Analytical Chemistry firstname.lastname@example.org Dr Kresimir Rupnik, Ph.D. LSU, Summer 2017
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The course web site: Moodle • Syllabus, E-mail, Phone • News updates, schedule/exams calendar • Lecture notes/supplements (you can print important pages !!!!!!, 4 or 6 on one page). You can fill in what is needed during the lecture!!! DO NOT OVERPRINT!!! • HW, pre- Exams • Check for updates and notes!!!! • E-mail if you have questions, e-mail to report interesting of difficult parts from reading a night before the class
If you want to do more-and get some credit for it… • Read additional material from the textbook • Read articles in Analytical Chemistry (Science, Nature , JACS.. also may have relevant research). Check websites
Introduction to The Analytical Process: Analytical Chemistry in application • Chapter 0 (read it !)
Chapter 0 contains IMPORTANT take home messages about the Analytical Chemistry: What, why, how Most answers are given in this “representative” example which deals with the analysis of chocolate. Q; What are we analyzing for? A: Analytes: caffeine and theobromine. Q: Why are we analyzing? A: We have a well defined goal related to some application such as are quality, CSI , etc……The questions asked here could be: How does the amount of caffeine compare with the quality of chocolate, say which is better white or dark chocolate? Or : Are the two chocolate samples from the same origin, say the one that a crime suspect is eating and the one that was found at the crime scene – and both have similar packing?
…and last but not least important question:Q : How can we (or a CSI lab) find the caffeine and its quantity in chocolate?A: Find or make the procedure. In chemical analysis that is a process that can be described in terms of 7 important steps • The real life analytical chemists knows the procedure, that is knows general steps in a Chemical Analysis
IMPORTANT THM: 7 General Steps in Chemical Analysis • Formulating the question • Selecting analytical procedures • Sampling • Sample preparation • Analysis (Chemical or Physical) • Reporting and interpretation • Drawing conclusions
Step 1-question • Is chocolate made of materials in the specific quantitative range? • Range is given by industry standards
CHAPTER 00:Unnumbered Figure 0-3 Step 1 :formulating question->analytes
NOTE : Analytical chemistry has its own language-learn it (see the “Terms to Understand at the end of the chapter). You can more about these concepts in chapters 0, 5, 28 PROCEDURES, PROTOCOLS, TECHNIQUES: A protocol is a fixed sequence of actions (events) to be carried out (example: by US EPA). These methods commonly define: -sample handling requirements -analytical TECHNIQUES VALIDATION: We need a validationof a new method by showing that its results agree with those obtained using older (other), accepted procedures. When validated, we know that the procedure measures what the analyst says it measures on a specific type of sample. . INTERFERENTS: They are “the enemy”. Interference occurs when a species (other compounds than analyte) contribute the instrument signal intensity or amplitude , by increasing it or decreasing it. So it looks like if there is more or less of the analyte then the real concentration. Interfering species determine what is the best method and protocol. We can MASK them by other chemicals so they do not interfere.
FYI STEP 1: Formulating the question: I need to know what I am looking for! Only then I can select an analytical procedure
FYI STEP 2 , selecting analytical procedure Choices of methods, more on methods throughout the textbook. Signal analysis , more in the first 5 chapters
Caffeine again: HPLC p. 4High Performance (Pressure) Liquid Chromatography Instrument, more on HPLC we will learn in “Separations”, Chapter 23 and on
STEP 3: SAMPLING • Sampling: how many chocolate bars, which chocolates? • Constructing a representative sample (Box 0-1, p.7): random, homogeneous, inhomogeneous, segregated material, composite sample • STEP 4: SAMPLE PREPARATION, • Sample preparation (for chemical analysis): transforming a sample into a state that is suitable for analyis. • More in chapter 28
STEP 3, STEP 4: terminology SAMPLES: Analytical chemist takes SAMPLES (small parts) of the materials for analysis. ALIQUOT: A small portion of the sample . Aliquotes masses are measured before analysis! ANALYTE: The compound you want to measure. SAMPLE is ANALYZED for a compound or analyte. Elements, ions, molecules, compounds are identified in sample (example: penicillin in antibiotic). A sample is ANALYZED for elements, ions, molecules, compounds (example: for penicillin). If the amount of elements, ions, molecules, compounds in the sample is found, we use the word quantitation (amount of penicillin in the sample is found). An ASSAYfor a compound or analyte If we intend to determine what fraction of a sample is some named material, we use the word determination or ASSAY. The named material is called the ANALYTE. We can run an assay for that material.
