DYNAMIC 3D LIGHT SCATTERING PARTICLE SIZE DISTRIBUTION MEASURING DEVICE AND METHOD FOR DETERMINING A PARTICLE SIZE DISTRIBUTION

Abstract

A dynamic 3D light scattering particle size distribution measurement device includes a polarization splitter for generating an s laser beam with perpendicular polarization and a p laser beam with parallel polarization that travels parallel to and spaced apart from the s laser beam. A lens is used to focus the s laser beam and the p laser beam onto a common focus area inside a sample holder holding a sample whose particle size is to be measured. An s light intensity detector measures a time-resolved s light intensity from s backscattered light from the focus area. An s-polarisation filter allows perpendicularly polarized light to pass, resulting in s measuring light, and includes a light detector for time-resolved intensity measurements of the s measuring light. A p light intensity detector measures a time-resolved p light intensity detects p backscattered light from the focus area, and includes a p polarization filter that allows parallel polarized light to pass. A light detector provides for time-resolved intensity measurement of the p measuring light, and an evaluation unit automatically calculates the particle size distribution from the time-resolved p light intensity and the time-resolved s light intensity.

Claims

1. A dynamic 3D light scattering particle size distribution measurement device, comprising: (a) a laser light source for emitting a laser beam, (b) a polarization splitter for generating (i) an s laser beam with perpendicular polarization, and (ii) a p laser beam with parallel polarization that travels parallel to the s laser beam, wherein the p laser beam is spaced apart from the s laser beam by a beam spacing other than zero, (c) a sample holder for holding a sample whose particle size distribution is to be measured, (d) a lens that focuses the s laser beam and the p laser beam onto a common focus area inside the sample holder, (e) an s light intensity detector for measuring a time-resolved s light intensity, wherein the s light intensity detector (i) is arranged to detect an s backscattered light beam from backscattered light of the s laser beam from the focus area, (ii) comprises an s-polarisation filter that allows perpendicularly polarized light to pass, resulting in s measuring light, and (iii) comprises a light detector for time-resolved intensity measurement of the s measuring light, (f) a p light intensity detector for measuring a time-resolved p light intensity, wherein p light intensity detector (i) is arranged to detect a p backscattered light beam from backscattered light of the p laser beam from the focus area, (ii) comprises a p polarization filter that allows parallel polarized light to pass, and (iii) comprises a light detector for time-resolved intensity measurement of the p measuring light, and (g) an evaluation unit designed to automatically calculate particle size distribution from the time-resolved p light intensity and the time-resolved s light intensity.

2. The dynamic 3D light scattering particle size distribution measurement device according to claim 0, wherein the p light intensity detector detects the p backscattered light beam at a different location than the s light intensity detector s detects the backscattered light beam.

3. The dynamic 3D light scattering particle size distribution measurement device according to claim 0, wherein the time-resolved intensity measurement of the p measuring light and the time-resolved intensity measurement of the s measuring light used for calculating the particle size distribution are measured at the same time.

4. The dynamic 3D light scattering particle size distribution measurement device according to claim 0, wherein the s light intensity detector and the p light intensity detector are arranged such that the s backscattered light beam and the p backscattered light beam travel from the focus area through the lens respectively to the s light intensity detector and the p light intensity detector.

5. The dynamic 3D light scattering particle size distribution measurement device according to claim 1 further comprising a lens adjustment device for adjusting the lens relative to the polarization splitter.

6. The dynamic 3D light scattering particle size distribution measurement device according to claim 1 wherein (a) the laser light source is designed to emit a laser beam with a beam propagation ratio (M.sup.2) of at most 1.2 and/or (b) the polarization splitter is a polarization beam splitter that has an optical axis and generates two parallel laser beams that are orthogonally polarized to each other.

7. The dynamic 3D light scattering particle size distribution measurement device according to claim 1, wherein (a) the laser light source comprises a diode laser and an optical fiber, and (b) the optical fiber is a single-mode fiber designed to generate the laser beam with a Gaussian profile with a beam propagation ratio (M.sup.2) of at most 1.2.

