Unit 1 Introduction To Analytical Chemistry PDF

Unit 1 Introduction to Analytical Chemistry Analytical chemistry is the science of how to properly design and perform experiments chemistry. We learn to compare and contrast different measurement techniques, learn how to know if our measurements are reliable, and learn how to ad...

Unit 1 Introduction to Analytical Chemistry Analytical chemistry is the science of how to properly design and perform experiments chemistry. We learn to compare and contrast different measurement techniques, learn how to know if our measurements are reliable, and learn how to address error in our experiments. Furthermore, we will lay the ground work for some experimental techniques that undergird much of chemistry, biology, and physics. The skills and techniques learned in this class can set one up to be competitive in science industries and prepare them to be competent researchers. By the end of this students should be able to: Objectives for Introduction to Analytical Chemistry 1. Outline and explain the scientific process and the analytic process. 2. Perform conversions between units and explain calculations of chemical concentrations. 3. Prepare a standard operating procedure for the preparation of a solution using proper glassware and techniques. Reading: Chapter 0 (all sections), Chapter 1 (sections 1-4) Homework: Why Analytical? Due Monday 9/2 9:00 am Canvas Chapter 0: 1, 2 Chapter 1: 4, 5, 8, 9, 10, 11, 12, 14-18, 20, 22, 24 As a group create an outline of the scientific method. STOP Fry-Petit 1 CHEM 315 FA24 Unit 1 Fry-Petit 2 CHEM 315 FA24 Unit 1 Fry-Petit 3 CHEM 315 FA24 Unit 1 Fry-Petit 4 CHEM 315 FA24 Unit 1 Many of the calculations that you will perform in quantitative analysis build off of problems that you learned to solve in general chemistry. You and your group will be assigned specific problems and will present them when time is up. Once you finish your problem be sure to work on the other problems and any you do not finish in class needs to be done at home. Calculation Review Fry-Petit 5 CHEM 315 FA24 Unit 1 1. Use appropriate metric prefixes to write the following measurements without use of exponents (it is okay to use the internet on your phone for help) 4.7×10-6 g 1.85×10-12 m 16.7 ×106 s 15.7×103 g 1.34×10-3 m 1.84×102 cm 2. The density of titanium metal is 4.51g/cm3 at 25 °C. What mass of titanium displaces 125.0 mL of water at 25 °C. Fry-Petit 6 CHEM 315 FA24 Unit 1 3. An individual suffering from a high cholesterol level in her blood has 242 mg of cholesterol per 100 mL of blood. If the total blood volume of the individual is 5.2 L, how many grams of total blood cholesterol does the individual’s body contain? 4. How many mL of concentrated (17.6 M) sulfuric acid are necessary to make 100.00 mL of a 1.00 M sulfuric acid solution? 5. What is the concentration in ppm of Cu2+ in a 3 x 10-4 M in the aqueous CuSO4 solution? Fry-Petit 7 CHEM 315 FA24 Unit 1 6. What is the concentration in ppb of lead in a groundwater solution containing 3 x 10-8 M Pb2+? 7. 25 µL of ethanol is added to a 1000 µL mixture of methanol and propanol. What is the volume percent of ethanol in the mixture? 8. Seawater contains 411 ppm calcium (Ca2+). What is the molar concentration (i.e., molarity) of calcium in seawater? STOP Fry-Petit 8 CHEM 315 FA24 Unit 1 9. Harris 1-19: This problem is from your book and is an example of the types of problems given both in the book, on exams, and more over in real life. Therefore, it is very important that you start practicing pulling out the important information now. This also highlights the importance of doing all of your homework for this class! I have always enjoyed tuna fish. Unfortunately, a study of the mercury content of canned tuna in 2010 found that chunk white tuna contains 0.6 ppm Hg and chunk light tuna contains 0.14 ppm. The U. S. Environmental Protection Agency recommends no more than 0.1 μg Hg/kg body weight per day. I weigh 68 kg. How often can I eat a can containing 6 ounces (1 lb=16 oz) of chuck white light tuna so