CATIONIC QUATERNARY COMPOUNDS 263 420 450 4 390 400 360 350 330 • 300 300 250 270 200 24O 150 210 i i , i ,• (B) j,(A)• 100 0 2 4 6 8 10 0.01 M SDS (ml) 0.05• Stearalkonium Chloride I I I I I I , o 2 4 6 8 10 0.01 M SDS (ml) 450 0.05% quaternium-26 4OO 350 300 25O 2OO s) • 150 0 2 4 6 8 0.01 M SDS (ml) 225 0.05% Cocodimonium 200 rein 175 150 125 100 75 , , I , (BI) (A) I 0 2 4 6 8 0.01 M SDS (ml) 225 O. 10% Laurdimonium n 2OO 175 150 125 100 (•) (A) 75 • • • • ' • • • 0 2 4 6 õ 10 12 14 0.01 M SDS (ml) Figure 1. Typical potentiometric titration curves of polyquaternium-4, stearalkonium chloride, quater- nium-26, cocodimonium hydrolyzed keratin protein, and laurdimonium hydrolyzed wheat protein solu- tions before (A) and after (B) treatment with bleached hair.

264 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a well-defined endpoint. It is therefore possible to potentiometrically titrate various cationic quaternary compounds, ranging from simple surfactants to macromolecules such as polymers and proteins. Figure 1 also demonstrates the application of the potentiometric titration to directly measure the amount of quaternary compounds adsorbed to bleached hair. As shown in Figure 1, the titration curves of the treated samples, compared to the untreated ones, show a decrease in the volume of SDS solution needed to reach the endpoint. The difference reflects the amount of cationic compounds adsorbed to hair. The results illustrate the feasibility of using this simple titration method to evaluate the substan- tivity of various cationic compounds to hair. In order to quantitate substantivity to hair, calibration curves for each cationic com- pound tested (Table I) were generated. As illustrated in Figure 2, the calibration curves show linearity (correlation coefficient = 0.99) over the range tested. The replication of the experimental points also indicates the reproducibility of the titration of various cationic quaternary ammonium compounds by means of the potentiometric titration by a surfactant electrode. Assessment of the substantivity of cationic compounds under various conditions by this convenient titration method was carried out, and the re- suits are shown below. Again, confidence in results is reflected by the low relative standard deviation (averaging about 2%) of the triplicate experiments throughout the study. Figure 3 shows the effect of the solution concentration of polyquaternium-4, laurdimo- nium hydrolyzed wheat protein, and quaternium-26 on the cationic uptake by bleached hair. Tests were performed using 0.05, 0.10, 0.20% (w/v) solutions of the quaternary compound. The results indicate that the cationic uptake of bleached hair increases with the concentration of the quaternary solution. The rate of increase is greatest with polyquaternium-4. However, laurdimonium hydrolyzed wheat protein has the highest cationic uptake at the lowest concentration. Similar concentration effects on the sub- stantivity of the cationic compounds has been demonstrated (8,13,18). The effect of treatment time on quaternary ammonium compound sorption is shown in Figure 4. Bleached hair was treated for 5, 15, and 30 minutes at 35øC with 0.10%, 0.05%, and 0.05% solutions of polyquaternium-4, cocodimonium hydrolyzed keratin protein, and quaternium-26, respectively. Figure 4 shows that increasing the treatment time results in increasing sorption of cationic compounds by hair. By means of colloid titration and radiotracer techniques, the same results were obtained with other quater- nary polymers (9,13). It has been suggested that this increased uptake is the result of the ability of the cationic compounds to penetrate or diffuse into the hair fiber. The sorption of quaternium-26, stearalkonium chloride, and laurdimonium hydrolyzed wheat protein was also determined at different temperatures. The experiments were performed at 23øC and 35øC for ten minutes with 0.05% (w/v) solutions ofquaternium- 26 and stearalkonium chloride and a 0.10% (w/v) solution of laurdimonium hydrolyzed wheat protein. The results (Figure 5) show an increase in cationic uptake of all com- pounds at higher temperature. The fact that the cationic sorption increases with in- creased temperature was also found in other studies and thought to be due to the higher penetration rate of the cationic compounds into the hair fiber (11). The effect of hair damage on cationic uptake by hair is shown in Figure 6. Qualitatively, hair damage is reflected by the chemical process applied to hair such as perm, tint, or