You'd want to call the manufacturer to be sure. This is from IAMS' website:
http://www.iams.com/cat-article/answ...edients.aspx#6
Are your diets low in sodium?
Sodium is an essential mineral for life and is not considered harmful, nor does it have a negative effect on blood pressure in normal, healthy dogs. Most of our products contain approximately 0.5% sodium. The sodium is balanced in proper proportions with the other vitamins, minerals, fats, proteins, and carbohydrates.
Their ingredients list includes Sodium Bisulfate.
Purina Naturals' ingredients list includes tetra sodium pyrophosphate, menadione sodium bisulfite complex (source of Vitamin K activity), and sodium selenite.
http://catchow.com/Cat-Chow-Naturals/