AMINE ADSORPTION ON KERATIN 287 For isotherms determined in the absence of electrolyte, a buffer was prepared by adjusting the initial pH of a boric acid solution (0.02 M) with small amounts of 2 M NaOH or HCI. As wool itself acts as a buffer agent, the pH at equilibrium varies considerably from the initial pH many iterative trials were required to attain uniform pH increments over the pH range 2-9. DETERMINATION OF ISOTHERMS The weighed wool sample (approx. 200 mg) was placed in a 25 ml screw-capped culture tube along with the amine solution (20 ml). After removing the entrained air bubbles by careful evacuation in a vacuum dessicator, the wool sample was teased out with a narrow glass rod so as to fill as completely as possible the volume occupied by the liquid. The tubes were capped and placed in a thermostated water bath. The contents of the tube were periodically mixed by inversion of the tube or movement of the wool through the solution with a glass rod. Equilibrium was considered to be established when the concentration of the amine was constant over a period of 30 mins. By this criterion equilibria were found to be established in 30-60 mins at 40 ø in the case of the monoamines, while at 60 ø and 80 ø the times were 10-15 mins and 5 mins respectively. Longer periods were found necessary for the diamines with times of 6-8, 3, and 1-2 hours for temperature of 40 ø , 60 ø , and 80 ø respectively.* DETERMINATION OF AMINE CONCENTRATION (a) Monoamines Concentrations of amine in this series were estimated by a two-phase titration against standard sodium lauryl sulfate (5 x 10-3M) using methyl yellow as indicator (9). The aqueous phase contained dilute sulfuric acid (approx. I M) for determinations of the C•0 and C• amines, while the C8 amine was found to give the sharpest end-point indication at a pH of 1.6 _+ 0.1. [The underlying theory of the significance of pH control in this type of volumetric estimation is discussed by Jansson et al. (10)]. Precision and reproducibility were found to be a maximum when the sample size required less than I ml of titrant. The presence of inorganic salts did not interfere with the end-point. (b) Diamines The determination of diamine concentrations in the sorption media was by a method adapted from that of Fields (11), which is based on the color resulting from reaction of an amino group with trinitrobenzenesulfonic acid (TNBS). This method was found to be unsuitable for long-chain amines and, more particularly, diamines, due to the water-insolubility of the yellow arylsulfonylamine. If, however, this derivative was extracted with a water-immiscible polar solvent such as butanone, the optical density of the butanone extract vs concentration relationship was found to be linear and *The times required to attain equilibrium refer to amine concentrations resulting in saturation uptake by the fiber. For low amine concentrations (log C = ca. -3) the times were much less. Several isotherms were determined in a stirred solution-fiber system the difference between the saturation uptake given by a stirred and intermittently mixed solution was found to be within the experimental error of the amine analysis.

288 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS reproducible. The detailed method is as follows: the aqueous diamine sample (approx. 1 ml containing 5-50 x 10 -8 moles diamine) was introduced into a stoppered tube. To this was added borate buffer (0.5 ml, 0.1 M Na2B407, 0.1 M NaOH), and the sides of the tube were washed down with water to give a total volume of 2 mi. A solution of TNBS dihydrate (0.05 ml of 0.55 M) was added, and the solution mixed by shaking. After standing for ten minutes, the solution was neutralized by the addition of glacial acetic acid (1 drop) and butanone (5 ml) added. The tube was then stoppered, and the contents shaken vigorously for 5 seconds. Saturated NaCI (1 ml) was added to speed-up phase separation when this was complete, the upper butanone layer was transferred by Pasteur pipette to a 10 ml volumetric flask. The aqueous layer was re-extracted with butanone (2 ml) which was combined with the first extract, and the volume made up to the mark with solvent. The optical density was measured at 415 nm against an extract of a water blank. The amount of diamine in the sample was estimated from a standard curve relating optical density to concentration. Precision was estimated to be _+ 2%. RESULTS AND DISCUSSION EFFECT OF pH ON SATURATION UPTAKE Figures ! and 2 show the dependence of equilibrium saturation uptakes (Cf) on the pH of the sorbing solution at 40 ø for dodecylamine and 1,12-diaminododecane.* Also shown in these two figures are the same relationships in the presence of sodium chloride (0.1 M). It is apparent from the plots that both adsorbing species have a low substantivity for the fiber at a pH of approximately 3, and it is only at pH values greater than 5 that appreciable fiber adsorption is observed in the pH range 7-9 the uptake shows a marked increase with increasing pH (pH values above 9 resulted in the incipient formation of insoluble free amine). The behavior just described for long-chain amines has been observed for other cationic surface-active species for example, Crewther (14) showed that the uptake of cetyltrimethylammonium bromide on wool increases as the pH of the adsorbate solution rises. The addition of sodium chloride (0.1 M) is observed from Figures 1 and 2 to cause a significant increase in the amount of amine taken up by the fiber at a given pH in the case of the monoamine the increase over the pH range 6-8 is approximately three-fold, while for the diamine the increase is approximately two-fold over the entire experimental range of pH. One further comment that could be made from the data shown in Figures 1 and 2 is that the use of the term "adsorption" as a description of the wool/amine interaction does not imply an external surface adsorptive process. When it is considered that wool has an apparent specific external surface area of approximately 0.5 m2/g •15), and the cross-sectional area of a straight-chain alkyl ammonium ion is around 24 (A) 2 (16), then according to the expression (17): S = Ym' N ß a ß 10 2ø, *Since the pKa values of all amine functions of the adsorbates used in this study are in the range 10-11 (12-13), the species present in solution of pH 8 and below will be essentially the ammonium ions. For the sake of brevity, however, only the free amine will be referred to.