Trace Level Detection and Quantification of Crystalline Silica in an Amorphous Silica Matrix with Natural Abundance 29Si NMR.

Radhakrishnan, Sambhu; Colaux, Henri; Chandran, C Vinod; Dom, Dirk; Verheyden, Loes; Taulelle, Francis; Martens, Johan; Breynaert, Eric

doi:10.1021/acs.analchem.0c01756

Trace Level Detection and Quantification of Crystalline Silica in an Amorphous Silica Matrix with Natural Abundance 29Si NMR.

Author:

Radhakrishnan, Sambhu

Colaux, Henri ; Chandran, C Vinod ; Dom, Dirk ; Verheyden, Loes ; Taulelle, Francis ; Martens, Johan ; Breynaert, Eric

Keywords:

Science & Technology, Physical Sciences, Chemistry, Analytical, Chemistry, QUANTITATIVE H-1-NMR, CONTROLLED-RELEASE, SPECTRA, SOLIDS, METH/14/04#53291607, 0301 Analytical Chemistry, 0399 Other Chemical Sciences, Analytical Chemistry, 3205 Medical biochemistry and metabolomics, 3401 Analytical chemistry, 4004 Chemical engineering

Abstract:

A protocol for the detection of trace amounts of quartz in amorphous silica gels by NMR spectroscopy was developed and tested on commercially available samples. Using natural abundance 29Si MAS NMR spectroscopy with CPMG acquisition and standard addition of crystalline quartz, quantitative detection of quartz concentrations down to 0.1% wt. was achieved. CPMG permitted to suppress the amorphous silica-derived signal, benefitting from the extremely long T2 relaxation time of quartz in 29Si and hence dramatically increasing the sensitivity. Dedicated post-processing exploiting the known CPMG spikelet frequencies allowed to probe the near-absence of quartz in commercial, 100% silica samples, enabling assessment of conformity of unknown samples to EU legislation (REACH).