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.