Thanks to everyone who gave great suggestions for grinding small samples. I've included a summary below of all the responses I received.
After experimenting with different grinding methods, our lab has settled on the SPEX 5100 Mixer/Mill (a ball mill). It grinds roots, leaves and wood samples to a fine powder. One nice feature about it is you can use different sized vials, which helps with varying sample sizes. It's intermediate in price (more expensive than coffee grinders, but more affordable than the highest end grinders) Here's the web-site: http://www.spexcsp.com/sampleprep/catalog/aid37.html LIQUID NITROGEN OR MORTAR AND PESTLE 1. We use liquid nitrogen and a mortar and pestle. It's tedious, but if you can't loose sample, it's a pretty good method. 2. For small soil samples, nothing beats the mortar and pestle. We also use a stainless steel rolling pin on a granite surface. 3. After grinding a few thousand leaf samples for my dissertation I have come to the conclusion that the most efficient method is using a mortar and pestle, with liquid nitrogen, followed by a healthy dose of elbow grease and some large paint brushes (for cleaning out the mortars to make sure you get the entire sample). Making sure the pestles don't get wet is a big concern. Before I settled on this method, I tried a coffee grinder, but found that it took much longer to clean the coffee grinder, and that the samples weren't ground to a fine enough powder, so I had to use the mortar and pestle anyway. With 3 people working, I could grind about 300 samples in a very focused, 8 hour day (of which it turns out, there are very few that occur). WIGGLE-BUGS AND OTHER BALL MILLS 1. So far the best things we found are the Wiggle-bugs. A shaker arm that holds stainless or plastic canisters and ball bearings and shakes them into powders. I have a very small one for periphyton but use a larger one in a friends lab. I'm not sure the manufacturer but could find out. Fisher might sell them. Good luck and let me know if you come up with a better alternative. 2. For smaller samples the Wigl-bug, or dental amalgamator, similar to the line shown here produce extremely fine powder: <http://www.medstad.com/product.asp?id=379140>http://www.medstad.com/product.asp?id=379140 The prongs at the top of the device hold a small stainless steel cylinder containing the sample and a small steel bead that acts as a pestle. Other manufacturers offer large devices similar in concept to the wigl-bug: <https://www1.fishersci.com/Coupon?gid=2796862&cid=1328>https://www1.fishersci.com/Coupon?gid=2796862&cid=1328 3. If you are processing large numbers of samples, you might consider a ball mill. One can be made with a paint shaker, processing samples with steel BBs inside plastic scintillation vials. One can grind 50 samples in the time it takes to put samples and BBs into vials and take BBs out (plus a few minutes of shaking time). We use this set-up to grind samples prior to chemical analyses and for stable isotopes. Works really well, with amazing throughput (relative to a Wiley Mill). 4. We have a Spex Certiprep cryogenic grinder that is excellent for grinding and homogenizing the sample types you mentioned. Our model is Spex 6750 but I believe they have a newer version on the market today. We have used ours for about 10 years with minimum maintenance. It does require having consistent access to liquid nitrogen within your lab or building. You can contact the Spex Sales rep: Melissa Davic Sales Specialist SPEX CertiPrep Group SPEX SamplePrep LLC 203 Norcross Ave Metuchen, NJ 08840 Tel: 732-549-7144 Ext.448 Toll Free: 800-522-7739 Fax: 732-906-2492 <mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED] 5. We use a Wig-L-Bug grinder (a ball grinder) <http://www.reflexusa.com/wiggrinmil1.html>http://www.reflexusa.com/wiggrinmil1.html 6. We have been using a dental amalgamator (Wig-L-Bug from Reflex Analytical Corporation) to grind small amounts of leaf and root tissue. Haven't tried it on soils or wood, but I suspect it would work well on soils. Wood might require some liquid N. The amalgamators are cheap, quick, and easy to use. 7. I have personally used wiggle bugs, a ball grinder, wiley mills, and a plain old mortal and pestle in my graduate studies which are finally coming to a close. My grinding method of choice would either be the coffee grinder or wiggle bug. However, by using a wiggle bug, your sample volumes have to be very small (<1cm3). For example, I only use the wiggle bug for grinding small leaf sections (5-10cm in length) of Phragmites australis for pigment analysis. This is about the maximum capacity for the wiggle bug to be effective. 