I think what they meant by detoxify is to have nitrite anion bind with cations (from Prime) to yield something which is not toxic. Another word, newly formed compound can not compete with Oxygen at gas exchange site of hemoglobin where O2and CO2 are exchanged.
How stable are these new compound formed or exact process/mechanism of Prime, I havnt been able to obtain from Seachem.
All I know is that before Prime, I was able to detox nitrite ion by adding extra salt to tank (do not overdose as tolerance to salt varies with species) as Nitrite is virtually non toxic in salt water. I guess Any Cations such as Calcium, Magnessium, Potassium, etc can affect the toxicity of free nitrite ions too.