PubMed · 7850348
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V A Politano. 1995. Incontinence treated with Teflon.. https://pubmed.ncbi.nlm.nih.gov/7850348/
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OBJECTIVES: To compare irrigant flow characteristics through standard working channels (3.6F to 4.5F) and a dual-diameter working channel. Irrigant flow is critical for adequate visualization during endoscopic procedures. METHODS: Working channels were created out of 80 cm of light wall polytetrafluoroethylene (PTFE) tubing (inner diameter 3.6F, 4.0F, and 4.5F) with a male Luer connector attached to one end by epoxy resin. The dual-diameter working channel was created with a 70-cm segment of PTFE (4.5F inner diameter, 0.059 in.) and a 10-cm segment of PTFE (3.6F inner diameter, 0.047 in.) with a male Luer connector attached to the free end of the 4.5F tubing. Stone basket shafts (100 cm in length, outer diameter 1.9F, 2.4F, and 3.0F) were created out of unmodified polyimide tubing with a 0.018-in.-diameter nitinol mandrel epoxy core for stability. Irrigant flow was measured at 100 mm Hg pressure for 1 minute with an empty channel and with stone basket shafts in the channel. RESULTS: The flow rates were significantly greater with the dual-diameter working channel than with the standard flexible ureteroscope (3.6F) working channel using an empty channel (79.2 versus 44.1 mL/min, P = 0.0001), 1.9F basket (35.9 versus 10.0 mL/min, P = 0.003), 2.4F basket (20.7 versus 4.3 mL/min, P = 0.002), and 3.0F basket (6.0 versus 0.7 mL/min, P = 0.0002) sheath. CONCLUSIONS: A dual-diameter working channel may optimize irrigant flow characteristics for flexible ureteroscopes while maintaining a small distal tip diameter.
A 6% slurry of polytetrafluoroethylene (PTFE) in 4% hydrofluoric acid and 1% nickel nitrate were used as modifiers for determination of selenium in soils by GF AAS. PTFE was used to remove silica from the soil sample, because this resulted in severe matrix effects. The temperature of fluorination, determined thermogravimetrically, was 600 degrees C. The yield of fluorination depends on the molar ratio of PTFE/silica, particle size, and the time and temperature of fluorination. The soil samples were pretreated with a small amount of concentrated hydrofluoric acid placed directly in the cup of autosampler. The results for the determination of selenium in the reference soil materials by means of the slurry-sampling technique and use of aqueous standards are in good agreement with the certified values.
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