INTRODUCTION

Among various analytical methods, NMR spectroscopy is a dominant technique due to its numerous experimental approaches and the high structural information that can be provided. In recent decades, considerable efforts have been made for NMR applications in crude extracts without previous separation and isolation of the individual analytes. In this presentation a critical overview of several applications will be summarised with emphasis (i) on the great potentialities of NMR spectroscopy in mixture analysis and (ii) in specific cases where combination with chromatographic–MS techniques is necessary.

METHODS AND RESULTS

(i) The use of 2,2,2 trifluoroacetic acid results in extensive sharpening of ¹H NMR signals of labile phenol and alcohol OH groups in natural products, in conjunction with the large ¹H NMR chemical shifts of up to 19 ppm, and ¹H-¹³C HMBC experiments can provide an excellent means for chemical analysis and direct monitoring of dynamic changes inmetabolites without isolation steps in a variety of complex natural products [1].

(ii) Selective 1D TOCSY experiments were shown to be an excellent method for the authentication of the metabolite profile in the lipid fraction of organic and conventional milk [2]. Identification and quantification of minor and complex oxidation products of lipids without previous separation and isolation of the individual compacts were performed[3].

(iii) In the case of gallic acid derivatives, primarily gallotannins, which are characterised byoverlapping aromatic singlets in the range of 6.8-7.0 ppm, combined use with UPLC – PDA – ESI/QToF is necessary, as in the case of carob leaf (ceratonia siliqua L.) crude extracts [4].