If you are working with any particular LPS, then find out why the LPS is produced or rather what are the inducing factors for production of the LPS. It will answer your question.

Are you buying LPS, or preparing it yourself?  When you prepare LPS by a method such as hot phenol-water extraction, it is commonly contaminated with bacterial proteins, nucleic acids and phospholipids.  Some of these are themselves bioactive; other contaminants are inactive and are a problem because they affect potency per milligram.  You can detect protein and nucleic acid in an LPS preparation by measuring its UV absorbance at 260 and 280 nm.  You may need to clean up your preparation by treatment with proteases and/or nucleases.  Contaminating lipids can be removed by extraction with solvents like ether. 

Thanks, no we buy it in, but even between purchased batches there is wide variability..