O-(2,3,4,5,6-Pentafluorobenzyl)formaldoxime is the pentafluorobenzyl oxime derivative of formaldehyde, commonly used as an internal standard or reference compound in analytical chemistry, particularly for gas chromatography-mass spectrometry (GC-MS) and electron capture detection (ECD). It aids in the accurate quantification of carbonyl compounds, such as aldehydes (e.g., formaldehyde, acetaldehyde) and ketones, by providing a stable, volatile derivative with strong electron-capturing properties due to the pentafluorobenzyl group. This is essential for trace-level analysis in environmental monitoring (e.g., air and water pollutants) and biological samples, enhancing method sensitivity, reproducibility, and detection limits for low-molecular-weight carbonyls.