2.5.3. Linearity range for quantifying concentration
Using a stock solution containing mixtures of SCFA, five calibration standards ranging from 0.5to10 mmol/L were prepared. For acetate , the linearity was investigated in the concentration range of 0.5–20 mmol/L due to the high concentration of acetate in the biogas digester studied herein. Four milliliters of 2.1mmol/L tert-pentanoic acid as the internal standard was added to each calibration standards followed by sample preparation and GC/MS measurement as described above. Individual calibration curves were plotted from the concentration ratio of each SCFA to internal standard against their peak area ratio.