You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Normal anion gap is mostly due to  : and explain in detail?
Normal anion gap is due to Unmeasured proteins. Normally in the plasma, the concentration of anion and cations are equal to maintain electrical neutrality. Thus, no real anion gap exists in the plasma and this is purely a diagnostic concept. 
Guyton and Hall Textbook of medical physiology Pg-426