Effects of cooling and freezing on pH of semen extender

The pH change of 10 different buffering systems with temperature ranging from room to 5 °C was examined; three were conventional buffers which included phosphate yolk, citrate yolk, and skim milk. Seven were Good's buffers with egg yolk which included TES, TRIS, BES, MOPS, PIPES, MES, and TEST. The pH of the three conventional buffers did not change with decreasing temperature, but Good's buffers showed an increase in pH with decreasing temperature from room to 5 °C. The pH change due to temperature was measured for TEST buffer solution with and without 20% egg yolk containing 2 or 6% of five different cryoprotective compounds. The pH at 5 °C was significantly higher than at room temperature. The addition of egg yolk and/or cryoprotective compound did not alter the pH significantly during cooling, even though a slight drop in pH was noted with the addition of egg yolk indicating that the change in pH is primarily due to the buffer. The pH of TEST yolk buffer (pH 7.2 at room temperature) was measured continuously from 37 °C to below freezing (?18 °C). The pH increased with decreasing temperature to 8.0 ± 0.2 from 37 to ?14 °C at which point it dropped abruptly to pH 6.5 ± 0.2.