PBS (phosphate buffered saline) is a common salt solution used in a number of pr

Question

PBS (phosphate buffered saline) is a common salt solution used in a number of protocols including protein assays, cell work, etc. The recipe for 10X PBS is as follows:

Dissolve the following into 800 mL distilled H20:

80 g of NaCl (MW = 58.44 g/mol)

2.0 g of KCl (MW = 74.55 g/mol)

2.4 g of KH2PO4 (MW = 136.09 g/mol)

14.4 g of Na2HPO4 (MW = 141.96 g/mol)

Adjust pH to 7.4.

Adjust volume to 1 L with additional distilled H20.

Sterilize by autoclaving.

5) UH OH! You made a mistake making the 1X solution. You added 100 mL 10X stock and 1000 mL H20.

What X concentration of PBS did you make?

What is the concentration of Na2HPO4 in this dilution?

Explanation / Answer

The recipe for 10X PBS is givenin the question, now if we add 100mL of 10X stock and 1000 mL oh H2O, then the concentration of PBS so obtaioned is-

For 1L of solution concentration is 10X

There fore no. of moles of PBS= concentration x volume = 10X x 1= 10X

Now new concentration will be= no. of moles of PBS/ (volume of solution in L )

= (10X )/((1000+100)/1000)= (10X)/1.1= 9.09X

we can also calculate this by molarity equation as

M1V1=M2V2

M1=10X, V1= 1L, V2= 1.1 L

=M2=(M1V1)/V2= (10X x 1)/1.1= 9.09X

The concentration of the new PBS solution is 9.09X

When the concentration of PBS solution was 10X , concentration of Na2HPO4 was-

Molarity = (no. of moles of Na2HPO4)/ volume os solution in L

= (Given mass of Na2HPO4/molar mass of Na2HPO4)/volume os solution in L

=(14.4/141.96)/1= 0.1 M

By using molarity equation we can calculate the new molarity of Na2HPO4

M1V1=M2V2

M1=0.1 M, V1= 1L, V2= 1.1 L

=M2=(M1V1)/V2= (0.1 X 1)/1.1= 0.09 M

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