Basics of Environmental Sampling and Analysis - Fundamentals of Environmental Sampling and Analysis - page 42

(a) Do the regression analysis (y¼mean signal, x¼concentration) using Excel. Include
at least the Summary Output, ANOVA, Line Plot, Residual Plot, and Normal
Probability Plot.
(b) What is the best straight line by least squares fit? Indicate the slope and intercept of
this linear fit. Indicate whether or not this linear regression is significant and whether
or not the intercept and slope are significant? Use significant level of 0.05.
(c) What is the calibration sensitivity in mv/(mg/L)?
21. A survey on the background concentration of lead in soil was conducted in an
Environmental Impact Assessment of a former battery plant. Preliminary results of six
soil samples in the protected area give results in mg/kg: 28, 32, 21, 29, 25, 22. (a) Is
there any value in this data set that can be discarded as an outlier at 90% confidence
level? (b) Calculate CV, RSD, and 95% Confidence Interval (CI)? (c) If sufficient
numbers of soil samples were taken and the population was known to have a normal
distribution with a mean of 25.5 mg/kg and standard deviation of 1.2 mg/kg, what would
be the probability of a soil sample having Pb concentration of greater than 29.8 mg/kg;
less than 21 mg/kg; and in the range of 23.1 to 27.4 mg/kg?
22. A new method is being developed for the analysis of a pesticide in soils. A spiked
sample with a known concentration of 17.00 mg/kg was measured five times using the
new method (data: 15.3, 17.1, 16.7, 15.5, 17.3 mg/kg) and the established EPA method
(data: 15.4, 15.9, 16.7, 16.1, 16.2 mg/kg). The Excel outputs of descriptive statistics and
one-way ANOVA are given below (a¼0.05). On the basis of these output, (a) are these
two methods significantly different at a 95% confidence level? (b) Which method is
more accurate, why? (c) Which method is more precise, why?

(1) Excel output of descriptive statistics

EPA method New method

Mean 16.06 Mean 16.38

Standard error 0.211187121 Standard error 0.412795349

Median 16.1 Median 16.7

Mode #N/A Mode #N/A

Standard deviation 0.472228758 Standard deviation 0.923038461

Sample variance 0.223 Sample variance 0.852

Kurtosis 1.012889863 Kurtosis 2.910136878

Skewness 0.105406085 Skewness 0.400799173

Range 1.3 Range 2

Minimum 15.4 Minimum 15.3

Maximum 16.7 Maximum 17.3

Sum 80.3 Sum 81.9

Count 5 Count 5

Largest(1) 16.7 Largest(1) 17.3

Smallest(1) 15.4 Smallest(1) 15.3

Confidence Level 0.586350662 Confidence Level 1.146106

(95.0%) (95.0%)