INTRODUCTION

This section does not discuss the special calorimeter designs such as reaction calorimeters (Mettler Toledo), designs for the measurement of partial molar heat capacities of biopolymers (CSC), or total absorption calorimeters (Opal), but only direct the reader to the web pages of their respective suppliers. Inferential calorimeters, which determine the heat content by calculation from composition and physical analysis, including chromatography (Section 8.12) and mass spectrometry particular atomic or molecular species by their mass-to-charge (m/e) ratios. For example, a diatomic nitrogen molecule with a mass of 28 might become a single charged ion, and it would have an m/e ratio of 28. If that diatomic molecule became a double charged ion, its m/e ratio would be 14. A mass spectrometer employs a vacuum environment in which ions are created, separated, and ultimately detected. This vacuum requirement allows collisions between the ions and molecules to be minimized. This is possible when the mean free path for the ions is very large. Typically, a vacuum in the order of 10 –4 to 10 –6 torr (mmHg) is required. Consequently, a mass spectrometer must include a sampling port into, as well as a vacuum pumping system that maintains the required vacuum envelope within, the spectrometer. In general, a very small gas sample is introduced from atmospheric pressure through the inlet port into the ion generator section of the spectrometer. Sample ions are produced by the collision of rapidly moving electrons with the gas molecules to be analyzed. The electrons ionize the sample by knocking out one or more electrons from an outer orbit of a neutral sample molecule.