We continually measure three different IAEA standards to estimate the machine uncertainty of the IRMS. We also track the reproducibility of our bone pretreatment by measuring replicates of, among other things an 8300 year old whale bone. Since we had poor reproduciblity of the δ13C on this bone, Dr Svetlana Svyatko has carried out a series of tests (2013)on bones of various animals and ages to test the effect of pretreatment on this variability. Sufficient material for 10 measurements was homogenised prior to pretreatment. As the table below shows, the variability on the sample population of 10 replicates is in most cases lower than the machine variability, measured with over 1500 replicates of R041. We conclude that the large variability on the long term replicates of UBA-No 8968 (shown in blue below) is due to bone inhomogeneity, which is not seen in the mammoth bone UBA-No 15593 (shown in brown below). However we conservatively report the machine variability from R041 as the uncertainty on our δ13C and δ15N measurements.
sigδ13C=0.22 |
sigδ15N=0.15 |
| type | UBA-No | n | avgδ13C | sigδ13C | avgδ15N | sigδ15N | age or F14C |
| bison | 21202 | 10 | -20.2 | .02 | 5.3 | .04 | 43436 |
| bovine | 19236 | 10 | -24.2 | .03 | 7.1 | .03 | 1.04675 |
| mammoth | 16666 | 10 | -22.0 | .33 | 8.8 | .06 | 42032 |
| dog | 19245 | 10 | -23.0 | .16 | 8.7 | .06 | 1.1539 |
| rhinoceros | 17181 | 10 | -20.7 | .04 | 5.1 | .05 | 32393 |
| narwhal | 17766 | 8 | -14.4 | .11 | 19.0 | .10 | 34973 |
| whale | 8968 | 10 | -16.7 | .03 | 12.4 | .07 | 8334 |
| whale | 8968 | 54 | -16.7 | .38 | 12.7 | .32 | 8338 |
| mammoth | 15593 | 98 | -21.6 | .094 | 8.94 | .12 | ∞ |
| R041 | >1500 | 0.22 | 0.15 |
- sigδ13C and sigδ15N are the variance of the reported number of measurements (n).
- avgδ13C and avgδ15N are the mean of the reported number of measurements (n).
- values in blue and brown are for unhomogenised samples
- values in green are F14C