Samples for Analysis

In order to perform an accurate analysis MyCore Scientific requests the following points are considered when samples are submitted for analysis. 

  1. Samples of at least 100 milligrams (0.1 gram) DRY weight are preferred for the sections between 0 to 10 cm and samples of at least 1000 milligrams (1.0 gram) are needed for deeper samples.  Smaller samples can be used (e.g. as little as 10 mg).  However the precision of the results may suffer and you should consult with us before submitting very small samples.
  2. Samples must be a sub-sample from a homogenized section of the core.  Large pieces of extraneous material (e.g. pieces of wood etc) should be removed prior to preparing the samples for 210Pb analysis.
  3. Samples should be dried and ground to pass through a screen with about 100 mesh size. If samples are not ground then they should be sufficiently friable that they can be physically desegregated in strong acid.
  4. Samples should be pre-weighed in 50 ml plastic centrifuge test tubes.
  5. Wet samples can be analyzed but often they contain such a small amount of dry sediment that the results of the analysis are not very accurate. 
  6. Samples cannot be ashed or subjected to other high temperature combustion or leaching. The Pb and Po isotopes can be volatilized from the samples at temperatures in excess of 150C.
  7. 12 to 20 sections of a sediment core must be analyzed before the core can be dated. Two sampling schemes can be used. Sections can be analyzed individually and results interpolated to derive data for the missing values or some samples can be composited together for analysis.  The latter approach is beneficial because it minimizes the amount of interpolation that must be performed. However it may decrease the amount of temporal resolution that can be obtained in the dating.

The sections of the core should be selected for analysis so that the depth(s) or sections of the core of primary interest are analyzed most intensely. However 210Pb dating requires information from the entire concentration-depth profile as well as from a background sample. Therefore the surface sample and a deep sample from near the bottom of the core must be analyzed.  In cores with an unknown stratigraphy we recommend using an exponential depth sequence. A two phase approach in which six or eight samples are analyzed and then more samples are selected based on the initial analysis is also useful.