Data Quality

To maintain high data quality, instrument performance is routinely monitored using one or more quality control reference materials (secondary standards), typically at both the beginning and end of each analytical session. When a new analytical routine is developed, it is typically tested against multiple reference materials to assess accuracy over a range of concentrations. To facilitate improved accuracy and precision, techniques such as combined EDS-WDS acquisition, blank corrections, quantitative interference corrections, mean atomic number backgrounds, and time-dependent intensity corrections are used on appropriate materials.

Concord's EPMA lab also participates regularly in interlaboratory exercises. This includes G-probe (one or two test glasses per year) and the 2011 INTAV intercomparison of tephrochronology laboratories (Kuehn et al., 2011). These provide a source of ongoing external quality testing. The lab's results on quality control samples are routinely excellent in terms of both accuracy and precision. Below are examples from the silicate glass trace elements procedure, which forms the basis of a family of analytical routines for silicate minerals and glasses, and the routine tephra glass procedure.

 

Sample Quality Control Data:  Silicate glass with trace elements

Sample   SiO2 TiO2 Al2O3 FeOT MnO MgO CaO Na2O K2O P2O5 Cl BaO CoO Cr2O3 NiO Rb2O SO3 SrO VO2 ZrO2 Total n
                                               
Lipari ID3506 obsidian Mean 74.13 0.070 13.16 1.55 0.066 0.039 0.735 4.07 5.18 0.009 0.333 0.003 0.001 0.003 0.005 0.031 0.000 0.004 -0.003 0.024 99.34 22
StDev 0.32 0.008 0.07 0.04 0.009 0.003 0.012 0.11 0.07 0.006 0.011 0.007 0.006 0.005 0.007 0.008 0.004 0.008 0.013 0.007 0.36  
                                               
INTAV Reference concentrations: 74.14 0.074 13.11 1.55 0.065 0.041 0.734 4.07 5.11 0.010 0.342 0.002   0.0005 0.0002 0.031   0.002 0.000 0.026 99.22  
                                               
Old Crow tephra Mean 72.61 0.278 12.73 1.60 0.055 0.257 1.40 3.73 3.69 0.034 0.253 0.110 -0.001 0.002 0.001 0.007 0.008 0.017 -0.001 0.033 96.75 9
StDev 0.91 0.010 0.19 0.04 0.007 0.016 0.02 0.12 0.09 0.005 0.009 0.006 0.002 0.007 0.004 0.004 0.004 0.006 0.008 0.004 1.29  
                                               
INTAV Reference concentrations: 72.09 0.297 12.51 1.62 0.052 0.275 1.43 3.66 3.56 0.036 0.267 0.107   0.000 0.001 0.011   0.015 0.002 0.032 95.90  
                                               
Sheep Track (Edziza) tephra Mean 61.06 0.235 17.23 4.54 0.133 0.128 1.05 7.57 5.26 0.050 0.211 0.000 0.001 0.001 -0.001 0.013 0.021 0.008 0.004 0.171 97.64 11
StDev 0.83 0.014 0.23 0.13 0.015 0.009 0.06 0.27 0.11 0.007 0.008 0.008 0.007 0.008 0.008 0.008 0.007 0.006 0.006 0.017 1.42  
                                               
INTAV Reference concentrations: 61.59 0.236 17.58 4.55 0.134 0.124 1.09 8.19 5.34 0.038 0.210 0.004   0.000 0.000 0.014   0.001 0.000 0.146 99.03  
                                               
Laki 1783 tephra Mean 49.36 3.13 12.90 14.27 0.237 5.35 9.81 2.81 0.461 0.336 0.015 0.011 0.007 0.006 0.000 0.000 0.092 0.032 0.053 0.025 98.90 7
StDev 0.25 0.02 0.10 0.09 0.015 0.06 0.06 0.06 0.011 0.009 0.002 0.005 0.004 0.003 0.004 0.008 0.009 0.005 0.015 0.006 0.36  
                                               
INTAV Reference concentrations: 49.71 3.11 12.94 14.18 0.233 5.32 9.65 2.88 0.460 0.350 0.020                   98.85  
                                               
