Potentiometric/turbidometric titration of antiperspirant actives.

A titration procedure that simultaneously monitors the pH and turbidity of an antiperspirant solution during neutralization with sodium hydroxide was developed to characterize antiperspirant actives. Aluminum chloride, aluminum chlorohydrate (ACH), and aluminum zirconium glycine complex (AZG) gave distinctive pH/turbidity profiles. The activated forms of aluminum chlorohydrate (ACH') and aluminum zirconium glycine complex (AZG') produced more turbidity than the non-activated forms. On an equimolar basis, AZG' produced more turbidity than any of the antiperspirant actives tested.

Using rate of acid neutralization to characterize aluminum phosphate adjuvant.

Five aluminum phosphate adjuvants having P/Al molar ratios ranging from 0.74 to 0.26 were prepared. The adjuvants were characterized by both protein adsorptive capacity and rate of acid neutralization at pH 2.25, 25 degrees C. The protein adsorptive capacity was not a useful parameter to compare the initial properties of the adjuvants, as differences in surface charge of the adjuvants required the use of different proteins. In contrast, the rate of acid neutralization allowed a comparison of the freshly precipitated adjuvants and revealed that the rate of acid neutralization was directly related to the P/Al molar ratio. The protein adsorptive capacity decreased slightly during 39 weeks of aging at room temperature. The changes in the rate of acid neutralization were much greater and indicated that a P/Al molar ratio of at least 0.5 was required to minimize the aging of the adjuvants. Thus, the rate of acid neutralization was found to be the most sensitive parameter to characterize aluminum phosphate adjuvants.