II-8
Matec Applied Sciences
56 Hudson St., Northborough, MA 01532 Ph: (508) 393-0155 Fax: (508) 393-5476
www.matec.com
e-mail: [email protected]
where D.O. is the detector signal for a particle of size i, Rext is the extinction cross section, and N is the
number of particles of size i. The computation of the extinction cross section by use of the Mie theory of
light scattering is currently being incorporated into the CHDF 2000 software. (D.O.) is multiplied by a
fractogram deconvolution parameter if the operator chooses to have the sample fractogram deconvoluted
into its primary components (See Software User’s Guide).
2.6 DATA ANALYSIS
The CHDF 2000 determines the concentration of particles exiting the fractionation cartridge as a function
of transit time from injection. This data is compared to a calibration curve generated by measuring the
transit times of monodisperse polystyrene latex size standards. The raw data can be mathematically
deconvoluted into component peaks. From the deconvolution and the absolute calibration using the
known size standards, the particle size and size distribution are automatically determined. The user may
also choose to not have the data deconvolved.
The CHDF 2000 Operating Software automatically calculates and displays the weight average, area
average, volume average, and number average particle size. In addition, the area, weight and number
relative and cumulative particle size distributions along with the standard deviation, half height width, and
the 25% and 75% percentiles are available on hard copy in either tabular or graphical form. The raw data,
which is the absolute detector output, is available as well.
It should be noted that both the theoretical foundation for CHDF and the calibration curve are for spherical
particles. If your particles are rod shaped or platelets, then the size measured by CHDF will be an
approximate spherical diameter. Distributions in size will still be absolutely determined, but no specific
information will be given on the aspect ratio of the particles.
2.7 SAMPLE PREPARATION
The CHDF 2000 requires 1 milliliter of sample at 0.1-5 volume %. The sample must be aqueous based.
The sample can be prepared in either of two ways; dilution of a concentrate or the addition of the disperse
phase to the eluant. It is recommended that the GR-500 be used for dilutions or making dispersions. The
concentration of the disperse phase should be high enough to obtain good resolution and a favorable signal
to noise ratio. This is particularly important when trying to identify very small sub-populations. On the
other hand, it should be kept low enough to avoid particle aggregation or injection valve clogging
problems. Do not run samples above 5 volume % or this may clog the injection valve or damage the
fractionation cartridge.
The CHDF 2000 can determine the complete particle size distribution over the entire specified size range.
Polydisperse samples do not need special pretreatment. The standard size range is 15 nm to 1100 nm
particle diameter. Other size ranges will be available in the future.
The actual state of dispersion and the stability of the sample are important considerations for any particle
characterization technique. The CHDF 2000 measures the effective hydrodynamic particle size. An
aggregate will behave as a larger particle and will not be resolved into the smaller primary particle size.
For some samples this may cause discrepancies between CHDF and transmission electron microscopy
(TEM).
The standard CHDF 2000 GR-500 eluant is designed for anionic dispersions. When diluting a
concentrate, use the GR-500 fluid as the dilutant. This will help ensure a stable, well dispersed system.
Most systems will be anionic when dispersed in GR-500. For specific systems, this can be checked using
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