Authors: Zhe Tang Kerstin Graefe Clark March H Thomas Karnes
Publish Date: 2003/12/22
Volume: 144, Issue: 1-3, Pages: 1-7
Abstract
Immunoassay IA is a sensitive and selective approach for low level quantitation of drugs Magnetic separation immunoassays use magnetic beads to facilitate the separation of bound labeled antigens from free antigens in solution Digoxin was chosen for this study because low level analysis ng mL−1 in biological samples isrequired antibodies to digoxin were commercially available and derivatization procedures for fluorescence labeling were well established A competitive immunoassay format was used in this study Streptavidin coated magnetic beads were attached to biotinylated antidigoxin antibodies for the separation The inhibition curve for offline magnetic separation immunoassay of digoxin in spiked plasma was characterized and the dynamic range of the curve was 025–25 ng mL−1 A power fit weighted by the inverse of concentration was found to provide the best fit to the data r=09934 The percent RSDs for the two controls 08 and 22 ng mL−1 were 995 and 2062 n=6 and the percent errors were 1175 and 2263 n=6 respectively The limit of detection LOD in plasma is 014 ng mL−1 The dynamic range of the inhibition curve for online magnetic separation immunoassay of digoxin was 05–15 ng mL−1 of digoxin A quadratic fit was found to provide the best fit to the data r=09937 The percent RSDs for the two controls 40 and 12 ng mL−1 were 141 and 107 n=6 and the percent errors were 58 and 33 n=6 from the spiked value respectively The LOD was estimated to be 044 ng mL−1 determined as two times the standard deviation of the blank n=6 The online method has the advantages of being relatively easy to automate in the continuous flow mode and is adaptable for use in conjunction with HPLC separations
Keywords: