Extended Data Fig. 3. LILBID spectrum with a 0.5 M phosphate concentration (similar to Fig. 2) and 0.01 M phosphite (Na₂HPO₃).

The phosphite peak Na₂HPO₃Na⁺ (149 u) is not in agreement with CDA spectra and only becomes undetectable in phosphate-bearing CDA spectra at phosphite concentrations below 0.005 M. Note, the CDA detection limit of phosphite in pure water (without phosphates) is approx. 1 nM, more than 3 orders of magnitude lower.