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1.1 This practice provides guidance for an alternate linear calibration for the determination of selected actinide isotopes in appropriately prepared aqueous solutions by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). This alternate calibration is mass bias adjusted using thorium-232 (²³²Th) and uranium-238 (²³⁸U) standards. One of the benefits of this standard practice is the ability to calibrate for the analysis of highly radioactive actinides using calibration standards at much lower specific activities. Environmental laboratories may find this standard practice useful if facilities are not available to handle the highly radioactive standards of the individual actinides of interest.

1.2 The instrument response for a series of determinations of known concentration of ²³²Th and ²³⁸U defines the mass versus response relationship. For each standard concentration, the slope of the line defined by ²³²Th and  ²³⁸U is used to derive linear calibration curves for each mass of interest using interference equations. The mass bias corrected calibration curves, although generated from interference equations, are specific to the instrument operating parameters and tuning in effect at the time of data acquisition. Because interference equations are part of the normal ICP-MS manufacturer's software package, this calibration methodology is widely applicable.

1.3 For this standard practice, the actinide atomic mass range that has been studied is from AMU 232 to 244. Guidance for an extended range of AMU 228 to 248 is given in this practice.

1.4 Using this practice, analyte concentrations are reported at each AMU and not by element total (that is, ²³⁹Pu versus plutonium).

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 One of the benefits of this standard practice is the ability to calibrate for the analysis of highly radioactive actinides using calibration standards at much lower specific activities (that is,  ²³²Th and ²³⁸U). Environmental laboratories may find this standard practice useful if facilities are not available to handle the highly radioactive standards of the individual actinides of interest.

5.2 The degree of actual mass bias is variable and is dependent upon instrument tune parameters. This standard practice uses universal interference equations to derive a mass bias correction that is specific to the instrument parameters and tune used for sample data acquisition and not based on a historical average.

5.3 Mass bias correction uses the instrument software interference equations and does not require additional subsequent off-line calculations.

5.4 The methodology that this standard practice is based on has been used for the determination of ²³²Th and  ²³⁷Np in enriched uranium solutions and the determination of  ²⁴¹Am in plutonium and uranium legacy oxides following dissolution and ion extraction chromatography separation.

5.5 Data presented in Section 12 were developed using a quadrupole ICP-MS. This practice can also be applied to high resolution ICP-MS with appropriate validation.