Background: There is a need of prolonged stability of certain chemical analytes in lithium heparin tubes with separators. A new tube with a mechanical separator has recently been launched (Barricor (TM)), which according to the manufacturer may have these benefits. The aim of this study was to evaluate stability performance of this tube in comparison with plasma gel tubes under clinically realistic circumstances. Methods: Blood was collected in tubes containing lithium heparin with different separators; gel separator (Vacutainer (R) PST (TM), Becton Dickinson and Vacuette (R), Greiner bio-one) and mechanical separator (Vacutainer (R) Barricor (TM), Becton Dickinson). All tubes had an aspiration volume of 3 mL and were centrifuged at similar time and force. Tubes were transported manually or by car. Seven analytes from 122 patients were analyzed after 3 to 80 hours by Cobas c701 (Roche). Results The Barricor (TM) tube showed increased stability of phosphate and potassium and similar stability of aspartate aminotransferase, glucose, homocysteine, lactate dehydrogenase, and magnesium compared with gel tubes. Maximal allowable bias for phosphate was exceeded after 68 hours for Barricor (TM) tubes compared with 29 or 35 hours for gel tubes and for potassium after 40 hours for Barricor (TM) tubes vs 9 or 12 hours for gel tubes. Transportation did not affect stability. Hemolysis index was slightly lower in Barricor tubes than in gel tubes (P = .01). Conclusion Implementing the new Barricor (TM) tube will improve stability of potassium and phosphate in plasma. Blood sampling facilities far from the laboratory may benefit from using these tubes, thus diminishing preanalytical errors.