ICUMSA accords each Method the status of Tentative, Accepted, Official or Offical Reference Status.
A method receives Tentative status under the following conditions: the method is fully developed (e. g. according to IUPAC Single-Laboratory Validation protocol); that is initial information on ‘repeatability’, ruggedness, precision, accuracy and interferences is available. The method will have been tested by more than one laboratory, using samples that cover the range of the analyte, but not tested by a full collaborative study at the time of its adoption. Tentative methods will be made available in a less formal manner than Approved methods and will not have a permanent number. Tentative methods would, however, be exactly described in the standard format before adoption. It is understood that Tentative status is temporary, and the method will undergo collaborative testing during the Session following its adoption and no more than four years after its introduction. The status of all Tentative methods should be reviewed at each Session, and status confirmed or revised as required. The review shall not be abused to establish a “permanent” Tentative status. Tentative methods will be published in the Methods Book.
When the Method is upgraded by a collaborative test, it will become OFFICIAL and will be re-published in the Methods Book.
This category of methods includes the following types:
1. Methods that have been in practical use for many years and that serve a useful function in industry and trade (i. e. they are considered to have utility). This includes many older Official ICUMSA® methods that have not undergone validation by a collaborative test, and which are not likely to be validated in the future.
2. Technical and process control methods that cannot meet the IUPAC standards, but which are of considerable usefulness and should be available in the ICUMSA® Methods Book.
3. Other methods that cannot meet the IUPAC standards for international collaborative tests by virtue of being performed on unstable materials which cannot be circulated internationally.
Accepted methods will be published in the Methods Book.
It is understood that if a collaborative test becomes possible, it should immediately be performed. If it is considered to be satisfactory, the method would be moved into the OFFICIAL category.
OFFICIAL METHOD and OFFICIAL (REFERENCE) METHOD
This is a method that has undergone full collaborative testing according to IUPAC standards. If it meets the criteria of acceptability for the ICUMSA® delegation, it can become Official immediately.
Official status may be assigned exceptionally to ICUMSA Methods, which could only be validated in a single laboratory, providing that sufficient statistical data are available to calculate the Reproducibility based on the Horwitz-Function, as outline in the IUPAC Guidelines , in section 4.4, Method and laboratory effects.
Where there is more than one Method published per sample/parameter type (and range) with Official status it shall be made clear which Method ICUMSA® recommends as to be used when assigning that Method OFFICIAL (REFERENCE) status.
Official Methods and Official (Reference) Methods are published in the Methods Book.
 Thompson, M., Ellison, S.L.R., Wood, R., Harmonized Guidelines for Single-Laboratory Validation of Methods of Analysis, Pure Appl. Chem., Vol.74, No.5, pp.835-855, 2002.
 Horwitz, W., Protocol for the Design, Conduct and Interpretation of Method-Performance Studies, Pure Appl. Chem., Vol.67, No.2, pp.331-343, 1995.