In LCMS 25% ammonium hydroxide is mainly used as a mobile phase modifier to adjust the pH of the solvent system and improve ionization efficiency particularly in negative ion mode. It helps enhance the separation of analytes especially basic and polar compounds and can improve peak shape and sensitivity. It is also used in sample preparation and dilution to maintain alkaline conditions and ensure compatibility with mass spectrometry detection.

for LC-MS

Ammonium hydroxide solution (25%) used in LCMS (liquid chromatographymass spectrometry) is a dilute aqueous solution of ammonia in water where water makes up about 25% of the composition. It is a clear colorless volatile and weakly alkaline solution with a strong pungent odor. In analytical chemistry especially LCMS it is valued for its high purity and volatility which helps minimize contamination and residue during analysis.