Method for preparing aqueous solutions of a defined pH

1. A method for preparing an aqueous solution of a defined pH comprising an acid, a base and one or more additives, wherein the method comprises the steps of:

a) calculating theoretical concentrations of acid and base for each of a plurality of solutions having a theoretical pH corresponding to the defined pH, and each of the plurality of solutions having a different additive concentration within a range of different additive concentrations, wherein said calculating is carried out using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) preparing the plurality of solutions and measuring an actual pH for each solution having a different additive concentration within the range of different additive concentrations;

c) for each solution, calculating a value for delta pH, ΔpH, being the difference between the theoretical pH and the actual pH;

d) generating a mathematical model describing a relationship of ΔpH with additive concentration;

e) selecting the defined pH and additive concentration for the aqueous solution to be prepared;

f) using the mathematical model generated in step d) to calculate ΔpH for the selected defined pH and additive concentration;

g) calculating a ΔpH-corrected pH by summing the defined pH and ΔpH;

h) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the additive by using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; and

i) preparing the aqueous solution including the one or more additives using the concentrations of acid and base calculated in step h).

2. A method for preparing an aqueous solution of a defined pH comprising an acid, a base and one or more additives, wherein the method comprises the steps of:

a) calculating theoretical concentrations of acid, base and additive for each of a plurality of solutions having a theoretical pH corresponding to the defined pH, and each of the plurality of solutions having a different additive concentration within a range of different additive concentrations, wherein said calculating is carried out using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) for each solution, calculating a value for ΔpH, being the difference between the theoretical pH and a value for actual pH, for each of the plurality of solutions having a different additive concentration;

c) generating a mathematical model describing a relationship of ΔpH with additive concentration;

d) selecting the defined pH and additive concentration for the aqueous solution to be prepared;

e) using the mathematical model generated in step c) to calculate ΔpH for the defined pH and additive concentration;

f) calculating a ΔpH-corrected pH by summing the defined pH and ΔpH;

g) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the additive by using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; and

h) preparing the aqueous solution including the one or more additives using the concentrations of acid and base calculated in step g).

3. A method for preparing an aqueous solution of a defined pH, comprising an acid, a base and an additive, wherein the method comprises the steps of:

a) calculating a theoretical pH for the aqueous solution using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) calculating a ΔpH-corrected pH for the aqueous solution by comparing the theoretical pH with a pH value calculated from an equation determined from a mathematical model of the difference between the theoretical pH and a value for actual pH of each of a plurality of solutions having a different additive concentration within a range of different additive concentrations;

c) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the additive using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; and

d) preparing the aqueous solution including the additive using the concentrations of acid and base calculated in step c).

4. The method according to claim 1 , wherein the aqueous solution is a buffer.

5. The method according to claim 4 , wherein the buffer is selected from the group consisting of tris buffers; sodium phosphate buffers; potassium phosphate buffers; sodium acetate buffers; MES buffers; and HEPES buffers.

6. The method according to claim 1 , wherein the one or more additives are salts selected from the group consisting of NaCl, KCl, Na 2 SO 4 , (NH 4 ) 2 SO 4 and (NH 4 ) 3 PO 4 and mixtures thereof.

7. The method according to claim 6 , wherein the salts are at a concentration of up to about 2M.

8. The method according to claim 1 , wherein a minimum additive concentration in the range of additive concentrations is selected to be below, and a maximum additive concentration in the range of additive concentrations is selected to be above, the additive concentration of the aqueous solution to be prepared.

9. The method according to claim 1 , wherein the range of additive concentrations comprises from 5 to 10 data points.

10. The method according to claim 1 , wherein the defined pH is selected to be within 1 unit of the solution's thermodynamic pKa value.

11. An apparatus for preparing an aqueous solution of a defined pH, wherein the apparatus comprises a metering device capable of feeding into a mixing device an acid, a base, and one or more additives, wherein the metering device operates under control of control apparatus for

a) calculating theoretical concentrations of acid and base for each of a plurality of solutions having a theoretical pH corresponding to the defined pH, and each of the plurality of solutions having a different additive concentration within a range of different additive concentrations, wherein said calculating is carried out using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) for each solution, calculating a value for delta pH, ΔpH, being the difference between the theoretical pH and the actual pH;

c) generating a mathematical model describing a relationship of ΔpH with additive concentration;

d) selecting the defined pH and additive concentration for the aqueous solution to be prepared;

e) using the mathematical model generated in step d) to calculate ΔpH for the selected defined pH and additive concentration;

f) calculating a ΔpH-corrected pH by summing the defined pH and ΔpH;

g) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the one or more additives by using the Henderson-Hasselbach equation in combination with the Debye Huckel theory.

