Elemental sulfur works well as a matrix for laser desorption time-of-flight
mass spectrometry of bacteriochlorophylls and carotenoids, the major pigme
nts in photosynthetic bacteria. Because sulfur lacks protons, pigment ioniz
ation probably involves electron, rather than proton, transfer. Fragmentati
on of chlorophylls that are esters of allylic alcohols occurs, but is parti
ally suppressed when sulfur is used as a matrix. Mass spectrometry on sulfu
r itself shows that the most abundant positive ion Is S-5(+), while the mos
t abundant negative ion is S-3(-), indicating that light absorption causes
photodissociation of S-8 rings into these products. A similar pattern was o
bserved with red selenium, which also occurs as 8-membered rings. Molecular
masses of other hydrophobic analytes, such as fullerene compounds, can als
o be determined using elemental sulfur as the matrix. Copyright (C) 1999 Jo
hn Wiley & Sons, Ltd.