Assignment 1 (due October 9, 2013)
You and your friend working in a different lab have been given an unknown water sample that contains potassium. You are both asked to measure the potassium concentration in the solution (10 replicate measurements). The methods that you and your friend are using are different. The results that were obtained are listed below. Determine:
(a) the concentration, standard deviation and relative standard deviation for the unknown as measured using the two methods (check for outliers!),
(b) calculate the detection limit (3s) for each method,
(c) compare the standard deviations and evaluate whether the two averages are significantly different (or not) at the 95% confidence level.
Provide calculations for each step. If a table (t, F or G) value is not available in the book (for example, if looking for a t-value for a degrees of freedom equal to 27 – hypothetical case), just interpolate the two closest values (25 and 30 in this hypothetical case).
RESULTS:
|
|
Standard |
Method 1 |
Method 2 |
|
|
Concentration |
Intensity |
Intensity |
|
|
(mg/L) |
(nA) |
(mV) |
|
|
0.000 |
0.624 |
1.955 |
|
|
0.000 |
0.488 |
2.490 |
|
|
0.000 |
0.522 |
2.166 |
|
|
0.000 |
0.355 |
1.500 |
|
|
5.000 |
9.245 |
15.644 |
|
|
10.000 |
17.069 |
31.220 |
|
|
15.000 |
26.200 |
44.266 |
|
|
20.000 |
33.881 |
62.394 |
|
|
25.000 |
43.826 |
75.611 |
|
|
|
|
|
|
Replicate |
|
|
|
|
1 |
|
26.544 |
46.977 |
|
2 |
|
25.449 |
49.120 |
|
3 |
|
21.053 |
50.998 |
|
4 |
|
24.353 |
46.615 |
|
5 |
|
23.899 |
49.326 |
|
6 |
|
24.010 |
46.666 |
|
7 |
|
25.554 |
45.291 |
|
8 |
|
23.549 |
42.995 |
|
9 |
|
26.008 |
43.678 |
|
10 |
|
24.404 |
49.012 |
