Biodiesel is a renewable energy source that is produced from plant oils. Biodiesel is chemically produced by taking plant oils and transforming them into the alkyl monoesters. During the conversion of oils to biodiesel water is produced through incomplete reaction or contamination. The presence of water is harmful to product yield and water in the final product greatly reduces shelf life because it supports biological activity. In order to effectively monitor or remove the water during the reaction, the quantity of water needs to be measured. A novel direct sampling mass spectrometry membrane is used to quantize the water. This process analysis technique enables effective monitoring of the chemical synthesis of biodiesel, which is crucial to efficient chemical production.