Merck, 1.07204.0105, Certified sec. standard reference buffer solution

The potassium tetraoxalate dihydrate certified secondary standard reference buffer solution is gravimetrically prepared using high-quality salt in high-purity water. Its pH value is measured by differential potentiometry with two platinum hydrogen electrodes against primary certified reference materials from NIST & PTB. The pH qualification is based on the 5-point calibration method, following DIN 19268, against certified primary reference standards as per DIN 19266. Please visit ISO certificates and Site Quality Self-Assessments to access the current certificates of accreditation. Download your certificate at http://www.sigma-aldrich.com to view certified values, including uncertainty and expiry date.