Figure 3. A. SdFFF fractogram of the reference sample of 70 and 250-nm particles mixed in surfactant. Thesecondary x-axis depicts the theoretical particle size corresponding to the elution time for two particle densities.
B. SdFFF fractogram of 70 and 250 nm particles isolated from homogenized lung tissue. The inset graph is the
circled area enlarged, emphasizing the 70 nm particle peak.
Well established FFF theory [11] allows the particle size corresponding to
a given elution time to be calculated directly from first principles [19]. For Sd-
FFF the calculation is based on measurable physical parameters of the apparatus,
the carrier fluid, and the particle density, and involves the equations for settling
velocity, particle diffusion rate, and laminar flow profile. Figure 3A shows the
theoretical particle sizes (top x-axis labels) corresponding to the measured elution
time (bottom x-axis labels) for two different particle densities. These assumed
densities, 2.65 and 2.0 g/cm3, correspond to quartz and the density of the 70-
nm particles obtained from the vendor datasheet. These assumed densities span a reasonable range for various amorphous and crystalline forms of SiO2. As can be seen from the differences between the two sets of theoretical sizes, the particle size corresponding to a given elution time is not strongly dependent on the assumed density. Thus nanoparticles can be distinguished from micron-sized particles even when the particle composition and density are uncertain. For example, detection of a particle mode within the time range corresponding to SdFFF separation of nano-sized particles for a plausible range of densities would provide useful hypothesis-generating information in a toxicology study of environmental exposures. Particle recovery for the experiment in figure 3A and 3B can be estimated from the integrated area under the curve for the SdFFF analysis of the tissue sample and the reference sample [19]. Particle recovery in the enzyme digestion processing was 30% for the 250 nm particles and 22% for the 70 nm particles.
Figure 3. A. SdFFF fractogram of the reference sample of 70 and 250-nm particles mixed in surfactant. Thesecondary x-axis depicts the theoretical particle size corresponding to the elution time for two particle densities.B. SdFFF fractogram of 70 and 250 nm particles isolated from homogenized lung tissue. The inset graph is thecircled area enlarged, emphasizing the 70 nm particle peak.Well established FFF theory [11] allows the particle size corresponding toa given elution time to be calculated directly from first principles [19]. For Sd-FFF the calculation is based on measurable physical parameters of the apparatus,the carrier fluid, and the particle density, and involves the equations for settlingvelocity, particle diffusion rate, and laminar flow profile. Figure 3A shows thetheoretical particle sizes (top x-axis labels) corresponding to the measured elutiontime (bottom x-axis labels) for two different particle densities. These assumeddensities, 2.65 and 2.0 g/cm3, correspond to quartz and the density of the 70-nm particles obtained from the vendor datasheet. These assumed densities span a reasonable range for various amorphous and crystalline forms of SiO2. As can be seen from the differences between the two sets of theoretical sizes, the particle size corresponding to a given elution time is not strongly dependent on the assumed density. Thus nanoparticles can be distinguished from micron-sized particles even when the particle composition and density are uncertain. For example, detection of a particle mode within the time range corresponding to SdFFF separation of nano-sized particles for a plausible range of densities would provide useful hypothesis-generating information in a toxicology study of environmental exposures. Particle recovery for the experiment in figure 3A and 3B can be estimated from the integrated area under the curve for the SdFFF analysis of the tissue sample and the reference sample [19]. Particle recovery in the enzyme digestion processing was 30% for the 250 nm particles and 22% for the 70 nm particles.
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