A Liquid Chromatography/Mass Spectrometry System Providing Continuous Monitoring with Nanogram Sensitivity

Abstract

Mass spectrometric monitoring of solutes eluted from a liquid chromatograph can be performed simply by directly introducing a small fraction (∼1%) of the liquid into the ion chamber of a chemical ionization mass spectrometer (CI-MS). The solvent acts as the ionizing reagent, so that solution flow rates can be orders of magnitude higher than analogous introduction into a normal (EI) MS. Fragmentation is not extensive in CI spectra, so that these show clear evidence of the molecular weights of the solutes. The LC/MS spectrum depends on both the solvent and the solute, but most of the ions due only to the solutes are usually above the solvent peaks. (M − H)⁺ is abundant with pentane or hexane as the solvent, (M + H)⁺ with tetrahydrofuran, acetonitrile, methanol, and water, and (M + H)⁺ and (M + CHCl₂)⁺ with chloroform. Sensitivities are high even in comparison to the UV detector, and are generally in the nanogram range. Applications including gradient elution, recycle operation, and on-line computer manipulation of the data will be described.