X-Message-Number: 12005
Date: Fri, 25 Jun 1999 06:25:29 -0700 (PDT)
From: Doug Skrecky <>
Subject: nitrogen vapour storage

  Mackey EA.  Demiralp R.  Fitzpatrick KA.  Porter BJ.  Wise SA.  Becker PR. 
  Greenberg RR.
  Analytical Chemistry Division, National Institute of Standards and
  Technology, Gaithersburg, MD 20899, USA. 
  Quality assurance in
  analysis of cryogenically stored liver tissue specimens from
  the NIST National Biomonitoring Specimen Bank (NBSB).
  Science of the Total Environment.  226(2-3):165-76, 1999 Feb 9.
  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.

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