4/30/2012 1 Lecture Date: January 14 th , 2008 Introduction to Analytical Chemistry What is Analytical Chemistry? Qualitative: provides information about the identity of an atomic, molecular or biomolecular species Quantitative: provides numerical information as to the relative amounts of species 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 Definitions from www.acs.org 4/30/2012 2 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/ Analytical chemists work to improve the reliability of existing techniques to meet the demands of for better chemical measurements which arise constantly in our society They adapt proven methodologies to new kinds of materials or to answer new questions about their composition. They carry out research to discover completely new principles of measurements and are at the forefront of the utilization of major discoveries such as lasers and microchip devices for practical purposes. Medicine Industry Environmental Food and Agriculture Forensics Archaeology Space science The Role of Analytical Chemistry 4/30/2012 3 History of Analytical Methods Classical methods: 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  Gravimetric Methods determine the mass of the analyte or some compound chemically related to it  Volumetric Methods measure the volume of a solution containing sufficient reagent to react completely with the analyte  Electroanalytical Methods involve the measurement of such electrical properties as voltage, current, resistance, and quantity of electrical charge  Spectroscopic Methods are based on the measurement of the interaction between electromagnetic radiation and analyte atoms or molecules, or the production of such radiation by analytes  Miscellaneous Methods include the measurement of such quantities as mass-to-charge ratio, rate of radioactive decay, heat of reaction, rate of reaction, sample thermal conductivity, optical activity, and refractive index 4/30/2012 4 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 • What accuracy is required? • Is there a time (or money) limit? • How much sample is available? • How many samples are to be analyzed? • What is the concentration range of the analyte? • What components of the system will cause an interference? • What are the physical and chemical properties of the sample matrix? (complexity) 4/30/2012 5 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 Performance Characteristics: Figures of Merit Which analytical method should I choose? How good is the measurement, information content How reproducible is it? Precision How close to the true value is it? Accuracy/Bias How small of a difference can be measured? Sensitivity What concentration/mass/amount/range? Dynamic Range How much interference? Selectivity (univariate vs. multivariate) 3. Plan of Action   2 1 1     N xx s N i i   x s RSD %100   x s CV N s Sm  s 2 m SS c blm m   bias =  - x t S = mc + S bl S m = S bl + ks bl 4/30/2012 6 4. Analyzing and Reporting Results No work is complete until the “customer” is happy! • Analytical data analysis takes many forms: statistics, chemometrics, simulations, etc… • Analytical work can result in: • peer-reviewed papers, etc… • how sample was collected, transported, stored • technical reports, lab notebook records, etc Components of an Analytical Method Perform measurement (instrumentation) Handbook, Settle Compare results with standards Pretreat and prepare sample Obtain and store sample Apply required statistical techniques Verify results Present information Extract data from sample Covert data into information Transform information into knowledge After reviewing results might be necessary to modify and repeat procedure 4/30/2012 7 Techniques Separation Techniques Gas chromatography High performance liquid chromatography Ion chromatography Super critical fluid chromatography Capillary electrophoresis Planar chromatography Spectroscopic techniques Infrared spectrometry (dispersive and fourier transform) Raman spectrometry Nuclear magnetic resonance X-ray spectrometry Atomic absorption spectrometry Inductively coupled plasma atomic emission spectrometry Inductively coupled plasma MS Atomic fluorescence spectrometry Ultraviolet/visible spectrometry (CD) Molecular Fluorescence spectrometry Chemiluminescence spectrometry X-Ray Fluorescence spectrometry More Techniques Mass Spectrometry Electron ionization MS Chemical ionization MS High resolution MS Gas chromatography MS Fast atom bombardment MS HPLC MS Laser MS Electrochemical techniques Amperometric technique Voltammetric techniques Potentiometric techniques Conductiometric techniques Microscopic and surface techniques Atomic force microscopy Scanning tunneling microscopy Auger electron spectrometry X-Ray photon electron spectrometry Secondary ion MS 4/30/2012 8 Technique Selection Location of sample bulk or surface Physical state of sample gas, liquid, solid, dissolved solid, dissolved gas Amount of Sample macro, micro, nano, … Estimated purity of sample pure, simple mixture, complex mixture Fate of sample destructive, non destructive Elemental information total analysis, speciation, isotopic and mass analysis Molecular information compounds present, polyatomic ionic species,functional group, structural, molecular weight, physical property Analysis type Quantitative, Qualitative Analyte concentration major or minor component, trace or ultra trace An Example: HPLC vs. NMR HPLC NMR Location of sample bulk or surface B B Physical state of sample gas, liquid, solid, dissolved solid, dissolved gas L,Ds L,S,Ds Amount of Sample macro, micro Ma, Mi Ma, Mi Estimated purity of sample pure, simple mixture, complex mixture Sm,M P,Sm Fate of sample destructive, non destructive N,D N Elemental information total analysis, speciation, isotopic and mass analysis Molecular information Compounds present, Polyatomic ionic species, Cp,Io,St Cp,Fn,St Functional group, Structural, MW, Physical prop Analysis type Quantitative, Qualitative Ql,Qt Ql,Qt T,S (ion) limited 4/30/2012 9 Review of Background Material  Chemical equilibrium  Activity coefficients  Ionic strength  Acids and bases  Titrations  Other simple chemical tests (“spot tests”)  Some important figures of merit  Review of a few other helpful concepts Chemical Equilibrium aA + bB  cC + dD K = [C] c [D] d / [A] a [B] b  There is never actually a complete conversion of reactants to product in a chemical reaction, there is only a chemical equilibrium.  