Restricted spectral accuracy analysis to identify the single correct organic compound elemental-composition from Orbitrap accurate mass data lists obtained at very high resolution.

Restricted spectral accuracy is applied to Orbitrap data (240 000 resolution at m/z 400) to more clearly break out the scoring and ranking of allowable elemental compositions (ECs) in a candidate list. The correct EC is usually top ranked and separated from other answers by 10 to 40% within the dimensionless 0 to 100% scale, providing a single, definitive EC. The A + 2 position (where A denotes the monoisotopic line position) is especially advantageous in restricted spectral accuracy. It has enough intensity and more complexity than (A + 1) fine lines and is like a fingerprint. Avoidance of coalescence phenomena and careful ion population control are essential.