Alkalinity determination in guanidine and hydroxide-containing hair straightening creams

Abstract

The purpose of the present investigation was to determine the alkalinity hair straightening creams, in order to accomplish the directives of the enforced law, which allows the maximum concentration of 7.0% w/w of calcium hydroxide. Two titrametric analytical techniques were compared. Two “blanks” (without active principle) were supplemented with calcium hydroxide at the concentrations of 3.0%, 6.0%, and 8.0% (w/w), and eight replicates for each concentration were prepared. Alkalinity determination was carried out by means of direct titration of calcium ions in samples. A sample corresponding to 0.1500 g calcium hydroxide concentration was diluted in solution containing water and hydrochloric acid under shaking and heating. After cooling, this samples was with 0.0500 mol/L EDTA, and hydroxynaftol blue was employed as indicator. Direct titration by means of OH- ions neutralization with HCl and phenolphtaleine showed that the recovery was unsatisfactory; this fact could be caused by the adsorption of OH- ions into cream mixture. The method precision ranged from 0.03 to 1.3% in the interval from 2.9 to 8.0% Ca(OH)2 (w/w). The recovery was obtained within the interval from 96.0% to 100.5%. For the present study the Food Chemical Code 4th edition technique was used and compared with the modified technique in the laboratory. The statistics T and f tests showed that both techniques are analytically equivalent.