Determination of Boron in Coal Samples with Microwave Digestion by Inductively Coupled Plasma-Mass Spectrometry

Accurate determination of boron in coal is significant to the understanding of the original peat-forming environment. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is a reliable technique to determine most trace elements in coal samples. However, the procedure for the determination of boron is complex and the results are inaccurate, due to the special chemical and physical properties of boron, such as high volatility. In this study attempts to determine boron in coal samples using an improved procedure of ICP-MS technique with microwave digestion are made. Samples were digested in a microwave oven with H₃PO₄, HNO₃ and HF, and then were heated to remove acid on the heating plate. Due to the high volatility of halogenides of boron, phosphoric acid was added to chelate the boron which minimizes boron volatilization during heating. Beryllium was added online as the internal standard, which compensated for matrix effects. Diluted ammonium hydroxide solution was used as the wash solution, which significantly reduced the memory effect of boron. Measurement was taken under high resolution mode, in order to minimize spectral interference from ¹²C and ⁴⁰Ar⁴⁺. The instrument detection limit was 0.22 ng/mL, and the method detection limit was 0.34 ng/mL with high sensitivity and accuracy, verified by standard materials. The results show that this method is a simple and rapid procedure, and can be used for routine determination of boron for batch coal samples.