DOC Determinations in Natural Water Samples by ICPIDMS.
The total DOC content of different natural water samples,
containing various concentrations of humic substances, and of two
solutions of isolated fulvic acids was analyzed by ICP-IDMS. After
filtration (0.45-ím filter), an exactly weighed amount of the 13C
enriched spike solution was added, and the samples were then
acidified and purged as described before. The results (mean with
standard deviation of three independent determinations) are
summarized in Table 4. The same samples were also analyzed
with a conventional DOC analyzer (Carbon Analyzer 555, Ionics
Inc., Watertown, MA) for comparison using IR detection of CO2.
In this case, the DOC content was not directly determined but
was analyzed as the difference of the total carbon and the inorganic
carbon. As can be seen from the results in Table 4, good
agreement between the ICP-IDMS data and those obtained by
the conventional method were obtained within the limits of error.
The standard deviations obtained are mainly influenced by
instrumental instabilities and uncertainties during sample pretreatment,
respectively.