Assessment of sample storage techniques for total alkalinity and dissolved inorganic carbon in seawater

Wei-Jen Huang, Yongchen Wang, Wei-Jun Cai

Limnol. Oceanogr. Methods 10:711-717 (2012) | DOI: 10.4319/lom.2012.10.711

ABSTRACT: The borosilicate glass bottle sealed with a ground stopper and vacuum grease is a high quality container for preserving seawater samples for total alkalinity (TA) and dissolved inorganic carbon (DIC); it is recommended in the standard methods, even though this bottle is expensive and hard-to-handle. As there is an increased demand for sample storage and transportation by laboratories involved in biological and ocean acidification research, we explore alternative sample storage techniques by testing four types of containers. The results demonstrated that over a period of 47 d, TA values from seawater samples stored in polypropylene (PP) bottles and high density polyethylene (HDPE) bottles were not statistically different from those stored in the benchmark borosilicate glass bottles, both at room and refrigerated temperatures. In addition, DIC concentrations from a seawater sample stored in soda-lime glass bottles and small volume borosilicate glass vials with screw caps were not statistically different from those stored in the borosilicate glass bottles over at least 148 d. However, the TA value of seawater stored in soda-lime glass bottles increased significantly with increasing storage time, indicating that this type of soft glass bottle is not suitable for TA sample storage. Therefore, we suggest that PP or HDPE bottles can be used for TA sample storage and small volume borosilicate glass vials with screw caps can be used for DIC sample storage for a period of at least 1.5 months. These storage containers provide economical and easy-to-transport alternatives to the recommended high-quality borosilicate glass bottles.