STEP 5: Chemical (or Physical) Analysis • Qualitative analysis: which substance • Quantitative analysis: how much of it Note: Analytical Chemistry is a Science that helps improve methods of analysis. Novel directions in analysis usually also include smaller, faster, simpler cheaper methods.
Our choice was HPLC –how it works? Column ~25cm long where the separation takes place
Results of the Caffeine Analysis: Chromatogram, it shows time on the x-axis and detector response or intensity of the signal on the y-axis. Note the three analytes in this example arrive at different (retention) times!!!
Analytical “two-step” • 1st step: Calibration with known standards. Use standards, pure compound same as analyte with known concentrations and record the reading on the instrument. Form a new diagram (Figure 0-7) to get the calibration curve – you can use Excel fitting. • 2nd step: Measurement of analyte and quantitative analysis from that known calibration curve.
Calibration curve shows the response of the instruments signal to different concentrations (quantities) of the analyte. It is done by the measurement of standards before the measurement of analyte!! Standards are prepared carefully, not from sample!! There are methods how to calculate the best fit: linear regression of straight-line calibration curves
HANDOUTS Textbook p 5 and6 Figures 0-5,0-6 and 0-7 Can you tell what is going on here?
SIGNALS Total analysis technique & Concentration techniques SA(signal due to analyte) =k CA (concentration of analyte) CALIBRATIONS -Accuracy, precision, sensitivity, selectivity, detection limits, noise -Robust and rugged method -Scale of operation (analytes classification ) STEP 6: terminology
STEP 6: Data Analysis and Reporting • This is what we will do in chapters 3, 4 and 5. We will discuss the so called statistical analysis which will give us uncertainty (error) limits to our data presentation and interpretation of our results. It will provide us with the limits of confidence and consequently the limits for possible answers to our question. • An example: After such analysis was done we can answer the question about caffeine in our chocolate: Table 0-2.
STEP 6:Reporting and STEP 7: Interpreting results • Analysis of dark and light chocolate, grams of analyte per 100g of chocolate
CHAPTER 00:Table 0-1 Results-step 6
CHAPTER 00:Table 0-2 Interpretation-answer on the question-step 7
Note on the methods • Not all instruments are “ LARGE” lab equipment. Read about biosensors, p 1 of your textbook.
Note on analytical Chemistry Applications • Industry (almost all need QC and analysis- food, materials, …) • Bio-Medicine (the basis of diagnosis, individual susceptibilities, changes..) • Environment (QC, monitoring, regulations) • Law (CSI, ..) • Others SEE ALSO: Analytical Chemistry Division at ACS and NSF. Check the pending changes in classifications! For new instrumentation see also DOE. For new protocols and standards NIST. For medical applications see NIH.
1. Measurements-Basic Tools-qualitative aspects (chemistry, physics)-quantitative aspects (numbers, units, uncertainty)A SHORT REVIEW
1-1Units of Measurement IMPORTANT • SI Units (from 1960) = Metric system • There are two types of units for measured physical quantities (=number and unit):(1) 7 fundamental (or base) units: and (2)(many) derived units obtained from base units (example velocity).
Mole = unit for the number of objects • 6.02 10 ^23 objects is in a mole. • 6.02 10 ^23 of oranges is one mole of oranges. • 6.02 10 ^23 = Avogadro’s number = 1 mole of objects Q: Who found or measured Avogadros’ number first?
IMPORTANT Units of Measurement: SI Units Powers of ten and exponential (scientific) notation are used for convenience with smaller or larger units in the SI system.