Thermal ionization -IDMS

A number of analytical techniques have been used to determine ppm to ppt levels of vanadium in biological materials. These include neutron activation analysis (NAA), graphite furnace atomic absorption spectrometry (GFAAS), spectrophotometry, isotope dilution thermal ionization-mass spectrometry (IDMS), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Table 6-1 summarizes the analytical methods for determining vanadium in biological materials. 

A known amount of Cr(III)- Cr(VI) enriched spike was added to the reconstituted sample. Extraction was carried out with liquid anion exchange solution (Amberlite LA 2/MIBK), followed by back-extraction with 1.5 mL of ammonia solution (6%). The aqueous ammonia phase was washed with n-hexane, followed by electrodeposition on Pt wire in ammonia solution (6%) at a voltage of 2.45 V. The detection was by IDMS (thermal ionization of masses 52 and 53). The calibrants used were Na2Cr207 for Cr(VI) and a commercial solution of CrCls for Cr(III). 

IDMS with thermal ionization is a very precise and accurate method of trace element analysis however, the method is laborious, time consuming, and requires technical expertise and extreme care in blank controls and all sample preparation steps. The method provides very reliable data for elements with appropriate enriched stable isotopes to use as internal standards but it too should only be considered as a reference method [44]. 

HV High voltage, high vacuum TI-IDMS Thermal ionization isotope dilution... 

Thermal Ionization Mass Spectrometry (TIMS). TIMS continues to be the standard method by which all other lead concentration measurements are evaluated (NRC 1993). TIMS is considered the definitive method for accuracy in elemental analyses using isotope dilution mass spectrometry (IDMS), and it provides unprecedented precision, sensitivity, and detection limits for lead concentration analyses (Heumann 1988). It also has been the method used to demonstrate that many previously reported lead concentrations in environmental and biological samples were orders of magnitude higher than the true values due to sample contamination and analytical inaccuracies (e.g., Ericson et al. 1979 Everson and Patterson 1980 Flegal and Coale 1989 Patterson 1965 Settle and Patterson 1980). 

---