It is actually 10 mM HCl, you can make that by adding 1 ml fuming HCl (10 M) to 1 litre of sterile water. Now steer well (with a glass spoon), and take out the amount that you need. Instead, you can also add 7 ml acetic acid ("vinegar" without the water) to 1 litre of water (100 mM). I am not too happy about the BA, and I will try the HCl method plus human serum albumin to get to low concentrations of 0.1 mg/ml of IGF. BTW, you also have to sterile filter with a syringe filter that does not cling onto the IGF. Forgot the type of filter, but look on the manufacturer pages.