I-6
Matec Applied Sciences
56 Hudson St., Northborough, MA 01532 Ph: (508) 393-0155 Fax: (508) 393-5476
www.matec.com
e-mail: [email protected]
24.
How long does a CHDF cartridge (capillary) last?
Fractionation capillaries do not have an exact life span. Cartridges may last several years since no particle
adsorption occurs inside the capillary. Capillary failures are frequently due to plugging right at the
capillary inlet. Cutting-off (“snipping”)a short piece at the capillary inlet frequently removes the plug.
The capillary can also be back-flushed as described in the hardware manual, troubleshooting section.
25.
How is the Weight Particle Size Distribution (PSD) calculated?
The particle weight percent is calculated as the Number percent multiplied by the particle diameter raised
to the third power: Wt
1
%= N
i
%(D
p
)
3
. This assumes that the particle density is the same for all
particles in the sample. The area percent is calculated as follows: A
i
% = N
i
%(D
p
)
2
26.
What particle Size Reproducibility should be expected from CHDF
About
±
5%.
27.
What is the mean, 25%, median, 75%, and FWHH in the text PSD report?
The 25%, median, and 75% are the 25th, 50th, and 75th percentiles of the particle size distribution (PSD).
They are calculated as the particle size evaluated at those values of the cumulative PSD. Physically,
for the 25% for example, they indicate that 25% of the particles are below the reported particle size.
The FWHH is the PSD Full Width at Half Height. It is the width of the differential PSD at 50%
height.
28.
What is the list of particle sizes at the bottom of the Text Report?
This list contains a description of all the particle size populations (also referred to as modes) automatically
detected by the software in the sample. Each mode is listed by the start and end particle size. The
percentages by Number, Area, and Weight are printed. The Area% is the average particle size of each
mode (Weight-Weighted). The mode detection sensitivity can be changed in the current method under
Optical Mode Detector. Lowering the value of Slope Sensitivity increases mode sensitivity.
29.
How can the Particle Size Distribution Report be Customized or Changed?
Open your current CHDF method, and select “Report Setup”. The text report, if used, should be
placed at the bottom of the report.
30.
What causes noticeable “tailing” in a fractogram?
The inlet to the fractionation capillary is likely dirty. Snip the fractionation (top) capillary (see
hardware manual section 6.6).
31.
How are odd-shape particles, e.g., discs, rods analyzed?
Particles spin in the capillary tube during CHDF fractionation. As a result, particles approach the
capillary wall at different orientations. Some positions result in an exclusion layer equal to the longest
particle dimension while other positions do the shortest or intermediate dimensions. The resulting
elution time is equivalent to an average of all the particle dimensions. Research done at Lehigh
University showed that particle doublets generated from partial latex coagulation produce a CHDF
particle size equal to one particle diameter multiplied by the square root of two, or 1.41*Dp (instead
of 1.5*Dp). Triplets appear to produce one diameter times the square root of 3.
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