Dilution of Impurities in Water Triple Point Cells

Controlled amounts of Si and Na impurities (0.1 to 0.5 mu mol.mol(-1) of Si and 0.2 to 1 mu mol.mol(-1) of Na) were diluted in the high-purity water of triple point of water (TPW) cells before sealing the cells. Water samples drawn from the manufactured doped cells were analyzed with high-resolution Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). The TPW temperature of one of the doped cells (the cell that showed a good agreement between the nominal Si and Na amounts and the Si and Na amounts measured by ICP-MS) was measured for different water/ice relative contents. The observed TPW depression was compared to 1) the TPW depression expected from the nominal doping and 2) the TPW depression expected from the total impurity content measured by ICP-MS.