Accurate detection of perchlorate in epoxy resins via chlorine-35 quantitative quadrupolar NMR (qQNMR)

Abstract

A qQNMR methodology using chlorine-35 as the employed quadrupolar nucleus has been introduced for the first time as a robust and validated method to determine and quantify perchlorate in epoxy resins. The quantification has been carried out by using a calibration curve of lithium perchlorate. The method was validated at seven concentration levels in the range of 0.16 to 2.0 mg mL⁻¹ (1.6 to 20 mM in perchlorate), affording intra- and inter-day accuracies lower than 0.66% (expressed in CV), robustness towards pH, temperature, resin concentration and recycle delay, a limit of detection (LOD) of 0.08 mg mL⁻¹ (0.8 mM in perchlorate), a limit of quantification (LOQ) of 0.16 mg mL⁻¹ (1.6 mM in perchlorate) and probably most important in such applications, having no matrix effect. The method was applied on epoxy resins containing three different types of perchlorate precursors (lithium, potassium and tetramethylammonium), affording excellent quantifications with relative errors below 2.3% compared to the spiked concentrations.