QUALITATIVE ELEMENTAL ANALYSIS
ANALYTICALOBJECTIVES,OR:WHATANALYTICAL CHEMISTSDO 1 1 WHAT IS ANALYTICAL SCIENCE?, 1 2 QUALITATIVE AND QUANTITATIVE ANALYSIS: WHAT DOES EACH TELL US?, 1 3 GETTING STARTED: THE ANALYTICAL PROCESS, 1 4 VALIDATION OF A METHOD—YOU HAVE TO PROVE IT WORKS!, 1 5 ANALYZE VERSUS DETERMINE—THEY ARE DIFFERENT, 1 6 SOME USEFUL WEBSITES, BASICTOOLSANDOPERATIONSOFANALYTICAL CHEMISTRY 2 1 THE LABORATORY NOTEBOOK—YOUR CRITICAL RECORD, 2 2 LABORATORY MATERIALS AND REAGENTS, 2 3 THE ANALYTICAL BALANCE—THE INDISPENSIBLE TOOL, 2 4 VOLUMETRIC GLASSWARE—ALSO INDISPENSIBLE, 2 5 PREPARATION OF STANDARD BASE SOLUTIONS, 2 6 PREPARATION OF STANDARD ACID SOLUTIONS, 2 7 OTHER APPARATUS—HANDLING AND TREATING SAMPLES, 2 8 IGNITING PRECIPITATES—GRAVIMETRIC ANALYSIS, 2 9 OBTAINING THE SAMPLE—IS IT SOLID, LIQUID, OR GAS?, 2 10 OPERATIONS OF DRYING AND PREPARING A SOLUTION OF THE ANALYTE, 2 11 LABORATORY SAFETY, STATISTICSANDDATAHANDLINGINANALYTICAL CHEMISTRY 3 1 ACCURACY AND PRECISION: THERE IS A DIFFERENCE, 3 2 DETERMINATE ERRORS—THEY ARE SYSTEMATIC, 3 3 INDETERMINATE ERRORS—THEY ARE RANDOM, 3 4 SIGNI?CANT FIGURES: HOW MANY NUMBERS DO YOU NEED?, 3 5 ROUNDING OFF, 3 6 WAYS OF EXPRESSING ACCURACY, 3 7 STANDARD DEVIATION—THE MOST IMPORTANT STATISTIC, 3 8 PROPAGATION OF ERRORS—NOT JUST ADDITIVE, 3 9 SIGNI?CANT FIGURES AND PROPAGATION OF ERROR, 3 10 CONTROL CHARTS, 3 11 THE CON?DENCE LIMIT—HOW SURE ARE YOU?, 3 12 TESTS OF SIGNI?CANCE—IS THERE A DIFFERENCE?, 3 13 REJECTION OF A RESULT: THE Q TEST, 3 14 STATISTICS FOR SMALL DATA SETS, 3 15 LINEAR LEAST SQUARES—HOW TO PLOT THE RIGHT STRAIGHT LINE, 3 16 CORRELATION COEF?CIENT AND COEF?CIENT OF DETERMINATION, 3 17 DETECTION LIMITS—THERE IS NO SUCH THING AS ZERO, 3 18 STATISTICS OF SAMPLING—HOW MANY SAMPLES, HOW LARGE?, 3 19 POWERING A STUDY: POWER ANALYSIS, 3 20 USE OF SPREADSHEETS IN ANALYTICAL CHEMISTRY, 3 21 USING SPREADSHEETS FOR PLOTTING CALIBRATION CURVES, 3 22 SLOPE, INTERCEPT, AND COEF?CIENT OF DETERMINATION, 3 23 LINEST FOR ADDITIONAL STATISTICS, 3 24 STATISTICS SOFTWARE PACKAGES, GOODLABORATORYPRACTICE:QUALITYASSURANCEAND METHODVALIDATION 4 1 WHAT IS GOOD LABORATORY