An aqueous composition suitable for use as a high-retention sanitizer, especially on irregular and/or non-horizontal surfaces and surfaces on which water does not readily spread, a method for sanitizing a surface using the composition, and kits comprising components of the composition. The composition contains an organic peracid, preferably peracetic acid, or other antimicrobial agent, and a retention aid. The retention aid preferably is provided as a concentrate for admixture with the antimicrobial agent at point of use and comprises a mixture of a non-ionic surfactant, an ionic surfactant, and optionally a water-soluble magnesium ion source; or a mixture of a biopolymer thickening agent and at least one surfactant, and optionally a water-soluble magnesium ion source. In either retention aid, the magnesium ion source stabilizes foams formed from the retention aids in hard water and maintains retention aidconcentrates in a liquid state at room temperature if one of the surfactants is sodium lauryl sulfate, or magnesium lauryl sulfate or mixture thereof. The composition is preferably applied as a foam to the surface of the object to be sanitized.

Claims data not available