Page 92 - Statistics for Environmental Engineers

L1592_Frame_C09 Page 85 Tuesday, December 18, 2001 1:45 PM

Exercises
9.1 Student Accuracy. Four students (A–D) each performs an analysis in which exactly 10.00 mL
of exactly 0.1M sodium hydroxide is titrated with exactly 0.1M hydrochloric acid. Each student
performs five replicate titrations, with the results shown in the table below. Comment on the
accuracy, bias, and precision of each student.
Student A Student B Student C Student D
10.08 9.88 10.19 10.04
10.11 10.14 9.79 9.98
10.09 10.02 9.69 10.02
10.10 9.80 10.05 9.97
10.12 10.21 9.78 10.04
9.2 Platinum Auto Catalyst. The data below are measurements of platinum auto catalyst in standard
reference materials. The known reference concentrations were low = 690 and high = 1130.
Make a Youden plot and assess the work of the participating laboratories.

Laboratory 1 2 3 4 5 6 7 8 9
Low Level 700 770 705 718 680 665 685 655 615
High Level 1070 1210 1155 1130 1130 1130 1125 1090 1060
9.3 Lead Measurement. Laboratories A and B made multiple measurements on prepared wastewater
effluent specimens to which lead (Pb) had been added in the amount of 1.25 µg/L or 2.5 µg/L.
The background lead concentration was low, but not zero. Compare the bias and precision
of the two laboratories.

Laboratory A Laboratory B
Spike == == 1.25 Spike == == 2.5 Spike == == 1.25 Spike == == 2.5
1.1 2.8 2.35 5.30
2.0 3.5 2.86 4.72
1.3 2.3 2.70 3.64
1.0 2.7 2.56 5.04
1.1 2.3 2.88 3.62
0.8 3.1 2.04 4.53
0.8 2.5 2.78 4.57
0.9 2.5 2.16 4.27
0.8 2.5 2.43 3.88

9.4 Split Samples. An industry and a municipal wastewater treatment plant disagreed about
wastewater concentrations of total Kjeldahl nitrogen (TKN) and total suspended solids (TSS).
Specimens were split and analyzed by both labs, and also by a commercial lab. The results
are below. Give your interpretation of the situation.

TKN TSS
Specimen Muni. Ind. Comm. Muni. Ind. Comm.
1 1109 940 1500 1850 1600 1600
2 1160 800 1215 2570 2100 1400
3 1200 800 1215 2080 2100 1400
4 1180 960 1155 2380 1600 1750
5 1160 1200 1120 2730 2100 2800
6 1180 1200 1120 3000 2700 2700
7 1130 900 1140 2070 1800 2000

9.5. Ruggedness Testing. Select an instrument or analytical method used in your laboratory and
identify seven factors to evaluate in a ruggedness test.

© 2002 By CRC Press LLC