In vitro human embryo culture is a critical process, which is performed in microdroplets of specialized culture medium with typical physicochemical properties. Since optimal embryo development completely depends on medium stability, microdroplets are covered with mineral oil to maintain pH, osmotic pressure, and temperature during manipulation and culture. Pharmaceutical-grade paraffin oil is widely used as a raw material for the production of mineral oil, used in assisted reproductive

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... y (ART) procedures. Although suited for pharmaceutical applications, further purification is essential to remove traces of embryotoxicants, including oxidative agents. In view of quality control testing, in-house analysis of oxidative content is routinely performed on each new batch of mineral oil. For this purpose, the European Pharmacopoeia (EP) describes an iodometric titration method with visual end point determination, the so-called peroxide value (POV) assay. Although being the gold standard in the pharmaceutical, food, and fuel industry, the test is not sensitive enough to detect very low levels of oxidative substances. Therefore, several modifications have been made to the EP method, including altered reagents concentration and oil sample quantity, combined with potentiometric end point determination. These efforts have resulted in a very sensitive test method, which is able to reliably detect oxidative content as low as 0.1 mEq/kg. In summary, a potentiometric POV assay, based on the EP method, has been specifically developed for QC analysis of ART mineral oils. A detailed overview of the applied modifications is presented, together with assay validation results, demonstrating excellent sensitivity and reproducibility.