8. The dynamic 3D light scattering particle size distribution measurement device according to claim 1 further comprising (a) an optical fiber that comprises an optical fiber input, which is connected to the laser light source for coupling in the laser beam, and an optical fiber output, and (b) an optical fiber adjustment device for adjusting the optical fiber output relative to the polarization splitter.

9. The dynamic 3D light scattering particle size distribution measurement device according to claim 1 wherein (a) the sample holder is designed to hold a sample with a diameter of at least 7 mm, and/or (b) a sample container is provided in the sample holder.

10. The dynamic 3D light scattering particle size distribution measurement device according to claim 9 wherein the sample container is a cuvette with a diameter of at least 7 mm.

11. A method for determining a particle size distribution of a sample, comprising: (a) emitting a laser beam from a laser, (b) generating from the laser beam using a polarization splitter (i) an s laser beam with perpendicular polarization, and (ii) a p laser beam with parallel polarization, wherein the p laser beam travels parallel to the s laser beam and is spaced apart from the s laser beam by a beam spacing other than zero, (c) focusing the s laser beam and the p laser beam on a collective focus area inside the sample, (d) polarization filtering of light backscattered at a backscatter angle from the focus area by an s polarization filter so that only s polarized light passes, resulting in an s backscattered light beam, (e) measuring a time-resolved s light intensity of the s backscattered light beam, (f) polarization filtering of backscattered light from the focus area at the backscatter angle by a p polarization filter so that only p polarized light passes, resulting in a p backscattered light beam, (g) measuring a time-resolved p light intensity of the p backscattered light beam, and (h) calculating the particle size distribution from the time-resolved p light intensity and the time-resolved s light intensity.

12. The method according to claim 11 wherein the backscatter angle is at least 165.

13. The method according to claim 11 wherein the focus area is spaced apart from a cuvette wall by at least 0.3 mm.

14. The method according to claim 13 wherein the focus area is spaced apart from the cuvette wall by 0.5 mm.

15. The method according to claim 11 wherein the sample is contained in a cuvette with a diameter of at least 0.5 mm.

16. The method according to claim 11 wherein the focus area is spaced apart from a point of incidence at which the laser beam enters the sample container by at most 2 mm.

17. The method according to claim 16 wherein the focus areas is spaced apart from the point of incidence by at most 1 mm.

Description

DESCRIPTION OF THE DRAWINGS

[0037] In the following, the invention will be explained in more detail with the aid of the accompanying drawings. They show:

[0038] FIG. 1 a schematic view of a 3D light scattering particle size distribution measurement device according to the invention,

[0039] FIGS. 2a-b in partial FIG. 2a, the measurement results on a sample with a method according to the prior art and in partial FIG. 2b, the measurement results on the same sample with a method according to the invention, and

[0040] FIGS. 3a-b in the partial FIG. 3a, the cross-correlation curves of propofol (concentration: 10 mg/ml), on the one hand measured undiluted with the method according to the invention and on the other hand measured with a method according to the prior art following a dilution of 1:100 and in the partial FIG. 3b, the cross-correlation curves during a measurement on 100 nm polystyrene latex particles (concentration: 1% volume by weight), measured on the one hand with the method according to the invention and measured on the other hand with a method according to the prior art.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a schematic view of a 3D light scattering particle size distribution measurement device 10 according to the invention with a laser light source 12, a polarization splitter 14, a sample holder 16, a lens 18, a p light intensity detector, an s light intensity detector 22 and an evaluation unit 24, which is connected to the light intensity detectors 20, 22.

[0042] In the present case, the laser light source 12 comprises a laser 26 and an optical fiber 28, which is coupled via its optical fiber input 30 with the laser 26. A laser beam 34 is emitted from an optical fiber output 32.

[0043] The laser beam 34 falls on the polarization splitter 14. It is possible, but not necessary, that the laser beam 34 passes through a laser intensity adjustment device 36 before it hits the polarization splitter 14. The polarization splitter generates an s laser beam 38 and a p laser beam 40, which travels parallel to the s laser beam 38 and has a beam spacing d from the latter. The s laser beam 38 has an s polarization, the p laser beam a p polarization.

[0044] The s laser beam 38 and the p laser beam 40 are bundled by the lens 18, which can, but does not have to, be designed as an achromat, on a common focus area F inside the sample holder 16. A sample container 42, for example in the form of a cuvette, is arranged in the sample holder 16, which contains a sample 44 to be measured.

[0045] The sample 44 contains a plurality of particles, so that the light of the s laser beam 38 generates scattered light which travels as an s backscattered light beam 46 at a backscatter angle to the s laser beam and strikes the lens 18 anew. In the present case =1762. The light of the p laser beam 40 generates scattered light that travels as a p backscattered light beam 48 at the same backscatter angle to the p laser beam 40 and strikes the lens 18.

[0046] It is possible, but not necessary, that the s backscattered light beam 46 is guided by means of a first optical fiber 50.1 to the s light intensity detector 22. It is also possible, but not necessary, that the p backscattered light beam 48 is guided by means of a second optical fiber to the p light intensity detector 20.

[0047] The p light intensity detector 20 comprises a p polarization filter 54 that only lets through p-polarized light. Correspondingly, the s light intensity detector 22 comprises an s polarization filter 52 that only lets through s-polarized light.

[0048] It is possible, but not necessary, for the s backscattered light beam 46 and the p backscattered light beam 48 to be mirrored in the direction of light propagation R behind the lens 18 by a deflection mirror 56 onto an adjustment mirror 58 that deflects at least one of the backscattered laser beams.

[0049] The lens 18 can be displaced in the direction of light propagation R by means of a lens adjustment device 60. The optical fiber output 32 can be moved by means of an optical fiber adjustment device 62 in such a way that the laser beam 34 strikes the center of the polarization splitter 14.

[0050] The sample holder 16 has a clear width w of more than w=10 mm, for example, so the sample container 42 can be a standard cuvette. It is beneficial, but not necessary, for the sample holder 16 to comprise a water bath 64, so that the sample container 42 can be brought up to a temperature T that can be pre-set. Preferably 0 C.<T<100 C.

[0051] FIG. 1 shows that the optical fiber 50.2 is attached to a first holder 64. The first holder 64 can be moved in at least two spatial directions, in the x- and z-direction in the coordinate system shown. Furthermore, the holder 64 is rotatable in at least two angles and . Preferably, the angles and are adjustable with an uncertainty of at most 0.1, in particular 0.025. Preferably, the x- and z-positions are adjustable with an accuracy of 20 m, preferably 10 m, or better. This is done, for example, by means of a plate of the holder 64 that can be moved via two or three fine-thread screws.

[0052] The optical fiber 50.2 is attached to a second holder 66. The second holder 66 can be moved in at least two spatial directions, in the y- and z-direction in the coordinate system shown. Furthermore, the second holder 66 is rotatable in at least two angles and . Preferably, the angles and are adjustable with an uncertainty of at most 0.1, in particular 0.025. Preferably, the y- and z-positions are adjustable with an accuracy of 20 m, preferably 10 m, or better. This is done, for example, by means of a plate of the holder 64 that can be moved via two or three fine-thread screws.

[0053] Preferably, the holders 64, 66 are first adjusted so that the s backscattered light beam 46 and the p backscattered light beam 48 have maximum intensity. Then a reference sample 44 is inserted into the sample holder 16 and the holders 64, 66 as well as the mirror 58 are further adjusted so that the maximum cross correlation is achieved.

[0054] The first holder 64 and/or the second holder 66 are preferred embodiments independent of other elements of the 3D light scattering particle size distribution measurement device 10.

[0055] In other words, the holders 64, 66 are adjusted so that the scatter vectors of the s backscattered light beam 46 and the p backscattered light beam 48 are as similar as possible, ideally identical. Especially scatter vectors of the s backscattered light beam 46 and the p backscattered light beam 48 are as similar as possible with respect to the magnitude and direction.

