Every time I use the ÄKTA Pure Protein Purification System for the separation of protein by ion exchange column, the units of the ordinate to indicate the salt concentration is mS/cm, rather than molarity.

But what is mS/cm? Wikipedia shows that it's the unit for conductivity. So is it possible to convert the mS/cm to molarity for convenience if the salt is NaCl?

I found a conversation about the reverse need with Google, to convert the molarity to electrical conductivity. An answer said:

Some data on the electrical conductivity of pure solutions relevant to saline soils or to seawater . As 10 mM NaCl has an EC of almost exactly 1.0 dS/m, and as it is the most common salt in solution in ground or river water, a ‘rule of thumb’ is to muliply the EC by ten to equate it to salt molarity.

So I get an equation: 10mM -> 1mS/cm, 1M -> 100mS/cm.

The equation may not be accurate according to my experience(high probability my error is much higher). My buffer is never the pure salt solution can be a reason. But tell the rough situation with the electrical conductivity is enough in my workflow.

Hope this little find will help you.

Reference:

Bouras, Hamza. (2022). Re: How is it possible to convert (NaCl concentration, in mM) to electrical conductivity (dS/m)or % of salts. ?. Retrieved from: https://www.researchgate.net/post/How_is_it_possible_to_convert_NaCl_concentration_in_mM_to_electrical_conductivity_dS_mor_of_salts/61f107189b9a8d052e6fb0cb/citation/download.