Used as an internal standard in analytical chemistry for the quantification of 4-aminophenazone in various samples. It is particularly useful in mass spectrometry and nuclear magnetic resonance (NMR) studies due to its deuterium labeling, which provides a distinct signal for accurate measurement. Commonly applied in pharmaceutical research to monitor drug metabolism and pharmacokinetics. Also employed in environmental analysis to detect trace amounts of related compounds in water or soil samples. Its stable isotopic labeling ensures minimal interference, enhancing the precision of analytical results.