Quaternary ammonium and tertiary sulfonium compounds can be measured directly by plasma desorption mass spectrometry (PD-MS). Betaines are typically detected as their protonated molecular ions (M+H⁺): glycine betaine = m/z 118; d9-glycine betaine = m/z 127; trigonelline = m/z 138. However, the compounds can also form adducts with sodium ions (M+Na⁺): glycine betaine = m/z 140; d9-glycine betaine = m/z 149; trigonelline = m/z 160. The following figures show typical PD-MS mass spectra of betaine fractions of leaf tissue from non-salinized and salinized plants of glycine betaine-deficient (bet1/bet1) and glycine betaine-containing (Bet1/Bet1) near-isogenic maize lines. All samples contain d9-glycine betaine as internal standard. Note the absence of glycine betaine (but presence of trigonelline) in the bet1/bet1 line, and the salinity stress-induced accumulation of glycine betaine in the Bet1/Bet1 line.

Choline [extracted from the dried base fraction with acetonitrile : methanol [20:1 v/v]) is detected as the molecular ion (M⁺) in PD-MS; choline = m/z 104, d9-choline = m/z113:

Bonham CC, Wood KV, Yang W-J, Nadolska-Orczyk A, Samaras Y, Gage DA, Poupart J, Burnet M, Hanson AD, Rhodes D 1995 Identification of quaternary ammonium compounds by plasma desorption mass spectrometry. Journal of Mass Spectrometry 30: 1187-1194.

Yang W-J, Nadolska-Orczyk A, Wood KV, Hahn DT, Rich PJ, Wood AJ, Saneoka H, Premachandra GS, Bonham CC, Rhodes JC, Joly RJ, Samaras Y, Goldsbrough PB, Rhodes D 1995 Near-isogenic lines of maize differing for glycinebetaine. Plant Physiol. 107: 621-630.