The invention relates to a method and apparatus for detecting elution of a sample from a sample substrate to incubation buffer contained in a sample well while the sample substrate is still within the well. The method comprises measuring light absorption of the contents of the sample well at a predefined wavelength or wavelength range, and determining, based on the absorption measurement, the degree of elution of the sample. According to the invention, a wavelength or wavelength range is used which is absorbed by at least one elutable component of the sample but transmitted by the sample substrate. The invention provides a reliable way of determining the degree of elution of blood samples in neonatal screening, for example.