The relation of hydrogen ion concentration to the action of the local anæsthetics / J.W. Trevan and E. Boock.
- Trevan, J. W. (John William)
- Date:
- [1927?]
Licence: In copyright
Credit: The relation of hydrogen ion concentration to the action of the local anæsthetics / J.W. Trevan and E. Boock. Source: Wellcome Collection.
6/14 page 310
![when subtracted from 1414 gives the pK (negative log of dissociation constant) with sufficient accuracy for our purposes. Fig. 3 gives the titration curves, and Table II the estimated pK for each. There is sufficient agreement between the estimated pK for novocaine and cocaine obtained bv us and those obtained by Kolthoff (1925). Table II.—Dissociation Constants (pKs) for Anesthetics. M/300 Stovaine Cocaine B.B.E. Novocain /3-Eucaine Conessine 55 5 5 55 55 5 5 6*14 5'69 (Kolthoff gives 5'59). 5T9 5-29 ( „ „ 5T5). 4*49 pK} ca 4'6 If only undissociated base is active, the amount of base present in the limiting active concentrations at different pH’s will be the same. The con¬ centrations of anaesthetic which contain equal quantities of base can be calculated from the equations :— = K X [BOH] ... 1 + [BOH] - C . . .2 [B+~ X OH- [B + ] + [BA] where C is the limiting molecular concentration to produce anaesthesia at any hydroxyl ion concentration [OH] (the square brackets represent molecular concentration), [B + ] is the molecular concentration of basic ion, [BA] that of salt. As a first approximation [BA] may be ignored, the dissociation of the salt into ions being taken as complete. Starting with the point at pH 7 on the anaesthetic curve for novocain, the amount of base in the limiting concentration may be calculated. Then the molar concentrations at pH 5, 6, 7 and 8, which contain the same amount of base, can be calculated (see Table III and Fig. 4). The curve is practically a straight line at 45° to the axis, but the slope becomes less between 8 and 9, where [BOH] becomes a large fraction of C. Similar curves drawn parallel to this, but separated by horizontal distances equal to the differences of pK, would represent the theoretical log C/pH curves for the same concentration of base as novocain for the other anaesthetics. Table III.— Values of the Molecular Concentrations of Novocaine at Different pHs, containing the Amount of Base Necessary to Produce Anesthesia at a pH of 7. (0’00013.) pH. B. c (B BOH). Log. C. 5 065554 0-656 1-8167 6 0-065554 0-657 2-818 7 0-0065554 0-0668 3-825 8 0 00065554 0-0078 4-894 9 0 000065554 0-00019 4-287](https://iiif.wellcomecollection.org/image/b30626468_0006.jp2/full/800%2C/0/default.jpg)
