Hi everyone,
Does anyone know how to make phosphate buffer with 0.06 M? I know to to make for example lactate buffer or sodium buffer, but for phosphate buffer it is strange. Most people use Sodium phosphate dibasic heptahydrate (mw: 268 g/mol)12.125 g which gives 0.0452 M and Sodium phosphate monobasic monohydrate (mw: 138 g/mol)2.036 g, 0.0148 M. First of all why for Sodium phosphate dibasic heptahydrate 0.045 M is calculated and the rest is 0.0148 M of Sodium phosphate monobasic monohydrate whythey did not use 0.05 M of the dibasic and 0.01M of monobasic?
Secondly in our lab we have Sodium phosphate dibasic and Sodium phosphate monobasic dihydrate . so how should I calculate to ge 0.06M pH 7.4?
Many thanks in advance
If you have a pH meter, prepare a 60 mM solution of monobasic and a 60 mM solution of dibasic. Add monobasic to dibasic while mixing until you reach the desired pH. The result will be a 60 mM solution of sodium phosphate with the desired pH. You can include NaCl in both of the stock solutions at the desired final concentration.
Dear Adam,
Many thanks for your replying. the method you mentioned is different from what I read. they made 0.045 mM of Sodium phosphate dibasic heptahydrate and 0.015mM of Sodium phosphate monobasic monohydrate. This method also is right? to me your method should be more accurate to make 60mM of each component and then mix it.
Also, if I do not have sodium phosphate monohydrate and instead have it in heptahydrate or higher I should calculate how much I need based on its molecular weight?
Many thanks
Yes, you should prepare the solution based on the molecular weight of the solid, including the water. The water content of the solid no longer matters once the solid is dissolved.
You may want to check my post at this related query:
https://www.researchgate.net/post/Why_do_I_struggle_to_adjust_lower_pH_of_my_phosphate_buffer_at_a_certain_pH_point_even_though_I_add_too_much_acidic_solution
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