Determination of arsenic in seagrass using inductively coupled plasma mass spectrometry

A study has been conducted for the determination of arsenic in seagrass using inductively coupled plasma mass spectrometry (ICP-MS) with emphasis on sample digestion procedures and interference reduction. Open-vessel digestion with four different media, HClO4/H2SO4/HNO3, H2SO4/HNO3, HNO3/H2O2, and HNO3, was tested and compared. The HNO3/H2O2 mixture was found to be the most suitable medium for sample digestion. Different inorganic and organic arsenic compounds gave similar ICP-MS responses, indicating that complete conversion from organic form to inorganic form in the sample digestion is not required. Although the HClO4/H2SO4/HNO3 mixture is frequently used in plant sample digestion for other analytical techniques, it is not recommended for the ICP-MS technique. The formation of the polyatomic interference ion, 40Ar35Cl+, hampers the determination of arsenic even when the interference equation is employed. The interference of 40Ar35Cl+ can be accurately corrected only at minimum chlorine concentration (<500 ppm). The concentrations of HNO3 in the final solutions have a significant effect on the arsenic signal. This type of interference cannot be corrected by internal standards (Sc, Y, and In) because the signal suppression due to the use of HNO3 is dependent on the mass number. The ratios of 75As/45Sc, 75As/89Y and 75As/115In vary with the concentrations of HNO3. Standard addition has been found to be an excellent method for reducing this type of matrix effect. The analytical procedure proposed in this paper has been validated by analyzing standard reference material 1572 (citrus leaves), and successfully used for the determination of arsenic in seagrass collected from Florida Bay.