A system for analyzing a sample includes a chromatographic device, an electrospray source, and a mass resolving device. The chromatographic device is configured to separate components of the sample as a function of retention time within a chromatographic column. The electrospray source is configured to direct a first portion of a flow from the chromatographic device via a waste outlet to a pressurized waste reservoir, direct a second portion of the flow to an electrospray ionization outlet to form a spray, and charge and desolvate the spray to form ions of the components of the sample. A flow rate of the second portion of the liquid flow is substantially determined by a pressure of the pressurized waste reservoir. The mass resolving device configured to receive the ions and characterize the mass-to-charge ratio of the ions.