Particle characterisation

1. A method of characterising particles in a sample, comprising:

obtaining a plurality of scattering measurements, each scattering measurement comprising a time series of measurements of scattered light from a detector, the scattered light produced by the interaction of an illuminating light beam with the sample;

identifying contaminated scattering measurements, in which a contaminant was contributing to the scattered light; and

determining a particle characteristic from scattering measurements that have not been identified as contaminated scattering measurements by:

determining an autocorrelation function for each scattering measurement that has not been identified as a contaminated scattering measurement;

combining the autocorrelation functions to produce an average autocorrelation function from which the particle characteristic is derived.

2. The method of claim 1 , wherein identifying contaminated scattering measurements comprises identifying scattering measurements within a predetermined time window from a time when the scattered light intensity exceeds a threshold.

3. The method of claim 2 , wherein the threshold is determined after a measurement.

4. The method of claim 3 , wherein the threshold is determined from the ensemble characteristics of the scattering measurements.

5. The method of claim 4 , wherein the threshold is derived from an average intensity taken across the scattering measurements.

6. The method of claim 2 , wherein the threshold is determined dynamically as the measurements are taken.

7. The method of claim 1 , wherein identifying contaminated scattering measurements comprises identifying scattering measurements within a predetermined time window from a time when fluctuations in the time series of measurements have a frequency below a cut-off frequency.

8. The method of claim 1 , wherein identifying contaminated scattering measurements comprises identifying scattering measurements within a predetermined time window from a time when the scattered light intensity exceeds a threshold and fluctuations in the time series of measurements have a frequency below a cut-off frequency.

9. The method of claim 1 , wherein identifying contaminated scattering measurements comprises; partitioning the scattering measurements, determining a comparative particle characteristic for each partitioned portion, and identifying partitioned portions where the comparative particle characteristic exceeds a threshold.

10. The method of claim 9 , wherein the comparative particle characteristic is particle size.

11. The method of claim 9 , wherein the comparative particle characteristic is polydispersity index.

12. The method of claim 11 , wherein the threshold is determined from a best fit normal distribution.

13. The method of claim 12 , wherein the threshold is three standard deviations from the average value determined from the best fit normal distribution.

14. The method of claim 9 , wherein the plurality of measurements is taken until a convergence criterion is met.

15. 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; and

the processor is configured to:

obtain a scattering measurement comprising a time series of measurements of the scattered light from the detector;

identify contaminated scattering measurements, in which a contaminant was contributing to the scattered light; and

determine a particle characteristic from scattering measurements that have not been identified as contaminated scattering measurements by:

determining an autocorrelation function for each scattering measurement that has not been identified as a contaminated scattering measurement;

combining the autocorrelation functions to produce an average autocorrelation function from which the particle characteristic is derived.