BHVO-2g glass USGS Mean 49.66 2.78 13.43 10.98 0.170 7.18 11.40 2.22 0.508 0.270 0.008 0.014 0.004 0.035 0.011 0.003 0.007 0.045 0.049 0.023 98.80 22
StDev 0.18 0.03 0.10 0.04 0.007 0.10 0.04 0.06 0.009 0.009 0.003 0.007 0.005 0.007 0.007 0.007 0.004 0.006 0.018 0.009 0.35  
                                               
USGS Reference concentrations: 49.50 2.77 13.55 11.00 0.170 7.20 11.40 2.30 0.51 0.280   0.015 0.006 0.043 0.014 0.001   0.046 0.052 0.022 98.88  
                                               
NKT-1g glass USGS Mean 38.58 3.93 10.33 12.00 0.207 14.64 13.19 3.51 1.27 0.934 0.005 0.086 0.007 0.061 0.036 0.005 0.005 0.149 0.041 0.041 99.02 26
StDev 0.18 0.03 0.05 0.13 0.009 0.12 0.07 0.08 0.01 0.013 0.003 0.010 0.006 0.007 0.007 0.007 0.004 0.010 0.021 0.008 0.26  
                                               
USGS Reference concentrations: 38.68 3.94 10.20 11.99   14.33 13.21 3.48 1.28 0.970   0.080 0.008 0.065   0.003   0.142 0.048 0.039 98.47  
                                               
Erebus phonolite 81003 Mean 54.73 1.03 18.68 5.36 0.288 0.880 1.92 9.12 5.50 0.283 0.168 0.064 0.002 0.004 0.006 0.015 0.099 0.040 0.000 0.219 98.36 7
StDev 0.33 0.02 0.22 0.05 0.009 0.016 0.02 0.17 0.06 0.011 0.002 0.009 0.003 0.006 0.006 0.006 0.003 0.008 0.009 0.010 0.39  
                                               
          Reference concentrations: 54.60 1.03 19.02 5.34 0.269 0.910 1.95 9.00 5.56 0.290 0.176 0.052           0.030   0.208 98.40  
                                               
StHs6-80 andesite MPI-DING Mean 62.58 0.701 17.22 4.40 0.075 2.03 5.32 4.61 1.29 0.159 0.019 0.037 0.002 0.006 0.006 0.003 0.003 0.058 0.019 0.018 98.55 8
StDev 0.14 0.008 0.07 0.05 0.007 0.02 0.03 0.16 0.02 0.005 0.002 0.012 0.006 0.004 0.005 0.006 0.003 0.007 0.006 0.007 0.26  
                                               
GeoREM preferred concentrations: 63.70 0.703 17.80 4.37 0.076 1.97 5.28 4.44 1.29 0.164 0.023 0.033 0.002 0.002 0.003 0.003 0.001 0.057 0.015 0.016 99.94  
                                               
ATHO-g rhyolite MPI-DING Mean 74.57 0.239 12.02 3.23 0.109 0.10 1.72 4.28 2.68 0.027 0.042 0.062 0.004 0.003 0.006 0.003 0.001 0.012 0.007 0.075 99.20 8
StDev 0.34 0.006 0.06 0.04 0.009 0.00 0.02 0.14 0.03 0.006 0.003 0.007 0.004 0.007 0.006 0.006 0.004 0.006 0.006 0.012 0.47 0.00
                                               
GeoREM preferred concentrations: 75.60 0.255 12.20 3.27 0.106 0.10 1.70 3.75 2.64 0.025 0.043 0.061 0.000 0.001 0.002 0.007 0.000 0.011 0.001 0.069 99.83  
                                               
T1-g qtz diorite MPI-DING Mean 58.68 0.714 16.65 6.24 0.132 3.59 7.00 3.24 2.04 0.180 0.009 0.047 -0.002 0.008 0.000 0.007 0.005 0.034 0.025 0.017 98.62 8
StDev 0.24 0.010 0.08 0.06 0.008 0.08 0.04 0.06 0.04 0.009 0.003 0.008 0.006 0.006 0.006 0.006 0.004 0.005 0.009 0.005 0.40  
                                               
