A sensitive and fast method for dir

A sensitive and fast method for direct determinations of
dissolved organic carbon (DOC) in bulk samples and in
chromatographically separated fractions by inductively
coupled plasma isotope dilution mass spectrometry (ICPIDMS)
is developed. A 13C-enriched spike solution of
benzoic acid is used for the isotope dilution step. Equal
ionization efficiencies are obtained for carbon, independent
of the type and molecular weight of the dissolved
organic substance, which is the most important precondition
for DOC determinations by ICP-IDMS. The detection
limits achieved are 0.3 mg L-1 for bulk analyses and
7  10-4 íg s-1 for transient signals of chromatographic
peaks. The results for different water samples, analyzed
by ICP-IDMS and a conventional DOC method, agree
well within the limits of error. By using a 13C spike
solution, which also contains enriched isotopes of heavy
metals, simultaneous determinations of DOC and heavy
metal concentrations in separated fractions of complexes
with humic substances are possible by coupling ICPIDMS
with HPLC and using size exclusion chromatography.