What do you mean by "hydrolysis"? Do you want to hydrolyse proteins into amino acids? To determine free amino acids in the samples, extraction with 80% methanol is OK before LC-MS analysis.

Zhiqian Liu ohk, is it same for HRLCMS by PDA? I am going to analyse sample for amino acid determination.

Extraction with 80% methanol , require any specific temperature or evaporation of methanol or incubation???

Extraction twice with 80% methanol at RT (with sonication 15 min for each cycle). After centrifugation, you can inject the supernatant directly into LC. You do not need to do evaporation unless you want to enrich the analytes.