The chain of custody, as established by the testimony of the detective and the chemist, provided reasonable assurances that the package in question was the same one the undercover officer purchased from defendant and that the package was kept in police custody from the time it was purchased up until the time it was admitted into evidence ( People v Smith, 189 AD2d 652, lv denied 81 NY2d 977). Any gaps in the chain of custody were insufficient to render the evidence inadmissible but were appropriately used to assess the weight of the evidence ( People v Julian, 41 NY2d 340, 344).