@article {MONTGOMERY391, author = {MARK A. MONTGOMERY and JORDAN L. HOLTZMAN}, title = {DETERMINATION OF SERUM MORPHINE BY THE SPIN-LABEL ANTIBODY TECHNIQUE}, volume = {2}, number = {4}, pages = {391--395}, year = {1974}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The spin-label antibody technique has been adapted to the determination of serum morphine concentrations. Our results indicate that with a 0.30-ml solution cell, the ultimate sensitivity of the assay is 35 nM (10 ng of morphine per ml) which is very close to the instrumental detection limit for spin-labeled morphine of 20 nM (5.7 ng/ml). Comparison of t{\textonehalf}{\textquoteright}S for disappearance of [N-methyl/-14C]morphine in a rabbit yielded 1.9 hr by 14C counting and 1.6 hr by the spin-label technique. Serum binding of morphine can be easily and rapidly determined utilizing the spin-labeled drug; the percentage of free (unbound) morphine in human serum was found to be 69.5{\textpm} 0.9\% by the spin-label technique and 64.6 {\textpm} 1.4\% by ultrafiltration. Our results would suggest that this method holds promise for the assay of serum concentrations and binding not only of morphine but of other drugs as well. Copyright {\textcopyright} 1974 by The American Society for Pharmacology and Experimental Therapeutics}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/2/4/391}, eprint = {https://dmd.aspetjournals.org/content/2/4/391.full.pdf}, journal = {Drug Metabolism and Disposition} }