Pigment analysis sampling considerations

Because they are important, the phenolics and their roles in wine have been studied considerably (I), but more needs to be known. Since different classes of phenols behave quite differently in the various roles as pigments, oxidation substrates, flavors, etc., separate consideration and analysis is essential to completely understand them. Every individual phenol should be separately determined precisely and quantitatively. Chromatography may solve these problems, but for now, chromatography and other detailed separatory methods have drawbacks, particularly for economical application to many individual wine or grape samples. 

The first requirement in an NMR analysis is to obtain basic one-dimensional proton ( H) and carbon ( C) spectra, including a C-DEPT (disproportionless enhancement by polarization transfer) spectrum. Typical proton spectra for the pigments 1 and 2 are shown in Figs. 6 and 7, respectively [27,28]. As a result of the relatively low natural abundance of the isotope, experiments require considerably longer periods (hours) to acquire sufficient data to yield a presentable spectmm, whereas proton spectra can be obtained in a few minutes. A reasonable proton spectrum can be obtained with as little as 0.3 mg, whereas spectra generally require larger samples, typically more than 1 mg. 

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