Storage bottle material and cleaning for determination of total mercury in seawater

Abstract

Accurate determinations of trace levels of mercury (Hg) in water require scrupulously clean sampling equipment and storage bottles. To avoid Hg contamination during storage, it has been presumed that water samples must be stored in either glass or Teflon bottles cleaned with a rigorous method, such as submersion in hot acid. These cleaning procedures are hazardous, and use of Teflon bottles can be cost prohibitive for major oceanographic programs. We investigated the suitability of alternative cleaning procedures and bottle materials for storage of seawater containing sub‐picomolar levels of Hg. We found that a simple technique with detergent, dilute acid, and bromine monochloride removes Hg from all bottle materials tested, which included FEP Teflon, glass, polycarbonate (PC), low‐density polyethylene (LDPE), and fluorinated polyethylene (FLPE). The technique is effective for bottles that are either new or used previously for trace‐level oceanographic samples (total Hg < 10 pM). Stability of seawater Hg levels differed dramatically among storage bottle materials during a 74‐ week test. Hg in seawater stored in LDPE, FLPE, and FEP bottles increased within 15 weeks of storage at room temperature. In contrast, Hg levels in seawater stored in PC bottles were increased modestly only after 74 weeks of storage and those in glass bottles were unchanged throughout the test. We recommend future use of this new cleaning method and encourage greater use of glass and PC bottles for storage of waters containing low levels of Hg.