Measurement of total boron and 10B concentration and the detection and measurement of elevated 10B levels in biological samples by inductively coupled plasma mass spectrometry using the determination of 10B:11B ratios

Abstract

Methods were developed to determine total B and ¹⁰ B content in various biological samples, media and reagents by ICP-MS. Open vessel, wet ash digestion protocols using HNO ₃ were developed for the biological and media samples. Digestion of blood and plasma also required H ₂ SO ₄ . Despite relatively high blanks, instrumental detection limits using 3 σ at or near the blank level were, for total boron (total B), <0.1 µmol l ^–1 (<1 µg l ^–1 ), and for ¹⁰ B, <0.01 µmol l ^–1 (<0.1 µg l ^–1 ). Problems with variable blanks, matrix suppression and peak overlap by ¹² C on ¹¹ B are discussed. The developed methods were used to analyse samples for a collaborative study with Clinical Neurosciences at Southampton General Hospital, related to boron neutron capture therapy of brain tumours, of the uptake of ¹⁰ B by tumour cells in vitro, using tissue culture, and in vivo, in the rat. Detection limits achieved in cells solubilised in 1 M NaOH and medium were <0.001 µmol ml ^–1 total B and <0.0001 µmol ml ^{–1 10} B and, for blood, 0.002 µmol g ^–1 total B and 0.0002 µmol g ^{–1 10} B, ∼10 ^–9 M boronophenylalanine solutions. The analytical precision for duplicate analyses gave mean within-run RSDs of ∼7% for ¹⁰ B concentration and <10% for total B concentration. The determination of ¹⁰ B: ¹¹ B ratios enabled statistically significant increases in ¹⁰ B concentration to be detected and confirmed at low B levels where sample digests and digest blanks had similar B contents. Running ¹⁰ B: ¹¹ B ratios for standard and sample solutions were utilised for novel methods of calculating elevated ¹⁰ B levels in the samples. Despite achieving low detection limits, elevated ¹⁰ B levels could not be confirmed without the determination of ¹⁰ B: ¹¹ B ratios.