I tried to isolate the lipid A moiety from LPS by ammonium isobutyrate-based protocol, which based on Lisa M. Leung et al. (J Antimicrob Chemother 2017; 72: 3035–3042) with slight modification.

1. The purified LPS was treated with ammonium/isobutyrate mixture, and then incubated at 100℃ for 30–45min.

2. After spun down to remove cell debris, the supernatants were transferred to clean tubes, combined in a 1:1 ratio of distilled water (400 µL), frozen on dry ice, and lyophilized overnight.

3. Resuspended in 200 µL of a 2:1:0.25 chloroform/methanol/water solvent mixture. Mass spectra were recorded in negative ion mode.

However, the mass peaks were around 500 Da rather than 1800 Da. I had tried to isolate the lipid A from the whole cells, but the peak intensity was too low.

Does anyone know how to improve the mass results?