Microscopy and Microtechnology


Table 1. Comparison of fractionated peaks with those from the complete 500 – 2000 micron multistandard.


Peak


#1 #2 #3 #4 #5 #6 #7 #8


Individual Sizes from fractions (µm) certificate (µm)


601 756 857


1108 1295 1447 1647 1865


592 758 858


1098 1301 1449 1640 1884


Figure 3. Repeatability measurement on 10 x 20g samples (Haver CPA).


Finally, a precision electroformed sieve analysis was performed to ensure the cumulative distribution overlaid that obtained from the microscope.


Certification Process


One of the disadvantages of using a simple laboratory microscope for particle size analysis is the time taken for a measurement, not only from the point of view of collecting and analysing the data but the mechanics of preparing and analysing the slides.


The 500 – 2000 micron multimodal standard is supplied in 20g bottles. To perform the certification, the standard was subdivided into 1gram subsamples using the spinning riffler. Data from each sub-sample were then combined until a statistically robust number of particles were counted, in this case 33,000.


Test Case – Repeatability


The first and most important question to be asked of a polydisperse standard is ‘How does each bottle of standard compare?’ This question was answered using a Haver CPA image analyser. When 10 x 20g bottles containing approximately 16,000 beads were analysed, the results were identical (Figure 3).


Test Case – Particle Count


Image analysers have become so powerful that it is now possible to count several million particles, but is


micron multimodal standard of 8 hours was reduced to less than 4 minutes for the same particle count.


Test Case – Resolution


Having established the optimum weight of the standard and the repeatability of measurement, the final analysis is the ability of an image analyser to correctly position all the eight peaks. The results in Table 2 show that, in the case of the Haver CPA, there is excellent agreement with the certified values.


Conclusion


The availability of an independent and challenging particle size reference standard for image analysis now enables the prospective purchaser to unequivocally assess the performance of this new class of particle size analyser.


Figure 4. Effect of weight on repeatability (Haver CPA).


that really necessary? In the case of this standard that would represent over 10kg of material.


To determine the optimal particle count, the Haver CPA was used to compare the results from 20g, 60g, 100g and 200g of the standard. Again the results were identical (Figure 4). This means that a 20g bottle of the standard is quite sufficient to obtain statistically robust data.


This last dataset also illustrates the speed of analysis that can be achieved with the latest automated image analysis instruments. The time required for the certification of the 500 – 2000


High-speed electronics both in the computer and camera have reduced analysis times using conventional microscopy from several hours, or even days, down to a few minutes. The debate on the particle numbers then becomes largely irrelevant as 50,000 particles can be counted in only about 5 minutes. However, it has been shown that about 16,000 particles are quite sufficient to give excellent repeatability, even at the extreme ends of the size distribution.


One of the biggest advantages of image analysis is the ability to identify and size closely lying peaks in a sample. This new standard now enables the resolution to be quantified and ensures that accuracy is maintained across the dynamic range of the instrument.


Table 2. Performance of Haver CPA in analysing the individual peaks in a 500 – 2000µm image analysis standard (multistandard).


Peak # Certificate (µm) 1 2 592 758


Haver CPA (µm) 610 750 *209.6 g or 153,420 particles


3


858 860


4 5 6 7 8


1098 1301 1449 1640 1884 1100 1300 1400 1650 1860


Interested in publishing a Technical Article?


Contact Gwyneth on +44 (0)1727 855574 or email:


gwyneth@intlabmate.com


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