Hi,

Depending on the salt type an concentration you might have to correct for the salt effect if running them by equilibration. Simply increase equilibration times for 18O und 2H might lower the problem but will not solve it.

Dissolved salts (salt type and its concentration) influence the oxygen and hydrogen stable isotope values determined by the CO2 equilibration method (δ18O and δ2H). This is referred to as the salt isotope effect in the literature. A more recent publication suggests a minor correction of seawater data (salinity of 35 psu). This correction is reported to be –0.15‰ for d18O (Lécuyer et al, 2009). However, other studies did not observe such an effect for seawater salt concentrations (Horita et al., 1993a,b; Bourg et al., 2001). For normal seawater (NaCl, 35 psu) you are almost fine but some very saline brines with Mg-salts this is indeed an issue and will shift your delta values by several permil. 

For d13C you can run them as normal DIC samples (we use 0.85mL in the Gasbench; seawater has around 2.2mmol C). If you do concentrations from the chromatogram and determine the injected sample volume by a balance (as we do) keep in mind that the density of seawater is not 1.

I have not yet seen a bad effect of salt waters in the Gasbench but things are different in the TC/EA or H/Device where the syringe comes in direct contact with the salt water.

regards,
Robert



suggested reading:

Bourg, C., Stievenard, M. and Jouzel, J. (2000), Hydrogen and oxygen isotopic composition of aqueous salt solutions by gas–water equilibration method. Chem. Geol. 173, 331- 337.

Horita J., Cole D. R., and Wesolowski D. J. (1993a) The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: I. I. Vapor-liquid water equilibration of single salt solutions from 50 to 100°. Geochim. Cosmochim. Acta 57(19), 2797-2817

Horita J., Cole D. R., and Wesolowski D. J. (1993b) The activity-composition relationship of oxygen and hydrogen isotopes in aqueous salt solutions: II. Vapor-liquid water equilibration of mixed salt solutions from 50 to 100°C and geochemical implications. Geochim. Cosmochim. Acta 57(19), 4703-4711

Lécuyer, C., Gardien, V., Rigaudier, T., Fourel, F., Martineau, F. and Cros, A. (2009): Oxygen isotope fractionation and equilibration kinetics between CO2 and H2O as a function of salinity of aqueous solutions. - Chemical Geology, 264, 122-126.

François Martineau, François Fourel, Anne-Marie Bodergat, Christophe Lécuyer (2012): D/H equilibrium fractionation between H2O and H2 as a function of the salinity of aqueous solutions.- Chemical Geology 291, 236–240




Am 13.05.2016 um 13:27 schrieb Andrew Cooper <[log in to unmask]>:

> Hello fellow isotope lovers,
> 
> We are more regularly receiving salt water samples to test for d13C, d18O and dD though our ThermoFisher MS and we are thinking if anyone has seen any ill effects from running these samples?  I find that I have to equilibrate longer to get a good d18O and dD value, but has anyone seen salt water samples clog up needles or water traps faster than say normal freshwaters?
> 
> We are trying to fix a problem before it happens and any advice or previous knowledge would be helpful.
> 
> Cheers,
> Andrew

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