PREPARATION OF SOLUTIONS

Standard Endotoxin Stock Solution— A Standard Endotoxin Stock Solution is prepared from a USP Endotoxin Reference Standard that has been calibrated to the current WHO International Standard for Endotoxin. Follow the specifications in the package leaflet and on the label for preparation and storage of the Standard Endotoxin Stock Solution. Endotoxin is expressed in Endotoxin Units (EU). [note—One USP Endotoxin Unit (EU) is equal to one International Unit (IU) of endotoxin. ]

Standard Endotoxin Solutions— After mixing the Standard Endotoxin Stock Solution vigorously, prepare appropriate serial dilutions of Standard Endotoxin Solution, using Water for BET. Use dilutions as soon as possible to avoid loss of activity by adsorption.

Sample Solutions— Prepare the Sample Solutions by dissolving or diluting drugs, or taking washes from medical devices using Water for BET. Some substances or preparations may be more appropriately dissolved, diluted, or extracted in other aqueous solutions. If necessary, adjust the pH of the solution to be examined (or dilution thereof) so that the pH of the mixture of the lysate and Sample Solution falls within the pH range specified by the lysate manufacturer, usually 6.0 to 8.0. The pH may be adjusted by use of an acid, base, or suitable buffer as recommended by the lysate manufacturer. Acids and bases may be prepared from concentrates or solids with Water for BET in containers free of detectable endotoxin. Buffers must be validated to be free of detectable endotoxin and interfering factors.