This accounted for the error and variability associated with any measurement performed by the HPLC instrument and hence can be associated with both the pKa measurements as well as the distribution coefficient measurements. As previously stated, limits on the amount of available drug substance made it not possible to prepare replicate samples for testing, as might commonly be expected of high throughput experimentation. Table below lists the mean absolute deviation (MAD) (Equation ) and the standard mean error (Equation ) for the three compounds that were subjected to replicate HPLC injections to ensure robustness in the chromatography instrumentation.