Can you add a thickener or viscosity modifier such as xanthan gum or carboxymethyl cellulose into your sample when performing laser particle size analysis to help keep particulate samples in suspension during measurement?
I am having trouble keeping a particulate sample adequately suspended during laser particle size measurement. The sample has a wide particle size range and is quite heavy (specific gravity = 2.7). During measurement, I suspect that some of the coarse particles are settling or are poorly suspended which leads to poor repeatability in my measurements.
I thought that maybe I could add an additive which helps to keep the particles in suspension or reduce particle settling.
Would this be a good idea, or would adding these substances significantly alter results?
Kevin Hii
You can use polymer stabilizers, but at the optimum concentration. At higher concentrations, they can act as flocculants, being adsorbed on two or more particles and precipitating them. If you get two particle sizes, one of them might be the gum.
Hi Kevin,
For stable particle suspension, using surfactant (dispersant) might be beneficial in reducing the surface tension between the solid particles and your solution. Another useful technique could be surface functionalizing of the particles using chemical methods.
Kevin Hii You are not indicating what system and accessory you are using and the top size of your distribution. What are you actually measuring?
2.7 g/cm3 (2700 kg/m3) is not a particularly high density considering that much denser materials are routinely measured on the Mastersizer 3000.
Are you measuring a soil or sediment with a small proportion of large material? The killer word in particle size distribution is the last one and 'distribution' is the bane of all particle size techniques. If so, representative sampling is going to be your major issue.
It is the function of the pump-stirrer to keep material in suspension and this is normally set to 90 - 95% of maximum to keep material in suspension (assuming a centrifugal, not peristaltic, pump). A thickening agent is likely to create more problems than it's worth possibly with foaming or difficulty in actually pumping the continuous phase.
Not exactly what you mean by repeatability here - are you talking about consecutive measurements ('intra-assay precision') or replicate aliquots/samples? See the following for method development and sampling (registration required):
PST & BDAS - An acronym approach to laser diffraction method development
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190815PST
Keys for Successful Analysis – Representative Sampling & Estimation of Standard Error Calculation
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190613KeysLD
Alan F Rawle
Hi Alan, thank you for your detailed reply. I am measuring a soil sample (D10 = 2.5 micron; D90 = 240 micron) containing small amounts of larger particles (600 micron). I am using a Bettersize BT2600 to perform these measurements. I am having trouble with the repeatability in terms of the "intra-assay precision", in the sense that one any given same subsample in the instrument, the instrument will plot distribution curves that vary between each time I take a measurement. This led me into thinking maybe some of my coarse particles were poorly dispersed in the dispersion unit and thus not being detected in the measurement cell. Maybe this is not the case. I will have a look at your provided links. Thank you.
Kevin Hii
You have a heterogeneity issue with an x90 at 240 microns. Carry out a minimum mass calculation and estimate the best standard error for your system as shown in the second webinar above. Then report back your answers in this question.
Dispersion issues only show with material < 20 microns or so - this is here a stabilizer may be needed (e.g. phosphate for oxides and clays. See the first webinar above). Verify your system first with the appropriate certified and traceable standard.
- Badges
- Science topic
- Similar topics
- Elementary Particle Physics
- Particle