that I do not average more than 0.1 μg Hg/kg body weight per day? STOP Fry-Petit 9 CHEM 315 FA24 Unit 1 Introduction to Data Analysis and Statistics Quantitative analysis is the chemistry of properly collecting and interpreting data. In a laboratory setting if you are lucky your data will lead to a clear answer to the question you are investigating. At times, however, you will find your data ambiguous or, more interestingly, that something unexpected is hidden within the data. This activity will guide you in exploring several important concepts in data analysis. By the end of this students should be able to: Objectives for Data Treatment 1. Calculate mean and standard deviation from given sample data. 2. Apply Grubbs test to given sample data for the identification of outliers. 3. Given an experimental framework, identify and explain the types of calibration methods (curves, addition, and internal standard) used. 4. Differentiate between calibration methods needed for the accurate measurement of an analyte in several different matrices. 5. Calculate and analyze FOM for calibration methods Objectives for Result Reporting 1. Carry out propagation of uncertainty in calculations and describe the type of experimental errors given sample data (systematic, random, gross). 2. Calculate confidence interval and interpret the level of accuracy and precision of given sample data and expected value. 3. Apply statistical tools, such as Student T’s and F tests to compare given sample data sets to identify different and/or equivalent results. 4. Explain accuracy and precision between data sets from the application of statistical tools. 5. Calculate and explain the meaning of limit of detection and limit of quantification for a given sample data set. For the first half of this lesson Reading: Chapter 2 (sections 1, 3 (first part), 4, 5, 6, 9), Chapter 3 (sections 1, 2, 3, 4) Homework: Chapter 1: 23 Chapter 2: 2, 3, 5, 10-12 Chapter 3:1-5, 9-14, 20-22 Questions listed at the end Fry-Petit 10 CHEM 315 FA24 Unit 1 Uncertainty Suppose you are analyzing soil samples from a school playground near a busy intersection. After collecting three samples, you return to the lab, extract the soil samples with water and, using an atomic absorption spectrometer (we will talk more about instrumentation later), determine the concentration of lead in the resulting extracts, obtaining an average result of 4.38 parts-per-billion (ppb). The actual value that you report is 4.38 ± 0.02 ppb. What does the 0.02 ppb indicate? STOP Brainstorm what errors might affect this result? STOP Fry-Petit 11 CHEM 315 FA24 Unit 1 Systematic and Random Error Systematic (Determinate) Random (Indeterminate) Separate the errors discussed in class into systematic vs. random Systematic (Determinate) Random (Indeterminate) STOP Fry-Petit 12 CHEM 315 FA24 Unit 1 Instrument noise Fry-Petit 13 CHEM 315 FA24 Unit 1 Often when discussing precision and accuracy we use a model of darts on a dartboard as shown below. As a group come to a conclusion of what accuracy and precision are based on previous knowledge and write your definition below. Accuracy: Precision: Fry-Petit 14 CHEM 315 FA24 Unit 1 Label the top and side of the table with accurate, not accurate, precise, and not precise. Circle the dartboard depictions that show random error and put a square around the dartboard depictions that show systematic error. Figure 1. Dart model of precision and accuracy. STOP Fry-Petit 15 CHEM 315 FA24 Unit 1 Measurement Exercise Experiment 1: Using a ruler with a millimeter scale, measure the big solid rectangle's width and length in millimeters on your own without any consultation of your group, then collect the values of your group mates in the table and calculate the average values. Group Members Length (mm) Width (mm) Average Are your measurements of the rectangle's length and width exactly the same as those of your classmates, or are they different? If there are differences in the measurements, is this the result of determinate errors, indeterminate errors or both? What are