WHOI-MAT253


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 above.
  • 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.