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32 | AUGUST 2014 | GENengnews.com | Genetic Engineering & Biotechnology News Mary Stellmack After routine cleaning of metal or glass sur- faces of pharmaceutical process tanks, resi- dues may remain and appear as faint whitish or dark stains that cannot be easily wiped off. To clean the residue without damaging the tank surface, it is necessary to identify the residue so that the correct solvent or cleaning method can be used. Due to the small amount of residue on the tank surface, it can be diffcult to obtain a large enough sample volume for analysis. For unambiguous identifcation of the residue, it is desirable to remove a pure sample from the sampling tool for analysis, without any at- tached material from the sampling tool. White cotton or polyester swabs are com- mon sampling tools, sometimes soaked in water or alcohol prior to wiping the tank sur- face. Swabs are poor sampling tools because only a small amount of residue is transferred to the swab, the material of interest is dif- fcult to remove from the swab for analysis, and light-colored residues cannot be seen on the white swab. Our objective was to develop an alter- native sampling method to obtain a larger volume of residue that could be easily iso- lated for micro-analysis to identify organic components by FTIR (Fourier Transform Infrared Spectroscopy), or EDS (Energy Dis- persive X-Ray Spectrometry) to identify in- organic components. We investigated several traditional and non-traditional scraping tools for removing residues from a metal or glass surface: • Cotton swab • Polyester swab • Double-edge razor blade • Tape lift with Scotch ® tape • Polypropylene spatula • Plastic polystyrene knife Our "tank surfaces" consisted of a fat stainless steel sheet having a thin spotty coat- ing of rust, and a stainless steel vessel having a faint coating of white-colored hard water de- posits. The stained surfaces were vigorously rubbed with the dry swabs, or moderately to lightly scraped with the other sampling devices while holding the device at about 45 degrees to the surface, except for the tape lift, which was obtained with a single frm compression of the tape against the stained surface. The sampling devices were examined un- der a stereomicroscope and photographed at magnifcations up to 25×. A fne tung- sten needle was used to remove some of the residue from the sampling device, then the residue was transferred to a glass slide. The residue on the slide was examined under a polarizing light microscope at 500× mag- nifcation to see whether particles from the sampling tool had contaminated the residue. Swabs When cotton or polyester swabs were used to sample a rust-colored surface, the residue was readily visible, but consisted of fne par- ticles trapped between and below the swab fbers. It was diffcult to remove the brown material from the swab for FTIR analysis without removing some cotton as well, but the entire swab head could be analyzed by EDS to identify the metallic residue (Figure 1). When swabs were used to sample light- colored residue, no residue was visible on the swab with the naked eye. At 25× mag- nifcation, a faint residue was seen on the swab, but the residue could not be manually removed from the fbers if it was not clearly visible in the microscope. If the residue had been pure white, it would not have been pos- sible to see the residue in the microscope, even at higher magnifcation. It was determined that swabs are most useful for dark-colored residues that consist of metal corrosion, or thick clumps of dark- colored organic materials, but are poor sam- pling tools for light-colored residues. Razor Blade The blade was held at about a 45 degree angle, and the tank surface was gently scraped. Light-colored and dark-colored residues were easily seen on the blade, and could be easily removed for analysis. The blade may scratch some tank surfaces, and fne metal wear par- ticles can be dislodged from the blade and mixed with the sample, making it diffcult to Conference: October 20-23, 2014 Exhibition: October 21-23, 2014 Hynes Convention Center • Boston, MA GEN Readers Save 20% of the Standard Rate with Priority Code BP14GEN Find New Ideas and Make New Contacts to Help You Meet the Demands of Diverse Product Portfolios in an Evolving Biomanufacturing Landscape • 160 Speakers and 80+ Poster Presenters sharing their latest research, strategies and innovations • Learn from over 65 Case Studies and 70 New Data Presentations • event-specifc networking tool to preschedule meetings • Casual, Fun Themed Networking Receptions and Lounges designed to facilitate open dialogue in the exhibit hall • BPI Theater with live interviews, new product demos and more • More than 150 Exhibitors in the exhibit hall ofering you access to network with every major bioprocess solution provider in the industry • Interactive Idea Exchange Q&A; Sessions designed for audience participation, so you can get the answers you need from the experts in the industry For complete event information and the agenda visit: www.IBCLIfeSciences.com/BPI Description of a Simple Sampling Technique Analyzing Pharmaceutical Process Tank Residues BIOPROCESSING Tech Note Figure 2. A white polystyrene knife was used to collect a residue sample (top). The loose residue is clearly visible (bottom), and can be easily removed for analysis. Figure 1. Rust-colored residue was collected on a dry cotton swab. The residue is readily visible (top left), but is trapped between and below the swab bers (bottom left), making it dicult to isolate the brown material without removing some cotton as well. A dry polyester swab (top right) was used to sample a rusty steel surface. The rusty residue is not visible as discrete particles (bottom right), and cannot be removed from the swab for analysis.