[0056] The optical fiber adjustment device 62 can be moved in at least two spatial directions, in the y- and z-direction in the coordinate system shown. Furthermore, the optical fiber adjustment device 62 is rotatable in at least two angles and . Preferably, the angles and are adjustable with an uncertainty of at most 0.1, in particular 0.025. Preferably, they and z positions are adjustable with an accuracy of 20 m, preferably 10 m, or better. This is done, for example, by means of a plate of the optical fiber adjustment device 62 movable via two or three fine-thread screws.

[0057] In partial FIG. 2a depicts three measurements on the same sample of 100 nm polystyrene latex particles with a volume concentration of 1%. It should be noted that each of the three measurements produce measurement results that deviate slightly from each other.

[0058] Partial FIG. 2b shows three measurements on the same sample with a 3D light scattering particle size distribution measurement device 10 according to the invention. It should be noted that the measured particle size distributions in the form of the particle size distribution density q barely differ from each other. In other words, measurement uncertainty is significantly reduced. With a method according to the prior art, the relative standard deviation is 4.17%; with a method according to the invention, it is 0.64%.

[0059] With the method according to the invention, the hydrodynamic median diameter x.sub.50 was measured at (100.270.64) nm and with the method according to the prior art at (94.193.92) nm. It should be noted that the multiple scattering has led to the anticipated effect that with the prior art, too small a value is determined, as the sample is a standardized sample with a specific hydrodynamic diameter of (97-103) nm.

[0060] The measuring time for the results depicted in the right-hand partial image 2b was 41 seconds; for the left-hand partial image 2a it was 398 seconds. The measuring time is thus 10 times faster with the method according to the invention, while at the same time the repeatability of the measurement results is significantly increased.

[0061] FIG. 3a shows the measured cross-correlation curves of propofol with a concentration of 10 mg/ml. The solid line shows the cross-correlation curve as a function of the delay time T, which could be measured after a dilution of 1:100 with a method according to the prior art. The dashed line shows the cross-correlation curve during a measurement with the method according to the invention without dilution.

[0062] Partial FIG. 3b depicts the cross-correlation curves during measurements on 100 nm polystyrene latex particles. The solid line shows the cross-correlation curve as a function of the delay time T, which could be measured after a dilution of 1:100 with a method according to the prior art. The dashed line shows the cross-correlation curve during a measurement with the method according to the invention. It should be noted that this is greater than with a method according to the prior art by a factor of approximately 15. This results in a significantly higher signal-to-noise ratio and thus a shorter measuring time with lower measurement uncertainly.

REFERENCE LIST

[0063] 10 3D light scattering particle size distribution measurement device [0064] 12 laser light source [0065] 14 polarization splitter [0066] 16 sample holder [0067] 18 lens [0068] 20 p light intensity detector [0069] 22 s light intensity detector [0070] 24 evaluation unit [0071] 26 laser [0072] 28 optical fiber [0073] 30 optical fiber input [0074] 32 optical fiber output [0075] 34 laser beam [0076] 36 laser intensity adjustment device [0077] 38 s laser beam [0078] 40 p laser beam [0079] 42 sample container, cuvette [0080] 44 sample [0081] 46 s backscattered light beam [0082] 48 p backscattered light beam [0083] 50 optical fibers [0084] 52 s polarization filter [0085] 54 p polarization filter [0086] 56 deflection mirror [0087] 58 adjustment mirror [0088] 60 lens adjustment device [0089] 62 optical fiber adjustment device [0090] 64 first holder [0091] 64 second holder [0092] backscatter angle [0093] d beam spacing [0094] F focus area [0095] M.sup.2 beam propagation ratio [0096] q particle size distribution density [0097] T temperature [0098] x.sub.50 hydrodynamic median diameter [0099] w width [0100] x spatial coordinate [0101] y spatial coordinate [0102] z spatial coordinate [0103] angle [0104] angle [0105] angle