Prepare 1 L phosphate buffer solution at pH = 7.4

Prepare 1 L phosphate buffer solution at pH = 7.4

 

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▶ 참고: 인산/인산염 완충용액 [ https://ywpop.tistory.com/7182 ]

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The first step in making a buffer solution at pH = 7.4 is to choose the appropriate acid-conjugate base combination.

The best choice is for the acid to have a pKa value close to the desired pH.

Therefore, the acid is sodium dihydrogen phosphate (NaH2PO4, pKa2 = 7.21) and the conjugate base is sodium monohydrogen phosphate (Na2HPO4).

 

 

 

The second step is to calculate the ratio [base]/[acid] using the Henderson-Hasselbalch equation as the following:

 

pH = pKa + log {[base]/[acid]}

7.4 = 7.21 + log {[base]/[acid]}

log {[base]/[acid]} = 7.4 – 7.21 = 0.19

[base]/[acid] = 10^0.19 = 1.55

 

 

 

The third step is to calculate the concentration of each component of the buffer (NaH2PO4 and Na2HPO4) according to the following:

[base]/[acid] = 1.55

[base] = 1.55 × [acid]

 

if [acid] = 0.1 M = [NaH2PO4]

then [base] = 1.55 × 0.1 M = 0.155 M = [Na2HPO4]

 

 

 

Finally, the mass of each salt is calculated. The molecular weight of NaH2PO4 is 119.98 g/mol and that of Na2HPO4 is 141.96 g/mol. The number of moles and mass of each salt is calculated as the following:

 

moles of NaH2PO4 = (0.1 mol/L) × 1 L = 0.1 mol

moles of Na2HPO4 = (0.155 mol/L) × 1 L = 0.155 mol

 

mass of NaH2PO4 = 0.1 mol × (119.98 g/mol) = 12 g

mass of Na2HPO4 = 0.155 mol × (141.96 g/mol) = 22 g

 

 

 

To prepare the above mentioned buffer solution, 12 g of NaH2PO4 and 22 g of Na2HPO4 are dissolved in freshly distilled water and the volume is brought to 1 L.

 

 

 

 

[키워드] sodium phosphate buffer 기준문서