The major challenge of chemical speciation analysis is the isolation, separation and quantification of the species leaving the original compound intact, which may be in some kind of equilibrium state with other species present in the sample. While it would be most logical to do the species analysis on-site, in real-time by probing the original “sample” in its natural environment, most of the available tools today require to collect a sample and to analyse it after some sample pre-treatment in the laboratory. It is clear that such practical approach has distinct drawbacks with respect to possible species transformation during analysis. It also requires a high degree of awareness for possible transformations when designing meaningful sample conservation and pre-treatment procedures. A particular difficult issue is the extraction of compounds of interest from a solid sample while preserving the molecular identity of the analyte.
Some recent semiautomated hyphenated techniques try to include part of the sample pre-treatment, offering better reproducibility and reduce the analysis time. Other developments in this area are assisted leaching procedures, where different types of interaction (microwave irradiation, ultrasonic agitation, high pressure etc.) enable the leaching of the analyte from the sample matrix by preserving the analyte species. New derivatization procedures such as ethylation and propylation with sodium tetraalkyl borates have been designed to meat the requirements of high conversion efficiency without the drawback of species transformation.
Another problem of elemental speciation analysis is the insufficient insurance for accuracy and traceability of the overall analytical process. Species selective isotope dilution analysis has been developed in order to monitor species transformation during the analysis and to avoid bias in the final results. However, this new approach is limited to those cases, where standards for element species of known isotopic composition exist. The more general absence of primary methods for speciation analysis implies necessarily the use of certified reference materials (CRMs) for quality control. The lack for species related CRMs has been recognized and may be partly addressed in the future by the CRM producers. Additionally there is also a lack with respect to pure species standards.
Up to now, existing methodologies are rather complex and not easy to adapt for routine applications. Further, commercially available instrumentation is rather limited to very few techniques (LC-ICP-MS, GC-MIP-OES). The dissemination of the analytical methods from specialised analytical chemistry laboratories to routine laboratories is not evident. New developments in this area try to fill this gap by providing commercial tools for specific speciation problems, such as an automated speciation analyser (ASA) for mercury speciation.
From the foregoing comments it is clear that the weakness in speciation procedures is not in the measurement process itself, but occur in the steps prior to the determination. More rugged and reliable analytical methods and instrumentation have to be developed. Additionally certified reference materials, intercomparison studies, and proficiency testing, are some of the steps that could help in pinpointing weaknesses and problems in the overall analytical process.
Related EVISA resources
Link Database: Research Groups working in the field of chemical speciation
Link Database: Research Projects
Brief summary: Certified Reference Materials for Speciation Analysis
Brief summary: Research fields related to elemental speciation
Brief summary: Tools for elemental speciation
Further chapters: About Speciation
Related EVISA News
September 10, 2009: Speciation Analysis - Striving for Quality
January 15, 2008: Species-specific isotope dilution analysis has been adopted as an official method under US legislation
February 9, 2006: Preservation of arsenic speciation in natural water samples for up to three months
last time modified: June 15, 2020