The　influence　of　impurities　on　the　shape　of　the　freezing　curves　of　the　triple　point　of　water　(TPW)　in　three　small　TPW　cells　was　investigated　using　the　freezing　curve　analysis　method.　We　describe　the　procedure　for　preparing　outer　ice　mantles　in　small　TPW　cells,　for　obtaining　freezing　plateaus,　and　for　comparing　the　results　between　the　old　cell　(s/n:　021)　and　the　new　cells　(s/n:　001　and　s/n:　008).　The　experimental　results　show　that　the　maximum　influence　of　impurities　on　the　observed　phase-transition　temperature　of　water　in　the　cell　(s/n:　021)　is　approximately　0.2　mK　below　the　peak　temperature　of　the　freezing　plateau　during　freezing.　Also,　jagged　temperature　fluctuations　were　observed　near　the　end　of　the　freezing　plateau　in　the　old　cell.　However,　these　phenomena　did　not　appear　in　the　freezing　plateaus　of　the　new　small　cells.　The　equilibrium　temperature　realized　with　the　old　cell　is　2.3　mK　lower　than　that　of　the　new　cells,　possibly　due　to　excessive　residual　air.　Therefore,　assessing　the　effects　of　impurities　on　the　TPW　using　an　outer　sheath　method　similar　to　that　used　in　obtaining　the　fixed　points　of　other　metals　is　useful.　Additionally,　an　estimated　total　mole　fraction　impurity　concentration　can　be　determined　using　Raoult＇s　Law　and　the　first　cryoscopic　constant　for　water.