those errors? Briefly explain your reasoning. STOP Fry-Petit 16 CHEM 315 FA24 Unit 1 When measuring the rectangle's length and width you had to make several decisions: How do you define the rectangle? Should you measure its length and width from the outside edges of the border, from the inside edges or from the middle of the border? Experiment 2: Decide as a group how you are going to define the rectangle and record your measurement to the tenth place (which is an estimation of one digit past the smallest gradation). Then measure the length and width of the rectangle and calculate its average. Group Members Length (mm) Width (mm) Average STOP Significant Figures Fry-Petit 17 CHEM 315 FA24 Unit 1 You may recall from general chemistry that we refer to the digits in our measurements as significant figures. A significant figure is any number in which we can express confidence, including those digits known exactly and the one digit whose value is an estimate. The lengths 154 mm and 154.3 mm have three and four significant digits, respectively. The number of significant figures in a measurement is important because it affects the number of significant figures in a result based on that measurement. How many significant figures do you have in each of your individual measurements of length and width? Group Members # sig figs in # sig figs in length width Before continuing, let's review the rules for including significant figures in calculations. When adding or subtracting, the result of the calculation is rounded to the last decimal place that is significant for all measurements. For example, the sum of 135.621, 0.33 and 21.2163 is 157.17 since the last decimal place that is significant for all three numbers (as shown below by the vertical line) is the hundredth's place. Note that rounding the answer to the correct number of significant figures occurs after completing the exact calculation. When multiplying or dividing, the result of the calculation contains the same number of significant figures as that measurement having the smallest number of significant figures. Thus, Fry-Petit 18 CHEM 315 FA24 Unit 1 because 0.152, with three, has the fewest number of significant figures. One way to think about this is that we cannot make a measurement more precise through a calculation than it is when we take the measurement. Check back to be sure that your group has the correct number of significant figures in the average length and width listed for Experiment 2, if not fix them. STOP Fry-Petit 19 CHEM 315 FA24 Unit 1 Three additional SF rules Fry-Petit 20 CHEM 315 FA24 Unit 1 Uncertainty in the lab Uncertainty is present in all tools, glassware, and equipment in the lab. Fry-Petit 21 CHEM 315 FA24 Unit 1 Fry-Petit 22 CHEM 315 FA24 Unit 1 Fry-Petit 23 CHEM 315 FA24 Unit 1 Fry-Petit 24 CHEM 315 FA24 Unit 1 If you took a measurement and found a value of 89.231 ± 0.008 what is the absolute uncertainty and the percent relative uncertainty of the measurement? STOP Fry-Petit 25 CHEM 315 FA24 Unit 1 The REAL significant figure rule in the lab The 1st digit of the absolute uncertainty is the last significant digit in the answer. Uncertainty (in all the forms we will see in this class and in CHEM 316) have only 1 sig. fig. e.g. 0.420034 (±0.00034) M → 0.4200(±0.0003) M Therefore, this can change the number of sig figs you determine from the math Propagation of Uncertainty As we have discussed, each instrument we use in a lab has an associated random error, which is often expressed as a tolerance factor by the manufacturer. A more rigorous approach to determining the uncertainty in a result is called a propagation of uncertainty and it combines the uncertainty in each measurement to estimate the uncertainty in the final result. Fry-Petit 26 CHEM 315 FA24 Unit 1 The following equations for propagation of uncertainty are from your textbook (as noted in parentheses): Addition and Subtraction: 𝑒𝑝𝑟𝑜𝑝 = √𝑒12 + 𝑒22 + 𝑒32 + ⋯ 𝑒𝑛2 Multiplication and Division: %𝑒𝑝𝑟𝑜𝑝 = √(%𝑒12 )+(% 𝑒22 ) + (%𝑒32 ) + ⋯ (%𝑒𝑛2 ) Where 𝑒𝑛 is the absolute uncertainty (often the tolerance factor) for measurement n and %𝑒𝑛 is the percent relative uncertainty for measurement n. Assuming that the error associated with the ruler is 0.1 mm, propagate the error associated with the average of the length and the width of the rectangle using the data from Experiment 2. 