Method for Preparing Aqueous Solutions of a Defined PH

Abstract

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

a) calculating the theoretical concentrations of acid and base for the solution to have the defined pH using the Henderson-Hasselbach equation in combination with the Debye Huckel theory for a range of different additive concentrations; b) preparing a sample of the buffer for the range of additive concentrations and measuring the actual pH for each additive concentration; c) calculating a value for delta pH, pH, being the difference between the theoretical pH and the actual pH, for each additive concentration; d) generating a mathematical model describing the relationship of pH with additive concentration; e) selecting the defined pH and additive concentrations; f) using the mathematical model generated in step d) to calculate pH for the defined pH and additive concentration; g) calculating a pH-corrected pH by summing the defined pH and delta pH; h) using the pH-corrected pH to calculate the concentrations of acid and base using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; i) preparing the solution using the concentrations calculated in step h).

Claims

1. A method for preparing an aqueous solution of a defined pH comprising an acid, a base and optionally one or more additives, the method comprising the steps of: a) calculating the theoretical concentrations of acid and base for the solution to have the defined pH using the Henderson-Hasselbach equation in combination with the Debye Huckel theory for a range of different additive concentrations; b) preparing a sample of the buffer for the range of additive concentrations and measuring the actual pH for each additive concentration; c) calculating a value for delta pH, pH, being the difference between the theoretical pH and the actual pH, for each additive concentration; d) generating a mathematical model describing the relationship of pH with additive concentration; e) selecting the defined pH and additive concentrations; f) using the mathematical model generated in step d) to calculate pH for the defined pH and additive concentration; g) calculating a pH-corrected pH by summing the defined pH and delta pH; h) using the pH-corrected pH to calculate the concentrations of acid and base using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; i) preparing the solution using the concentrations calculated in step h).

2. A method for preparing an aqueous solution of a defined pH comprising an acid, a base and optionally one or more additives, the method comprising the steps of: a) calculating the theoretical concentrations of acid, base and additives for the solution to have the defined pH using the Henderson-Hasselbach equation in combination with the Debye Huckel theory for a range of different additive concentrations; b) calculating a value for pH, being the difference between the theoretical pH and a value, preferably a predetermined value, for the actual pH, for each additive concentration; c) generating a mathematical model describing the relationship of pH with additive concentration; d) selecting the defined pH and additive concentration; e) using the mathematical model generated in step c) to calculate pH for the defined pH and additive concentration; f) calculating a pH-corrected pH by summing the defined pH and pH; g) using the pH-corrected pH to calculate the concentrations of acid and base using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; h) preparing the solution using the concentrations calculated in step g).

3. A method for preparing an aqueous solution of a defined pH, comprising an acid, a base and an additive, the method comprising the steps of: a) calculating the theoretical pH for the solution using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; b) calculating a pH-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, preferably a predetermined value, for the actual pH of the aqueous solution for a range of additive concentrations; c) using the pH-corrected pH to calculate the concentrations of acid and base using the Henderson-Hasselbach equation in combination with the Debye Huckel theory; d) preparing the solution using the concentrations calculated in step c).

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

5. A 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. A method according to claim 1, wherein the additive is a salt selected from the group consisting of NaCl, KCl, Na.sub.2SO.sub.4, (NH.sub.4).sub.2SO.sub.4 and (NH.sub.4).sub.3PO.sub.4 and mixtures thereof.

7. A method according to claim 6, wherein the salt is at a concentration of up to about 2M.

8. A method according to claim 1, wherein the minimum additive concentration in the range of additive concentrations is selected to be below, and the 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. A method according to claim 1, wherein the number of data points in the range of additive concentrations is from 5 to 10.

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

11. Apparatus for preparing an aqueous solution comprising a metering device capable of feeding into a mixing device an acid and a base, one or more additives, and optionally a diluent wherein the metering device operates under the control of control apparatus for carrying out steps a) and c) to h) of claim 1.

12. Apparatus according to claim 11, and further comprising a means for carrying out a bioprocessing operation.

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

14. 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. Apparatus for preparing an aqueous solution comprising a metering device capable of feeding into a mixing device an acid and a base, one or more additives, and optionally a diluent wherein the metering device operates under the control of control apparatus for carrying out steps a) to g) of claim 2.

16. Apparatus for preparing an aqueous solution comprising a metering device capable of feeding into a mixing device an acid and a base, one or more additives, and optionally a diluent wherein the metering device operates under the control of control apparatus for carrying out steps a) to c) of claim 3.

Description

EXAMPLE 1

Preparation of Phosphate Buffers

[0079] A range of phosphate buffers were prepared having a range of different NaCl concentrations (0, 100, 250, 500, 1000, 2000 mM) and a range of different buffer concentrations (10, 25, 50, 100 mM) with target pH in each case being pH7.0 at a temperature of 20 C. The concentrations of acid and base to achieve these values were initially calculated using the Henderson-Hasselbach equation in combination with the Debye Huckel theory. Solutions were prepared in accordance with these values using concentrated stock solutions for each buffer component, 200 mM Sodium dihydrogen phosphate (acid), 200 mM disodium hydrogenphosphate (base) and 5M sodium chloride. The concentrations and quantities employed are given in Table 1 below.

