In LC-MS assays, a mechanical region in the flow path is often the source of carryover. Most commonly, carryover occurs in the autosampler needle or chromatographic column used for the assay. Lab technicians can inject blanks during LC-MS analysis to gradually dilute the hold-up of partial samples, resulting in less carryover with each pass. Similarly, we can apply an organic solvent as a needle wash solution when analyzing hydrophobic samples to minimize carryover by solubilizing and washing away the adsorbed sample components. Here, the analyst must handle the needle wash solution in the same way as the mobile selection during the method development of LC-MS assay. Advanced instrument models allow for more solvents, higher flow rates, and other advanced washing mechanisms to help reduce autosampler-based carryover. We can minimize chromatographic carryover by sample dilution, smaller injection volumes, or changes in the stationary and mobile phases of the assay.