Why are my lignin results higher than expected?

With the lignin procedure, two common errors will create false high values. 

(1) The first error is placing the F57 Filter Bags into the 72% sulfuric acid when there is moisture in the bags and samples. To avoid this situation, after the ADF procedure is complete and the Filter Bags have been dried and weighed, place the Filter Bags back into the oven at 102°C+=/- 2°C for 30 to 60 minutes. When the bags have been dried, place them into a desiccant pouch and allow them to cool to room temperature. Once they have been cooled, immediately place them into the 72% sulfuric acid and begin the procedure. 

(2) The second error occurs in the rinsing of the bags after the three-hour soaking in 72% sulfuric acid. It is vital that all the acid is rinsed out of the bags before the F57s are placed into the oven for drying. The rinsing process uses copious amounts of fresh water. After several minutes of rinsing, touch several bags with litmus paper. If the litmus paper shows the presence of acid in any of the bags, continue rinsing for several more minutes and test again. Continue to test the bags with litmus paper until no bags show the presence of acid. Place the bags into a beaker, pour enough acetone to cover the bags, and soak for three to five minutes. When the soaking is complete, pour off the acetone, lay them on a clean surface, and allow the acetone to evaporate from the bags. Place the filter bags into the oven at 102°C +/- °C for at least two hours. When the bags have been dried, place them into a desiccant pouch and allow them to cool to room temperature. Once they have been cooled, weigh the bags one final time.

NOTE: Lignin analysis must be performed with F57 BAGS ONLY.