14N NQR Quantification of Sodium Nitrite and Urotropin Using Singular Spectrum Analysis (SSA) for Data Filtering

Abstract

An 14N nuclear quadrupole resonance (NQR) spectroscopy method has been developed using the singular spectrum analysis (SSA) based on the principal components concept. For the first time, it was demonstrated that this method can be used as a low cost and non-destructive quantitative method for analyses of small amounts (< 100 mg) of nitrogen containing solids. NQR technique is closely related to nuclear magnetic resonance, but without need for external magnetic field, applicable to solid compounds with quadrupolar nuclei. The hardware configuration using a broadband matching transformer was constructed and advanced algorithms for quantitative analyses of 14N NQR spectra were outlined. The calibration curves obtained, after optimization, for the model compounds, sodium nitrite and urotropin (hexamethylenetetramine), showed excellent linearity up to 500 mg for sodium nitrite at a frequency of 4642 kHz and up to 300 mg for urotropin at a frequency of 3307 kHz. The limits of detection were determined as 41 mg and 24 mg, respectively. The experimental and analytical procedure was simple enough to allow relatively easy practical implementation.