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Chlorate and perchlorate compounds, used as herbicides, solid fuel propellants, and explosives, are increasingly recognized as pollutants in groundwater. Stable isotope characterization would permit both environmental monitoring of extent of remediation and forensic characterization. Stoichiometric reduction to chloride (greater than 98% yield), by Fe(II) for chlorate and alkaline fusion-decomposition for perchlorate, allows analysis by standard methods to give highly reproducible and accurate delta37Cl results (0.05/1000, 2 x standard error). Analysis of various compounds from different suppliers yielded delta37Cl values for chlorate samples near to +0.2/1000 (SMOC), but one has within-sample heterogeneity of 0.5/1000, possibly due to crystallization processes during manufacture. Results for perchlorate samples also are generally near +0.2/1000, but one is +2.3/1000 (SMOC). The initial results suggest that both forensic and environmental applications might be feasible.

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The use of isotope ratio mass spectrometry (IRMS)-derived data in forensic contexts has increased in recent years, particularly as a tool for source inference. 1 The forensic application of analytical techniques (e.g. for resolving legal disputes or matters of law/regulation and/or for use by legal tribunals/regulators in reaching judicial or quasi-judicial decisions) requires methods that are capable of providing data of sufficient quality to be fit-for-their intended purpose thereby meeting the needs of the stakeholder(s). The quality of data can be assured via (i) the use of validated methods; (ii) suitable internal quality control (QC) and quality assurance (QA) procedures; (iii) the use of certified reference materials (CRMs); and (iv) participation in external comparative studies such as proficiency testing (PT) schemes. 2 Obtaining accreditation to the International Standard, ISO/IEC 17025:2005, 3 as interpreted for forensic science providers by, e.g., the Forensic Science Regulator in England and Wales, can only be achieved for validated methods. There are also other regulatoryrequirements where method validation can be necessary, e.g., compliance with Good Laboratory Practice. Method validation is therefore a key requirement for establishing whether or not a specific method is indeed fit-for-purpose and meets stakeholder needs in terms of the quality and utility of results produced.One definition of method validation is "confirmation by examination and the provision of objective evidence that the particular requirements for a specific intended use are fulfilled." 3 There are many references available on general aspects of "method validation" including the guidelines from the International