Elemental formula

Abstract: Formula assignment is one of the key challenges in evaluation of dissolved organic matter analyses using ultrahigh resolution mass spectrometry (FTICR MS). The number of possible solutions for elemental formulas grows exponentially with increasing nominal mass, especially when non-oxygen heteroatoms like N, S or P are considered. Until now, no definitive solution for finding the correct elemental formula has been given. For that reason an approach from the viewpoint of chemical feasibility was elucidated. To illustrate the new chemical formula assignment principle, a literature data set was used and evaluated by simplified chemical constraints. Only formulas containing a maximum of one sulphur and five nitrogen atoms were selected for further data processing. The resulting data table was then divided into mass peaks with unique component solutions (singlets, representing unequivocal formula assignments) and those with two or more solutions (multiple formula assignments, representing equivocal formula assignments). Based on a [double bond equivalent (DBE) versus the number of oxygen atoms (o)] frequency contour plot and a frequency versus [DBE minus o] diagram, a new assessment and decision strategy was developed to differentiate multiple formula assignments into chemically reliable and less reliable molecular formulas. Using this approach a considerable number of reliable components were identified within the equivocal part of the data set. As a control, a considerable proportion of the assigned formulas deemed to be reliable correspond to those which would have been obtained by CH 2 -based Kendrick mass defect analysis. We conclude that formula assignment in complex mixtures can be improved by group-wise decisions based on the frequency and the [DBE minus o] values of multiple formula assignments.

Abstract: The application of accurate mass measurement for the determination of elemental formula has its origin in the 1950s and for many years was only carried out using magnetic sector mass spectrometers. The availability of such measurements was limited due to the cost and complexity of the instrumentation and the need for considerable expertise to acquire and interpret the spectra. In recent years the incredible pace of instrumental development has changed this, particularly with the renaissance of time of flight mass spectrometry. This has resulted in instrumentation capable of making accurate mass measurements in a robust fashion becoming available to most practitioners of (mass spectrometry) MS, without some of the earlier technical challenges and at lower cost. In this review the variety of accurate mass measurement instrumentation and techniques and their relative capabilities are discussed, along with a range of applications requiring the determination of elemental formula.

Abstract: "Uses of Elemental Diets in Clinical Situations" presents contributions from the world's foremost experts on the uses of elemental predigested formula diets in the prevention and management of intestinal disorders. Experimental reviews dealing with pancreatic enzymes, intestinal bacterial translocation, and immunity provide background information for understanding the mode of action of elemental diets. Practical information concerning various compositions, methods of administration, osmolarity, physiology of nutrients absorbtion, and possible problems related to the use of elemental diets is provided, and the subject of enteral vs parenteral nutrition is discussed. Clinical studies cover a wide spectrum of intestinal conditions: radiation-induced and chemotherapy-induced enteropathies, Crohn's disease in children and adults, intractable diarrohea in infants, food allergy in chilodren, immediate postoperative feeding short-gut and AIDS-related enteropathy. The scientific value of the book is further enhanced by clinical studies in which an elemental formula diet is compared to a control non-hydrolized formula diet.