Merck, 1072020105, Certified sec. standard reference buffer solution

The certified secondary standard reference buffer solution (potassium dihydrogen phosphate/disodium hydrogen phosphate) is gravimetrically prepared using high-quality reagents 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. It is qualified using a 5-point calibration method, in accordance with 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.