We determine the bulk boron concentration of silicate rocks using a new method that does not require sample evaporation. After spiking (10B enriched NIST SRM 952) and HF attack, the rock solution is directly aspirated into the ICP-MS, and B concentration is determined by isotopic dilution. This technique is applied to samples with B contents in the range of 0.1-30 ppm. The very low blank (< 0.5 ng B) makes this procedure particularly suitable for samples with low B content. Repeated analysis of the basaltic reference sample BHVO-2 yields a B concentration of 2.81 ± 0.09 ppm (2σ), giving a 3% relative error. This concentration, like those obtained for other basaltic and andesitic reference materials (BIR-1a, BCR-2, JB-1 and JA-1), agrees well with previously published values.