Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage.

We compared the effects of preservation and storage methods on total alkalinity (A) of seawater, estuarine water, freshwater, and groundwater samples stored for 0-6 months. Water samples, untreated or treated with HgCl, 0.45 µm filtration, or filtration plus HgCl, were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean A of samples treated with HgCl was reduced by as much as 49.1 µmol kg (1.3%). Borosilicate glass elevated A, possibly due to dissolving silicates. There was little change in A of control and filtered samples stored in polypropylene, except for untreated groundwater (~ 4.1% reduction at 6 months). HgCl concentrations of 0.02-0.05% reduced the A of fresh, estuarine, and ground water samples by as much as 35.5 µmol kg after 1 month, but had little effect on the A of seawater. Adding glucose as a carbon source for microbial growth resulted in no A changes in 0.45 µm-filtered samples. We suggest water samples intended for A analyses can be filtered to 0.45 µm, and stored in polypropylene vials at 4 °C for at least 6 months. Borosilicate glassware and HgCl can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg.