Table 2.

The triterpenoids observed in the DAPPI-MS studies of B. pendula bark fractions. The detected ion, main MS² product ions, suggested ion identity, and level of identification are presented

Detected ion	DAPPI-MS2 main product ions	Tentative identification	Referencea	Level of identificationb
442	424, 411, 427, 318, 189, 220, 203, 234	Betulin M+•	–	1
426	204, 411, 189, 218, 383, 408	Lupeol M+•	–	1
441	423, 411	Allobetulone [M + H]+	–	1
443	425	Allobetulin [M + H]+	–	1
424	409, 381, 189	[M-H2O]+ fragment of betulin M+•	–	2b
425	407, 217, 189, 191, 205, 203, 201, 177, 245	[M + H-H2O]+ fragment ion from betulin or allobetulin [M + H]+	[32–34] (for betulin)	3
454	190, 191, 439, 436, 410, 408, 248	Betulonic acid M+•	–	1
455	437, 409	Betulonic acid [M + H]+	[34]	1
456	438, 441, 248, 410, 234	Betulinic acid M+•	–	1
457	439, 411, 191	Betulinic acid [M + H]+	[32]	1

^aReference not found is marked with -

^bThe levels of identification as presented in ref. [36]. 1 = confirmed identification based on MS² spectra and GC-MS measurements of the standard compounds and the samples; 2b = probable structure, identification based on MS² spectra of the detected ions and standard compounds, ionization behavior of the compounds, and the experimental context; 3 = tentative structure, identification based on MS² spectra of the detected ions and standard compounds, ionization behavior of the compounds, and the experimental context, but one exact structure is uncertain