How to create a BufferPrep recipe

About BufferPrep recipes	New BufferPrep recipes are created in the Method Editor. The list of recipes is not linked to a specific method. Which recipe to use in a certain method is selected on the BufferPrep tab in the Run Setup.

How to create a recipe

The table below describes how to create a new BufferPrep recipe in the Method Editor:

Step	Action
1	Choose Edit:BufferPrep Recipes. Result: The BufferPrep Recipes dialog box opens. The illustration below shows the BufferPrep Recipes dialog box with a recipe selected:
2	Click the New button. Result: The New Recipe dialog box opens. The illustration below shows a complete example of a BufferPrep recipe in the New Recipe dialog box.
3	Select buffers from the Buffer substances droplists and type stock concentrations in the corresponding Stock conc box. See “How to define a new buffer substance” below if the desired substance is not available.
4	Select either HCl (acid) or NaOH (base) from the Acid/Base droplist and type the required stock concentration (typically 0.1 M)
5	Select a salt from the Salt droplist and type the maximum outlet concentration of the salt for 100%B (typically 1.0 M). See “How to define a new salt” below if the desired salt is not available.
6	Type the desired pH range minimum and maximum values in the From and To boxes. See “How to select the pH range” below this table.
7	Click the Notes button (optional). Type your notes about the recipe in the displayed dialog box. Click OK to return to the New Recipe dialog box.
8	Click Save as to save the recipe under a new name. Note: A warning message will appear if any of the recipe values are unfeasible.
9	Type a name in the dialog box. Click OK. Result: The new recipe is added to the recipe list.

Note: It is recommended that restricted access be given to the right to edit global recipes.

The recipes are either globally available to all users, or only personally available. It is best not to edit the globally available recipes, unless you save the changes under a new recipe name, since other users may not appreciate the changes.

Buffer concentration

Use buffer concentrations that are 2-4 times higher than the concentration that is used in the normal preparation. When BufferPrep is used, the buffer will be diluted 2-10 times depending on the amount of acid/base that has to be used to reach the desired pH value.

Up to five different buffering components can be selected. To prevent a too high ionic strength, the sum of the concentrations for all selected buffers should be between 0.03 M and 0.2 M (typically 0.1 M).

How to select the pH range

The useful pH range depends on the pKa value. The table below describes how to determine a pH range based on the pKa value:

Step	Action
1	Choose Edit:BufferPrep Recipes and click the New button.
2	Click the Buffer substance button in the New Recipe dialog box. Result: The Define buffer substance dialog box opens.
3	Select the buffer component from the Name droplist and note the displayed pKa value.
4	Click Cancel to return to the New Recipe dialog box.
5	Use the pKa value to determine the pH range. Typically a range of +/- 0.5 units around the pKa value is useful. Note: Check buffer tables for the exact ranges.

How to define a new buffer substance

Note: Before you can define a new buffer substance you must ensure that all pKa values are available for the substance. The pKa values should be true (i.e. the pKa value at indefinite dilution) and not apparent pKa values (i.e. measured at a non-zero concentration). The pKa values should be given at 25° C.

The table below describes how to define a new buffer substance:

Step	Action
1	Choose Edit:BufferPrep Recipes and click the New button.
2	Click the Buffer substance button in the New Recipe dialog box. Result: The Define buffer substance dialog box opens.
3	Click the New button. Result: The New component dialog box opens.
4	Type a name for the new component and click OK to return to the Define buffer substance dialog box.
5	Type appropriate values in the Value cells for each pKa and dpKa/dT parameter. Note: All values must fall within the stated Range limits. Up to three values can be entered for each buffering component. When the component has less than three pKa values, the other values should be set to zero. A dpKa/dT value of zero means that the pKa does not change with temperature.
6	Type the number of acidic protons for the buffer substance in the form that it is actually weighed in. Example: The number is 2 for NaH2PO4, 1 for Na2HPO4 and 0 for Tris. Type the charge of the completely de-protonated ion. This will be a negative value for an acid and zero for a base. Example: The value is -3 for NaH2PO4 and 0 for Tris. Click OK. Result: The new buffer substance is added to the list of available substances.

How to define a new salt

Before you can define a new salt you must ensure that the new salt is inert, i.e. a salt with no buffering properties. The table below describes how to define a new salt:

Step	Action
1	Choose Edit:BufferPrep Recipes and click the New button.
2	Click the Salt button in the New Recipe dialog box. Result: The Define salt dialog box opens.
3	Click the New button. Result: The New component dialog box opens.
4	Type a name for the new salt and click OK to return to the Define salt dialog box.
5	Type the appropriate charge of anion value in the corresponding Value cell. Example: The value for Cl- is - 1. The value for SO42- is -2. Type the appropriate charge of the cation value in the corresponding Value cell. Example: The value for Na+ is 1. The value for Mg2+ is 2. Click OK. Result: The new salt is added to the list of available salts.

2005-06-15