title: "Carryback": effect of viscous liquid controls on the preceding sample analyzed with the SMA II continuous-flow analyzer.
abstract: We systematically studied the "carryback" effect of ethylene glycol-based controls on the preceding sample on an SMA II continuous-flow analyzer. Including Beckman Level 1 unassayed liquid control material as a sample lowered the 12 analyte values of the preceding sample by an average of 2.7%, Level 2 (the most viscous) by an average of 4.4%, and Level 3 by 3.2%. Water-reconstituted lyophilized control material caused no carryback effect, but lyophilized control reconstituted with 330 mL/L ethylene glycol decreased the preceding sample's results by 4.1% (average carryback). We believe that carryback is caused by the drag placed on the sample line by a viscous sample, which decreases the volume of the preceding sample that is delivered to the reagent or pre-dilution mixing coils. Our findings were confirmed on another SMA II. Limited study of a SMAC analyzer gave inconclusive results, but further evaluation of continuous-flow systems for carryback is warranted. Carryback substantially increases total analytical variability.
mesh_terms: D001322:Autoanalysis / Q000295:instrumentation*; D001774:Blood Chemical Analysis / Q000295:instrumentation; D002624:Chemistry, Clinical / Q000295:instrumentation*; D019855:Ethylene Glycol; D005026:Ethylene Glycols; D005612:Freeze Drying; D006801:Humans; D013048:Specimen Handling; D014783:Viscosity; D014867:Water
chemical_list: D005026:Ethylene Glycols; D014867:Water; D019855:Ethylene Glycol