A precise method for the analysis of d18O of dissolved inorganic phosphate in seawater

Limnology and Oceanography: Methods
By: , and 


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A method for preparation and analysis of the oxygen isotope composition (d18O) of dissolved inorganic phosphate (DIP) has been developed and preliminary results for water samples from various locations are reported. Phosphate is extracted from seawater samples by coprecipitation with magnesium hydroxide. Phosphate is further purified through a series of precipitations and resin separation and is ultimately converted to silver phosphate. Silver phosphate samples are pyrolitically decomposed to carbon monoxide and analyzed for d18O. Silver phosphate samples weighing 0.7 mg (3.5 mol oxygen) can be analyzed routinely with an average standard deviation of about 0.3. There is no isotope fractionation during extraction and blanks are negligible within analytical error. Reproducibility was determined for both laboratory standards and natural samples by multiple analyses. A comparison between filtered and unfiltered natural seawater samples was also conducted and no appreciable difference was observed for the samples tested. The d18O values of DIP in seawater determined using this method range from 18.6 to 22.3, suggesting small but detectable natural variability in seawater. For the San Francisco Bay estuary DIP d18O is more variable, ranging from 11.4 near the San Joaquin River to 20.1 near the Golden Gate Bridge, and was well correlated with salinity, phosphate concentration, and d18O of water.

Publication type Article
Publication Subtype Journal Article
Title A precise method for the analysis of d18O of dissolved inorganic phosphate in seawater
Series title Limnology and Oceanography: Methods
Volume 2
Issue JUL.
Year Published 2004
Language English
Description 11 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Limnology and Oceanography: Methods
First page 202
Last page 212
Online Only (Y/N) N
Additional Online Files (Y/N) N
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