DPBS Powder without Calcium, Magnesium, or Phenol Red

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• PBS vs DPBS: What Is Different, and Which One to UsePBS and DPBS are both phosphate-buffered saline solutions; the difference is the recipe, not the function. Dulbecco's formulation (DPBS) adds potassium chloride and carries roughly twice the phosphate of a typical PBS (about 9.5 mM versus about 4 mM), and it is sold in two versions - with calcium and magnesium, and without. In practice the with-or-without-divalent-cations choice matters far more than the PBS-or-DPBS label: use a calcium- and magnesium-free solution to wash cells before trypsinisation or EDTA dissociation, because Ca2+ and Mg2+ support the cadherin and integrin bonds you are about to break, and use the version containing calcium and magnesium when cells must stay attached and intact through the wash.
• Cell culture buffersCell culture buffers hold medium in the pH 7.2-7.4 range that mammalian cells require, against the acid load cells generate as they metabolise. The default system in almost every classical medium is sodium bicarbonate working with the CO2 in the incubator atmosphere, which is why bicarbonate content must be matched to the incubator setting: about 1.5-2.2 g/L NaHCO3 for 5% CO2 and 3.7 g/L for 10% CO2. Organic buffers such as HEPES (pKa 7.48) are added at 10-25 mM to hold pH when cultures are outside a CO2 atmosphere, while phosphate-buffered solutions such as PBS and DPBS are used for washing and short-term handling rather than for growth.