PRACTICE?, 4 2 VALIDATION OF ANALYTICAL METHODS, 4 3 QUALITY ASSURANCE—DOES THE METHOD STILL WORK?, 4 4 LABORATORY ACCREDITATION, 4 5 ELECTRONIC RECORDS AND ELECTRONIC SIGNATURES: 21 CFR, PART 11, 4 6 SOME OF?CIAL ORGANIZATIONS, STOICHIOMETRICCALCULATIONS:THEWORKHORSEOF THEANALYST 5 1 REVIEW OF THE FUNDAMENTALS, 5 2 HOW DO WE EXPRESS CONCENTRATIONS OF SOLUTIONS?, 5 3 EXPRESSIONS OF ANALYTICAL RESULTS—SO MANY WAYS, 5 4 VOLUMETRIC ANALYSIS: HOW DO WE MAKE STOICHIOMETRIC CALCULATIONS?, 5 5 VOLUMETRIC CALCULATIONS—LET’S USE MOLARITY, 5 6 TITER—HOW TO MAKE RAPID ROUTINE CALCULATIONS, 5 7 WEIGHT RELATIONSHIPS—YOU NEED THESE FOR GRAVIMETRIC CALCULATIONS, GENERALCONCEPTSOFCHEMICALEQUILIBRIUM 6 1 CHEMICAL REACTIONS: THE RATE CONCEPT, 6 2 TYPES OF EQUILIBRIA, 6 3 GIBBS FREE ENERGY AND THE EQUILIBRIUM CONSTANT, 6 4 LE CHˆATELIER’S PRINCIPLE, 6 5 TEMPERATURE EFFECTS ON EQUILIBRIUM CONSTANTS, 6 6 PRESSURE EFFECTS ON EQUILIBRIA, 6 7 CONCENTRATION EFFECTS ON EQUILIBRIA, 6 8 CATALYSTS, 6 9 COMPLETENESS OF REACTIONS, 6 10 EQUILIBRIUM CONSTANTS FOR DISSOCIATING OR COMBINING SPECIES—WEAK ELECTROLYTES AND PRECIPITATES, 6 11 CALCULATIONS USING EQUILIBRIUM CONSTANTS—COMPOSITION AT EQUILIBRIUM?, 6 12 THE COMMON ION EFFECT—SHIFTING THE EQUILIBRIUM, 6 13 SYSTEMATIC APPROACH TO EQUILIBRIUM CALCULATIONS—HOW TO SOLVE ANY EQUILIBRIUM PROBLEM, 6 14 SOME HINTS FOR APPLYING THE SYSTEMATIC APPROACH FOR EQUILIBRIUM CALCULATIONS, 6 15 HETEROGENEOUS EQUILIBRIA—SOLIDS DON’T COUNT, 6 16 ACTIVITY AND ACTIVITY COEF?CIENTS— CONCENTRATION IS NOT THE WHOLE STORY, 6 17 THE DIVERSE ION EFFECT: THE THERMODYNAMIC EQUILIBRIUM CONSTANT AND ACTIVITY COEF?CIENTS, ACID–BASEEQUILIBRIA 7 1 THE EARLY HISTORY OF ACID—BASE CONCEPTS, 7 2 ACID–BASE THEORIES—NOT ALL ARE CREATED EQUAL, 7 3 ACID–BASE EQUILIBRIA IN WATER, 7 4 THE PH SCALE, 7 5 PH AT ELEVATED TEMPERATURES: BLOOD PH, 7 6 WEAK ACIDS AND BASES—WHAT IS THE PH?, 7 7 SALTS OF WEAK ACIDS AND BASES—THEY AREN’T NEUTRAL, 7 8 BUFFERS—KEEPING THE PH CONSTANT (OR NEARLY SO), 7 9 POLYPROTIC ACIDS AND THEIR SALTS, 7 10 LADDER DIAGRAMS, 7 11 FRACTIONS OF DISSOCIATING SPECIES AT A GIVEN PH: ? VALUES—HOW MUCH OF EACH SPECIES?, 