Glucuronic acid conjugates desorption

A number of authors have pointed out that spectra acquired using various desorption techniques have many features in common (11-14). Generally the ions detected are even electro ionj molecular ions formed by protonation or addition of NH-, Na, etc., and fragment ions formed by elimination of neutral molecules. It is not clear to what extent pyrolysis and solvolysis reactions augment the contributions of unimolecular gas phase decompositions to spectra obtained using the various desorption techniques. Glucuronic Acid Conjugate Desorption... 

In recent years, several techniques have been developed for mass spectrometry, whereby samples are ionized and analysed from a condensed phase, without prior volatilization. These desorption techniques have permitted the extension of mass spectrometric analyses to sulfate and glutathione conjugates, as well as to underivatized and labile glucuronic acid conjugates. Primary among these techniques are field desorption 6, plasma desorption (7), laser desorption (8), fast atom bombardment (or secondary ion mass spectrometry with a liquid sample matrix) ( ) and thermospray ionization ( O). The latter can also serve to couple high pressure liquid chromatography and mass spectrometry for analysis of involatile and thermally labile samples. 

Features common to the spectra of glucuronic acid conjugates analysed by FAB, laser and field desorption were summarized several years ago (15). These appear to hold as well as for plasma desorption and thermospray spectra more recently examined. The situation with thermospray is somewhat more complicated as will be discussed later. Generally speaking, positive ion spectra contain protonated, natri ted or analogous molecular ions species, and usually (M+H-176) ions formed by the elimination of neutral dehydroglucuronic acid. 

Figure 1. Laser desorption mass spectrum of the glucuronic acid conjugate of 1-naphthylacetic acid ( ). The spectrum is provided by Dr. Robert Cotter.

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