CHNO

CHNO is an acronym for the elements carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). In chemistry and related fields, CHNO describes the elemental composition of many organic substances and is commonly used when discussing empirical formulas, purity, and composition analysis. The term highlights the four elements that together make up a large portion of organic matter, biochemicals, polymers, pharmaceuticals, and soils.

Elemental analysis using CHNO involves determining the amounts of C, H, N, and O in a sample. Carbon, hydrogen, and nitrogen are typically measured directly through combustion and subsequent detection of CO2, H2O, and N2 or NOx. Oxygen content is often not measured directly; it is frequently calculated by difference from the sample’s total mass and the measured percentages of the other elements, or assessed by specialized methods when precise O quantification is required. Modern instruments may be CHN or CHNO analyzers, and some configurations can extend to measuring additional elements such as sulfur or chlorine.

Applications of CHNO analysis span organic synthesis, polymer science, pharmaceuticals, and environmental chemistry. It supports the verification of molecular formulas, assessment of sample purity, and calculation of empirical and molecular formulas when combined with molecular weight data. Understanding CHNO composition also informs interpretations of functional groups, oxidation states, and the overall stoichiometry of chemical reactions.

Limitations and considerations include potential measurement errors from moisture, inorganic contaminants, or sample incompatibilities. Oxygen quantification can be less straightforward than for C, H, and N, requiring careful method selection and calibration.

See also: CHN analysis, elemental analysis, empirical formula, molecular formula.