Spooling Wire Microcombustion (SWiM)

Studies of biogeochemical processes are fundamentally limited by our analytical capabilities. Compounds and mixtures that are amenable to analysis fall within what is often called the “analytical window,” and the analogy with a clear pane of glass – set into a much larger opaque wall – is appropriate. As we look through the window we see what is happening inside our window, but outside our field of view we can only guess at what is going on.

We are therefore working to develop new techniques for measuring stable isotopes in compounds that are too involatile to analyze by gas chromatography. These include such biologically important molecules as RNA and proteins, as well as whole microbial cells and much of the complex sedimentary organic matter present in most rocks. Our general approach is to use spooling wire microcombustion (SWiM, formerly known as the "moving-wire interface") such as the one shown above that was originally developed by Finnigan-MAT. In essence, the liquid sample is dried onto a thin wire, which then carries the nonvolatile sample into the mass spectrometer. We have built a second-generation SWiM device here at Caltech, and are currenty working to apply this technology to the analysis of whole cells sorted from environmental samples by flow cytometry (FACS).