US 6,774,994 B1Granted

Method and apparatus for determining absolute number densities of particles in suspension

AssigneeWyatt Technology Corporation

InventorsPhilip J. Wyatt, Miles J. Weida

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Abstract

A method for determining absolute number densities of particles in a solution is disclosed based on a light scattering method. A light scattering photometer is calibrated to produce the Rayleigh ratio at each angle measured with respect to light scattered per unit incident intensity, per unit volume illuminated within the field of view of each detector per steradian subtended by said detector. In order that the numbers calculated be accurate, the illuminated particles should be effectively monodisperse. From the excess Rayleigh ratios measured at a plurality of angles with respect to the incident light beam illuminating said sample particles, an effective size is calculated which, in turn, is used to calculate the differential scattered intensity at each angle. The number of particles per unit volume element is then determined from the measured excess Rayleigh ratio divided by the corresponding differential scattered intensity.

Claims29

Dependent claims

A method for determining the number density of monodisperse particles in solution comprising the steps of

A) Normalizing and calibrating a light scattering photometer, incorporating a fine beam of monochromatic light operating at a wavelength λ0, to produce measurements at a plurality of scattering angles θi, of the corresponding Rayleigh ratios Rs (θi) of the light scattered into the corresponding direction θi from a contributing illuminated volume;
B) Introducing a particle-containing solution into said normalized and calibrated photometer;
C) Measuring the Rayleigh ratios Rs (θi) of said particle-containing solution;
D) Subtracting from said measured Rayleigh ratios, Rs (θi), the corresponding Rayleigh ratios Rf (θi) of the suspending fluid at the same scattering angles θi to derive the excess Rayleigh ratios R(θi)=Rs (θi)−Rf (θi)at each said scattering angle θi;
E) Selecting a model to describe the scattering particles;
F) Deriving the effective size of said monodisperse particles in said particle-containing solution from said measured excess Rayleigh ratios at said plurality of scattering angles based on said particle model selected;
G) Calculating the differential scattered intensity i(θi)of a single particle at each of said scattering angles from said derived effective size of said suspended monodisperse particles, the model selected of the individual scattering particles, and the refractive index of each said particle;
and
H) Calculating the number density N of said monodisperse particles in said contributing illuminated volume by multiplying a selected excess Rayleigh ratio at one measured angle θi by k2=(2 πn0/λ0)2 and dividing said product by said calculated differential scattered intensity corresponding to said same angle to yield N=R(θi)k2/i(θi), where n0 is the refractive index of the solution and λ0 is the vacuum wavelength of the incident light.

6 more elements

A method for determining the differential number fraction distribution for a suspension of polydisperse particles comprising the steps of

A) Injecting an aliquot of said particle suspension into a separation means, said means separating said particles based on their size;
B) Measuring the Rayleigh ratio Rf (θi) at a set of scattering angles θi of the fluid suspending said particles;
C) Measuring the Rayleigh ratio Rs (θi) at a set of scattering angles θi of each eluting fraction of such separated particles by passing them through an absolute light scattering photometer means, each said eluting fraction corresponding to a monodisperse size fraction of said original suspension of particles;
D) Determining the excess Rayleigh ratios R(θi)=Rs (θi)−Rf (θi) at each said scattering angle θi, for each said eluting fraction;
E) Selecting a model to describe the scattering particles of each said eluting fraction;
F) Deriving the effective size of said eluting monodisperse particles in said eluting fraction from said measured excess Rayleigh ratios at said plurality of scattering angles using said particle model selected;
G) Calculating the differential scattered intensity i(θi) of a single particle at each selected scattering angle θi from said derived effective size of said suspended monodisperse particles, the model selected of the individual scattering particles, and the refractive index of each said particle;
and
H) Calculating the number density N of said monodisperse particles in said contributing illuminated volume by multiplying said selected excess Rayleigh ratio at said selected angle θi by k2 =(2 πn0/λ0)2 and dividing said product by said calculated differential scattered intensity i(θi) corresponding to said same angle to yield N=R(θi)k2/i(θ);
I) Multiplying said number density of particles in each said eluting volume by the corresponding volume of each said eluting volume to obtain number of particles in said eluting volume;
and
J) Summing the total number of particles so-determined in a range of eluting fractions to obtain the total number of particles injected into said separation means;
and
K) Dividing said number of particles of said eluting by said total number of particles injected to obtain the differential number fraction for said eluting fraction.

11 more elements

Dependencies are inferred from the claim text.