Method validation of particle size distribution using static image analysis

Test & Measurements conference

Fortunate Modiba

Material characterisation

17 September 2019

Outline

INTRODUCTION

EXPERIMENTAL

RESULTS

Introduction

Particle size distribution

The particle-size distribution (PSD) of a powder, or granular material, or particlesdispersed in fluid, is a list of values or a mathematical function that defines therelative amount, typically by mass, of particles present according to size [1].

[1] Ujam, A. J., & Enebe, K. O. Experimental Analysis of Particle Size Distribution using Electromagnetic Sieve.http://www.ajer.org/papers/v2(10)/H02107785.pdf

Optical microscope

Optical Microscope is a technique that has

been used for many years within the NMISA,

to determine the shape, morphology and

size of particles

• Resolution: 250 μm

ISO 13322 :2014 the analysis of images for

the purpose of determining particle size

distributions [2].

[2] www.iso.org/standard/51257.html

Fish-Bone diagram

PSD

Calibration

ThresholdSample preparation

Experimental

As-received samples for PSD analysis

Sample preparation

• ISO 14887:2000, sample preparation can be done by following dispersing procedures for

powders in liquids [3].

• The sample is dispersed with the selected dispersant by first adding a small amount of the

sample on the glass slides and four drops of the dispersant (preferably isopropanol) are

added on the sample .

Sample dispersion

[3] https://www.iso.org/standard/25861.html

Obeservations

Agglomerated Crushed Well dispersed

Results

10 slides 10 areas on 1 slide

Analyst Mean (µm) %RSD Mean (µm) %RSD

1 2.2 ± 0.2 9.24 2.3 ± 0.4 17.94

2 2.7 ± 0.5 15.5 2.3 ± 0.2 6.83

Table 1: Sample preparation precision.

❖ Sample preparation

10 slides 10 areas on 1 slide

AnalystMean (µm) %RSD Mean (µm) %RSD

2.3 ± 0.35 6.13 2.3 ± 0.4 7.05

• F-test: standard deviations (SD) for the 10 slides for both analysts do not differ significantly.

• This implies that the mean and standard deviation are significantly comparable which makes the method reproducible.

• Comparing the two experimental means on the 10 areas SDs differs significantly.

Reproducibility

Repeatability

Observation

Effect of pixel size

pixel decreases

CalibrationTo ensure SI traceability of measurement results, the microscope was calibrated by using a certified calibration artefact from NIST.

NIST RM 8820 magnification artefact at 100x (10x lens).

Y

X

• Theoretical calibration based on the objective (magnification), camera pixel size and camera adopter which is setup in the microscope calibration.

• As no optical element can be produced the same therefore it’s required to create a manual calibration using a stage micrometre to ensure that the theoretical calibration it’s still within range.

Results

MagnificationTheoretica

l ratio (µm)

X1 %ErrorX1 X2 %ErrorXMean (X1X2)

%Error(X1X2)

50x 0.62 0.62 0.62 0.62 0.62 0.62 0.62

100x 0.31 0.31 0.61 0.32 3.84 0.31 0.61

200x 0.16 0.15 0.00 0.16 0.00 0.16 0.00

500x 0.06 0.06 1.24 0.06 0.55 0.06 1.24

1000x 0.03 0.03 0.95 0.03 0.20 0.03 0.95

MagnificationTheoretical ratio(µm)

Y1 %ErrorY1 Y2 %Error YMean (Y1Y2)

%Error(Y1Y2)

50x 0.62 0.62 0.62 0.62 0.69 0.62 0.62

100x 0.31 0.31 0.61 0.31 0.45 0.31 0.61

200x 0.16 0.16 0.00 0.15 0.00 0.16 0.00

500x 0.06 0.06 1.24 0.06 0.55 0.06 1.24

1000x 0.03 0.03 0.95 0.03 0.20 0.03 0.95

Table 3: Calibration

❖ Calibration

Reproducibility

The x and y are the co-ordinates used in the software for calibration. The X1 and Y1 represent the results for analyst 1 and X2, Y2 for analyst 2.

