9/8/11 1 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 1!Figures of Merit and Selection of Analytical Methods 1 - Analytical problem: topics and hypothesis 2 - Figures of merit 3 - Calibration of analytical methods external calibration curves standard addition (matrix interference) internal standard (variable instrument response) -Section 1D, Appendices a1A – a1D Suggested exercises: 1-9, 1-10, 1-12, a1-1, a1-2, a1-12, a1-19, a1-20, a1-21 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 I. Industrial (R&D, manufacturing, sales, etc.) – TABLE 1 II. Legal and Regulatory – TABLE 2 III. Environmental - TABLE 3 IV. Medical and health Related – TABLE 4 V. Food and agriculture - TABLE 5 Analytical Problem - Topics 1. Sit at the Table that best matches your analytical problem topic 2. Describe to your two nearest neighbors your current topic. Explain why this topic is important. What is your hypothesis (current explanation of what is behind the problem)? 3. Explain your neighbor’s analytical problem topic to the rest of the class. (Random selection of one or two persons). Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Table 1-3 (Section 1E) Accuracy (eq 1-9) Ability to discriminate small differences in analyte concentrations (eq 1-10, 1-11) Concentration with signal ~ 3xsb (eq 1-12, 1-13) Response to interferents in the matrix (eq 1-14 to 1-17) Concentration with signal ~ 10xsb; 5% deviation from linearity9/8/11 2 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Confidence interval of the mean (Example a1-6) (Do on your own) 5!Analysis: alcohol in blood. Do part a. Calculate the 95% Confidence interval (Cl) of the mean Key data: s = 0.0050% Ethanol N = 3 Average = 0.084% Ethanol € CI = X ±tsNEquation a1-24 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Error Propagation (Example a1-7) (Do on your own) 6!Analysis: HPLC peak for hexachlorobenzene. Calculate N and the standard deviation for N. Key data: tR = 13.36 min ; stR = 0.043 min W = 2.18 min; sW = 0.061 € N = 16tRW 2See: Table a1-6 (Error propagation equations) Return to Table 1-39/8/11 3 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Figures of merit obtained from calibration curve Figure 1-13 Return to Table 1-3 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Example 1-2 Calculate (1) calibration sensitivity (2) analytical sensitivity at 1.00 ppm (3) LOD (4) LOQ 8!Analysis: Lead in gasoline, based on its flame emission Calibration curve: S = 1.12 C + 0.312 S: Signal (arbitrary units) C: Concentration (ppm) Key data: For 1.00 ppm Pb, S = 1.12, Std.Dev. = 0.025 For blank (0.00 ppm Pb), S = 0.0296, Std.Dev. = 0.0082 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Example 1-3 (Do on your own) Calculate error due to interferent (i.e. Na+) 9!Analysis: K+ in the presence of Na+, based ion selective electrode Key data: kNa+/K+ = 0.052 For blank (0.00 M K+), S = 0.0 [K+] = 3.00x10-3 M ; interferent [Na+] = 2.00x10-2 M Note: the book should say, “selectivity coefficient of Na+ with respect to K+ is reported to be 0.052”9/8/11 4 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 11!Calibration of Instrumental Methods External Standard Calibration Figure 1- 9 (Section 1D) Std. Dev. of the response Std. Dev. of Conc. Lecture 02 – Sep 9 Chem 4101 – Fall 2011 Standard Addition Methods -Analytical response versus added amount - Spiking the sample (Vx) with standard (Vs) - Matrix interference - Equations 1-3 to 1-8 - Practice use of Excel spread sheets to solve problems (Example 1-1) Figure 1-10 (Section 1D) € m =kcsVt € b =kVxcxVtMethod 1 Method 2 € cx=bcsmVx(Eq.1− 4)9/8/11 5 Lecture 02 – Sep 9 Chem 4101 – Fall 2011 13!Calibration of Instrumental Methods Internal Standard Calibration Figure 1- 12 (Section 1D) With I.S. Without I.S. INa (INa))/(ILi)) [Na]
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