Acid cleaning processes were performed on a class 100 laminar flow clean bench assembled inside a class 1000 clean room.The ultrapure water was produced by Millipore RO (Reverse Osmosis) and Milli-Q water purification systems.The three purity grades of nitric acid used for cleaning include Merck reagent grade HNO3,Fisher "TraceMetal" grade HNO3,and the purest Fisher "Optima" grade HNO3.The various bottles,containers and other labware,which are in contact with the samples,are made of low-density polyethylene (LDPE) and FEP or PFA Teflon materials.The acid cleaning procedures of the bottles and other containers follow a successive four times cleaning through immersion in increasing purity of nitric acid baths at different concentrations during four weeks.The first acid bath is performed at room temperature,but the following three acid baths are heated on ceramic hotplates with a surface temperature of 45℃.In order to verify the efficiency of the acid cleaning method,cleaned bottles underwent a blank determination procedure using ELAN 6100 inductively coupled plasma spectrometry (ICP-MS).Results show that most measured trace elements are not detected and the elements detected are at very low concentrations.The blank values are comparable with that of bottles cleaned at Korea Polar Research Institute (KOPRI).Although the acid cleaning method is developed mainly for reliable measurements of trace elements in snow and ice samples,it can also be used for investigations of trace elements in other environmental samples.
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