Fig. 3 shows the typical data obtained from commercial antisunlight oil products. In the blank spectrum (Fig. 3a), there are
several peaks detected with abundant signal intensities (∼102, cps),
but no much signal appears at m/z 138. The outstanding signals were also detected from the anti-sunlight oil sample while the analytes such as 4-aminobenzoic acid was spiked, indicating that these
compounds were ingredients of the sample and the addition of the
analyte caused no alteration of the matrix of the sample; however, the identification of these signals remains further studies. InFig. 3b,
the GIND-EESI-MS spectrum of a skin care cream sample spiked
with 4-aminobenzoic acid (100 ppb) was shown. Among several
predominant signals, 4-aminobenzoic acid (MW 137) was clearly
seen as the protonated molecule atm/z138. The precursor ions (m/z 138) fragmented into ionic species of m/z 120 or 94 by the loss of
H2O or CO2, respectively. A tiny peak atm/z121 was also detectable
in the MS/MS spectrum (inset of Fig. 3b) due to the loss of NH3; the
low abundance of this peak indicated this fragmentation pathway