Buffers is a simple tool for designing buffer solutions for pH control. Buffers is useful both as a handy reference of available buffering agents and as an accurate, portable buffer calculator for chemical, biochemical and biological research.

With Buffers you can:

1. •Select from 35 commonly used buffering agents
   

2. •Generate accurate recipes covering broad pH, concentration and temperature ranges
   

3. •Access detailed information about each available buffering agent
   

4. •Send your buffer recipes from your iPhone or iPod Touch via e-mail
   

To use Buffers, just choose a buffer and target pH along with the desired solution volume, temperature and buffer concentration. The recipe is calculated with the push of a button. The calculations do not rely on simple use of the Henderson-Hasselbalch equation, but instead use a more sophisticated and flexible algorithm that is accurate with both monoprotic and polyprotic buffers and at pH extremes.

An information page for each buffering agent lists the pKa, appropriate pH range, and temperature dependence, along with molecular weights and CAS numbers for the acid and base forms and other pertinent information.

Buffers is available now on the iPhone App Store.

Using Buffers

Choosing a buffer

To ensure adequate buffer capacity, a buffering agent should be chosen that has a pKa that is within approximately 1 pH unit of your target pH (the closer the better). The pKa listed in the program for each buffer is the thermodynamic value (zero ionic strength, 25 degrees C) so for a given set of conditions the effective pKa might differ significantly from that value, particularly at high buffer concentrations. A warning will appear when you have chosen conditions that are outside of the effective range of a particular buffer.

Concentration dependence

The apparent pKa of a buffer can change significantly as the buffer concentration is increased because of the accompanying increase in the ionic strength of the solution. This may lead to unexpected results at high buffer concentrations. The program allows very high buffer concentrations to be used because many people routinely make highly concentrated stock solutions of their buffers, but please keep in mind that the pH of these solutions could change significantly when diluted.

Temperature dependence

The change in pH with temperature for a buffered solution can be dramatic with some buffering agents. Buffers uses the most accurate temperature-dependence data available for each buffer. In the great majority of cases, the pKa value at a given temperature is interpolated from published data measured experimentally at five degree intervals rather than the more common practice of using a single temperature coefficient (which rarely gives accurate results because the temperature dependence generally is not linear and sometimes is not even monotonic).

Results

In most cases, the recipes generated by Buffers should have an error of less than 0.1 pH unit, though the error may be somewhat larger in certain instances. This, of course, assumes “ideal” reagents. Your results will also depend on the quality of your laboratory water supply, the age and quality of your buffer components and other factors. You should always check the results with a properly calibrated pH meter.