It is interesting to study whether or not the MB-AS associate can be adsorbed onto a glass container surface. In this paper, we report that an addition of a small amount of heptane is effective to promote adsorption of the AS-MB associate onto the wall of a glass separatory funnel. It is also found that the adsorption of free MB onto the glass surface can be suppressed to a considerable extent by adding sulfuric acid. The present method can be used to determine AS (DBS or DS) of the 10μg/l level in tap and river water samples.