GeoREM preferred concentrations: 58.60 0.755 17.10 6.44 0.127 3.75 7.10 3.13 1.96 0.168 0.011 0.043 0.002 0.003 0.001 0.009 0.001 0.034 0.031 0.019 99.28  
                                               
GOR132-g komatiite MPI-DING Mean 45.39 0.293 11.04 10.17 0.152 22.66 8.57 0.85 0.04 0.036 0.001 -0.001 0.010 0.338 0.154 -0.001 0.005 0.009 0.035 0.004 99.75 8
StDev 0.25 0.015 0.12 0.11 0.010 0.25 0.03 0.03 0.00 0.002 0.002 0.007 0.005 0.006 0.010 0.003 0.003 0.006 0.005 0.007 0.52  
                                               
GeoREM preferred concentrations: 45.50 0.306 11.00 10.10 0.154 22.40 8.45 0.83 0.03 0.036 0.001 0.000 0.012 0.369 0.151 0.000 0.000 0.002 0.035 0.001 99.38  
                                               
GSC-1g USGS Mean 51.16 1.56 13.79 13.94 0.010 3.52 7.74 3.44 2.71 0.020 0.003 0.008 -0.001 -0.001 -0.003 -0.001 0.007 0.001 0.021 0.001 97.91 8
StDev 0.29 0.01 0.08 0.14 0.009 0.04 0.04 0.13 0.02 0.004 0.002 0.010 0.003 0.008 0.005 0.006 0.004 0.008 0.007 0.006 0.36  
                                               
GeoREM preferred concentrations: 52.60 1.37 13.50 13.70 0.023 3.60 7.10 3.60 3.06     0.004 0.001 0.002 0.003 0.001   0.004 0.001 0.001 98.80  
                                               
GSE-1g USGS Mean 53.03 0.071 13.12 12.45 0.078 3.59 7.24 3.72 2.58 0.023 0.049 0.052 0.062 0.056 0.064 0.042 0.013 0.058 0.078 0.057 96.41 8
StDev 0.33 0.007 0.13 0.09 0.005 0.03 0.03 0.15 0.02 0.003 0.003 0.012 0.005 0.006 0.004 0.005 0.005 0.006 0.006 0.007 0.31  
                                               
GeoREM preferred concentrations: 53.70 0.075 13.00 12.70 0.076 3.50 7.40 3.90 2.60 0.016   0.048 0.048 0.058 0.056 0.039   0.053 0.072 0.055 97.50  
                                               
NIST 612 trace elements in glass Mean 71.44 0.007 2.60 0.00 0.006 0.003 12.22 13.05 0.011 0.014 0.011 0.005 0.008 0.010 0.012 0.003 0.082 0.016 0.009 0.010 98.22 8
StDev 0.71 0.004 0.45 0.02 0.005 0.002 0.43 0.15 0.003 0.003 0.003 0.007 0.006 0.009 0.008 0.005 0.006 0.005 0.005 0.007 1.49  
                                               
GeoREM preferred concentrations: 72.10 0.007 2.03 0.01 0.005 0.012 11.90 13.70 0.007 0.011 0.014 0.004 0.005 0.006 0.005 0.003 0.095 0.009 0.007 0.005 99.93  
                                               
Sample   SiO2 TiO2 Al2O3 FeOT MnO MgO CaO Na2O K2O P2O5 Cl BaO CoO Cr2O3 NiO Rb2O SO3 SrO VO2 ZrO2 Total n
                                               
All results from a single analytical session run in November, 2017 which also included the G-probe 19 test glass
Analytical conditions 15 kV, 40 nA, 15 to 20 mm beam diameter, 5 minute total analysis time; Si and Al by EDS (8 second acquisition time); All other elements by WDS; Mean Atomic Number X-ray backgrounds used for WDS elements
Time-dependent intensity correction used as needed for Na (Lipari, Old Crow, Sheep Track, Erebus, StHs6-80, ATHO-g, T1-g, NIST 612); Multi-standard concensus blank correction for trace-level accuracy
Quantitative corrections implemented for interference of Ti on Ba, Ba on Ti, Mn on Fe, Fe on Co, Co on Ni, Ca on Mg, Si on Sr, Ca on P, P on Zr, Ti on V, V on Cr, and Si on Rb
FeOT is total iron oxide as FeO; n is number of analyses
INTAV reference concentrations are from Kuehn et al., 2011, The INTAV intercomparison of electron-beam microanalysis of glass by tephrochronology laboratories, results and recommendations: Quaternary International. doi:10.1016/j.quaint.2011.08.022
USGS reference concentrations are from USGS certificates of analysis
GeoREM reference concentrations were downloaded from the GeoREM reference material database in fall 2017
                                               

