“…Naturally, the use of HF implies the use of Teflon flasks that can be open or, in order to reduce the time required for sample preparation, sealed pumps, at high pressure and high temperatures (>160 C), obtained by microwave or conventional heating (Yu, Robinson, and McGoldrick 2001). According to Kramer et al (1999Kramer et al ( , 2002, the use of HF is essential for silicate dissolution and accurate quantification of REE in geological samples, such as sediment and soil. However, REE, as well as other elements, can coprecipitate with Ca, Mg, and Al, also present in mineral samples, which form fluoride complexes (Yokoyama, Makishima, and Nakamura 1999;Tanaka et al 2003;Lu, Makishima, and Nakamura 2007).…”