TABLE-US-00001 TABLE 1 Buffer Salt Stock Stock Stock 5M water Conc Base Acid Conc Base Acid salt Vol Vol (mM) (mM) (mM) (mM) (mL) (mL) (mL) (mL) 1 10 4.81 5.19 0 2.4 2.6 0 95.0 2 25 13.25 11.75 0 6.6 5.9 0 87.5 3 50 28.69 21.31 0 14.3 10.7 0 75.0 4 100 61.7 38.3 0 30.9 19.2 0 50.0 5 10 5.81 4.19 100 2.9 2.1 2 93.0 6 25 14.9 10.1 100 7.5 5.1 2 85.5 7 50 30.7 19.3 100 15.4 9.7 2 73.0 8 100 63.54 36.46 100 31.8 18.2 2 48.0 9 10 6.27 3.73 250 3.1 1.9 5 90.0 10 25 15.82 9.18 250 7.9 4.6 5 82.5 11 50 31.98 18.02 250 16.0 9.0 5 70.0 12 100 64.77 35.23 250 32.4 17.6 5 45.0 13 10 6.49 3.51 500 3.2 1.8 10 85.0 14 25 16.25 8.75 500 8.1 4.4 10 77.5 15 50 32.53 17.47 500 16.3 8.7 10 65.0 16 100 64.95 35.05 500 32.5 17.5 10 40.0 17 10 6.37 3.63 1000 3.2 1.8 20 75.0 18 25 15.87 9.13 1000 7.9 4.6 20 67.5 19 50 31.55 18.45 1000 15.8 9.2 20 55.0 20 100 62.27 37.73 1000 31.1 18.9 20 30.0 21 10 5.42 4.58 2000 2.7 2.3 40 55.0 22 25 13.45 11.55 2000 6.7 5.8 40 47.5 23 50 26.59 23.41 2000 13.3 11.7 40 35.0 24 100 51.94 48.06 2000 26.0 24.0 40 10.0

[0080] The pH value at 20 C. for the prepared buffers given in table were measured and the difference from theoretical value were calculated as delta pH. The results are given in Table 2, below.

TABLE-US-00002 TABLE 2 Measured Delta pH pH 1 7.03 0.03 2 7.02 0.02 3 7.02 0.02 4 7.02 0.02 5 6.93 0.07 6 6.95 0.05 7 6.95 0.05 8 6.96 0.04 9 6.85 0.15 10 6.87 0.13 11 6.88 0.12 12 6.87 0.13 13 6.72 0.28 14 6.74 0.26 15 6.75 0.25 16 6.73 0.27 17 6.51 0.49 18 6.5 0.5 19 6.5 0.5 20 6.48 0.52 21 6.03 0.97 22 6.03 0.97 23 6.02 0.98 24 5.99 1.01

[0081] Linear regression analysis of the value of delta pH (y) against salt concentration (x) generates the equation (1):

y=0.0005x

[0082] Equation (1) was employed to calculate the delta pH value for the salt concentrations for each of the phosphate buffers A, B, C and D given in Table 3 below, and the values of delta pH so calculated used to calculate the delta-pH-corrected pH for each of the buffers.

[0083] The delta-pH corrected pH for each of the salt concentrations was then employed to calculate the concentrations of acid, base and salt to achieve these values using the Henderson-Hasselbach equation in combination with the Debye Huckel theory, and the concentrations are also given in Table 3.

TABLE-US-00003 TABLE 3 5M Buffer Salt Stock Stock salt Target Conc Base Acid Conc Base Acid Vol water pH (mM) (mM) (mM) (mM) (mL) (mL) (mL) (mL) A 7.0 20 11.58 8.42 50 5.8 4.2 1 89.0 B 7.0 60 48.62 11.38 750 24.3 5.7 15 55.0 C 6.5 50 25.57 24.43 500 12.8 12.2 10 65.0 D 7.5 25 21.05 3.95 100 10.5 2.0 2 85.5

[0084] Buffers were prepared using the stock acid, base and salt solution employed to generate the data in Table 1 in the quantities given in Table 3, and the pH values obtained were measured at 20 C. The pH values achieved are given in Table 4.

TABLE-US-00004 TABLE 4 Measured Target pH pH A 7.07 7.0 B 7.03 7.0 C 6.47 6.5 D 7.52 7.5

[0085] All pH value were within the range of +/0.1 pH unit of the target value, indicating the high the accuracy of the method of the present invention.

