Graduate Thesis Or Dissertation
 

Non-biological uptake of zinc-65 from a marine algal nutrient medium

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  • The nature and magnitude of experimental errors due to ⁶⁵Zn adsorption by inorganic surfaces was examined in a laboratory system designed to measure ⁶⁵Zn uptake by marine phytoplankton. In the pH range, 6.3±.1 to 7.5±.1, a precipitate formed in the algal nutrient medium selected for the system. To this seawater-base medium, zinc was added only as carrier-free ⁶⁵Zn. The precipitate increased in both volume and tendency for ⁶⁵Zn uptake as the pH increased. At a pH of 7.5±.1 the particles, predominantly orthophosphates, accumulated 70 percent of the ⁶⁵Zn in the medium in 24 hours. It was therefore concluded that ⁶⁵Zn adsorption by undetected precipitates could result in serious errors in measurements of ⁶⁵Zn uptake by marine phytoplankton. Equilibrium of ⁶⁵Zn adsorption by Pyrex glass surfaces was attained between .50 and 2.0 hours elapsed time. Found to be negligible at pH values less that 6.0±.1, such uptake was a linear function of the hydrogen ion concentration in the pH range, 6.7±.1 to 8.2±.1. Pretreatment of the glass surfaces with dimethyldichiorosilane (General Electric "Dry Film") reduced ⁶⁵Zn adsorption by over 80 percent. The relationship between percent ⁶⁵Zn sample adsorption and wetted glass surface area/pipette sample volume was shown to be linear for volumetric pipettes of the size range, 1-15 ml. At a pH of 7.5±.1, ⁶⁵Zn adsorption was negligible for most laboratory glassware, but increased with increased pH. At a pH value of about 8.0, glassware having surface area/sample volume ratios as small as those of 15 and 20 ml volumetric pipettes adsorbed 7 to 11 percent of the contained sample activity. Two prerinses with the sample liquid were required to reduce such errors by a factor of one half.
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file details TomlinsonRichardDouglas1971.pdf 2017-08-19 Öffentlich Herunterladen