The product remains active for at least 2 years. This product will react with water since alkylsilanes react with hydroxyl groups. An ethanol solution remains active for one day. For more information please see this data sheet: https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/139/774/m6514pis.pdf.
The product specification sheet for this product contains a recommended retest date period of two years after the quality release date. A recommended retest date is the period of time during which the product is expected to remain within established stability specifications, provided that it has been stored under defined conditions. After the Retest Date, product samples should be examined to ensure that the product is still in compliance with the established specifications. For more information, you may access the "Product Dating Information" document under "ADDITIONAL USEFUL DOCUMENTS ABOUT OUR PRODUCTS" at the bottom of the Quality Services page with this link: https://www.sigmaaldrich.com/US/en/life-science/quality-and-regulatory-management/quality-services.