Description
In a steelworks chemical laboratory the nickel content of steel is determined using flame atomic absorption spectrometry (FAAS). For the estimation of the within lab reproducibility they use a steel control sample with nickel content of around 8%. An X control chart is maintained with control sample (data are below). The laboratory has participated in 5 interlaboratory comparisons (data are below).
Data
X control chart:
No |
Ni content (%) |
01.08.2015 |
7.96 |
02.08.2015 |
7.77 |
05.08.2015 |
8.03 |
06.08.2015 |
7.92 |
07.08.2015 |
8.21 |
08.08.2015 |
8.27 |
09.08.2015 |
8.17 |
12.08.2015 |
8.10 |
11.08.2015 |
8.27 |
13.08.2015 |
8.16 |
14.08.2015 |
8.00 |
15.08.2015 |
8.04 |
16.08.2015 |
7.79 |
19.08.2015 |
8.08 |
20.08.2015 |
7.76 |
21.08.2015 |
8.20 |
22.08.2015 |
7.72 |
23.08.2015 |
7.82 |
26.08.2015 |
7.68 |
27.08.2015 |
7.96 |
Proficiency tests data:
No |
Consensus value (%) |
Standard deviation of participants (%) |
Result of the laboratory (%) |
No of participants |
1 |
7.72 |
0.19 |
8.06 |
30 |
2 |
8.49 |
0.20 |
8.67 |
29 |
3 |
9.23 |
0.30 |
9.66 |
35 |
4 |
7.89 |
0.21 |
8.11 |
30 |
5 |
10.25 |
0.16 |
10.01 |
32 |
Clues
[accordion][acctitle]Clue 1[/acctitle]From the control chart the random component u(Rw) can be calculated. That is actually the standard deviation.[/accordion]
[accordion][acctitle]Clue 2[/acctitle]Using the proficiency tests data, calculate the biasi, u(Crefi), RMSbias and u(Cref). Combine RMSbias and the u(Cref). Consensus values can be considered as the Cref values in the Nordtest approach.[/accordion]
[accordion][acctitle]Clue 3[/acctitle]Combine the u(Rw) and the u(bias). Calculate the expanded uncertainty from the standard uncertainty (via multiplying with coverage factor).[/accordion]