An experimental approach to evaluate the capabilities and limitations of polyacrylamide gel electrophoresis (PAGE) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for quantitative elemental speciation is presented. Two metalloproteins (superoxide dismutase, containing Cu and Zn, and thyroglobulin, containing I) with high binding affinity for metals, and metal-dissolved organic matter (DOM) complexes (from a compost leachate sample) which show different types of metal binding are studied. Iodine can be quantitatively detected in thyroglobulin after PAGE-LA-ICP-MS using either sodium dodecyl sulfate (SDS) PAGE or native PAGE. However, detection of Cu and Zn in superoxide dismutase after PAGE-LA-ICP-MS depends on the conditions of the PAGE method because possible metal losses can occur (either with SDS-PAGE or with native PAGE). The use of PAGE-LA-ICP-MS to study the contribution of DOM to the mobilization of metals from environmental samples is possible, but it depends also on the PAGE separation conditions owing to disequilibrium effects of metal-DOM complexes.