1. What is the absolute uncertainty of each measurement? 2. Should you use the addition/subtraction or multiplication/division equation above to propagate the error? 3. Calculate the error and write it with the proper number of sig. figs is the table below. Average length Average width (mm) (mm) Error Fry-Petit 27 CHEM 315 FA24 Unit 1 Asking yourself the same questions as above, calculate the average area of the rectangle, including the propagated error and the correct number of sig figs, and write the value in the table. Average area w/ error (mm2) STOP As a group, think of times in the lab you may want to use the addition and subtraction rule to propagate uncertainty and one time in the lab you would want to use the multiplication and division rule to propagate uncertainty. STOP Fry-Petit 28 CHEM 315 FA24 Unit 1 Often propagation of error includes mixed operation. Like finding the average area of the rectangle, except I walked you through how to do that. Now you are going to propagate error for a scientific system you have never seen before. For a concentration technique, the relationship between the signal and the analyte’s concentration is Stotal = kACA + Smb What is the analyte’s concentration, CA, and its uncertainty if Stotal is 24.37 ± 0.02, Smb is 0.96 ± 0.02, and kA is 0.186 ± 0.003 ppm–1. STOP Fry-Petit 29 CHEM 315 FA24  Unit 1 Given the following masses of deionized water measured during the calibration of a Class A pipet at 15 °C, what average volume of water is the 10.00 mL Class A (± 0.02 mL) pipet actually delivering? Measurement Mass of H2O (g) 1 10.1578 2 10.1341 3 10.1425 4 10.1453 5 10.1672 6 10.1587 7 10.1611 STOP Fry-Petit 30 CHEM 315 FA24 Unit 1 Explain, with numerical values, glassware, and instruments, how you would prepare 50 mL of a 1.40 M aqueous stock solution of sodium thiosulfate, Na2S2O3 (MW= 158.11 g/mol) (which is a solid that must be dissolved) while introducing the least amount of error. (similar example pg 23 of the textbook) STOP Explain, with numerical values, glassware, and instruments how you would prepare a 100 mL of a 0.140 M aqueous solution of sodium thiosulfate from the 1.40 M stock solution in the previous problem while introducing the least amount of error. STOP Fry-Petit 31 CHEM 315 FA24 Unit 1 Additional Homework for data analysis How is systematic error identified and accounted for in measurements? How is random error identified and accounted for in measurements? In a lab at 27°C you weigh an empty volumetric flask at 468.654 g you then fill the flask up to the calibration mark with DI H2O and weigh the flask at 543.635 g. What is the true volume contained in the volumetric? What is the true concentration of dissolved 0.1567 g of Na2S2O3 in molarity if you made it in the volumetric flask in the previous example? Fry-Petit 32 CHEM 315 FA24 Unit 1 What portion of the analytical process do the tools we talked about today fall under? If you made a 5 M solution via dilution of a 10 M solution using volumetric glassware and you performed several forms of analytical analysis and determined that the true concentration of the solution was 4.5 M what should be done to avoid this problem in the future? Fry-Petit 33 CHEM 315 FA24 Unit 1 Statistics For the second half of this lesson Reading: Chapter 4 (sections 1-3, 5, 6, 7), Chapter 5 (all sections) Homework: Chapter 4: 1-7, 9-15 Chapter 5: 4, 11, 14.b, 18, 22, 23, 24 As a group decide if the probability says that 1 out of each 6 rolls I should get each number once why when I roll the dice 6 times I don’t get each number once? STOP Fry-Petit 34 CHEM 315 FA24 Unit 1 Fry-Petit 35 CHEM 315 FA24 Unit 1 In “Measurement Exercise” you calculated the average of the length and width of your measured rectangle 2 