The appropriate composition of the anticoagulant in tubes for coagulation testing is crucial, as it directly affects result interpretation and subsequent clinical decision-making. In this master's thesis, I therefore evaluated the ionic balance of the anticoagulant solution in blood collection tubes intended for coagulation assays. For this purpose, I applied ion chromatography and pH measurements. Using ion exchange chromatography, I determined the concentration of citrate – the anticoagulant that prevents blood clotting – and identified several previously unexplained peaks in the chromatograms of the samples. In tubes from three manufacturers, I detected at least some of the following ions: sodium, potassium, magnesium and calcium cations as well as chloride, nitrate, nitrite, sulfate, bromide, oxalate, acetate and formate anions. Apart from sodium, their concentrations were very low, and their contribution to the overall ionic balance negligible. Based on the lower pH compared with a pure trisodium citrate solution, the molar ratio of sodium to citrate – which was lower than the theoretically expected value of three – and the calculated ionic balance, it can be concluded that all analyzed tubes contain citrate buffer rather than only trisodium citrate. For one manufacturer, this is not indicated in the product declaration. Comparison with theoretical values also shows that the concentration of the anticoagulant in all tested tubes is slightly higher than the nominal value of 0.109 mol/L, which was expected.
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