Determination of Boron Concentration by Means of Direct Current Plasma - Atomic Emission Spectroscopy

Abstract

The accurate measurement of total boron content in biological samples with a sensitivity in the ppm range is essential for evaluating the potential usefulness of various tumor localizing boron-containing compounds for Boron Neutron Capture Therapy (BNCT)1. Among the procedures that have been used are spectrophotometric analyses involving various complexing agents2–4. These methods are time consuming and require that the boron compounds can be oxidized to boric acid. Relatively low sensitivity and interference from various contaminants further limit their usefulness. Recently, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) has been shown to be sensitive enough for the detection of microgram quantities of boron in biological samples5,6, although the sensitivity is adversely affected by high concentrations of inorganic salts in the samples7. Since alkaline fusion is not suitable for use with ICP8, samples were digested by exposure to either perchloric acid5,6 or nitric acid6. There may be a danger of explosion with the former, and with the latter, it may be necessary to decompose the tissues in teflon-lined digestion bombs. Both procedures, therefore, have their limitations. The objectives of the present study were to determine whether DCPAES could be used to quantify boron in a variety of chemical compounds including polyhedral boranes and carboranes, to improve the procedure for the digestion of tissue samples, to determine if this method could be used to quantify cellular uptake of boron, and finally to define the limits of boron detection in biologic samples by means of this method.