| Author | Message | ||
     Michael C Mound (mike) Senior Member Username: mike Post Number: 54 Registered: 7-2007 |
Hello, again, Yavor, Some additional thoughts: The processes for sample splitting/separation in the applications I noted in my previous post have as one of their common requirements the avoidance of fracturing or otherwise destroying the wanted discrete contained content (microfossils, microminerals, etc: see also details describing maceration of microsamples). This was why I mentioned the various disciplines that face this routine constraint. As far as finely divided materials are concerned, it is not clear whether you are interested in separation alone, or are trying to quantify whole (i.e.,unbroken) specimens. Either way, the fineness of the materials will have an additional effect, known as the zeta-potential (an inverse cohesive force quantum which increases geometrically with reduction in particle size) on the apparent or real "stickiness". That is to say, that this force combines with the natural stickiness that has more to do with interlamellar electrical forces than the zeta potential. Removing or reducing these forces will be necessary to facilitate sample preparation by liberating the wanted components, if that is your objective. What you might have to do is to perform a surface tension evaluation to determine what hydrophilic or hydrophobic reagents might be required to condition the sampled materials before attempting splitting (disagglomerating, etc). As far as the suppliers are concerned, I will let them push via their own versions of hype, but I caution you that sample conditioning before splitting will provide more reliable and repeatable results by first identifying the effects of said zeta potential and interlamellar forces (such as Van der Waal's forces) that may otherwise complicate truly representative sampling (note the comments made by Howard Mark). For some additional help in deciding on the actual dividers, once you have resolved the intrinsic issues of the material conditioning, you could, for example, check out the various helpful data sheets, etc. One such example can be found by scanning their application notes, such as can be found (you mentioned Retsch)in the following link: http://spectroscopymag.findpharma.com/spectroscopy/data/articlestandard//spectroscopy/442007/469993/article.pdf I have no connection, commercial or otherwise with any of these suppliers, but my experience is that any and all will be delighted to help. Further Good Luck, Mike | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 189 Registered: 9-2001 |
Yavor - Mike made some good specific suggestions. I have a couple of more general ones: 1) The best way to see if a piece of equipment works well on the types of samples you intend to use it on, is to try it out. Some manufacturers will let you send (or bring) in some of your samples to their site, some actually have field personnel who will bring the equipment to your laboratory, so you can see how it works on your samples. So contact the companies with equipment that looks promising and see what they can do for you. 2) The problem of dividing large samples to get a representative small sample is not unique to NIR, it's general problem for all chemical analysis. Therefore you would do well to look for a forum on general techniques for analytical chemistry, and bring up your questions there, too. Also, many manufacturers of the equipment you're looking for will have a discussion forum (for their equipment, of course) and/or an FAQ section that might answer some of your questions. Howard \o/ /_\ | ||
| Michael C Mound (mike) Senior Member Username: mike Post Number: 53 Registered: 7-2007 |
Hello, Yavor, I am sure you will get many responses, so I will only make a general suggestion: For isolating acicular materials, or very small samples, you need to research the current offerings being made to micromineralogists who specialize in liberating cenospheres and plerospheres from ore-bearing prospects. Other, more gentle devices will be undoubtedly found by checking the buyer's guides in the journals dealing with palynology and the mysterious annals of coccolithology, siliceous diatoms, and ostracods. I, myself, was a specialist for several years in conodontology, and the techniques for obtaining representative microsamples constituted even then, a very deep adventure into arcana. I'll check into my old files to see if there is something more substantial, but I believe that it would be worthwhile to check out the above, as the people working in these fields then and now, are very concerned about representative sampling and splitting. Good luck, Mike | ||
| Yavor (nir_greenhorn) New member Username: nir_greenhorn Post Number: 5 Registered: 5-2007 |
Dear NIR-community, I know that the topic is slightly off. Nevertheless, I consider it an inseparable part of the NIR measurements of solid samples and that's why I wanted to bring it up among the NIR users. TOS is certainly a developed scientific theory with a rigorous mathematical apparatus behind, but when it comes down to choosing the right piece of equipment I have encountered difficulties. I have been focusing on rotary sample dividers, as they are considerd as being the best. Among them however exist a number of different options, namely Laborette 27 (Fritsch), Retsch's PT 100 and PK 1000, Repro by Buerkle, Microriffler by Quantachrome etc. Does anybody have experience with these instruments? What do you recommend for small volumes (NIR samples)? What is the smallest volume you have ever representatively mass reduced (I know it depends on the material, but still). Have you ever divided a sample with needle-like crystals? Are they not damaged in the process? Does anybody have experience with fine (100um - 1 mm) and sticky powders? Any Info is appreciated! Best, Yavor |