The long term solution storage of this product has not been investigated. However, loss of potency may be caused by a number of factors:
1. The shelf life of the stored solution may been exceeded.
2. Repeated freeze/thaw cycles may have caused degradation of the product.
3. The LPS may be present, but bound or 'stuck' to the walls of the container - vortex solutions at least 30 minutes to redissolve.
Solutions of LPS should be stored at a minimum concentration of 1 mg/ml. It may be necessary to prepare a fresh solution.
To discuss further, please navigate to the link https://www.sigmaaldrich.com/techservice, click on "Product Technical Inquiries" under the Products Section and respond with all the required information so that a member of the Technical Service team can reach out to assist further. Thank you.