Citric acid (Standard) is the analytical standard of Citric acid and is intended for research and analytical applications. It is a natural preservative and food tartness enhancer. Citric acid induces apoptosis and cell cycle arrest at G2/M phase and S phase in HaCaT cells and causes oxidative damage of the liver by decreasing antioxidative enzyme activities. It is also an acidulant, emulsifier, sequestrant, and buffering agent widely used across many industries. This compound is commonly used in qualitative, quantitative, and methodological research experiments in HPLC, GC, and MS.