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What is the difference between XF RPMI medium (without phenol red, p/n 103336-100) and XF RPMI medium pH 7.4 (p/n 103575-100)?

Both media are of RPMI composition and contain NO phenol red.  However, XF RPMI medium (without phenol red) does not contain HEPES and requires adjustment of pH value to 7.4 after the addition of supplements and/or HEPES, followed by filtration to ensure sterility.  XF RPMI Medium pH 7.4 contains 1 mM HEPES and the pH of this medium is pre-adjusted to 7.4.  This medium provides consistent buffer factor, allowing quantitative measure of ECAR and accurate calculation of Proton Efflux Rate (PER).  When used with XF supplements at the recommended concentrations, no pH adjustment is required after supplements are added.   Seahorse XF RPMI Medium pH 7.4 is compatible with all XF assays and recommended for assays using cell models requiring an RPMI medium composition.