MEASUREMENT OF BORON ISOTOPE RATIOS IN GROUNDWATER STUDIES

Boron is present at low levels in groundwater and rainfall in the UK, ranging between 2 and 200 ng ml(-1). A sensitive technique has been de veloped using inductively coupled plasma mass spectrometry (ICP-MS) to measure boron isotope ratios at low concentrations with a precision ( s(r)) of between 0.1 and 0.2%, Samples were evaporated to increase ele mental boron concentrations to 200 ng ml(-1) and interfering matrix el ements were removed by an adapted cation-exchange separation procedure . The validity of measuring boron isotopic ratios by ICP-MS at this co ncentration level is discussed in relation the theoretical instrument precision attainable based on counting statistics. Using the developed procedure it is possible to use ICP-MS to establish a reliable databa se documenting the natural variation in boron isotope compositions in aquifers and rain water in the UK. Preliminary results demonstrate a t rend in boron isotopic compositions with increasing boron concentratio n. The method may be used to evaluate possible levels of boron polluti on from anthropogenic inputs into natural aqueous systems.