Why is analytical grade potassium hydroxide only about 85% pure?

Why is analytical grade potassium hydroxide only about 85% pure?
The purity gap stems from feedstock economics. Purifying potassium chloride is far costlier than sodium chloride, so KOH production retains a meaningful sodium hydroxide fraction. Since high-purity caustic soda has massive demand that absorbs purification costs, producers have little incentive to push KOH to near-100%. Additionally, KOH's strong hygroscopicity and CO2 absorption make it harder to maintain high assay during storage and handling. For buyers, this means spec-grade KOH typically sits around 85%, and the sodium content must be factored into process chemistry, especially in fine chemical or pharmaceutical applications where sodium ions are undesirable.