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Genetic Engineering & Biotechnology News | GENengnews.com | AUGUST 2014 | 33 identify residues that consist of metal corro- sion. The razor blade is most useful for hard or soft nonmetallic residues. Polypropylene Spatula The edge of a plastic spatula was used to scrape the tank surface to remove the resi- due. The spatula used in this test was dark blue in color, and light-colored residues were readily visible. For dark-colored residues, a light-colored spatula should be used. However, polypropylene is a somewhat soft material, and rolls of plastic are generat- ed along the edge of the spatula with the par- ticles of interest entrained within. The residue cannot be separated from the loose plastic flaments for analysis. Some loose particles of residue (not mixed with polypropylene) were also spattered on the surface of the spatula trough, not immediately in the area of con- tact of the spatula with the tank surface, and these particles can be removed for analysis. Soft plastic scraping tools are best suited for soft waxy residues that do not require hard scraping of the surfaces. Tape Lift The tape picked up a good quantity of res- idue, but the particles needed to be removed from the adhesive and cleaned with a solvent to remove any attached adhesive. This can be diffcult if the particles are very small or crumbly, and some particles may be soluble in common solvents. The tape lift cannot be used for soft residues; it is only useful if the residue consists of hard material that is not frmly adhered to the tank surface. Plastic Polystyrene Knife The plastic knife that was used was a standard disposable plastic knife available at any grocery store. We removed the handle from the knife, and the blade end was held at about a 45 degree angle while frm pressure was applied as the teeth were scraped over the tank surface. The teeth of the knife col- lected a good amount of residue, and a large amount of loose residue clung to the surface of the blade adjacent to the teeth (Figure 2). The loose residue on the blade was eas- ily removed for analysis. The residue on the teeth contained a few scattered fne polysty- rene particles that were abraded during the scraping process; polystyrene is readily sol- uble in many common solvents and if con- tamination of the residue with knife debris is suspected, it can be easily dissolved. The infrared spectrum of polystyrene is unique, and it is substantially different from most process tank residues, thus it is easy to check for the presence of polystyrene in the sample, and in most cases the dissolution process should not be necessary. The polystyrene knives' hardness and solubility characteristics made them the best tools for sampling hard residues (the polysty- rene knives are good sampling tools for soft residues as well). These tools are stiff enough to remove the residue without generating a large amount of abraded plastic, but do not damage the metal surfaces. The knives are convenient because very little sample preparation is needed, and they can be obtained in many different colors; a knife color can be chosen that contrasts with the color of the tank residue, enhancing the visibility of small amounts of sample, and making it possible to isolate the sample from the sampling tool for analysis. The selection of a scraping tool depends somewhat on the type of residue to be sam- pled. This brief study focused on hard resi- dues on metal surfaces, as these are the most challenging residues for sampling. If the resi- due consists only of metal corrosion, any of these sampling methods, except the razor blade, are suitable. However, if the residue contains some organic material, is present in a very small amount, or if one wishes to perform solvent extractions on the residue to look for the presence of oils or other soluble materials, the residue should be removed from the sampling tool for analysis by IR or other methods. The polystyrene knife provides a good combina- tion of clean sample removal and little con- tamination from the sampling tool. The knife, or any of the other sampling tools, can be attached to a glass slide with tape, and inserted into a standard 50 mL plastic tube with a threaded cap for shipping or safe transport to the lab for analysis. The standard glass slide fts frmly into such a tube, and will not move during shipping. Ki-67, HER2, EGFR, Beta-Catenin & more Specificity Matters For research use only. Not intended for diagnostic purposes. UltraMAB is a trademark of OriGene Technologies Inc. 2013 BIOPROCESSING Mary Stellmack (mstellmack@mccrone. com) is a senior research chemist at McCrone Associates, the analytical services division of The McCrone Group. Website: www.mccrone.com. Tech Note