Method for adjusting pH value of culture medium

Q: When adjusting the medium, adjust the pH to 7.25, and store it in -20 degrees aliquots. After a few days, thaw it and measure it at 7.80. What happened? Is it necessary to adjust it to below 7 each time it is mixed? After thawing, readjust the PH value, and then filter and repack, can it still be used? Can it be stored at -20 degrees?

A: According to your explanation, you can conclude that you are using powder DMEM. The instructions say that 3.7 g of sodium bicarbonate should be added, and the pH value is increased by 0.1-0.2 when filtering. But 3.7 g of sodium bicarbonate corresponds to 10% CO2 culture environment, if you use 5% CO2, then you only need to add 1.85 g of sodium bicarbonate, then basically do not need to adjust the PH value, and then start filtering, the pH will increase during filtering, but basically also in The scope of requirements. But even if you only add 1.85 g of sodium bicarbonate, the pH value will rise even if it is too long, because the bottle of your assembly base is not sealed and has contact with the CO2 in the air, and the concentration of CO2 in the air is lower than 5%, then with the extension of time, the sodium bicarbonate buffer works, and the PH value rises again, which is inevitable. Of course, HEPES can be added to introduce new buffer pairs, and the PH is relatively difficult to change.

to sum up:

To measure the pH of the culture medium, a common method is to determine the pH. The pH range is 1-14, and the pH is 7 when it is neutral. Down to 6, 5, 4, 3, 2, 1, the acidity becomes stronger and stronger, up to 8, 9, 10, .... The stronger. The measurement of pH can be carried out with commercially available broad-spectrum pH test paper.

To measure the pH of the solution, a wide-spectrum pH test paper can be taken, the solution to be tested is dropped on the test paper, and then compared with the standard version, the same color can be expressed as this value. For measuring the pH of the culture material, weigh 5 grams of culture material, add 10 ml of neutral water, and then stir and clarify. Dip the clarified liquid with a broad-spectrum pH test paper and measure the pH test paper into the material. Make it wet on the test paper, and then confirm the pH with the standard version. When measuring, the material should be mixed well; when touching the ph test paper, both hands should be dried to avoid measurement errors.

If the raw material pH is detected to be acidic, quick lime powder, 1 ï¹ª -5 ï¹ª quicklime (or sodium hydroxide) solution can be added for adjustment; if the raw material pH is alkaline, calcium superphosphate, 3 ï¹ª -5 ï¹ª dilute hydrochloric acid solution, etc. can be added Make adjustments.

Many experimenters don't measure the PH value now, it's almost the same as visual observation. As long as it is the kind of rosy red, it is the normal range. When you find that there is purple in the light, it must be that the pH has risen again. Adjust the PH value. If it's just normal purple, no problem, you can try, put the culture bottle into the incubator, but be sure to unscrew the bottle cap, so that after a few hours, the pH of your ligand will return to normal levels This is because the ligand is exposed to 5% CO2 at this time.

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