Determining ion concentration through downhole optical spectroscopy

A method comprising:

• disposing a fluid sampling tool into a wellbore wherein the fluid sampling tool comprises:
• at least one probe to fluidly connect the fluid sampling tool to a formation in the wellbore;
• and
• at least one passageway that passes through the at least one probe and into the fluid sampling tool;
• drawing a formation fluid from a first sampling zone, as a fluid sample, through the at least one probe and through the at least one passageway;
• and
• analyzing the fluid sample in the fluid sampling tool for one or more ion components, wherein analyzing the fluid sample comprises:
• using a downhole spectroscopy device;
• and
• using spectral deconvolution to quantify ions concentrations, wherein peak height, or Full Width Half Max (FWHM), or integrated area, or a combination thereof in combination with temperature and a model are used to quantify ion concentrations.