Table 1.
Investigated digestion methods for samples containing SiO2.
| Method | Digestion | Analysis | |||||
|---|---|---|---|---|---|---|---|
| max. SiO2 (mg L−1) | max. KOH (M) | range of molar ratio KOH: SiO2 | Digested by | max. Si (mg L−1) | max. KOH (mM) | Analyzed by | |
| High SiO2 | 4110 | 0.958 | 0.6–60.1 | Microwave | 1921 | 958 | DLS |
| KOH0.1 | 8.53 | 0.06 | 423–1922 | 1.98 | 30 | ICP | |
| KOH0.5 | 70 | 0.5 | 0.4–1.7 | 0.75 | 100 | ||
| KOH1.0 | 4.50 | 0.60 | 8017–36916 | 1.05 | 300 | ||
| RT + KOH0.1 | 100 | 0.1 | 60.1 | RT | 4.45 | 10 | UV-Vis |
| RT + KOH1.0 | 2.61 | 0.6 | 13803–14704 | 0.57 | 300 | ICP | |
| 85 | 1 | 462–707 | 2.39 | 39 | UV-Vis | ||
High_SiO2: high SiO2-NP concentrations were used to find the lowest KOH concentration leading to complete solubilization. KOH0.1, KOH0.5, KOH1.0: different KOH concentrations were tested to assess Si recovery in simple and complex matrices. RT + KOH0.1, RT + KOH1.0: the solubilization of SiO2-NPs at room temperature (RT) was tested (recoveries: refer to Table 2).