12. The apparatus according to claim 11 , wherein the apparatus further comprises a means for carrying out a bioprocessing operation.

13. The apparatus according to claim 12 , wherein the bioprocessing operation comprises chromatography, viral inactivation, filtration, refolding, ultrafiltration, diafiltration, microfiltration, in-line conditioning or refolding.

14. The apparatus according to claim 11 , wherein the metering device comprises a pump located downstream of a multiple inlet flow-controller and upstream of a mixing device.

15. The method according to claim 2 , wherein the value for the actual pH in step b) is a predetermined value.

16. The method according to claim 3 , wherein the value for the actual pH in step b) is a predetermined value.

17. An apparatus for preparing an aqueous solution of a defined pH, wherein the apparatus comprises a metering device capable of feeding into a mixing device an acid, a base, and one or more additives, wherein the metering device operates under control of control apparatus for

a) calculating theoretical concentrations of acid, base and additive for each of a plurality of solutions having a theoretical pH corresponding to the defined pH, and each of the plurality of solutions having a different additive concentration within a range of different additive concentrations, wherein said calculating is carried out using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) for each solution, calculating a value for ΔpH, being the difference between the theoretical pH and a value for actual pH, for each of the plurality of solutions having a different additive concentration;

c) generating a mathematical model describing a relationship of ΔpH with additive concentration;

d) selecting the defined pH and additive concentration for the aqueous solution to be prepared;

e) using the mathematical model generated in step c) to calculate ΔpH for the defined pH and additive concentration;

f) calculating a ΔpH-corrected pH by summing the defined pH and ΔpH;

g) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the one or more additives by using the Henderson-Hasselbach equation in combination with the Debye Huckel theory.

18. The apparatus according to claim 17 , wherein the apparatus further comprises a means for carrying out a bioprocessing operation.

19. The apparatus according to claim 18 , wherein the bioprocessing operation comprises chromatography, viral inactivation, filtration, refolding, ultrafiltration, diafiltration, microfiltration, in-line conditioning or refolding.

20. The apparatus according to claim 17 , wherein the metering device comprises a pump located downstream of a multiple inlet flow-controller and upstream of a mixing device.

21. An apparatus for preparing an aqueous solution, wherein the apparatus comprises a metering device capable of feeding into a mixing device an acid, a base, and one or more additives, wherein the metering device operates under control of control apparatus for

a) calculating a theoretical pH for the aqueous solution using the Henderson-Hasselbach equation in combination with the Debye Huckel theory;

b) calculating a ΔpH-corrected pH for the aqueous solution by comparing the theoretical pH with a pH value calculated from an equation determined from a mathematical model of the difference between the theoretical pH and a value for actual pH of each of a plurality of solutions having a different additive concentration within a range of different additive concentrations;

c) using the ΔpH-corrected pH to calculate concentrations of acid and base for the preparation of the aqueous solution including the one or more additives using the Henderson-Hasselbach equation in combination with the Debye Huckel theory.

22. The apparatus according to claim 21 , wherein the apparatus further comprises a means for carrying out a bioprocessing operation.

23. The apparatus according to claim 22 , wherein the bioprocessing operation comprises chromatography, viral inactivation, filtration, refolding, ultrafiltration, diafiltration, microfiltration, in-line conditioning or refolding.

24. The apparatus according to claim 21 , wherein the metering device comprises a pump located downstream of a multiple inlet flow-controller and upstream of a mixing device.

25. The method of claim 1 wherein the defined pH is 3.5 to 9.

26. The method according to claim 3 , wherein the aqueous solution is a buffer.

27. The method according to claim 26 , wherein the buffer is selected from the group consisting of tris buffers; sodium phosphate buffers; potassium phosphate buffers; sodium acetate buffers; MES buffers; and HEPES buffers.

28. The method according to claim 3 , wherein the additive is a salt selected from the group consisting of NaCl, KCl, Na 2 SO 4 , (NH 4 ) 2 SO 4 and (NH 4 ) 3 PO 4 .

29. The method according to claim 28 , wherein the salt is at a concentration of up to about 2M.

30. The method according to claim 3 , wherein a minimum additive concentration in the range of additive concentrations is selected to be below, and a maximum additive concentration in the range of additive concentrations is selected to be above, the additive concentration of the aqueous solution to be prepared.

31. The method according to claim 3 , wherein the range of additive concentrations comprises from 5 to 10 data points.

32. The method according to claim 3 , wherein the defined pH is selected to be within 1 unit of the solution's thermodynamic pKa value.