Preservation of arsenic(III) and arsenic(V) in samples of sediment interstitial water

Abstract

The effects of temperature, pH and the presence of oxygen on the stability of arsenic(III) in interstitial water samples from Lake Ohakuri sediments have been studied. The most effective means of preserving a sample with 1–4 µg ml^–1 of arsenic(III) for up to 6 weeks was found to be by acidifying the sample to pH 2 and refrigerating near 0 °C. In the samples studied, deoxygenation appeared to be unnecessary. However, in the absence of refrigeration, acidified samples were safely stored for up to 2 weeks, provided that they were deoxygenated and in well sealed glass containers. Because of the likely differences in the behaviour of natural water samples, the safest method of preserving arsenic(III) samples is therefore acidification to pH 2, refrigeration and deoxygenation.