A method is described which determines sub-ppb amounts of boron in high-purity sulfuric acid by inductively coupled plasma mass spectrometry (ICP-MS) with methyl borate ester generation. 15 g of sulfuric acid sample is placed into a PFA reaction vessel with 50 mL of methanol, and heated at about 60 °C on a quartz hot plate, while an argon carrier gas flow of 0.1 L min⁻¹ is passed through the vessel into a PFA collection bottle filled with 20 mL of 0.05 M NaOH solution. The volatile ester generated in the reaction vessel is collected in the 0.05 M NaOH solution for about 30 min. The collection solution is then passed through a cation-exchange column to remove Na⁺ in the solution. The isotope dilution method is used for quantification to overcome poor reproducibility of the ester generation and collection efficiency. The detection limit of the proposed method is 0.27 ng g⁻¹.