were weighted into ceramic crucibles, and then added with
10 mL 5% (v/v) HCl. The crucibles were then heated in a 60 C water
bath for 1 h to remove the carbonate minerals (He et al., 2009). The
residue was washed by triple-distilled water until the pH of the
solution reached neutral. The TOC contents of the residues were
analyzed with a Leco C230 elemental analyzer after being oven
dried at 60 C for 24 h.
(Liu et al., 2013b). The signal of m/z 75 was recorded while that
of m/z 35 was monitored simultaneously to track the potential
inference from 35K+ and 35Cl+, which could form interference ions
of 40Ar35Cl+, 35Cl40Ar+, and 35K40Ar+. The concentrations of the analytes
were calculated from the areas of the corresponding chromatogram
peaks based on calibration curves established using
standard solutions.