3.2. Analysis of bulk organic fractions using ICPMS
Aliquots of each fraction (F1, F2, F3) were dried and oxidized in
30% H2O2 at 90 C for 24 h to convert OS to SO4
2. Resulting SO4
2
was purified on AG1-X8 anionic exchange resin according to the
method described by Paris et al. (2013). Resin was washed with
ten column volumes (CVs) 10% HNO3, conditioned with 10 CVs
10% HCl and 10 CVs 0.5% HCl, loaded in trace HCl, and washed
3 with 5 CVs Milli-Q H2O before SO4
2 was eluted in 0.5 N
HNO3. SO4
2 samples were quantified using ion chromatography
(IC; Dionex ICS-2000) with an AS-19 anion column and AERS 500
ion regeneration. Concentrations were used to intensity-match
samples and the required Na+ supplement for ICPMS analysis
(Paris et al., 2013). Samples were injected into the plasma torch
with a desolvating nebulizer (Aridus) and bracketed with known
d34S NaSO4 standards. The Neptune was operated in high resolution
(M/DM ca. 10,000) to fully resolve oxygen interference on
m/z 33 and 34. Accuracy was assessed by repeated analysis of a
seawater SO4
2 standard. Both accuracy and precision for d34S values
in this mode of analysis were typically better than ± 0.2‰.
4. R