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(T)) of seawater, estuarine water, freshwater, and groundwater samples stored for 0-6 months. Water samples, untreated or treated with HgCl2, 0.45 mu m filtration, or filtration plus HgCl2, were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean A(T) of samples treated with HgCl2 was reduced by as much as 49.1 mu mol kg(-1) (1.3%). Borosilicate glass elevated A(T), possibly due to dissolving silicates. There was little change in A(T) of control and filtered samples stored in polypropylene, except for untreated groundwater (similar to 4.1% reduction at 6 months). HgCl2 concentrations of 0.02-0.05% reduced the A(T) of fresh, estuarine, and ground water samples by as much as 35.5 mu mol kg(-1) after 1 month, but had little effect on the A(T) of seawater. Adding glucose as a carbon source for microbial growth resulted in no A(T) changes in 0.45 mu m-filtered samples. We suggest water samples intended for A(T) analyses can be filtered to 0.45 mu m, and stored in polypropylene vials at 4 degrees C for at least 6 months. Borosilicate glassware and HgCl2 can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg2+.

Automated summary

The study compared the effects of preservation and storage methods on the total alkalinity of different water samples. Borosilicate glass may elevate alkalinity, while treatment with HgCl2 may lead to a reduction. It is recommended to filter water samples to 0.45 micrometers and store them in polypropylene vials to avoid uncertainties and risks associated with the use of borosilicate glassware and HgCl2.