qNMR ? a versatile concept for the validation of natural product reference compounds

Abstract

The validation of reference compounds for natural products is a domain of the same physico‐chemical methods that are used for their isolation, especially those techniques involving coupled high‐resolution chromatography. Acknowledging the great problem of co‐eluting impurities contained in the ‘biogenetic cocktail’ of a plant extract, there is a strong demand for non‐chromatographic alternatives in the quality assessment of reference compounds. Because of this, the concept of qNMR is introduced as a versatile tool based on qualitative and quantitative 1H‐NMR allowing the precise and simultaneous determination of both the compound content as well as the amount and nature of the impurities. As opposed to measuring carbons, 1H‐NMR benefits from much higher sensitivity and is far more versatile for routine analysis with respect to time and cost. Since quantification of impurities is reliant upon their identification and, therefore, limited by knowledge about their structure, the concept emphasizes the high demand for qualitative reference dossiers including quality NMR data for profiling potential impurities which may be analogues, isomers, or degradation or oxidation products of the reference compounds. The qNMR concept is developed with focus on its potential in the certification and quality control of reference compounds. Taking into account published work in the field of quantitative NMR, selected natural products are analysed in order to elaborate suitable experimental parameters and to obtain preliminary validation data. The method is discussed with respect to sensitivity, precision and selectivity. Typical relative errors are found to be below 2% for the quantification of both the major analyte and the minor impurities even when the latter are contained at the 1% level only. Documentation of the conformity of signal integration and precision is based on measurements of a certified reference standard. Determination of the natural 13C isotope is suggested as an elegant method of validation because the content values could be reproduced with errors below 1%. The qNMR concept offers a rapid and efficient way to assess the purity of natural products in a single analytical step without the need of performing multiple analyses, while still offering the option to retain the substance. Thus, qNMR pays tribute to the increasing demands in reference compound certification, but also holds out the prospect of easy access to the valid characterisation of natural products tested in vitro or in vivo for their biological and pharmacological effects. Copyright © 2001 John Wiley & Sons, Ltd.

Quantitative NMR in synthetic and combinatorial chemistry

“…[14][15][16]) and the source and magnitude of errors has been thoroughly discussed by Griffiths and Irving [17]. The use of a long pulse interval (e.g.…”

Quantitative NMR in synthetic and combinatorial chemistry

“…[14][15][16]) and the source and magnitude of errors has been thoroughly discussed by Griffiths and Irving [17]. The use of a long pulse interval (e.g.…”

The Assessment of Plant Metabolite Profiles by NMR-Based Methodologies

“…These analytical platforms address different analyte concentration ranges (ppm vs. ppb) with comparable dynamic ranges. About four to five orders of magnitude have been reported for NMR spectroscopy [34], [35], the same holds true for mass spectrometry. One major advantage of NMR spectroscopy over other analytical techniques used for metabolite profiling is its unequalled reproducibility and stability.…”

Use of NMR for the Analysis and Quantification of the Sugar Composition in Fresh and Store-Bought Fruit Juices

“…16 In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations. 17 However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas. 18 The strong concentration differences between the water and the compounds of interest, which is of several orders of magnitude when the solvent is mostly not deuterated water as in fruit juices, cause digitization issues and also impacts the spectrum baseline, especially in the region close to the water peak.…”

“…In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations . However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas .…”

Quantitative NMR in synthetic and combinatorial chemistry

“…[14][15][16]) and the source and magnitude of errors has been thoroughly discussed by Griffiths and Irving [17]. The use of a long pulse interval (e.g.…”

The Assessment of Plant Metabolite Profiles by NMR-Based Methodologies

“…These analytical platforms address different analyte concentration ranges (ppm vs. ppb) with comparable dynamic ranges. About four to five orders of magnitude have been reported for NMR spectroscopy [34], [35], the same holds true for mass spectrometry. One major advantage of NMR spectroscopy over other analytical techniques used for metabolite profiling is its unequalled reproducibility and stability.…”

Use of NMR for the Analysis and Quantification of the Sugar Composition in Fresh and Store-Bought Fruit Juices

“…16 In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations. 17 However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas. 18 The strong concentration differences between the water and the compounds of interest, which is of several orders of magnitude when the solvent is mostly not deuterated water as in fruit juices, cause digitization issues and also impacts the spectrum baseline, especially in the region close to the water peak.…”

“…In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations . However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas .…”

Quantitative NMR in synthetic and combinatorial chemistry

“…[14][15][16]) and the source and magnitude of errors has been thoroughly discussed by Griffiths and Irving [17]. The use of a long pulse interval (e.g.…”

The Assessment of Plant Metabolite Profiles by NMR-Based Methodologies

“…These analytical platforms address different analyte concentration ranges (ppm vs. ppb) with comparable dynamic ranges. About four to five orders of magnitude have been reported for NMR spectroscopy [34], [35], the same holds true for mass spectrometry. One major advantage of NMR spectroscopy over other analytical techniques used for metabolite profiling is its unequalled reproducibility and stability.…”

Use of NMR for the Analysis and Quantification of the Sugar Composition in Fresh and Store-Bought Fruit Juices

“…16 In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations. 17 However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas. 18 The strong concentration differences between the water and the compounds of interest, which is of several orders of magnitude when the solvent is mostly not deuterated water as in fruit juices, cause digitization issues and also impacts the spectrum baseline, especially in the region close to the water peak.…”

“…In small molecule quantitative analysis by NMR, there are a number of well-defined rules that ensure that the NMR peak areas reflect accurately the analyte concentrations . However, in the case of food samples such as fruit juices, additional complexity arises from the need to suppress the solvent signal, as it is a major source of inaccuracy in the determination of the analyte peak areas .…”