title: Rapid measurement of leucine-specific activity in biological fluids by ion-exchange chromatography and post-column ninhydrin detection.
abstract: Commonly used methods for the measurement of leucine-specific activity use either high-performance liquid chromatography (HPLC) and pre-column derivatization or conventional ion-exchange chromatography. These are time-consuming, labor-intensive, relatively costly procedures, requiring high concentrations of radioactivity for accuracy. The present paper describes a method for the measurement of plasma leucine-specific activity using HPLC equipment, a large-bore ion-exchange column and post-column ninhydrin detection. With this method, determination of leucine concentration and leucine radioactivity was found to be linear (r2 greater than 0.999) over physiological ranges for both standards and deproteinized plasma. The intra- and inter-assay coefficients of variation for leucine concentrations were 1.4 and 2.7%, respectively. The intra- and inter-assay coefficients of variation for leucine-specific activities were 1.5 and 1.9%, respectively. The automated method is relatively fast (injection to injection time approximately 45 min), economical and capable of accurately assessing relatively small amounts of radioactivity.
authors.affiliation: Department of Surgery, Vanderbilt University Medical Center, Nashville, TN 37232.
authors.forename: E P
authors.initials: EP
authors.lastname: Donahue
authors.forename: L L
authors.initials: LL
authors.lastname: Brown
authors.forename: P J
authors.initials: PJ
authors.lastname: Flakoll
authors.forename: N N
authors.initials: NN
authors.lastname: Abumrad
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods; D002852:Chromatography, Ion Exchange / Q000379:methods*; D006801:Humans; D007930:Leucine / Q000097:blood*; D009555:Ninhydrin / Q000032:analysis*
chemical_list: D007930:Leucine; D009555:Ninhydrin