1. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실

2. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 2

3. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 3

4. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 4 0.1N HCl 1ml pH 4.7 H2OH2ONaCl HAc, NaAc pH 7 33 4.58

5. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 HA + OH - 5 A- + H2OA- + H2O A - + H 3 O + HA + OH - Combination of a weak acid and its conjugate base Combination of a weak base and its conjugate acid

6. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 6

7. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A Weak Acid and Its Salt 7 H 3 O + + Ac - HAc + H 2 O -log[H 3 O + ]= - logKa - log[acid] + log[salt] salt acid K a = [H 3 O + ][Ac - ] [HAc] K 1 [HAc][H 2 O] = K 2 [H3O + ][Ac - ]

8. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A Weak Acid and Its Salt 8 pH= pK a +log [salt] [acid] Buffer equation or Henderson-Hasselbalch equation Dissociation exponent

9. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 9 H 3 O + + Ac - HAc + H 2 O * when Sod. acetate is added to acetic acid… is momentarily disturbed since the acetate ion supplied by the salt increases the [Ac - ] K a = [H 3 O + ][Ac - ] [HAc] The ionization of HAc is repressed upon the addition of the common ion [Ac - ]

10. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A Weak Base and Its Salt 10 Kb =Kb = [OH - ][BH + ] [B] OH - + BH + B + H 2 O salt base

11. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A weak base and its salt 11 [H 3 O + ] [OH - ] = K w [ OH - ] = K b [ base ] [ salt ] -log[H 3 O + ]= - logKw – log1/K b - log[salt]/[base]

12. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A Weak Acid and Its Salt 12 pH= pK w - pK b + log [base] [salt] * Buffers are not ordinarily prepared from weak bases because of the volatility & instability of the bases and because of the dependence of their pH on pK w, which is often affected by temp. changes.

13. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 13 H 3 O + + Ac - HAc + H 2 O a H 3 O + a Ac - a HAc K a = [H 3 O + ][Ac - ] [HAc] = (γ H 3 O + c H3O + )(γ Ac- C Ac- ) (γ HAc C HAc ) = Molar conc. Activity coefficients activity

14. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 * activity coefficient of the undissociated acid γ HAc is essentially 1 and may be dropped. 14 a Ac - a HAc - log[ a H 3O + ] = - log Ka + log [salt] [acid] pH = pK a + log + log γ Ac-

15. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 1. Altering the ionic strength ① Addition of neutral salts ② Dilution (alter activity coefficients) The pH of the most basic buffer was found to change more markedly with temp. than that of acid buffers, owing to Kw. 2. Temperature

16. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Acid indicator 의 경우 16 HIn + H 2 O H 3 O + + In - Alkaline colorAcid color K In = [H 3 O + ][ In - ] [HIn] base acid

17. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 17 pH = pK In + log [base] [acid] 1/10~10/1 pH =pK In +1 base acid 10/1 1/10 * From experience, one cannot discern a change from the acid color to the salt color the ratio of [base] to [acid] is about 1 to 10 * The effective range of the indicator is…

18. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Characteristics of colorimetric method 18 ① less accurate ② less convenient but less expensive than electrometric method ③ difficult to apply for the unbuffered pharmaceutical preparation (change the pH - indicator itself is acids or base) ④ error may be introduced by the presence of salts & proteins

19. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 19

20. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 20 ΔB : small increment in gram equivalents/Liter of strong base (or acid) added to the buffer soln. to produce a pH change of ΔpH β= B pH buffer capacity = buffer efficiency = buffer index = buffer value …t he magnitude of the resistance of a buffer to pH changes

21. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 21 HAc (0.1- 0.01) NaAC (0.1+ 0.01) 0.01 + NaOH + H 2 O pH=pKa + log [salt] + [base] [acid] - [base] = 4.85 pH=pKa + log [salt] [acid] = 4.76 = 0.01 0.09 = 0.11= pH β B Before the addition of NaOH After the addition of NaOH

22. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 A more exact equation for buffer capacity (1914, 1922) 22 β ---- at any [H 3 O + ]. K a [H 3 O + ] β = 2.3 C (K a + [H 3 O + ]) 2 c : total buffer conc.(sum of the molar conc. of the acid & the salt)

23. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 β max occurs where pH = pK a ([H 3 O + ] = K a ) 23 ( pH = pK a ) β max = 0.576 C 4 2.303 C [H 3 O + ] 2 β max = 2.303 C (2 [H 3 O + ]) 2 =

24. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 24 …is not a fixed value, but rather depend on the amount of base added …depends on the value of the ratio [salt]/[acid] and magnitude of the individual concentrations of the buffer components The greatest capacity(βmax) occurs where [salt]/[acid] = 1 and pH = pKa Because of interionic effects, buffer capacities do not in general exceed a value of 0.2

25. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Total buffer capacity of a universal buffer (combination of several buffers) 25

26. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 26

27. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Blood ① Primary buffers : Plasma ; NaHCO 3 -- H 2 CO 3, NaHPO 4 --NaH 2 PO 4, protein ② Secondary buffers : Erythrocytes ; hemoglobin-oxyhemoglobin, K 2 Hpo 4- -KH 2 PO 4 Lacriminal fluid - pH: 7.4 (range 7 – 8 or slightly higher) Urine - pH: 6.0 (range 4.5 – 7.8) - below normal…hydrogen ions are excreted by the kidney. - above pH 7.4…hydrogen ions are retained by action of the kidney. 27

28. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 28 ophthalmic soln. colormetric determination of pH research studies in which pH must be held constant

29. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 29 Clark-Lubs mixtures and pH (a) HCl & KCl, pH 1.2 - 2.2 (b) HCl & potassium biphthalate, pH 2.2 - 4.0 (C) NaOH & potassium biphthalate, pH 4.2 - 5.8 (d) NaOH & KH 2 PO 4, pH 5.8 - 8.0 (e) H 3 BO 3, NaOH & KCl, pH 8.0 - 10.0

30. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 30 Steps for development of a new buffer ① Select a weak acid having a pK a approximately equal to the pH at which the buffer is to be used. ② Calculate the ratio of salt & weak acid required to obtain the desired pH. ③ Consider the individual conc. Of the buffer salt & acid needed to obtain a suitable buffer capacity * Individual conc. : 0.05 ~ 0.5M * buffer capacity : 0.01 ~ 0.1

31. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 31 Steps for development of a new buffer ④ Availability of chemicals, sterility of the final soln, stability of the drug & buffer, cost of materials, freedom from toxicity ex) borate buffer – toxic effect – not be used for oral or parenteral products. ⑤ Determine the pH and buffer capacity using a reliable pH meter

32. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 32 Influence of buffer capacity and pH on tissue irritation * Tissue irritation will be minimal when… (a)Buffer solution – β, Volume (b) Physiologic fluid - β, Volume

33. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 33 Stability vs. optium therapeutic response * Undissociated form of a weakly acidic or basic drug has a higher therapeutic activity than the dissociated salt form. * Molecular form is lipid soluble & can penetrate body membranes readily, where the ionic form, not being lipid soluble, can penetrate membranes only with greater difficulty.

34. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 34 pH and solubility * Influence of buffering on the solubility of base -At a low pH : base is in the ionic form & usually very soluble in aqueous media -As the pH is raised : more undissociated base is formed when the amount of base exceeds the limited water solubility of this form, free base precipitates from soln. Base soln. should be buffered at a sufficiently low pH for stabilization against precipitation.

35. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 35 (Example) GOAL: Compute the mole percent of free base present on 25 ℃ and at a pH of 7.4. The pK b of pilocarpine is 7.15 at 25 ℃. Buffer in pharmaceutical and biologic systems

36. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 36 Example At pH 7.4 C 11 H 16 N 2 O 2 + H 2 OC 11 H 16 N 2 O 2 H + + OH - (Pilocarpine base) (Pilocarpine ion) pH= pK w - pK b + log [base] [salt] At pH 4.0 7.4 = 14 – 7.15 + log [base] [salt] [base] [salt] = 3.56 / 1 Mole percent of base = 3.56 / (1 + 3.56) 100 = 78% 4.0 = 14 – 7.15 + log [base] [salt] = 0.0014 / 1 Mole percent of base = 0.0014 / (1 + 0.0014) 100 = 0.13% [base] [salt]

37. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 37

38. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 38 Red blood cell NaCl solution 2.0 % Hypertonic, Shrink 0.9 % Isotonic 0.2 % Hypotonic, Hemolysis

39. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The term Isotonic should be restricted to solutions having equal osmotic pressures which respect to a particular membrane (Husa) Isotonicity value…the concentration of an aqueous NaCl soln. having the same colligative properties as soln. (Goyan & Reck) 39

40. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Hemolytic method …apply red blood cells …based on the fact that a hypotonic soln. liberates oxyhemoglobin in direct proportion to the number of cells hemolyzed determine colligative properties (chapter 5) …modifications of the Hill-Blades Technique …based on a measurement of the slight temp. differences arising from differences in the vapor pressure of thermally insulated samples contained in constant-humidity chambers 40 T f = 0.52 ºC (Freezing point lowering of human blood & lacrimal fluid)

41. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Van’t Hoff expression 41 T f = L · c (Chapter 6) Conc. that is isotonic with body fluids L iso = T f / c 0.52 ° Molal freezing point depression of water

42. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 42 Calculating Tonicity Using L iso values

43. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 The Buffer Equation Buffer Capacity Buffers in pharmaceutical and Biologic Systems Buffered Isotonic Solutions Methods of Adjusting Tonicity and pH 43

44. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 44 Class I … add Sod. Chloride to lower the freezing point of soln. to -0.52° ① White-Vincent method ② Sprowls method ① Cryoscopic method ② Sodium chloride equivalent method Class II … add Water to form an isotonic soln.

45. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Cryoscopic method ( 빙점강하도법 ) (Example) How much NaCl is required to render 100mL of a 1% soln. of apomorphine HCl isotonic with blood serum? Δ T f 0.9% of NaCl soln : 0.52°(Isotonic with blood) Δ T f 1% of apomorphine HCl soln : 0.08° (from table) to reduce the freezing point by an additional 0.44°(0.52-0.08) Δ T f 1% of NaCl soln : 0.58° 1(%)/X = 0.58/0.44 ; X = 0.76 (%) Dissolve 1 g apomorphine HCl + 0.76g NaCl make 100mL soln. with water 45

46. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 Sodium chloride equivalent(E) method ( 염화 나트륨당량법 ) by Mellen & Seltzer 1g drug tonicity = Eg NaCl tonicity 46 ΔT f = L iso · c ΔT f = L iso · 1g/MW c = 1 g / molecular weight 3. 4 58.45 E E : weight of NaCl with the same freezing point depression as 1g of the drug. E ≈ 17 · L iso / MW

47. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 47 White-Vincent method (Example) GOAL: make 30mL of a 1% soln. of procaine HCl isotonic with body fluid

48. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 48 Steps for White-Vincent method ① Weight in grams of drug(0.3 g) Sod. Chloride equivalent E(0.21..from table) = quantity of sod. Chloride equivalent to w of drug(0.063 g) ② 0.9 g/100mL = 0.063 g / V ③ V = 0.063 100/0.9 ④ V = 7.0 mL ⑤ Add isotonic-buffered diluting soln. to complete V = w E 111.1

49. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 49 White vincent method 0.3g drug (E=0.21) 7ml add 0.9%NaCl or Isotonic buffered sol. 30ml water 0.9%NaCl isotonic GOAL: make 30mL of 1% soln. of procaine HCl isotonic with body fluid

50. SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 SKKU Physical Pharmacy Laboratory 성균관대학교 물리약학연구실 50 Sprowls method w E V = 0.9 g 100 ml W = 0.3 g (1% solution) ? TABLE