Particle characterisation
Disclosed herein is a method of characterizing particles in a sample. The method comprises illuminating the sample in a sample cell with a light beam, so as to produce scattered light by the interaction of the light beam with the sample; obtaining a time series of measurements of the scattered light from a single detector; determining, from the time series of measurements from the single detector, which measurements were taken at times when a large particle was contributing to the scattered light; determining a particle size distribution, including correcting for light scattered by the large particle.
1. A method of characterising particles in a sample, comprising:
illuminating the sample in a sample cell with a light beam, so as to produce scattered light by the interaction of the light beam with the sample;
obtaining a time series of measurements of the scattered light from a detector;
determining, from the time series of measurements from the detector, which measurements were taken at times when a large particle was contributing to the scattered light;
determining a particle characteristic from the time series of measurements, including correcting for light scattered by the large particle;
wherein correcting for light scattered by the large particle comprises determining a model of the background due to the large particle, and removing the model from the measurements.
2. The method of claim 1 , further comprising determining a photon count rate signal from the time series of measurements.
3. The method of claim 2 , wherein removing the model from the measurements comprises subtracting the model from the photon count rate to determine a corrected photon count rate, and determining a particle characteristic comprises determining a particle characteristic using the corrected photon count rate.
4. The method of claim 1 , wherein determining a model of the background due to the large particle comprises filtering the photon count rate.
5. The method of claim 4 , wherein filtering the photon count rate comprises low-pass filtering.
6. The method of claim 5 , wherein the low-pass filter comprises a cut-off frequency of less than 10 Hz or less than 1 Hz.
7. The method of claim 4 , wherein filtering photon count rate comprises determining a moving average of the photon count rate.
8. The method of claim 4 , wherein filtering the photon count rate comprises using a Savitzky-Golay filter.
9. The method of claim 4 , wherein filtering the photon count rate comprises using a digital IIR or FIR filter.
10. The method of claim 1 , wherein the particle characteristic is one of a particle size distribution, an electrophoretic mobility, a magnetophoretic mobility and a microrheological property.
11. An apparatus for characterising particles comprising: a light source, a sample cell, a detector and a processor; wherein
the light source is operable to illuminate a sample within the sample cell with a light beam so as to produce scattered light by interactions of the light beam with the sample;
the detector is configured to detect the scattered light and produce a time series of measurements;
the processor is configured to:
receive the time series of measurements, and
determine, from the time series of measurements, which measurements were taken at times when a large particle was contributing to the scattered light;
determine a particle characteristic from the time series of measurements, including correcting for light scattered by the large particle;
wherein correcting for light scattered by the large particle comprises determining a model of the light scattered by the large particle, and removing the model from the measurements.
12. The apparatus of claim 11 , wherein the processor is configured to determine a photon count rate signal from the time series of measurements.
13. The apparatus of claim 12 , wherein removing the model from the measurements comprises subtracting the model from the photon count rate to determine a corrected photon count rate, and determining a particle characteristic comprises determining a particle characteristic using the corrected photon count rate.
14. The apparatus of claim 11 , wherein determining a model of the background due to the large particle comprises filtering the photon count rate.
15. The apparatus of claim 14 , wherein filtering the photon count rate comprises low-pass filtering.
16. The apparatus of claim 15 , wherein the low-pass filter comprises a cut-off frequency of less than 10 Hz or less than 1 Hz.
17. The apparatus of claim 14 , wherein filtering the photon count rate comprises determining a moving average of the photon count rate.
18. The apparatus of claim 14 , wherein filtering the photon count rate comprises using a Savitzky-Golay filter.
19. The apparatus of claim 14 , wherein filtering the photon count rate comprises using a digital IIR or FIR filter.
20. The apparatus of claim 11 , wherein the particle characteristic is one of a particle size distribution, an electrophoretic mobility, a magnetophoretic mobility and a microrehological property.