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A precise method for the analysis of ??18O of dissolved inorganic phosphate in seawater

Limnology and Oceanography: Methods

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Abstract

A method for preparation and analysis of the oxygen isotope composition (??18O) 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 ??18O. 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 ??18O 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 ??18O 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 ?? 18O of water. ?? 2004, by the American Society of Limnology and oceanography. Inc.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A precise method for the analysis of ??18O of dissolved inorganic phosphate in seawater
Series title:
Limnology and Oceanography: Methods
Volume
2
Issue:
JUL.
Year Published:
2004
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
202
Last page:
212
Number of Pages:
11