different times, before you agreed on how to measure the rectangle (Experiment 1) and after you agreed on how to measure the rectangle (Experiment 2), calculate the standard deviation of the length for both measurements. Experiment Average ± Standard deviation Experiment 1 Experiment 2 STOP Discuss as a group how does the accuracy and the precision of the two data sets compare for these 2 data sets? Fry-Petit 36 CHEM 315 FA24 Unit 1 On the axes below draw two Gaussian curves that represent the data before you agree on how to measure the rectangle and after. Label the average and standard deviation, and be prepared to defend why you have drawn them that way. Fry-Petit 37 CHEM 315 FA24 Unit 1 Now imagine that your averages and standard deviations were very different, on the axes below draw two Gaussian curves that represent those two data sets, label the average and standard deviation, and be prepared to defend why you have drawn them that way. Discuss as a group how does the accuracy and the precision of the two data sets compare for these 2 data sets? STOP Fry-Petit 38 CHEM 315 FA24 Unit 1 Fry-Petit 39 CHEM 315 FA24 Unit 1 Calculate the confidence interval of the length for both Experiment 1 and Experiment 2. Problem from Measurement Average ± Confidence interval Exercise Experiment 1 Experiment 2 Fry-Petit 40 CHEM 315 FA24 Unit 1 As a group discuss how your confidence intervals compare between the two experiments and does it make sense that one of them should be lower than the other. Why or why not? Discuss what are two ways that you could lower your confidence intervals? 1. 2. When you look up the t-value on the table, you have been told to use the column labeled 95%, as a group, discuss what that means. STOP Fry-Petit 41 CHEM 315 FA24 Unit 1 As a group discuss what values would we want to compare if we wanted to determine which experiment was more precise? And which experiment was more accurate? STOP Fry-Petit 42 CHEM 315 FA24 Unit 1 Fry-Petit 43 CHEM 315 FA24 Unit 1 Determine if the standard deviations of the two experiments are statistically different. STOP Fry-Petit 44 CHEM 315 FA24 Unit 1 Determine if the length and thus the measurements themselves are statistically different. Fry-Petit 45 CHEM 315 FA24 Unit 1 As a group discuss what can you say about the relative precision and accuracy of the two methods (ie. is the precision and accuracy statically the same or statistically different?). STOP Fry-Petit 46 CHEM 315 FA24 Unit 1 Should any data points be removed from this set before it can be compared to Method 2 (not shown)? (Note: you should check all highs and lows until there is no change, so after doing the first calculation, explain what you would do next) STOP We have talked about the tolerance factor, standard deviation, and confidence interval. As a group discuss and be prepared to defend the differences between these three values that can give information about the range of a measurement. Fry-Petit 47 CHEM 315 FA24 Unit 1 Additional Homework Explain what each of these different tests/statistical values are used for: Confidence interval t-test F-test Grubbs test Fry-Petit 48 CHEM 315 FA24 Unit 1 What would the Gaussians of 2 methods look like if they passes the F-test but failed the t-test? vice versa? Fry-Petit 49 CHEM 315 FA24 Unit 1 Concentration Calibration Procedures Activity Accurately knowing the amount, in terms of concentration, of a particular substance (analyte) is important in fundamental research and also in many applied fields of study, such as medicine, environmental studies, and the food industry. In medicine, many drug dosages are effective within a narrow concentration range. If too little is administered, the benefits of the drug will not be obtained. However, if too much is administered in a particular time frame, overdose or toxicity can occur. Therefore, many patients must have their blood tested on a regular basis to determine the amount of such drugs in their system. Also, many common analytes, such a metals, are required by the human body at low levels but are