The two-point calibration for the pH electrode uses two buffers. Which of the following pH val-ues are correct for these two buffers? 1. 6.839 2. 6.840 3. 7.384 4. 7.495

a. 1 and 3 c. 2 and 4
b. 1 and 4 d. 2 and 3

ANS: D
The National Institute of Standards and Technology (NIST) and the International Federation of Clinical Chemistry (IFCC) have established standards for the calibration of blood gas electrodes. A one-point calibration uses a nearly normal pH buffer with a pH of 7.384. A second, lower pH buffer, pH 6.840 is analyzed in the two-point calibration to ensure that the electronic output of the electrode is linear over a wide range of pH levels.