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In Beckman capillary zone electrophoresis (CZE), the separation of serum protein fractions occurs in a liquid medium in a narrow bore capillary (20-200 [micro]m) exposed to extremely high voltages. The velocity of electroendosmosis by positively charged buffer ions from the positive electrode at the inlet towards the negative electrode at the outlet exceeds the electrophoretic mobilities of the protein fractions, leading to a cathodal migration of molecules. These are detected and measured by monitoring absorbance at 214 nm. 1 Results are presented in traditional electrophoretic fractions-albumin, α1, α2, β, and [GAMMA] fractions-as percentages of total protein detected. A total protein value, which is measured by Biuret on Abbott Aeroset, is then used in the CZE system to calculate the concentrations of the fractions, including monoclonal bands (in g/litre). However, it had been noted that, in certain samples only, the concentration of albumin calculated by this means gave lower results than albumin measured on the Abbott Aeroset routine analyser by the bromocresol green (BCG) method. Because the BCG albumin result had previously been used in this laboratory as the basis for calculation of monoclonal band concentrations by agarose gel electrophoresis, the introduction of CZE resulted in significant discrepancies in concentrations of certain monoclonal bands compared with previous results. This study...