A comparison of digestion techniques (ultrasound versus microwave) was made using methods M2 and U1, because those methods used the same digestion solution but different
digestion techniques. As can be seen in Table 3, the ultrasound-assisted digestion U1 was slightly better than microwave method M2. The element recoveries were 2–15%
higher for method U1 than method M2 with one exception, arsenic, having similar recoveries in both methods. In a comparison of element recoveries between EPA-3052 digestion method and ultrasound method the studied methods were M1 and U1. As can be seen in Table 3, the barium, strontium and zinc concentrations were higher in the ultrasound method U1 than the microwave method M1. The U1 method resulted in Ba, Sr and Zn recoveries significantly better than the method M1. In general, the ultrasound assisted digestion method with 10mL aqua regia and 0.5mL hydrofluoric acid as the digestion solution and the standard method