toxic to the cells at high levels. In environmental studies, it is important to ensure that levels of environmental contaminants are monitored. In 2010 the BP Oil spill devastated the wildlife on the Gulf Coast of Mexico in the United States. It was one of the worst environmental accidents in the history of the United States. Years and vast amounts of money were required to clean up the spill. The Gulf waters have since been deemed safe to use; however, four years later, scientists still monitor the concentration of oil contaminants to ensure the safety of Gulf water for patron use. The previous examples provide important reasons for knowing the concentration of a particular analyte in a sample (biological fluid, water, food, etc.). The substance that we want to know the amount of in a sample is called the analyte. In order to determine the concentration of a particular analyte in a sample, we must perform a procedure called “concentration calibration”. This module discusses the three most common types of concentration calibration procedures. Analytes themselves cannot be measured directly; however, specific properties of the analyte can. Many analysis techniques that we will talk about at the end of the semester provide a response to a solution containing some concentration of an analyte. Two common ways to get a response for an analyte is to measure light absorbance or an electrochemical property. However, the absorption or electrochemical response of an analyte can rarely be used alone to determine the concentration in the sample. For example, the absorption or electrochemical measurement might be slightly different from one day to the next for the exact same sample due to a variety of uncontrollable variables, including background noise from the instrument. Fry-Petit 50 CHEM 315 FA24 Unit 1 If an instrument response to the same concentration of an analyte varies from day-to-day, can you devise a general procedure to determine the concentration of an analyte in a solution despite this issue? Report to your professor when done before moving on. General steps of a concentration calibration: Finding suitable standard solutions A primary standard analyte solution is a solution that contains a known amount of the analyte called the standard. The standard may be a pure analyte, a solution containing the analyte, or a solution containing the analyte along with other solutes; in either case, the analyte concentration is accurately known. The solution may be a solid, liquid, or gas phase solution, and the standard analyte may exist in either of these three phases as well. Standards are referred to as Standard Reference Materials (SRM) because they have been tested by The National Institute of Standards and Technology (NIST). This agency ensures the analyte concentration in many types of samples is accurate. The picture below is an SRM for Gulf of Mexico Crude Oil, which may be used to test for crude oil contaminants, for example, to monitor the safety of the gulf waters after the BP oil spill. Figure taken from: http://www.nist.gov/publication- portal.cfm?defaultSearch=false&researchfield=245 What are common characteristics of a primary standard such as the one shown above? Fry-Petit 51 CHEM 315 FA24 Unit 1 Do you think that standards are available for all analytes? Why or why not? Elaborate. STOP Calibration Curve To help you understand the ideas of calibration curve and standard addition curves we are going to use a cartoon example, but it translates directly into any chemistry scenario where the dependent variable (y) varies linearly with the independent variable (x). Imagine that you have 5 containers, as shown below, and assume that each ball gives an instrument response of 3. Determine the instrument response for each of the containers, plot the instrument response (dependent variable) vs. number of balls (independent variable), and determine using the graph how many balls are present if the instrument response is 26. Be sure to label the graph. Fry-Petit 52 CHEM 315 FA24 Unit 1 Instrument Response (a.u.) STOP Fry-Petit 53 CHEM 315 FA24 Unit 1 Fry-Petit 54 CHEM 315 FA24 Unit 1 As a group work through this real lab problem on using calibration This is very similar to what you will do in Quantitative Analysis Laboratory and EXAMS for this class. Using a Calibration Curve Below is a calibration curve for the determination of vitamin C (ascorbic acid [AA]) via voltammetry. This allows us to plot the current as a function of concentration. Four standards have been made (4.00, 8.00, 12.00, and 16.00 μM) and run to create the calibration curve. Then three fruit juice samples with an unknown amount of vitamin C are run and the current is recorded (Fruit Juice). [AA] (µM) Current (µA/cm2) 4.00 1.35 8.00 2.76 12.00 4.12 16.00 5.32 Fruit Juice 4.51 Fruit Juice 4.63 Fruit Juice 4.49 LINEST Output m 0.33175 0.070000 b sm 0.008526 0.093394 sb R2 0.998681 0.076256 sy Other Variables y-bar 3.388 Σ(xi-x-bar)2 80 The table above is readily available from Excel whenever you create a calibration curve and use the LINEST function. You will learn how to create this table in CHEM 316, but you need to know how to use the data in it for this class. Therefore, label all variables in the tables above so you will be able to readily use them. *Note: standard deviation is always given as “s” with a subscript denoting what it is the standard deviation of. Fry-Petit 55 CHEM 315 FA24 Unit 1 What is the average concentration of vitamin C in the 3 samples? Draw a horizontal line on the plot from the average measured current for the diluted sample to the calibration curve. Then draw a vertical line from the curve to the appropriate concentration on the x-axis. This provides a graphical check of your math. Does your graphical check confirm your math? Determine the uncertainty, sx, of the sample concentration. Calculate the confidence interval and write the complete confidence interval (e.g. XX±YY μM) with the correct number of significant figures. Fry-Petit 56 CHEM 315 FA24 Unit 1 If the detection limit is 0.20 µM, what is the quantitation limit? (come back to after we learn LOD, LOQ, and sensitivity) The y-intercept is non-zero. What could this be indicative of? STOP Assuming that we have to take the measurement in the presence of the purple solution which is very hard to make or may not have a standard solution. We start with some unknown amount of balls that I am covering up with a black box so you can’t see them. We put 2 additional balls in and collect an instrument response. We repeat this spiking procedure 4 more times. This is referred to as a constant volume standard addition, for which the initial concentration is given by the absolute value of the x-intercept. (The derivation of this fact is in section 5-3 if you are interested) Fry-Petit 57 CHEM 315 FA24 Unit 1 Given the standard addition graph below determine the initial concentration of the solution that has been spiked. STOP Fry-Petit 58 CHEM 315 FA24 Unit 1 Fry-Petit 59 CHEM 315 FA24 Unit 1 Using a Standard Addition Curve Brilliant Blue G (BBG) dye was recently discovered as promising dye to analyze the extent of spinal cord injury. In this experiment, standard addition was used to minimize the matrix effect in determining concentration of BBG in a sample of spinal fluid. [BBG]s (nM) Abs (a.u.) 0.00 0.038 5.00 0.074 10.00 0.111 15.00 0.149 LINEST Output m 0.007400 0.037500 b sm 6.325x10-5 5.916x10-4 sb R2 0.999854 7.071x10-4 sy Other Variables y-bar 0.0930 Σ(xi-x-bar)2 125 Fry-Petit 60 CHEM 315 FA24 Unit 1 Determine the concentration of BBG in the unspiked sample using the standard addition curve. Second, determine the uncertainty in the concentration of BBG. Calculate and write the complete confidence interval with the correct number of significant figures. The y-intercept is non-zero. What could this be indicative of? STOP Fry-Petit 61 CHEM 315 FA24 Unit 1 Internal Standard Activity Suppose you wanted to measure the quercetin concentration in a plant food such as Prunus serotina. Before performing the measurement, you would first need to remove quercetin from