Ammonia and/or oxygen were used to enhance the delignification of miscanthus dissolved in 1-ethyl-3-methylimidazolium acetate at 140 degrees C. After dissolution of the gas at 9 bar, water was added as antisolvent to regenerate the dissolved biomass. In a next step, an acetone/water mixture was used to remove carbohydrate-free lignin from the regenerated biomass. The lignin content in the final product was around 10%, much lower than the ca. 23% lignin content of the raw dry miscanthus. This lignin reduction is achieved without diminution of cellulose or of total carbohydrates recovered, relative to the recovery achieved with the ionic liquid pretreatment in contact with air or nitrogen. (C) 2011 Elsevier Ltd. All rights reserved.