a) The negative-ion FAB spectrum of triethanolamine (TEA) matrix is shown below. Assign general formulas to those peaks with a mass label.
The TEA matrix has a molecular weight of 149 u, and thus, the peaks are due to the formation of [Man-H]– cluster ions.
b) Provided sufficient intensity, what purpose can matrix peaks serve?
They can serve for mass calibration. In particular in the lower mass range, matrix peaks are useful for internal mass calibration for accurate mass measurements.
c) The above FAB spectrum shows a high noise level which is particularly obvious in the region where the intensity has been 10-fold expanded. Where does the noise come from?
The noise is chemical in nature, not electronic. Radiolytic decomposition of the matrix generates an large diversity of radicals and ions which may deliberately recombine to form almost any cluster ion composition one can think of.