Validation of quantitative nuclear magnetic resonance (QNMR) spectroscopy as a primary ratio analytical method for assessing the purity of organic compounds: a metrological approach

摘要

Recently, there has been a strong demand for non-chromatographic alternatives for the purity assessment of organic compounds. The potential offered by quantitative NMR spectrometry (QNMR) as a viable alternative to chromatographic methods for quantifying major component and impurity is considerable. The NMR spectrum of a solution shows all soluble organic substances present, and the signal intensity is directly proportional to the quantity of the nucleus being measured. QNMR is a primary ratio analytical method (i.e. one that does not depend on calibration with a pure sample of the analyte) as just a single internal standard, unrelated to the target analyte, can be used to determine the percentage purity of the analyte providing the NMR signals of the internal standard do not overlap with those of the target analyte. A method validation study for QNMR methodology (Chapter 2) was performed and statistical designs were applied to examine the following validation aspects: accuracy, precision, sensitivity, selectivity, repeatability, reproducibility, robustness and ruggedness, limits of detection and limits of quantification. The QNMR method and validation was documented so that it can be clearly and unambiguously implemented. The amount of substance (as % active ingredient) was measured for a range of commercial agricultural and pharmaceutical organic compounds by 1H, 31P and 19F NMR spectrometry.The measurement uncertainty associated with these quantitative analyses is described in compliance with ISO guide 17025, and a detailed description of the preparation of the related uncertainty budgets is reported (Chapter 3). The traceability of the measurements to the SI is demonstrated by the use of certified reference standards.QNMR is shown to be one of the most precise and accurate quantitative methods that gives highly repeatable and reproducible measurements provided that certain requirements are met. Such influence factors and requirements are discussed in depth from the experimental and theoretical point of view (Chapter 4). Results show that the accuracy and precision are dependent on the selected acquisition and processing parameters. Results for 1H QNMR of the purity of the chosen chemical were compared with HPLC data and found to be of better precision (Chapter 5). Measurements obtained by 31P and 19F NMR (Chapter 6 & 7) were also of high quality and agreed with the 1H QNMR measurements.