Chemistry
Isotopic Dilution in Quantitative Mass Spectrometry
Quick fact
Isotopic dilution can achieve accuracy of better than 1% even when 80% of the sample is lost during preparation, because the internal standard is lost at the same rate as the analyte, so the ratio remains constant.
Why this is interesting
You're measuring a trace amount of a drug in blood. Every step—extraction, evaporation, injection—loses some of your sample. How can you get an accurate number if the method itself is sloppy?