8. The other option is a standard ball grinder. <<http://www.vwrsp.com/catalog/product/index.cgi?catalog_number=16003-606&inE=1&highlight=16003-606>http://www.vwrsp.com/catalog/product/index.cgi?catalog_number=16003-606&inE=1&highlight=16003-606>, which I have used as well. This is essentially a very large wiggle bug. It does work very well, but you are limited by the number of grinding chambers you can afford, and clean up between samples is the rate limiting step. For small samples, I found the Braun microdismembtaor to work spectacularly. It is a bit expensive but definitely worth it, especially if you have many samples. <http://www.usedlabequip.com/details.aspx?itemID=2566>http://www.usedlabequip.com/details.aspx?itemID=2566 9. We have used a Wig-L-Bug successfully- we use microfuge tubes with stainless beads, rather than the amalgamator capsule, so there is no cleaning or cross contamination between samples. What works even better for production scale work is a paint shaker- make a holder for your microfuge tubes out of rigid foam, pop a few bearings in each one, and shake away. These methods are not effective on woody material- we end up pre-grinding stems with liquid N in a mortar, pouring the liquid N plus fragments onto weighing paper, and transferring from there into the microfuge tube. We have also used a Cyclotec grinder for moderate size tissue samples. You haven't defined "small", but I've ground mg-size plant tissue samples with the bead-shaker technique. WILEY MILL I grind small plant samples for our work including finer grasses like Bouteloua gracilis. We use a baby Wiley with a 20 or 30 seive for these samples and it works well. COFFEE GRINDERS 1. I have most often used coffee grinders (in fact, they are the most popular device for grinding leaf/plant samples in my department at the University of California, Riverside). They are small, cheap, and do a great job. They do suffer quite a bit with soil samples (we have ground more sand samples that I care to think about). Eventually, their tiny little blades get ground down to a nub. Of course, they are about $15 to replace. 2. I guess it depends on how small your samples actually are and the type of wood you are grinding, but we used a metal blade coffee grinder for very small samples. 3. I have used a Braun (or similar make/model) home coffee and spice grinder with great success and they are readily available, easy to clean, sturdy and much cheaper than lab equipment. I did not use it on soil (you may reconsider using a grinder for both vegetation and/or soil) but it pulverized dried plant material - leaves, stems, seeds etc. to a very fine powder. Plants ground included cassava, soy bean, pine needles. 4. I have used a simple coffee grinder to grind samples of a few grams and they work well for digestions. loss on ignition and elemental analyzers. 5. I tried a coffee grinder but I could not get the materials fine enough. 6. I have used coffee grinders previously. As long as there is enough biomass you should be fine. Like with all grinders there is always the possibility of some contamination of metal from the blade but it is often minimal and is not of concern if the grinding is not for purposes of examining metal accumulation. 7. It may not be as well suited for roots or other woody tissue, but the grinder we use quite successfully for soil and foliage is a basic Braun coffee mill. They're cheap (about $20), and we modify them slightly by fashioning a piece of Plexiglas over the top of the lid so that the grinding chamber has about one quarter the original volume. The blades will wear out long before an Wiley mill, but at $20 it's a pretty easy thing to replace. 8. We use a coffee grinder for small samples. 9. I am currently grinding hundreds of plant samples (mainly Phragmites and Spartina), and I would suggest using a modified coffee grinder, such as the Krupps one below: <<http://www.bedbathandbeyond.com/product.asp?order_num=-1&SKU=10151112>http://www.bedbathandbeyond.com/product.asp?order_num=-1&SKU=10151112> The only modification would be to fit a piece of plexiglass onto the bottom of the clear dome to reduce the volume of the grinder. By doing this, you can consistently grind your samples to a fine powder, which is what I use for stable isotope and elemental analysis. Plus, at such a low cost, they are easy to replace and purchase multiple units. 10. I worked in a lab where we used an ordinary coffee grinder, but we froze the tissue first. MISC 1. I study seedlings, so I've done my share of small plant grinding. Depending on the size, I've had good success with the following 3 (not very technologically advanced) methods: test tube with sterilized sand and glass rod to grind (good for VERY small plants) mortar and pestle (never fails) coffee grinder 2. For small plant samples a coffee grinder is pretty good, holding it upside down while grinding helps. I don't know if the Perten mill will work with plants (a co-worker uses it for grain). We also will use the old mortar and pestle, cutting the plants first with a scissors to make the parts smaller. Also, we have a "mini" Wiley mill. Just like the large size, but ~1/0th the size, this grinds pretty well, but narrow grass leave easily fall through the bottom sieve and don't grind as easily. 3. To finely ground plant samples we prefer to use the UDY mill, but you have to be careful with small sample sized. 4. We use a soil mill (Cianflone) for fine grinding of soil for our C & N analyses, however we do grind (or crush) the soil first to pass a 2 mm sieve. ------------------------------------------------------------------------ Pamela H. Templer Assistant Professor Department of Biology Boston University 5 Cummington Street Boston, MA 02215 phone 617-353-6978 fax 617-353-6340 people.bu.edu/ptempler ------------------------------------------------------------------------
