Intro to Analytical Chemistry

4/30/2012 Introduction to Analytical Chemistry Lecture Date: January 14th, 2008 What is Analytical Chemistry? Analytical chemistry seeks ever improved means of measuring the chemical composition of natural and artificial materials The techniques of this science are used to identify the substances which may be present in a material and determine the exact amounts of the identified substances Qualitative:provides information about the identity of an atomic, molecular or biomolecular species Quantitative: provides numerical information as to the relative amounts of species Definitionsfrom www.acs.org 1 4/30/2012 The Role of Analytical Chemistry -Friedrich Wilhelm Ostwald “Analytical Chemistry, or the art of recognizing different substances and determining their constituents, takes a prominent position among the applications of science, since the questions which it enables us to answer arise wherever chemical processes are employed for scientific or chemical purposes.” http://www.pace.edu/dyson/academics/chemistryplv/ The Role of Analytical Chemistry Analyticalchemists work to improvethe reliability of existing techniques to meet the demands of for better chemical measurementswhich arise constantly in our society They adapt proven methodologiesto new kinds of materialsor to answer new questions about their composition. They carry out research to discover completely new principles of measurementsand are at the forefrontof the utilizationof major discoveriessuch as lasers and microchipdevicesfor practical purposes. Medicine Industry Environmental Food and Agriculture Forensics Archaeology Space science 2 4/30/2012 History of Analytical Methods Classicalmethods: early years (separation of analytes) via precipitation,extraction or distillation Qualitative:recognized by color, boiling point, solubility,taste Quantitative:gravimetric or titrimetric measurements Instrumental Methods: newer, faster, more efficient Physical properties of analytes: conductivity, electrode potential,light emission absorption, mass to charge ratio and fluorescence,many more… Classification of Modern Analytical Methods  GravimetricMethods determine the mass of the analyte or some compound chemically related to it  VolumetricMethods measure the volumeof a solution containing sufficientreagent to react completely with the analyte  ElectroanalyticalMethods involvethe measurement of such electricalproperties as voltage,current, resistance, and quantity of electricalcharge  SpectroscopicMethods are based on the measurement of the interactionbetween electromagnetic radiation and analyte atoms or molecules, or the production of such radiation by analytes  MiscellaneousMethods include the measurement of such quantitiesas mass-to-charge ratio, rate of radioactivedecay, heat of reaction, rate of reaction, sample thermal conductivity,optical activity,and refractiveindex 3 4/30/2012 Analytical Methodology 1. Understanding and defining the problem 2. History of the sample and background of the problem 3. Plan of action and execution 4.Analysis and reporting of results 1. Understanding and Defining the Problem • Whataccuracy is required? • Is there a time (or money) limit? • How much sample is available? • How many samples are to be analyzed? • Whatis the concentration range of the analyte? • Whatcomponents of the system will cause an interference? • Whatare the physical and chemical properties of the sample matrix? (complexity) 4 4/30/2012 2. History of sample and background of the problem Background info can originate from many sources: • The client,competitor’s products • Literature searches on related systems • Sample histories: • synthetic route • how sample was collected,transported, stored • the sampling process 3. Plan of Action Performance Characteristics:Figures of Merit Whichanalytical method should I choose? How good is the measurement,informationcontent How reproducible is it? Precision How close to the true value is it?Accuracy/Bias How small of a differencecan be measured? Sensitivity Whatconcentration/mass/amount/range?Dynamic Range How much interference? Selectivity (univariatevs. multivariate) N (xi − < x >)2 Sm = i=1 N −1 RSD = < x > s N s2 CV = < x > 100% bias =  - xt Sm = Sbl+ ksbl Sm + Sbl m m S = mc + Sbl 5 ... - tailieumienphi.vn