Interference of Iodinated Contrast Media in Serum Capillary Zone Electrophoresis To the Editor:

Automated capillary zone electro-phoresis (e.g., on the Paragon 2000 CZE, Beckman Instruments) is an al-ternative to conventional electro-phoretic methods for the separation of serum proteins (1–3). The tech-nique uses ultraviolet (UV) detection at 214 nm for direct quantification of peptide bonds, whereas conven-tional methods detect the protein fractions by staining with various reagents. CZE has the advantage of im-proved precision and a faster turn-around (4). Recent reports indicate, however, that the Paragon CZE 2000 masks deficiencies of a1-antitrypsin (5) and that some radio-opaque agents simulate a monoclonal com-ponent in the a2-globulin fraction in the CZE electropherogram (6, 7). We encountered an interference from the contrast medium Omni-trast®, which produced an unex-pected peak in the a2-zone of the CZE electropherogram. We have now investigated the effect of 12 io-dinated radio-opaque media (com-mercially available in Spain) on in-strumentation (Paragon CZE 2000) operated as described by Bossuyt et al. (6). When we used the desalting method described by Blessum et al. (7) to remove the observed interfer-ences (see below), we found undesir-able obstruction in Paragon system capillaries. Therefore, we investi-gated alternative desalting proce-dures. The studied contrast media wer