Merck, 1.07200.0105, Certified sec. standard reference buffer solution

The certified secondary standard reference buffer solution of potassium hydrogen phthalate is gravimetrically prepared using a high-quality reagent 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 5-point calibration method is used for its pH qualification, 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.