Studies were carried out on the use of NaCl instead of sodium carbonate or sodium hydroxide for the formation of Na₂BO₂⁺ ion used for the determination of isotopic composition of boron by TIMS. The addition of mannitol which forms an anionic complex with boron was found to be essential when using NaCl. The investigations showthat whenNaCl is used, B/Na molar concentration ratio need not be critically adjusted to 1 as required in case of sodium carbonate or sodium hydroxide. The ¹⁰B/¹¹B ratiowas found to be independent of B/Na molar concentration ratio in the range of 25–0.05. This aspect is extremely useful in carrying out isotopic analysis of B in unknownsamples solutions. NIST boron isotopic standard SRM-951 having ¹⁰B/¹¹B isotopic ratio of 0.2473±0.0002was used in these studies and a value of 0.24742±0.00006 (1s) was obtained.