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/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
- 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 above.
- C13OUTLIER & 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.