A chemical equilibrium state occurs when the ratio of concentration of reactants and products is constant. An equilibrium-constant expression is an algebraic equation that describes the concentration relationships that exist among reactants and products at equilibrium 4/30/2012 10 Chemical Equilibrium Dissociation of water 2H 2 O  H 3 O + + OH - K w = [H 3 O + ][OH - ] Acid base NH 3 + H 2 O  NH 4 + + OH - K b = [NH 4 + ][OH - ] / [NH3] Solubility PbI 2 (s)  Pb 2+ + 2I - K sp = [Pb 2+ ][I - ] 2 Oxidation-Reduction IO 3 - + 5I - + 6H +  3I 2 (aq) + 3H 2 0 K eq = [I 2 ] 3 / [IO 3 - ][I - ] 5 [H + ] 6 Cl 2 (g) + 2AgI(s)  2AgCl(s) + I 2 (g) K eq = pI 2 / pCl 2 Typical Equilibrium Constant Expressions [...]... Important Concepts  Limit of detection (LOD): the  Linearity: the degree to which a response of an analytical detector to analyte concentration/mass approximates a linear function Limit of linearity Detector response lowest amount (concentration or mass) of an analyte that can be detected at a known confidence level Slope relates to sensitivity LOQ LOD Dynamic range Concentration  Limit of quantitation... structure) colorimetric -subjective sensitive to skill of analyst reagents unstable Chemical Stoichiometry Stoichiometry: The mass relationships among reacting chemical species The stoichiometry of a reaction is the relationship among the number of moles of reactants and products as shown by a balanced equation Mass Moles Moles Mass Divide by molar mass Multiply by stoichiometric ratio Multiply by molar mass... Definition: an analytical technique that measures concentration of an analyte by the volumetric addition of a reagent solution (titrant)- that reacts quantitatively with the analyte  For titrations to be useful, the reaction must generally be quantitative, fast and well-behaved Advantages great flexibility suitable for a wide range of analytes manual, simple excellent precision an accuracy readily automated... 0.001 M, a shielding effect occurs around ions Cations tend to be surrounded by nearby anions and anions tend to be surrounded by nearby cations This shielding effect becomes significant at ion concentrations of 0.01 M and greater Doubly or triply charged ions "charge up" a solution more than singly charged ions, so we need a standard way to talk about charge concentration Activity Coefficients Dilute... a strong – Any added OH- reacts with the weak acid HA:  OH- (aq) + HA (aq) -> H2O + A-(aq) steal H+ from A-)  (since OH- can Example: if 1 mL of 0.1 N HCl solution to 100 mL water, the pH drops from 7 to 3 If the 0.1 N HCl is added to a 0.01 M solution of 1:1 acetic acid/sodium acetate, the pH drops only 0.09 units Calculating the pH of Buffered Solutions Henderson-Hasselbach equation 18 4/30/2012... Aqueous Solution Equilibria Equilibria classified by reaction taking place 1) acid-base 2) oxidative-reductive Bronsted-Lowry definitions: acid: anything that donates a [H+] (proton donor) base: anything that accepts a [H+] (proton acceptor) HNO2 + H2O  NO2- + H3O+ ACID HA + H2O  A- + H3O+ BASE NH3 + H2O  NH4+ + OH- Ka = [A- ] [H3O+ ] / [HA] Kb = [NH4+][OH-] / [NH3] 13 4/30/2012 Strength of Acids and Bases... LOD Dynamic range Concentration  Limit of quantitation (LOQ): the range over which quantitative measurements can be made (usually the linear range), often defined by detector dynamic range  Selectivity: the degree to which a detector is free from interferences (including the matrix or other analytes) 21 4/30/2012 Simple Chemical Tests  While most of this class is focused on instrumental methods, a... in units of kg/L or g/mL Specific Gravity: The ratio of the mass of a substance to the mass of an equal volume of water at 4 degrees Celsius Dimensionless (not associated with units of measure) 23 4/30/2012 Other Helpful Information Prefixes for SI Units gigaG megaM kilok decid centic millim microu nanon picop femtof attoa 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12 10-15 10-18 24 ... 20 4/30/2012 Notes on Solutions and Their Concentrations Molar Concentration or Molarity – Number of moles of solute in one Liter of solution or millimoles solute per milliliter of solution Analytical Molarity – Total number of moles of a solute, regardless of chemical state, in one liter of solution It specifies a recipe for solution preparation Equilibrium Molarity – (Species Molarity) – The molar... Hg2+ developed using DNA and relying on the formation of a thymidineHg2+-thymidine complex  LOD = 100 nM (20 ppb) in aqueous solution  Linearity from the high nanomolar to low micromolar range  Selective for Hg2+ and insensitive to Mg2+, Pb2+, Cd2+, Co2+, Zn2+, Ni2+, and other metal ions Angew Chem Int Ed., DOI: 10.1002/anie.200700269 http://pubs.acs.org/cen/news/85/i19/8519news6.html 22 4/30/2012 . 4/30/2012 1 Lecture Date: January 14 th , 2008 Introduction to Analytical Chemistry What is Analytical Chemistry? Qualitative: provides information about the identity of an atomic, molecular or biomolecular. necessary to modify and repeat procedure 4/30/2012 7 Techniques Separation Techniques Gas chromatography High performance liquid chromatography Ion chromatography Super critical fluid chromatography Capillary. purposes. Medicine Industry Environmental Food and Agriculture Forensics Archaeology Space science The Role of Analytical Chemistry 4/30/2012 3 History of Analytical Methods Classical methods: early years (separation of analytes)