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Do you need an acidic buffer?
Why is pH control so important? As we discussed in the December, 2012 newsletter, we use buffers because we want to control the equilibrium in acid-base dissociation reaction:
A mixture of the two forms (HA and A-) will resist a change in pH in the solution. This control is important in a static solution reaction, but when we are continuously pumping a solution through a column, as in HPLC, the need for a buffer to control pH is less important.
We often see methods that require an acidic buffer at a pH near 2.5. This buffer requires sodium dihydrogenphosphate (NaH2PO4) and phosphoric acid. In the earlier newsletter we talked about the problems that buffers can cause:
- They may be corrosive to stainless steel.
- Some are not very soluble in organic solvents.
- Buffers may precipitate from solution after preparation (bad news if it happens inside an HPLC).
- They may contain particulates.
Why should we accept these problems when there is a very simple alternative. A solution of 0.10% phosphoric acid (H3PO4) in water (about 10 mM) produces a pH of about 2.2. This solution is easy to prepare and phosphoric acid is miscible with all common organic modifiers, so there is no risk of precipitation. All modern instruments and columns are stable at this pH and you should see few changes in your chromatography. We actually find that often the chromatography is actually better using this mobile phase. We have had similar success with dilute sulfuric acid. However, hydrochloric and nitric acids should never be used for this purpose.
Need a volatile buffer because you are using LC-MS? Again, use the pure acid rather than the salt - formic acid rather than ammonium formate adjusted to a low pH with formic acid. Acetic acid and TFA would be other options.
To summarize, if you need to prepare a mobile phase at an acidic pH below about 3.5, you could probably substitute 0.10% of the pure acid for the buffer system. The acid produces a similar pH and similar chromatography, but is easier to prepare and less corrosive to your system.
Next month we will continue this discussion. Look for details in March.
Are you having problems choosing, preparing, or using buffers in your mobile phases? Call us for a review and assistance. We have a long record of saving labs time and money on their procedures . . . but you have to contact us to see the benefit. |
The article "Investing to Save" by Dr. Merlin Bicking has been published in the December issue of Lab Manager Magazine.
This article discusses how laboratories can properly calculate the benefits of an investment in process improvements, technology changes, and even training. By learning to calculate Return on Investment (ROI), laboratory staff have more tools to sell their proposals to management.
The article is available on-line. Click here to view.
Would You Like to Learn More?
We would be happy to discuss this specific issue in more detail, but let's make it part of an overall discussion of how we can help you reduce the stress on your lab and lab staff and your budget. Click here to contact us.
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Expense Saving Solutions from
ACCTA, Inc.
With three decades of experience teaching labs about how to get the most from their chromatography systems, we are confident that we can make improvements to your methods and procedures, and save your laboratory both time and money. We might save you months of trial-and-error mistakes in a three day visit. Click here for more details. |
Regards,
Merlin K. L. Bicking, Ph.D.
ACCTA, Inc. |
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| Concerned about the cost and benefits of the investments that we describe? Contact us for a personalized Cost-Benefit Analysis (CBA) that will show your management what a good investment this can be. Contact Robert Zarracina for details. |
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ACCTA, Inc.
Phone: (651) 731-3670
Email: info@accta.com |
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