Interference of metamizol (dipyrone) on the determination of creatinine with the Kodak dry chemistry slide comparison with the enzymatic method from Boehringer.

In order to eliminate positive interferences that take place with the Jaffé technique, the Kodak Ektachem and Boehringer Mannheim Companies have chosen an enzymatic method for the determination of creatinine in serum and urine. Pathological and clinical samples often contain metabolites in elevated concentrations or exogenous compounds such as drugs or toxic compounds. We noticed that patients receiving metamizol-containing drugs showed unusually low values of creatinine when determined with an Ektachem analyser. We investigated the effect of the main metabolites of this prodrug on the creatinine enzymatic methods of Kodak and Boehringer. We concluded that methyl-amino-antipyrine, the active substance after administration of metamizol (prop. INN) was responsible for the interference, and that no reliable determination of creatinine could be performed with these methods in the serum of patients receiving this drug.

Enrichment of complexing analytes on a copper-loaded silica surface and on-line coupling with high-performance liquid chromatography, using L-tryptophan and L-tyrosine as model compounds.

A chemically modified silica (bisdithiocarbamate) strongly binds copper and has a loading capacity of 0.5 mmol g-1 for the copper ion. This new metal-loaded silica, packed in a short stainless-steel pre-column, is highly selective for the enrichment of two amino acids chosen as model compounds. On-line coupling of this pre-column with an analytical RP-18 column allowed the separation and detection of L-tryptophan and L-tyrosine at parts per billion levels in aqueous media with good accuracy. Separation was achieved by ion-pair chromatography and the solutes were detected by fluorescence. The ions generally present in natural aqueous media did not interfere.