Abstract: Objective  Indoxyl sulfate (IS) is a typical uremic toxin accumulated in chronic kidney disease (CKD) patients, and higher IS level is closely associated with cardiovascular complications. Accurate evaluation of IS adsorption performance of hemoperfusion devices is essential for their clinical effectiveness. This study systematically compares the applicability of ultra-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) and ultraviolet-visible spectrophotometry (UV-Vis) in evaluating IS adsorption by hemoperfusion devices, and clarifies the impact of IS concentration on adsorption efficiency.  Method  LC-MS/MS: bovine plasma containing IS was treated with acetonitrile for protein precipitation. IS concentrations pre-/post-adsorption were quantified, establishing a linear model of 0.0850～1.3080μg/mL (Y=36045.242X + 763.841, R²=0.9987). UV-Vis: IS in bovine serum albumin solution was detected, demonstrating dual linear relationships of 3.75～120μg/mL (Y=77.337X - 0.5316, R²=0.9977; Y=93.014X - 0.4991, R²=0.9996). Both methods showed precision of RSD ＜5% and recovery rates of 86～110% (LC-MS/MS) and 91～110% (UV-Vis).  Result  LC-MS/MS has the advantages of high sensitivity (LOQ=0.0212μg/mL), strong anti-matrix interference, and suitability for batch plasma testing. UV-Vis is applicable for rapid screening of high-concentration IS (＞3.75μg/mL) but is significantly interfered by protein binding. For adsorption dynamics: at low IS concentrations (＜30μg/mL), insufficient molecular diffusion kinetics reduced efficiency; at high concentrations (＞100μg/mL), saturation of active sites decreased binding efficiency per molecule. Peak efficiency occurred at ～60μg/mL, balancing diffusion kinetics and site competition.  Conclusion LC-MS/MS serves as the core method for evaluating IS adsorption performance in hemoperfusion devices, providing a basis for quality standards. UV-Vis is limited to preliminary high-concentration screening during adsorbent development. This study offers critical technical support for optimizing clinical protocols and establishing industry standards.

Key words: Hemoperfusion device, Indoxyl sulfate, Adsorption performance, LC-MS/MS, UV-Vis spectrophotometry, Uremic toxin