Detection of rhEPO is conducted using a mass spectrometer. The mass-to-charge ratio (m/z) is roughly the same as the protein mass in Dalton. We use a urine sample for substance detection. In most cases, it is better to use a urine sample instead of blood to test for prohibited substances. This is because urine collection is non-invasive and yields a large sample volume with a higher drug concentrations than blood. Also, urine has fewer cells and proteins that would complicate extraction.
Figure 1: Diagram of glycan that comprises of monosaccharide building block
To detect prohibited substances in urine, we have to first make a standard spectrum of uncontaminated urine (negative standard), as well as of the prohibited substance (positive standard). Once we have these two standards, we can compare them with a sample spectrum. If the sample spectrum exhibits the same peaks that the positive standard has, we can conclude that the sample contains the prohibited substance. Mass spectrometry can also detect glycosylation, as the data from the mass spectrometer is processed and displayed in peaks. Usually, glycosylation peaks are marked with an asterix or a diagram of glycan.