Assessment of element-specific homogeneity in reference materials using microanalytical techniques

The IAEA established in 1994 a co-ordinated research programme (CRP) on "Reference Materials for Microanalytical Nuclear Techniques" as part of its efforts to promote and strengthen the use of nuclear analytical technologies in member states with the specific aim of improving the quality of analysis of nuclear, environmental, and biological materials. The objectives of this initiative were: to identify suitable biological reference materials which could serve the needs for quality control in microanalytical techniques; to evaluate existing CRMs for use in microanalytical investigations; to evaluate appropriate sample pretreatment procedures for materials being used for analysis with microanalytical techniques; to identify analytical techniques which can be used for characterisation of homogeneity determination, and to apply such techniques to the characterization of candidate reference materials for use with microanalytical techniques. The CRP lasted for 4 years and seven laboratories and the Agency's Laboratories in Seibersdorf participated. A number of materials including the candidate reference materials IAEA 338 (lichen) and IAEA 413 (single cell algae, elevated level) were evaluated for the distribution of elements such as Cl, K, Ca, Cr, Mn, Fe, Zn, As, Br, Rb, Cd, Hg, and Pb. The results obtained during this CRP suggest that: each element exhibits its characteristic distribution in a matrix described by the "Ingamels' sampling constant" or the "relative homogeneity factor" of Kurfuerst; both concepts are valid over a large range of sample mass used for analysis (from 0.1 g to around 100 mg); and materials being characterised quantitatively for element homogeneity could be used for the experimental determination of total uncertainty of other analytical techniques. As far as we are aware this is the first time the concept of quantitative characterisation of homogeneity has been applied to potential reference materials and the first demonstration of the feasibility and usefulness of the concept with particular emphasis on enhancing quality control opportunities for microanalytical techniques.     

Analysis of acrylamide in food by isotope-dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A confirmatory method for the determination of low levels of acrylamide in different food products is presented. The method entails extraction of acrylamide with water, precipitation of matrix constituents with acetonitrile, and two clean-up steps consecutively over Isolute Multimode and cation-exchange cartridges. The final extract is analyzed by liquid chromatography (LC) coupled to positive electrospray ionization tandem mass spectrometry employing [13C3]-acrylamide as internal standard. For the chromatographic step, a LC column based on a polymethacrylate gel is employed which shows good retention of acrylamide under isocratic flow conditions (k' = 1.2). Mass spectral acquisition is done by selected reaction monitoring, choosing the characteristic transitions m/z 72-->55, 72-->54 and 72-->27. In-house validation data for breakfast cereals and crackers show good precision of the method, with intra- and interassay variation below 10%. The limits of detection for crackers and breakfast cereals, respectively are estimated at 15 and 20 microg/kg, and recoveries of fortified samples ranged between 58 and 76%. Furthermore, the method is applicable to a number of different food products, including biscuits, crisp bread, wafers, confectionery cocoa liquor, and nuts. Finally, the good results obtained in several small-scale interlaboratory tests provided additional confidence in the performance of the method.