Summative mass analysis is vital to prove the reliability of a compositional analysis of biomass. In OPF compositional analysis, summative mass closure includes the summation of total structural carbohydrate, total lignin, ash and total extractives and gave a final mass balance of 103.7%. The value was in within ±5% of 100% and thus, the summative mass in current OPF analysis is balanced and the analytical result was therefore considered reliable.