the plant sample because the plant itself will not be compatible with the measurement technique. For example, most measurement techniques require the sample in liquid form. A likely procedure for removing the quercetin from the plant is to use an extraction process. A sample of the plant might be mixed with a suitable solvent in a blender, homogenized, and filtered. One concern in this process is whether all of the quercetin has been extracted from the plant. If a lesser amount is extracted, the concentration of quercetin in Prunus serotina will be underestimated using an external standard curve. Can your group think of a way to determine the extraction efficiency of an analyte such as quercetin? STOP Fry-Petit 62 CHEM 315 FA24 Unit 1 A standard solution containing 75 ppm of quercetin and 60 ppm of internal standard kaempferol gave peak areas of 300 and 200, respectively. A plant sample is spiked such that the extract to be analyzed should have 60 ppm of kaempferol. Analysis of the sample gives a peak area for the kaempferol of 163. The quercetin peak in the same extract has an area of 407. What is the concentration of quercetin in the extract? STOP Fry-Petit 63 CHEM 315 FA24 Unit 1 Fry-Petit 64 CHEM 315 FA24 Unit 1 What are the LOD, LOQ, and sensitivity for the calibration curve made for [Cu2+] via AA? STOP Fry-Petit 65 CHEM 315 FA24 Unit 1 Additional Homework From a previous exam: Trace elements, such as Sr, in teeth of archeological specimens provide anthropologists with clues about diet and diseases of ancient people. Atomic absorption spectroscopy measurements were collected to determine the amount of Sr in a tooth specimen. Use the data to answer the following questions a-f. Table 1 Table 2 Added Sr Signal Number of Absorbance (ppb) (a.u.) replicate from zero spike 0.00 28.0 measurments sample (a.u.) 2.50 34.3 1 25.0 5.00 42.8 2 25.0 7.50 51.5 3 25.0 10.00 58.6 4 25.0 m 3.136 27.36 b 5 25.1 sm 0.0945445 0.578965 sb 6 25.1 7 24.9 R2 0.9972807 0.74744 sy 8 25.0 9 25.0 sx=0.427 ppm 10 25.0 25.0 s 0.1 a. What is the 95% confidence interval for unknown Sr concentration? Write the confidence interval in this form: XX ± YY. Fry-Petit 66 CHEM 315 FA24 Unit 1 b. What is the limit of detection for the calibration curve? c. What is the limit of quantification for the calibration curve? d. What is the sensitivity for the calibration curve? 𝑦𝑒𝑠 𝑜𝑟 𝑛𝑜 e. Could the concentration 0.2 ppb be measured via this method? 𝑐𝑖𝑟𝑐𝑙𝑒 𝑜𝑛𝑒 𝑦𝑒𝑠 𝑜𝑟 𝑛𝑜 f. Could the concentration 0.2 ppb be quantified via this method? 𝑐𝑖𝑟𝑐𝑙𝑒 𝑜𝑛𝑒 Fry-Petit 67 CHEM 315 FA24  Unit 1 From a previous exam: Standard solutions of a blue protein were made, and their absorbance was measured at 508 nm using UV-vis spectroscopy. The standard calibration curve and LINEST output are shown below in Table 1. An unknown sample was also measured, and the 3 replicate measurements are listed in Table 1. The measurements of the lowest concentration sample, 1.6670 µg/mL, were measured 10 times and the resulting absorbance values are list in Table 2. Table 1 Table 2 [X] (µg/mL) Absorbance (a.u.) Number of Absorbance from 0.0000 0.1000 replicate 1.6670 µg/mL 1.6670 0.2500 measurments sample (a.u.) 5.0000 0.5000 1 0.2500 8.3330 0.7500 2 0.2499 9.5507 0.8413 3 0.2497 11.6667 1.0000 4 0.2503 18.1600 1.4870 5 0.2508 Unknown 1 0.8671 6 0.2510 Unknown 2 0.8659 7 0.2489 Unknown 3 0.8689 8 0.2498 LINEST output 9 0.2500 m 0.0758 0.1149 b 10 0.2499 sm 0.0006 0.0055 sb 0.2500 R2 s 0.0006 0.9997 0.0086 sy Σ(x i - mean x) 2 231.9166 0.7040 Fry-Petit 68 CHEM 315 FA24 Unit 1 a. What is the 95% confidence interval for unknown protein concentration? Write the confidence interval in this form: XX ± YY. b. What is the limit of detection for the calibration curve? c. What is the limit of quantification for the calibration curve? d. What is the sensitivity for the calibration curve? 𝑦𝑒𝑠 𝑜𝑟 𝑛𝑜 g. Could the concentration 0.06 µg/mL be measured via this method? 𝑐𝑖𝑟𝑐𝑙𝑒 𝑜𝑛𝑒 𝑦𝑒𝑠 𝑜𝑟 𝑛𝑜 h. Could the concentration 0.06 µg/mL be quantified via this method? 𝑐𝑖𝑟𝑐𝑙𝑒 𝑜𝑛𝑒 Fry-Petit 69 CHEM 315 FA24