pH, buffers and Isotonic solutions:
Sorensen’s pH scale, pH determination (electrometric and calorimetric), applications of buffers, buffer equation, buffer capacity, buffers in pharmaceutical and biological systems, buffered isotonic solutions.
Buffers are compounds that resist changes in pH upon the addition of limited amounts of acids or bases. Buffer systems are usually composed of a weak acid or base and its conjugate salt. The components act in such a way that addition of acid or base results in the formation of a salt causing only a small change in pH. Buffer capacity is a measure of the efficiency of a buffer
in resisting changes in pH. In practice, smaller pH changes are measured and the buffer capacity is quantitatively expressed as the ratio of acid or base added to the change in pH produced. The
buffer capacity depends on various factors. The addition of any compound to a solution affects the isotonicity. The osmotic pressure of a solution is affected not only by the drug but also by any
of the buffer components that are included in the formulation. But even after these buffers have been added, it is still possible that the solution may not be isotonic. Thus, it may be necessary to
add additional sodium chloride to bring the solution to isotonicity.
Upon studying this unit, students should be able to:
• Define and determine pH and pOH.
• Define buffers, buffer capacity, isotonicity, iso-osmoticity, osmotic pressure, hypertonicity, hypotonicity.
• Describe the uses of buffers in pharmaceutical solutions.
• Identify the range of solution pH considered safe for ophthalmic solutions.
• Formulate and analyze a buffer solution of desired pH and buffer capacity.
• Explain the importance of isotonicity in ophthalmic solutions.
• Formulate and prepare pharmaceutically and physiologically acceptable parentral solutions.
1. Define the terms:
(a) pH (b) pOH
(c) Buffers (d) Buffering agent
(e) Buffer capacity (f) Activity
(g) Buffer action (h) Tonicity
(i) Pharmaceutical buffers (j) Osmolality
(k) Hypotonicity (l) Hypertonicity
(m) Isotonicity (n) Isosmotic solution
(o) Isotonicity value
2. Explain relation between pH and solubility.
3. Explain measurement of pH. Also add note on temperature compensation for the pH measurement.
4. Enlist different types of buffers. Add note on acidic buffers.
5. Enlist properties of buffers.
6. Describe the use of buffers in pharmaceutical preparations.
7. Identify pH range considered to be safe for ophthalmic solutions.
8. Formulate and analyze a buffer solution of desired pH and buffer capacity.
9. Explain the importance of isotonicity in ophthalmic solutions.
10. Calculate the pH of a buffer solution prepared by dissolving 242 mg of Tris in 10 mL of 0.170 M HCl and diluting to 100 mL with water. (Molecular weight of Tris is 121 g/mol and pKa for the its conjugate acid is 8.08)
11. Differentiate between buffered and unbuffered solutions. Explain how the pH of unbuffered solution changes when acid or base added to it.
12. What is Henderson-Hasselbalch equation? Give its applications in pharmaceutical
sciences.
13. What is the importance of isotonic solutions in formulation development?
14. Differentiate between isosmotic and isotonic solutions.
15. Differentiate between buffering agent and buffer solution.
16. List out types of formulations that require the isotonicity adjustment.
17. Write on methods that determines tonicity.
18. Describe methods that are used to adjust pH and isotonicity.
19. Give some examples of pharmaceutical buffer solutions.
20. Write note on biological buffers.
21. Give applications of buffers in pharmacy.
22. Enlist and explain factors affecting buffer capacity.
23. Describe a method that estimates effectiveness of buffer.
24. Write note on:
(a) Sorenson’s pH scale.
(b) Temperature compensation in pH meter.
(c) Acidic and alkaline buffers.
(d) Henderson-Hasselbalch equation.
(e) Buffer capacity.
(f) Preparation of buffer solution
(g) Buffer salts.
25. Enlist commonly used methods to prepare buffer solutions.
26. Describe standard buffer solutions.
27. What do you mean by biological buffers? Explain any one buffer from this category.
