Novel approaches to the determination of trace elements by atomic spectrometry

Two perceived limitations of conventional atomic spectrometry were addressed in these studies. One limitation is that the time required for sample preparation can exceed the actual analysis time by two or more orders of magnitude. High pressure homogenization in combination with high speed blending was evaluated for the preparation of slurries which could be directly analyzed by graphite furnace atomic absorption spectrometry (GF-AAS). Cadmium, copper and lead concentrations were successfully determined in certified reference materials (CRMs) of biological origin and frozen cervine liver and kidney. By capping the flat valve head of the homogenizer with a ruby disc, metal contamination introduced by the processing was reduced appreciably (but not eliminated) and the procedure was extended to the determination of chromium, iron, manganese and nickel in botanical CRMs and air dried animal feeds. The one problematic analyte element proved to be selenium which was consistently underestimated with this procedure. However, the combination of high pressure homogenization and partial enzymatic digestion with a crude protease alone or admixed with lipase or cellulase, released Se-residues from zoological and botanical CRMs so that Se could be accurately determined by slurry introduction GF-AAS. This technique was also applied successfully to freeze-dried, fresh and boiled fish tissues. The principal advantages of the slurry preparation technique are its speed, simplicity and lack of operator intervention.The second limitation involved the loss of chemical speciation information during analysis. To preserve this speciation information, individual chemical species were separated chromatographically then detected in the column eluate using a novel all silica T-tube interface coupled with AAS. The advantages of the current interface design over previous prototypes were the compatibility with both organic or aqueous mobile phases and the low limits of detection (LODs) for Ag, Cd, Cu or Zn. The feasibility of the approach was demonstrated by monitoring levels of metal analyte bound to individual metallothionein isoforms which had been partially resolved by size exclusion or ion exchange HPLC. Whereas the metallothionein-I (MT-I) isoform was enriched in Cu relative to the MT-II isoform, the reverse was true for Zn. Also, a Ag-saturation procedure rapidly and efficiently replaced the bound Cd, Cu and Zn in these polypeptides