Quality assurance in analysis of cryogenically stored liver tissue specimens from the NIST National Biomonitoring...

Portions of liver tissue specimens originally stored in the National Biomonitoring Specimen Bank (NBSB) and analyzed between 1980 and 1987 were re-analyzed in 1997 using instrumental neutron activation analysis (INAA) for the determination of 17 trace elements. Duplicate portions of each specimen had been stored at two different temperatures. The first was stored in a liquid nitrogen vapor-cooled freezer at -150 degrees C, standard NBSB storage conditions, and the other in an electric freezer maintained at -80 degrees C. Two portions of seven livers from each storage temperature were re-analyzed for this work. Results showed no changes in trace element content as a function of storage temperature, within the uncertainty of the method used. Results from these analyses agreed with results of initial analyses for most analytes in most sub-samples. Of the exceptions, five were due, in part, to an incorrect basis mass for the initial sub-specimen of one tissue, five with variable Zn results were attributed to difficulties in peak fitting for this element during INAA data processing, and the remaining were isolated differences discussed in this paper. Results of this work indicate that specimen storage and processing protocols are adequate to prevent noticeable contamination of specimens with trace elements, with the exception of Cr. Variability in Cr content was observed for the liver tissues which may have been caused by Cr contamination of the samples by the Teflon mill. Analyses of portions of Standard Reference Material (SRM) 1566a Oyster Tissue (certified in 1989) and SRM 1577a Bovine Liver (certified in 1982) were also included in this study for the purpose of quality control and to assess the stability of these freeze-dried powders that were stored at room temperature. No changes were observed in these materials.