Data Evaluation for the WHOI MicroPaleo Finnigan MAT 253's
We send your entire dataset, with no analyses removed. It is
up to each individual user to evaluate their data. Within the
dataset you have been sent are many clues to the validity of each
data point. Please look at ALL of the mass spec analysis data
as you review your dataset. From left to right in the dataset,
please look at:
- STDVOLT - The standard voltage should be “close”
to the SAMPVOLT, or the sample voltage. The voltages should
be above 0.6 volts.
- STDVOLT minus SAMPVOLT should be lower
than 2.5. This is the degree of balancing between the standard
and sample pressures.
- COMMENT - Look to see if the operator added comments
which may have affected the individual analysis such as “dirty
bugs” or “small sample”.
- PRES - Pressure is the amount of gas produced
before any expansion. Pressures above 1200 mbar are expanded
once. Pressures above 1600 are expanded until the pressure falls
below 1200 mbar.
- EXPAND - Expand details the number of expansions
that the software used to lower pressures to the before introduction
into the mass spec. Ideally, all of your samples should run
under the same number of expansions.
- LEAKRATE - The normal leakrate is below 500 mbar.
Numbers above 500 are still fine, as non-condensibles are pumped
away before analysis in the mass spec.
- PREREACT - This is the background vacuum in mbar.
The value should be less than 80. But as with the leakrate,
analysis may still be fine with high prereact values as noted
- C13OUTLIER and O18OUTLIER – The number
of outliers should be less than 4. If greater than 4 the software
did not know which of the 8 scans was bad and you may need us
to manually calculate the raw mean values.
- C13ERROR and O18ERROR – these values
should be less than 0.10.
If you find problems with many of these individual indicators,
the individual analysis may be "bad" and you can justifiably
delete the datapoint.