I want to know about the calculation of osmolality of phosphate buffer pH 7.0.
Similarly, Osmolality of 450 mM sucrose and lactose. As they are non-dissociated compounds, should they refer to 450 mOsmol /kg in solution???
How can I determine the osmolality of 10 % PEG 6000 solution ???
Dear Nageena,
For calculating the osmolarity of phosphate buffer pH 7.0, you should list all components of the buffer and use the following equation:
The osmolarity of a solution may be given as the sum of (yi)(ni)(Ci), where yi is the osmotic coefficient of solute i, n is the number of particles that solute i dissociates into and Ci is the molarity of solute i.
The following an example for calculating the osmolarity of the following formula:
120mM NaCl
0.5mM CaCl2
2.5mM KCl
1.0mM MgCl2
10mM Glucose
so the osmolarity of your solution should be
2 x 120 (NaCl) + 3 x 0.5 (CaCl2) + 2 x 2.5 (KCl) + 3 x 1 (MgCl2) + 1 x 10 (Glucose) = 259.5 mOsm/L
The osmolarity of 450 mM sucrose and lactose should be x 450 450 mOsm/L
Regarding 10 % PEG 6000 solution, you should convert the concentration in % to mM and then use the equation depicted above.
Please note that the osmotic coefficient (yi) has a range of 0 to 1 - the osmotic coefficient will be 1 when the solute is completely dissolved and 0 when insoluble.
http://www.scientistsolutions.com/forum/organic-chemistry-assay-development-protocols/calcuting-osmolarity
Hoping this will be helpful,
Rafik
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