Lecture 1 - Evaluation of Experimental Data Chem 420...

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Unformatted text preview: Evaluation of Experimental Data Chem 420 January 18, 2011 Types of analytical methods Classical methods Information extracted from human observables Color, melting/boiling point, solubilities, odors, refractive index, (taste) Gravimetric or Volumetric Instrumental methodsearly 1900s Measure less readily observable physical characteristics Conductivity, light absorption or emission, m/z ratio Improved methods of separation Chromatography and electrophoresis Definitions Detector: A mechanical, electrical, or chemical device that identifies, records, or indicates a change in one of the variables in its environment. Transducer: A device that converts nonelectrical information to the electrical domain. Sensor: An analytical device that is capable of monitoring specific chemical species continuously and reversibly. Coupled transducer and recognition material Selecting the right method Define by asking the following questions: What do we want to know? What accuracy and precision are required? How much sample is required? What is the likely concentration range of analyte? Are there likely interferences? What are the physical and chemical properties of the matrix? How many samples are there? Turn around time? Is the image on the Shroud of Turin paint or blood? What analytical tools would you use to determine whether red pigments were from blood or from paint pigments? What other considerations would you need to take into account? Figures of merit: Performance characteristics of instruments Precision Accuracy Sensitivity Limit of Detection Dynamic range Selectivity Precision vs. Accuracy in the common verbiage (Websters) Precision : The quality or state of being precise ; exactness; accuracy ; strict conformity to a rule or a standard; definiteness. Accuracy : The state of being accurate ; exact conformity to truth, or to a rule or model; precision These are not synonymous when describing instrumental measurements! Precision and accuracy in this course Precision : Degree of mutual agreement among data obtained in the same way. Absolute and relative standard deviation, standard error of the mean, coefficient of variation, variance....
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This note was uploaded on 03/06/2011 for the course CHEMISTRY 420 taught by Professor Mcdonald during the Spring '11 term at University of Illinois, Urbana Champaign.

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Lecture 1 - Evaluation of Experimental Data Chem 420...

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