Human serum albumin (HSA) is the most abundant protein in the human plasma. HSA has several physiological roles in the human body, including storage and transport. Owing to the predominance of albumin in plasma, HSA is often involved in the protein binding of drugs. The aim of this work was to develop a selective, quantitative method for determining albumin in plasma with the purpose of clarifying the fate of metal-based drugs in biological systems. The method can also be applied for determination of urine albumin, which is of relevance in diagnostics of kidney disease. A selective method for quantification of HSA based on labelling the protein with iophenoxic acid (IPA) was developed. Samples were subjected to size exclusion chromatography (SEC) and detection by inductively coupled plasma mass spectrometry (ICP-MS) monitoring iodine and platinum. The iodine signal for the HSA-IPA complex showed linearity in the range 1 to 250 mg L⁻¹. The precision was 3.7 % and the accuracy 100.7 % determined by analysis of a certified HSA reference material. The limit of detection (LOD) and limit of quantification (LOQ) were 0.23 and 9.79 mg L⁻¹, respectively. The method was applied for analysis of HSA in human plasma and urine samples and for studying the binding of cisplatin to proteins in the human plasma.