How to perform extraction practically using liquid water as extractant? First, water, either deionized or tap water, is used as the extractant. The water should be oxygen-free in order to prevent oxidation of the analytes. The methods commonly used for achieving water degassing are ultrasound (sonication) or helium purge, of which the former is low cost if an ultrasound
bath is available, if much slower than the latter. At least 60 min of degassing by sonication is necessary to ensure that most of the oxygen gas is removed from the water.