previous investigations by our research group [33 (link)]. The dried and powdered subsamples (0.25 g) were first placed in the digestion tubes with 5 mL of HNO₃, 2 mL of HCl, and 2 mL of nanopure water. Next, they were digested by applying a stepwise temperature increase procedure for 20 min up to 65 °C and maintaining this temperature for a total of 30 min. The second digestion was performed after a cooling step by adding 3 mL of H₂O₂, gradually increasing the temperature for 30 min up to 110 °C, and holding it for a total of 60 min. Prior to analysis, the digested samples were filtered through a 0.45-μm filter (DigiFILTER; SCP Science; Montreal, Quebec, Canada) using a –600 mbar vacuum port. They were then transferred to a clean 50-mL volumetric DigiTube, which was completed with nanopure water to 50 mL. All samples were carried out in triplicate.