EXAMPLE 2

Preparation of Acetate Buffers

[0086] A range of acetate buffers were prepared having a range of different NaCl concentrations (0, 100, 250, 500, 1000, 2000 mM) and a range of different buffer concentrations (10, 25, 50, 100 mM) with target pH in each case being pH4.5 at a temperature of 20 C. The concentrations of acid and base to achieve these values were initially calculated using the Henderson-Hasselbach equation in combination with the Debye Huckel theory. Solutions were prepared in accordance with these values using concentrated stock solutions for each buffer component, 200 mM acetic acid (acid), 200 mM sodium acetate (base) and 5M sodium chloride. The concentrations and quantities employed are given in Table 5 below.

TABLE-US-00005 TABLE 5 Buffer Salt Conc Base Acid Conc Base Acid 5M salt water (mM) (mM) (mM) (mM) (mL) (mL) Vol (mL) (mL) 1 10 3.69 6.31 0 1.8 3.2 0 95.0 2 25 9.44 15.56 0 4.7 7.8 0 87.5 3 50 19.31 30.69 0 9.7 15.3 0 75.0 4 100 39.75 60.25 0 19.9 30.1 0 50.0 5 10 4.16 5.84 100 2.1 2.9 2 93.0 6 25 10.42 14.58 100 5.2 7.3 2 85.5 7 50 20.94 29.06 100 10.5 14.5 2 73.0 8 100 42.21 57.79 100 21.1 28.9 2 48.0 9 10 4.33 5.67 250 2.2 2.8 5 90.0 10 25 10.85 14.15 250 5.4 7.1 5 82.5 11 50 21.73 28.27 250 10.9 14.1 5 70.0 12 100 43.58 56.42 250 21.8 28.2 5 45.0 13 10 4.42 5.58 500 2.2 2.8 10 85.0 14 25 11.06 13.94 500 5.5 7.0 10 77.5 15 50 22.12 27.88 500 11.1 13.9 10 65.0 16 100 44.26 55.74 500 22.1 27.9 10 40.0 17 10 4.38 5.62 1000 2.2 2.8 20 75.0 18 25 10.96 14.04 1000 5.5 7.0 20 67.5 19 50 21.9 28.1 1000 11.0 14.1 20 55.0 20 100 43.75 56.25 1000 21.9 28.1 20 30.0 21 10 4.07 5.93 2000 2.0 3.0 40 55.0 22 25 10.16 14.84 2000 5.1 7.4 40 47.5 23 50 20.3 29.7 2000 10.2 14.9 40 35.0 24 100 40.51 59.49 2000 20.3 29.7 40 10.0

[0087] The pH value at 20 C. for the prepared buffers given in table were measured and the difference from theoretical value were calculated as delta pH. The results are given in Table 6, below.

TABLE-US-00006 TABLE 6 Measured Delta pH pH 1 4.48 0.03 2 4.48 0.04 3 4.49 0.03 4 4.5 0.03 5 4.46 0.07 6 4.45 0.08 7 4.45 0.07 8 4.46 0.06 9 4.45 0.08 10 4.42 0.11 11 4.43 0.1 12 4.44 0.09 13 4.39 0.17 14 4.38 0.15 15 4.39 0.14 16 4.4 0.13 17 4.34 0.24 18 4.32 0.23 19 4.33 0.23 20 4.34 0.21 21 4.2 0.39 22 4.2 0.37 23 4.2 0.36 24 4.22 0.37

[0088] Linear regression analysis of the value of delta pH (y) against salt concentration (x) generates the equation (1):

Y=0.0002x0.0516

[0089] Equation (1) was employed to calculate the delta pH value for the salt concentrations for each of the buffers E to M given in Table 7 below, and the values of delta pH so calculated used to calculate the delta-pH-corrected pH for each of the buffers.

[0090] The delta-pH corrected pH for each of the salt concentrations was then employed to calculate the concentrations of acid, base and salt to achieve these values using the Henderson-Hasselbach equation in combination with the Debye Huckel theory, and the concentrations are also given in Table 7.

TABLE-US-00007 TABLE 7 5M Tar- Buffer Salt salt get Conc Base Acid Conc Base Acid Vol water pH (mM) (mM) (mM) (mM) (mL) (mL) (mL) (mL) E 4.5 20 8.66 11.34 50 4.3 5.7 1 89.0 F 4.5 60 32.51 27.49 750 16.3 13.7 15 55.0 G 4.0 50 12.72 37.28 500 6.4 18.6 10 65.0 H 5.0 25 18.09 6.91 100 9.0 3.5 2 85.5

[0091] Buffers were prepared having the concentrations given in Table 7, and the pH were measured at 20 C. The pH values achieved are given in Table 8.

TABLE-US-00008 TABLE 8 Measured Target pH pH E 4.47 4.5 F 4.44 4.5 G 3.93 4.0 H 4.98 5.0

[0092] All pH value were within the range of +/0.1 pH unit of the target value, indicating the high the accuracy of the method of the present invention.