Samples can be found in solid, liquid, or gaseous form. While one might argue that solids are the most ubiquitous type of sample analyzed, it would be difficult to defend the convenience of handling liquids. Indeed, most of our analytical instrumentation, from the electro-chemical through chromatographic to the spectroscopic, requires samples in liquid form. After a decade of effort in our laboratory developing solid-sample introduction methods for inductively coupled plasma emission and mass spectrometry, we have come to appreciate the convenience of liquid samples. As we approached parts per billion detection limits in solid samples using electro-thermal vaporization, we encountered inhomogeneity problems in our solid samples and standards. When tackling difficult "real" solid-sample types, we were forced to use methodologies such as standard additions and internal standardization, which are exceedingly cumbersome with solid samples. Indeed, it was our experience with solid-sample analyses that led us to search for better ways to convert solid samples into a liquid format.
Guy Légère and Eric D. Salin, "Capsule-Based Microwave Digestion," Appl. Spectrosc. 49, 14A-22A (1995)