Environmental Engineering Reference
In-Depth Information
Table 7.3 Ortho-P control
chart
OP standards concentrations (mg/L)
0.005
0.020
0.050
0.100
% transmittance
99.1
96.8
91.8
84.8
99.2
96.7
91.6
84.6
99.2
96.8
92.6
84.3
99.3
96.2
91.0
84.0
99.8
96.8
92.6
86.9
98.9
96.2
92.8
85.4
98.8
96.6
91.8
84.8
Calculated OP concentrations (mg/L)
0.005636
0.020227
0.053180
0.102463
0.005009
0.020869
0.054535
0.103930
0.005009
0.020227
0.047789
0.106138
0.004383
0.024090
0.058618
0.108353
0.001262
0.020227
0.047789
0.087264
0.006891
0.024090
0.046448
0.098082
0.007520
0.021512
0.053180
0.102463
Mean
SD
CV
RSD
MDL
pH of a 0.1 M hydrochloric acid solution? What is the molar concentration of H
+
in a
hydrochloric acid solution at pH 3? Given a 1 L container of pure water, how many
hydrogen ions are present?
Classroom Exercise 2: Calculating Detection Limits
An analytical laboratory ran quality control charts to determine the method detec-
tion limit for their ortho phosphorus test method. They used the ascorbic acid
method and read the color change on a spectrophotometer. The lab assistant made
four standard solutions containing 0.005, 0.020, 0.050, and 0.100 mg/L PO
4
3
-P.
The results are given in Table
7.3
. The standard curve was determined before the
control samples were run and the regression equation is as follows: LN(Y)
ΒΌ
1.6094X + 4.6052, where Y represents the % transmittance values and X
represents the concentration. The curve was used to determine the associated
concentration of the control sample results.
Calculate the mean (x), standard deviation (SD), coefficient of variation (CV),
relative standard deviation (RSD) and the MDL for each of the control standard
