* All data was initially processed via Agilent Masshunter software into CSV files and then further processed in Iolite (version3) to give average values for each ablation line.
* The data has been split to align with the 3 figures in the paper.
* Concentrations were determined via microwave digestion and ICP-MS analysis.
* Laser fluence is displayed as a value in units J/cm2
* All values for iron or selenium are average measurements from each standard, normalised to the corresponding average sulphur value. 
* Within-line relative standard deviations (RSDS) were determined for each line and then average RSD reported for each standard.
* For methanol addition average selenium counts were calculated for each percentage of methanol addition, whilst maintaining a constant selenium concentration.