Figure AF1. Comparison of N concentrations and isotopic compositions of untreated samples and H2O- and 6-N HCl-rinsed samples, showing that H2O tends to remove a small fraction of N with lighter N isotopic species, possibly ammonium cation, and HCl tends to remove a larger fraction of N without an isotopic preference, perhaps a combination of N as free ions/cations, surface absorbed material, and loosely bound organic N. See Table AT2, p., for data.

Figure AF1. Comparison of N concentrations and isotopic compositions of untreated samples and H₂O- and 6-N HCl-rinsed samples, showing that H₂O tends to remove a small fraction of N with lighter N isotopic species, possibly ammonium cation, and HCl tends to remove a larger fraction of N without an isotopic preference, perhaps a combination of N as free ions/cations, surface absorbed material, and loosely bound organic N. See Table AT2 for data.