Biosynthetic product molecular weight determinations by solution phase secondary ion mass spectrometry employing group 1a metal salts

Sulfolane was found to be an excellent solvent for solution phase SIMS mass measurements of natural products employing group 1A metal iodides for molecular ion complex enhancement. Lithium iodide generally afforded maximum molecular ion complex formation. Although this very important effect was found to decrease through the series sodium→potassium→rubidium→cesium iodides, it remained quite useful. The ⁸⁵Rb and ⁸⁷Rb isotopes (ratio of 72:28) proved especially effective for detection of molecular ions and recognizing other metalcomplex ions. A mixture of lithium and sodium iodides was also found helpful for the latter purpose. Application of, e.g., the sodium iodide-sulfolane technique for increasing the intensity of molecular ion complexes proved to be a very simple and reliable method for conducting natural product molecular weight determinations.