The final volume in the tube is approx. 10.3 mL when the sample is solubilised in 2 mL KOH, 8 mL of acetate buffer and 0.1 mL of enzyme (however, this volume will vary particularly if wet samples are analysed, and appropriate allowance for volume should be made in the calculations).
This figure is given from the average of a large range of samples analysed. It is possible to use a volumetric flask (e.g. 20/25mL) and alter the calculation accordingly.