ISO INTERNATIONAL STANDARD 16720 First edition 2005-03-15 Soil quality Pretreatment of samples byfreeze-dryingfor subsequent analysis Qualitedusol-Pretraitement des échantillonsparlyophilisation pour analysesubsequente Reference number ISO 16720:2005(E) @ISO 2005 ISO16720:2005(E) Foreword IsO (the International Organization for Standardization)is a worldwide federation of national standards bodies (iSO member bodies). The work of preparing International Standards is normally carried out through IsO InternationalElectrotechnicalCommission(lEC)onallmattersofelectrotechnicalstandardization. International Standards are drafted in accordance with the rules given in the ISO/lEc Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75%of the member bodies castinga vote Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. IsO shall not be held responsible for identifying any or all such patent rights. ISO16720 was prepared by Technical Committee ISO/TC 190, Soil quality,Subcommittee SC 3,Chemical methodsandsoilcharacteristics. ISO 2005All rights reserved ii INTERNATIONALSTANDARD ISO16720:2005(E) Soil quality - Pretreatment of samples by freeze-drying for subsequent analysis Scope 1 This International Standard specifies a method for pretreatment of soil samples by freeze-drying for subsequentanalysis This International Standard is applicable to soil samples for subsequent determination of elements or organic compounds recognized as non-volatile underfreeze-dryingconditions.Generally,this International Standard can also be applied to samples from sludges and sediments. This method is also applicable as a first step for the determination of dry matter (or water) content, for instance in the case of samples with high water content. 2Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Iso11464,Soilquality-Pretreatmentofsamplesforphysico-chemicalanalyses method 3Principleandgeneralrequirements Before freeze-drying, samples shall be cooled below their eutectic points. These are rarely known, but freezing the samples below -40 C is usually sufficient. During freeze-drying, water is removed from the sample under vacuum conditions by direct conversion from into ice.Generally a temperature below-5o c inside the condenser is suitable for usual applications. Sublimation requires heat in order to take place within an acceptable range of time. When the frozen sample containers are connected to an external inlet manifold (see 5.1.2), heat energy is supplied by the laboratory atmosphere. In case of a drying chamber equipped with temperature-controlled carriers (see 5.1.1), this energy is provided by heating the carriers. Vacuum conditions shall allow the generation of vapour pressure difference needed for sublimation and the continuous evacuation of water vapour from the sample. Throughout the drying process, the pressure inside non-volatile, a final temperature of the sample between -20 C to -25 °C is suitable. Other final temperatures maybe neededfor compoundsrecognized as morevolatile.Inall cases,thefinal step shall beas short as possible. @ ISO 2005 All rights reserved 1 ISO 16720:2005(E) thickness of the sample should not exceed 2 cm. If the representative amount exceeds a thickness of 2 cm, multiple drying may be applied. subsequent determinations. Sample containers forfreeze-drying are selected accordingly NOTE Soil samples often need to be dried before analysis. In the case of very humid or clayey soils, the technique of of a quicker dryin