Results
Spike 1
All of the averages here are presented for seven replicates.
| Data: | Zn-64 He mode | Zn-66 He mode | Zn-66 No gas mode | Zn-67 He mode | Zn-68 He mode | Zn-68 No gas mode | Zn-70 He mode | As-75 He mode |
| average | -0.83 | -0.96 | -0.91 | -0.80 | -0.85 | -0.90 | 25.22 | 0.02 |
| stdev | 0.02 | 0.02 | 0.01 | 0.03 | 0.03 | 0.00 | 5.56 | 0.00 |
| actual | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 | 0.05 | 0.03 |
| avg/actual | -15.42 | -17.96 | -16.99 | -14.82 | -15.84 | -16.80 | 469.91 | 0.86 |
| ave %QRSD | 3.23 | 5.00 | 1.30 | 11.58 | 5.71 | 2.80 | 66.38 | 59.11 |
All of the measured zinc isotopes for spike 1 had negative concentrations, which indicates that they were below the detection limit of the instrument. This follows from the calculated detection limits from this run, which ranged from 0.07 to 0.25. The average %QRSD values for the zinc isotopes were less than 6%, excluding Zn-67 and Zn-70 measured in helium mode.
The arsenic measurement (0,02 ppb) was less than the limit of detection calculated from the blanks (0.05 ppb). Additionally, the average %QRSD for arsenic was 59.11%, meaning that there is a lot of uncertainty associated with the replicate measurements of the arsenic for this spike. Spike 1 had the lowest concentration for arsenic at 0.03 ppb. There is a significant amount of variation within replicate measurements within the same analysis (represented by a high average %QRSD value). This indicates that the concentrations of As in spike 1 cannot be reliably replicated and the limit of quantification is higher than 0.03 ppb for As using the ICP-MS in He mode.
Spike 2
| Data: | Zn-64 He mode | Zn-66 He mode | Zn-66 No gas mode | Zn-67 He mode | Zn-68 He mode | Zn-68 No gas mode | Zn-70 He mode | As-75 He mode |
| average | -0.75 | -0.91 | -0.86 | -0.75 | -0.80 | -0.85 | 15.72 | 0.05 |
| stdev | 0.01 | 0.03 | 0.01 | 0.09 | 0.02 | 0.01 | 16.11 | 0.01 |
| actual | 0.11 | 0.11 | 0.11 | 0.11 | 0.11 | 0.11 | 0.11 | 0.05 |
| avg/actual | -7.09 | -8.58 | -8.09 | -7.10 | -7.52 | -7.96 | 148.11 | 0.92 |
| ave %QRSD | 3.36 | 4.09 | 0.83 | 16.97 | 5.56 | 1.68 | 66.29 | 50.97 |
All of the measured zinc isotopes for spike 2 had negative concentrations, which indicates that they were below the detection limit of the instrument. The calculated zinc concentration in this spike was 0.11 ppb, which is above the calculated limit of detection for Zn-66 and Zn-68 in no gas mode. But, those concentrations were not measured in the spikes even though they were above the detection limit, indicating that the detection limit is lower than the limit of quantification, or what can repeatedly be measured by the instrument. The average %QRSD values for the zinc isotopes were less than 6%, excluding Zn-67 and Zn-70 measured in helium mode. The Zn-66 %QRSD for no-gas mode was 0.83%, which is very small and indicates that the concentrations of the in-analysis replicates were very close to each other.
The average arsenic measurement (0,05 ppb) was equal to the limit of detection calculated from the blanks (0.05 ppb). Additionally, the average %QRSD for arsenic was 50.97%, meaning that there is a lot of uncertainty associated with the replicate measurements of the arsenic for this spike.
Spike 3
| Data: | Zn-64 He mode | Zn-66 He mode | Zn-66 No gas mode | Zn-67 He mode | Zn-68 He mode | Zn-68 No gas mode | Zn-70 He mode | As-75 He mode |
| average | -0.59 | -0.71 | -0.67 | -0.59 | -0.60 | -0.67 | 30.37 | 0.06 |
| stdev | 0.02 | 0.06 | 0.00 | 0.11 | 0.06 | 0.01 | 11.57 | 0.02 |
| actual | 0.21 | 0.21 | 0.21 | 0.21 | 0.21 | 0.21 | 0.21 | 0.11 |
| avg/actual | -2.76 | -3.32 | -3.14 | -2.77 | -2.80 | -3.13 | 142.01 | 0.55 |
| ave %QRSD | 7.76 | 7.88 | 1.90 | 25.73 | 14.17 | 2.60 | 35.61 | 53.08 |
All of the measured zinc isotopes for spike 3 had negative concentrations, which indicates that they were below the detection limit of the instrument. The calculated zinc concentration in this spike was 0.21 ppb, which is above the calculated limit of detection for all Zn isotopes except for Zn-67 and Zn-70 in helium mode. But, the calculated concentrations were not measured in the spikes even though they were above the detection limit, indicating that the detection limit is lower than the limit of quantification, or what can repeatedly be measured by the instrument. The average %QRSD values for the zinc isotopes varied more for this spike compared to the other two, see Tables 8-10. The Zn-66 %QRSD for no-gas mode was 1.90%, which is very small and indicates that the concentrations of the in-analysis replicates were very close to each other.
The average arsenic measurement (0,06 ppb) was slightly above the limit of detection calculated from the blanks (0.05 ppb). But, the calculated concentration of arsenic in this sample was 0.11 ppb. Several of the replicates had concentrations near 0.11 ppb, but others were lower as seen by the average value and the high %QRSD. This indicates that the arsenic limit of quantification is higher than the limit of detection calculated using the blanks because the arsenic measurements for a known concentration are not repeatable.