Stability of stored salinity samples

Abstract

Oceanographers measure water sample salinity in a laboratory environment to calibrate conductivity sensors or as a sole measure of in situ salinity. Established practice compares instrument performance against IAPSO Standard Seawater standards. Secondary standards can be used to reduce costs associated with assessing performance. However, results from our studies show the use of a secondary standard can also track the potential impact of prolonged sample storage. Initial results from secondary standard samples, used to trace instrument drift, showed erratic salinities. Two storage experiments were conducted to determine the potential cause of these results, and establish stability of stored salinity samples. The cause was identified as the plastic insert used to seal the glass bottles that originated from a faulty batch. We recommend that, where salinity samples are stored for subsequent analysis (longer than 1 month in our storage conditions), a secondary standard is used to track instrument drift and sample storage as a matter of course.