Bringing Out the Best in Analytical Samples
Mills and grinders are used to prepare samples (of minerals, plants, food, drugs, pigments, and forensic materials, for example) through particle size reduction (comminution). Afterward, samples are analyzed for their components or to demonstrate specific properties. Milling/grinding methods may be classified as impact, crushing, cutting, and abrasion, operations that Glen Mills’ (Metuchen, NJ) director Stanley Goldberg compares to using a “hammer, pliers, scissors/knife, and nail file.”
Over the last decade, specified target particle sizes have become smaller and size ranges narrower, two factors enabled by more powerful milling/ grinding machines that are safer and easier to clean and more rapidly achieve desired particle sizes.
More and more industries are interested in generating nanoparticles, which are smaller than about one 100 nanometers in diameter. Nanoparticles are readily generated with modern highenergy bead, jet and planetary mills but were unattainable using older hammer, ball and knife mills.
Goldberg defines nanotechnology as “the ability to engineer new attributes through controlling features at a very small scale.”
Pharmaceuticals have been a briskly growing market for millers/grinders. Insoluble pharmaceuticals, for example, are milled to 100nm to maximize their absorption into the bloodstream, from which they reach cells.
Experts believe that a significant fraction of drugs that fail in clinical trials could be improved by producing them as nanoparticles or within very narrow size ranges. Similarly, existing solid drugs might benefit from tailoring their particle size. Lab-scale mills can rapidly produce small sample batches of a drug during product R&D for subsequent testing. “Every major pharmaceutical company in the U.S. uses a planetary mill for that purpose,” says Kyle James, sales manager at Retsch (Newtown, PA).
Established industries such as those producing food, pharmaceuticals, paints and pigments, electronics, magnetics, cosmetics, and personal hygiene products have all discovered their own ways of benefiting from working with smaller particles. “Working in nanoscale provides greater bang for the buck,” Goldberg tells Lab Manager Magazine. “Whether it’s greater coverage area for pigments, taste enhancement for foods, or improved efficacy for drugs, the control of size is important, and smaller is often better.”
Alternative energy is another growth market, although as Kyle James notes, energy is a “trend that seems to come and go depending on the political climate.” In this area, mills are used to pulverize energy source materials (for example, plants or coal) as a prelude to calorimetric analysis. Related environmental and personal safety applications have shown steady growth. Mills are routinely used to test imported toys, materials that come into contact with food, and clothing.
Purchase decision factors
For Tim Osborn-Jones of Spex SamplePrep (Metuchen, NJ), throughput is the leading issue factoring into purchase decisions. “Labs are taking in more and more samples and need to process them in a shorter time frame. They have the option of doing one sample at a time manually or employing a miller or grinder that handles multiple samples.” Two other related factors are reproducibility and yield. Analytical labs must be assured that grinding a particular sample under specified conditions will always lead to the same result and provide the same quantity of the target material. Price, according to Osborn- Jones, is a relatively minor factor since “the purchase price is paid back relatively quickly, particularly for grinders with automation features.”
“Customers are interested in how fast the machine does its job, how easy it is to clean between operations, and whether the machine itself can contaminate samples,” notes Stanley Goldberg. In addition, mills serving FDA-regulated industries usually include documentation for safety, contamination and performance.
Versatility is another plus for lab mills/ grinders. According to Kyle James of Retsch, depending on their needs, customers should consider mills that serve quality assurance and research customers. One could add that manufacturing companies should look for grinders that can rapidly generate high-quality samples for QA or testing.
Milling the unmillable
Freezer mills (also called cryogenic mills or cryomills), a Spex specialty, have been around for about forty years. Cryogenic mills pulverize nonbrittle materials by first freezing and then milling them in specialized sample containers. The U.S. Consumer Product Safety Commission, for example, has issued guidelines based on cryomills for extracting and analyzing phthalates from children’s toys. Test method CPSC-CH-C1001-09.1, for example, directs analysts to “Grind, mill or otherwise comminute the entire sample … to a fine powder” using a cryogenic or ball mill.
Although not appropriate for every sample, freezer mills work wonders with samples that typically do not grind well—plastics, rubber, biological articles, and heat-sensitive materials, for example. “When we used a conventional laboratory blender, our product was coarser and took twice as long to grind. Incorporating the freezer mill into our protocols has increased throughput and efficiency,” says Sharhara Anderson at RiceTec (Alvin, TX), which researches rice plants and seed.
Angelo DePalma holds a Ph.D. in organic chemistry and has worked in the pharmaceutical industry. You can reach him at firstname.lastname@example.org.
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