ICP protocol

Boron (B), silicon (Si), and strontium (Sr) ion release was measured with an Inductively Coupled Plasma mass spectrometer (ICP-MS) (Agilent 7500 with Autosampler ASX-500, Santa Clara, CA, USA). The ICP-MS detected the absorbance wavelengths of the ions in the collected PBS. High-purity nitric acid (Lot #NX0407, EMD; Millipore, Billerica, MA, USA) and MilliQ water were used to prepare a 2% nitric acid solution for sample and standard preparations. A standard mixture containing Si (50 µg/mL), Sr, Na, B, and Ca (each at 100 µg/mL) was used (Lot #89800-568; BDH Chemicals, Darmstadt, Germany). The standard mixture was diluted 20-fold with 2% nitric acid to 1/1000, such that the solution contained 50 ng/mL of Si and 100 ng/mL each of Sr, Na, B, and Ca ions. The internal standard was lutetium (10000 µg/mL) (Lot #{"type":"entrez-nucleotide","attrs":{"text":"R01254","term_id":"750990","term_text":"R01254"}}R01254; Ultra Scientific, North Kingstown, RI, USA).

Standards and samples were spiked with the internal standard of lutetium at a concentration of 100 ng/mL. Phosphate-buffered saline (PBS) was diluted 20-fold with 2% nitric acid for use as a matrix blank. Matrix blanks, standard solutions, and samples were assayed in duplicate or triplicate. Counts per second (CPS) for each analyte of interest in the matrix blank were subtracted from the standard and sample results for corresponding analytes. The absorbance wavelength was measured in ng/mL for each of the samples. All samples were measured in ng/mL within the PBS solution.