Hi all,
my name is masooma and I am doing PhD I have developed a model for particles sizes obtained from DSL exp values but now I want to do some error analysis for the calibration . My supervisor told me to get some research paper that describes the acceptable range of errors in this field but I am not finding exactly relevant paper can anybody help me in this issueI shall be extremely thankful to you
topic: error analysis and acceptable error range in modelling particle size distribution i emulsion technology … oil in water emulsions
Masooma Qizilbash
You have posted one discussion and one question in the forum which is confusing as they contain different information. I will append the same answer to both your question and discussion.
One quotation to begin with: '... as Sir Cyril Hinshelwood has observed ... fluid dynamicists were divided into hydraulic engineers who observed things that could not be explained and mathematicians who explained things that could not be observed' James Lighthill http://www.kurims.kyoto-u.ac.jp/EMIS/journals/IJMMS/22/4667.pdf
Defining acronyms is very important in science, and you have written ‘DSL’. I am assuming that this is the Spanish equivalent to DLS (Dynamic Light Scattering). If it isn’t, then please let us know. You claim that you have agreement with the distributions, but you do not specify which points in the distribution you are comparing – typically the extremes of the distribution are prone to larger variation (note that I use the term ‘variation’ and not ‘error’. This is an important point to understand. Error assumes someone or something is at fault. Variation can be the natural variation in a system due to its inherent heterogeneity).
DLS is a powerful but low-resolution technique. It is a first-principles technique, so instruments are verified, not calibrated. Verification is via an accepted certified traceable standard material. In your case, there are many latex standards that can be used to verify the performance. The ISO and ASTM standards in this area (excellent reference documents) recommend a known standard around 100 nm but you can use many others in the 20 – 1000 nm region. DLS initially provides an intensity distribution and the z-average and PDI (polydispersity index) are the most robust parameters. Are you using these for comparison? The generation of number-based statistics from it is ‘deprecated’ in the ISO standards and the conversion from intensity to number should never be undertaken. DLS does not ‘count’ particles.
Important documents discussing the potential variation in the technique are:
- ASTM: E2490-09(2021) Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
In this standard, Section 7.1 Verification is important. There is a precision and bias section (Section 10) within this document in which the 3 NIST RM 801x (nominally 10, 30, and 60 nm Au colloid) and 2 G6 dendrimers were examined. These indicate practical values of ~ < 5% variation for reproducibility. This document can be purchased from ASTM.
- ISO: ISO 22412:2017 Particle size analysis Dynamic light scattering (DLS)
In this document Section 10.1 System Qualification is important. For reference materials acceptable variation is stated to be 2% (repeatability) & 5% (reproducibility). For real-world materials (such as yours), these values must be significantly increased. This document can be purchased directly from ISO or your local standards authority.
Another useful document is the NIST publication indicating how an uncertainty balance was conducted on the SRM1693 100 nm latex standard via Differential Mobility Analysis (DMA). This shows what can and should be factored in. It may be a little optimistic for real-world materials. I attach 2 documents from George Mulholland that may be useful.
A general chapter (obtainable from the author through RG) may be useful:
Chapter 12: “Instrument qualification and performance verification for particle size instruments” in “Practical Approaches to Method Validation and Essential Instrument Qualification” Eds: Chung Chow Chan, Herman Lam, Xue-Ming Zhang (Wiley) 2010
A couple of webinars may be helpful for general considerations (free registration required):
• International standards in particle characterization
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W140422-international-standards-in-particle-characterization
Deals with material and documentary standards in particle sciences
• Instrument performance verification in laser diffraction
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W141028InstrumentPerfVerificationLaserDiffraction.html
This deals with concepts such as repeatability, reproducibility, and robustness – the 3R quality markers for particle size measurements.
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