Results

MagnificationTheoretical

(µm)Experimental

(µm)%Bias %RSD

50x 0.63 0.62 0.58 0.07100x 0.31 0.31 0.42 0.07200x 0.16 0.16 0.00 0.07500x 0.06 0.06 0.16 0.09

1000x 0.03 0.03 0.33 0.04

MagnificationTheoretical

(µm)Experimental

(µm)%Bias %RSD

50x 0.63 0.62 0.62 0.07100x 0.31 0.31 0.35 0.09200x 0.16 0.16 0.00 2.51500x 0.06 0.06 0.16 0.08

1000x 0.03 0.03 0.33 0.04

Table 4: Calibration results on the x-direction

Table 5: Calibration results on the y-direction

• The %RSD was calculated from the experimental data was observed to the of < 3%.

• The y -direction in this case is found to be more stable and precise as compared to the x-direction.

Threshold

Polystyrene microspheres sphere Over threshold Good threshold

Results

10x mag 20x mag

Analyst Mean (µm) %RSD Mean (µm) %RSD

1 2.54 ± 0.05 2.15 1.51 ± 0.06 3.90

2 2.50 ± 0.03 1.38 1.47 ± 0.04 2.54

Table 2: Threshold precision.

• The F-test was used to compare the standard deviation (SD) and precisions of the two analysts.

• The test indicated that the two SDs do not differ significantly which implies that there is no significant difference in precision (<5%).

• The means are significantly accurate according to the t-test.

❖ Threshold

Reproducibility

Repeatability

10x mag 20x mag

Analyst Mean (µm) %RSD Mean (µm) %RSD

1 2.54 ± 0.03 2.15 1.50 ± 0.05 2.08

Repeatability

How accurate?

Results

Polystyrene microspheres3 µm 10 µm 30 µm

Experimental. mean 3.17 9.97 30.88

Experimental. Std. dev. 0.29 0.80 0.66Certified mean 3.01 9.71 30.39

Certified standard deviation 0.02 0.02 0.10%Bias 5.22 2.65 1.60

Degrees of freedom n-1 = 9tcalc 2.00 1.00 2.00tcrit 2.26 2.26 2.26

Decision rulestcalc<tcrit, the

method is accurate

The largest bias was observed at the smallest particle size. This may in part be related to

working at close to the method’s detection capability. Bias of 5% would still be fit for purpose.

The t-test with the value of t for a confidence interval of 95% (critical value of |t| for p value of

0.05).

Table 8: Bias results.

❖ Bias

Limit of detection and

quantification

Results

CRM size (µm)

Magnification

5x 10x 20x 50x 100x

3.00 3.34 2.75 3.39 3.36 3.51

1.50 2.20 2.32 2.30 1.70 2.01

1.00 2.71 1.83 1.77 1.99 2.47

0.70 2.38 1.45 1.45 1.50 1.32

0.50 3.30 1.73 1.40 1.45 0.00

The 3.0 µm results were observed to be comparable to the reference value, with the resultsfor the smaller particles not agreeing with the reference values.The SD for the 3.0 µm CRM (0,30 µm) was therefore used to determine the LOD and LOQ forthe methods:LOD = 0.86 µmLOQ = 2.90 µm

❖ Limit of detection/quantification

Table 9: CRM results for LOD/LOQ determination

What does it mean?

Results

SRW (%) Sr (%) %uCRM %Bias

5.00 16.00 8.96 0.05

• The NORT-test determined the Rw to be 17% and the %uBiasto be 9%.

• The method was observed to have the precision of 19%.

Table 10: NORT-test results

❖ Method precision using NORT-test

Conclusion

❖ The method proves to be accurate within 5% and precise within 19%.

❖ The particle size analysis can be conducted on powders with good accuracy and

±19% precision.

❖ The future work will be on evaluation of uncertainty on the sample preparation.

Acknowledgement

NMISA Green Economies

&

Particle Size cross-cutter project