Boron determination - A review of analytical methods

This paper reviews published methods of sample preparation, determinand purification, and the determination of baron concentration and isotopic composition in a sample. The most common methods for the determination of B concentration are spectrophotometric and plasma-source spectrometric methods. Although most spectrophotometric methods are based on colorimetric reactions of B with azomethine-H, curcumin, or carmine, other colorimetric and fluorometric methods have also been used to some extent. These methods, in general, suffer from numerous interferences and have low sensitivity and precision. Application of nuclear reaction and atomic emission/absorption spectrometric (AES/AAS) methods has remained limited because these methods have poor sensitivity and suffer from serious memory effects and interferences. Among large number of published nuclear reaction methods only prompt-gamma spectrometry has been of practical use. The prompt-gamma method can determine B concentration in intact samples, which makes this method especially useful for some medical applications, including boron neutron capture therapy. However, this is a time-consuming method and not suitable for detection of low levels of B. Inductively coupled plasma optical emission spectrometry (ICP-OES) created a new dimension in B determination because of its simplicity, sensitivity, and multielement capability. However, it suffers interferences and is not adequately sensitive for some nutritional and medical applications involving animal tissues that are naturally low in B. All methods involving the measurement of B isotopic composition require a mass spectrometer. Thermal ionization mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS) have been used to measure isotopic composition of B; however, these methods are time consuming and require extensive sample preparation and purification. Development of inductively coupled plasma mass spectrometry (ICP-MS) not only overcame most of the drawbacks of earlier methods, but also its capability of measuring B isotopes made possible (1) B concentration determination by isotope dilution, (2) verification of B concentration by isotope fingerprinting in routine analysis, and (3) determination of total B concentration and B isotope ratio for biological tracer studies in the same run. Therefore, plasma source MS appears to be the method of choice among present-day technologies. (C) 1997 Academic Press.