 

Sample Quality Control Data:  Routine Tephra Glass

Sample   SiO2 TiO2 Al2O3 FeOT MnO MgO CaO Na2O K2O P2O5 Cl BaO Total   n
                                 
Lipari ID3506 obsidian Mean 73.94 0.072 13.05 1.56 0.064 0.040 0.740 4.13 5.18 0.012 0.337 0.000 99.05   22
  StDev 0.41 0.007 0.21 0.05 0.020 0.008 0.023 0.25 0.06 0.006 0.014 0.015 0.66    
                                 
INTAV Reference concentrations: 74.14 0.074 13.11 1.55 0.065 0.041 0.734 4.07 5.11 0.010 0.342 0.002 99.16    
                                 
Old Crow tephra Mean 72.61 0.294 12.57 1.63 0.053 0.274 1.44 3.86 3.61 0.039 0.269 0.108 96.69   30
  StDev 0.93 0.014 0.20 0.05 0.014 0.019 0.03 0.25 0.07 0.007 0.011 0.026 1.20    
                                 
INTAV Reference concentrations: 72.09 0.297 12.51 1.62 0.052 0.275 1.43 3.66 3.56 0.036 0.267 0.107 95.74    
                                 
Sheep Track (Edziza) tephra Mean 61.02 0.237 17.15 4.54 0.136 0.133 1.10 8.19 5.33 0.050 0.205 0.008 98.05   25
  StDev 0.88 0.016 0.23 0.22 0.021 0.010 0.12 0.43 0.15 0.009 0.011 0.021 1.52    
                                 
INTAV Reference concentrations: 61.59 0.236 17.58 4.55 0.134 0.124 1.09 8.19 5.34 0.038 0.210 0.004 99.03    
                                 
Laki 1783 tephra Mean 49.41 3.16 12.99 14.16 0.231 5.27 9.85 2.75 0.463 0.338 0.015 0.013 98.65   36
  StDev 0.31 0.06 0.13 0.18 0.021 0.13 0.10 0.14 0.013 0.012 0.005 0.023 0.47    
                                 
INTAV Reference concentrations: 49.71 3.11 12.94 14.18 0.233 5.32 9.65 2.88 0.460 0.350 0.020   98.85    
                                 
BHVO-2g glass Mean 49.77 2.77 13.52 10.90 0.171 7.17 11.37 2.20 0.513 0.271 0.007 0.017 98.68   27
  StDev 0.33 0.02 0.14 0.10 0.020 0.12 0.09 0.08 0.016 0.012 0.004 0.018 0.46    
                                 
USGS Reference concentrations: 49.50 2.77 13.55 11.00 0.170 7.20 11.40 2.30 0.51 0.280   0.015 98.68    
                                 
NKT-1g glass Mean 38.56 3.94 10.35 11.99 0.202 14.67 13.15 3.47 1.26 0.931 0.005 0.086 98.61   27
  StDev 0.26 0.02 0.10 0.11 0.021 0.23 0.06 0.08 0.03 0.017 0.004 0.023 0.44    
                                 
USGS Reference concentrations: 38.68 3.94 10.20 11.99   14.33 13.21 3.48 1.28 0.970   0.080 98.08    
                                 
Analysed in two analytical sessions (Oct & Nov 2017); Analytical conditions 14 kV, 10 nA, 8 mm defocussed beam, 3 minute total analysis time
Si and Al by EDS (8 second analysis time), All other elements by WDS
Time-dependent intensity correction for Na on Lipari, Old Crow, and Sheep Track tephras; Multi-standard blank correction for trace-level accuracy