Determination of boron in biological tissues by inductively coupled plasma optical emission spectrometry (ICP-OES)

Abstract

The application of inductively coupled plasma optical emission spectrometry (ICP-OES) to the determination of boron was studied with regard to the optimization of boron neutron capture therapy (BNCT), a method used in cancer radiotherapy. In order to enable trace determinations of B in tissue down to the sub μg/g-level (as this application requires), the different parameters of ICP-OES (gas flow, power, observation height) were optimized towards highest power of detection. Two different nebulizers (Babington and Meinhard nebulizer) as well as ICPs with argon or nitrogen as outer gases were used. The optimization was carried out with the aid of a modified simplex. The lowest detection limit for B (25 ng/ml) is obtained in the case of a Babington nebulizer and with an ICP using Ar as outer gas as well as a forward power of 1.3 kW (plate voltage at the r.f. generator: 2.75 kV). Therefore, the nebulizer gas flow had to be set at 1.1 l/min (at 4.5 bar) and an intermediate gas flow of 5 l/min in the case of a Greenfield-type torch was required. After optimization the natural concentration of B in biological tissues (0.1–0.3 μg/g) could be determined after decomposition of 1–1.5 g of the sample with 5 ml HNO3 (63%) at high temperature and pressure during 2 h in closed PTFE vessels. Results obtained with spiked liver standards were precise (RSD 5%–8%) and accurate in a concentration range of 5 μg/g to 100 μg/g. The method developed could be satisfactorily used for the analysis of tissue samples of mice tumors. Furthermore, the uptake and metabolization of boron and its derivatives could be well monitored at the 1–5 μg/g level.