Sodium chloride solutions come in different strengths. So, to figure this out, you need to know the concentration of the salt solution. Eor example, the 0.9% NaCl solution contains 0.9 gm of sodium in 100 ml of liquid, while the more concentrated 23.5% NaCl solution contains 23.5 gms of sodium in the same 100 ml...in other words, it is ~25 times saltier. Given that you are giving a relatively small amount of liquid, you are probably using the 23.5 % solution (but, you should double check this, just to be sure).

If you work through the math, you should find that 2.1 ml of the 23.5% solution contains 493.5 mg of sodium. Ordinary table salt contains 590 mg of sodium per 1/4 tsp (you can check your box of Morton’s). Therefore, 2.1 ml of the 23.5 % solution is equivalent to a little less than a 1/4 tsp of ordinary table salt.....about what Louise’s baby is getting.