Figure 3B shows the enzyme-digested rat lung tissue containing 70- and
250-nm manufactured SiO2 particles at the same concentration as in the reference
sample (2:1 ratio). The inset graph is a magnified version of the circled area
showing that we were clearly able to detect 2 particle sizes from a tissue sample. particles. The difference in the relative sizes of the 70- and 250-nm peaks in the
reference samples is due to the size-dependent sensitivity of the light scattering
detector. Rayleigh scattering theory predicts that scattering intensity from a single
particle varies with the dp6 where dp is particle geometric diameter. However,
the number of particles for a given mass increases inversely with the dp3, and the
mass ratio of the 70 to 250 nm particles was 2:1. Thus the expected ratio of peak
areas would be about 23:1. A similar experiment using a mixture of 80-nm and
500-nm particles in enzyme-digested rat lung tissue also produced the expected
bimodal fractogram (data not shown). The geometrical size of the 70-nm particles
was confirmed by transmission electron microscopy (TEM) of a sample collected
after the SdFFF separation [19].