7 12 SALTS OF POLYPROTIC ACIDS—ACID, BASE, OR BOTH?, 7 13 PHYSIOLOGICAL BUFFERS—THEY KEEP YOU ALIVE, 7 14 BUFFERS FOR BIOLOGICAL AND CLINICAL MEASUREMENTS, 7 15 DIVERSE ION EFFECT ON ACIDS AND BASES: CKA AND CKB—SALTS CHANGE THE PH, 7 16 LOG C—PH DIAGRAMS, 7 17 EXACT PH CALCULATORS, ACID–BASETITRATIONS 8 1 STRONG ACID VERSUS STRONG BASE—THE EASY TITRATIONS, 8 2 THE CHARGE BALANCE METHOD—AN EXCEL EXERCISE FOR THE TITRATION OF A STRONG ACID AND A STRONG BASE, 8 3 DETECTION OF THE END POINT: INDICATORS, 8 4 STANDARD ACID AND BASE SOLUTIONS, 8 5 WEAK ACID VERSUS STRONG BASE—A BIT LESS STRAIGHTFORWARD, 8 6 WEAK BASE VERSUS STRONG ACID, 8 7 TITRATION OF SODIUM CARBONATE—A DIPROTIC BASE, 8 8 USING A SPREADSHEET TO PERFORM THE SODIUM CARBONATE—HCL TITRATION, 8 9 TITRATION OF POLYPROTIC ACIDS, 8 10 MIXTURES OF ACIDS OR BASES, 8 11 EQUIVALENCE POINTS FROM DERIVATIVES OF A TITRATION CURVE, 8 12 TITRATION OF AMINO ACIDS—THEY ARE ACIDS AND BASES, 8 13 KJELDAHL ANALYSIS: PROTEIN DETERMINATION, 8 14 TITRATIONS WITHOUT MEASURING VOLUMES, COMPLEXOMETRICREACTIONSANDTITRATIONS 9 1 COMPLEXES AND FORMATION CONSTANTS—HOW STABLE ARE COMPLEXES?, 9 2 CHELATES: EDTA—THE ULTIMATE TITRATING AGENT FOR METALS, 9 3 METAL–EDTA TITRATION CURVES, 9 4 DETECTION OF THE END POINT: INDICATORS—THEY ARE ALSO CHELATING AGENTS, 9 5 OTHER USES OF COMPLEXES, 9 6 CUMULATIVE FORMATION CONSTANTS ? AND CONCENTRATIONS OF SPECI?C SPECIES IN STEPWISE FORMED COMPLEXES, GRAVIMETRICANALYSISANDPRECIPITATION EQUILIBRIA 10 1 HOW TO PERFORM A SUCCESSFUL GRAVIMETRIC ANALYSIS, 10 2 GRAVIMETRIC CALCULATIONS—HOW MUCH ANALYTE IS THERE?, 10 3 EXAMPLES OF GRAVIMETRIC ANALYSIS, 10 4 ORGANIC PRECIPITATES, 10 5 PRECIPITATION EQUILIBRIA: THE SOLUBILITY PRODUCT, 10 6 DIVERSE ION EFFECT ON SOLUBILITY: KSP AND ACTIVITY COEF?CIENTS, PRECIPITATIONREACTIONSANDTITRATIONS 11 1 EFFECT OF ACIDITY ON SOLUBILITY OF PRECIPITATES: CONDITIONAL SOLUBILITY PRODUCT, 11 2 MASS BALANCE APPROACH FOR MULTIPLE EQUILIBRIA, 11 3 EFFECT OF COMPLEXATION ON SOLUBILITY: CONDITIONAL SOLUBILITY PRODUCT, 11 4 PRECIPITATION TITRATIONS, ELECTROCHEMICALCELLSANDELECTRODE POTENTIALS 12 1 WHAT ARE REDOX REACTIONS?, 12 2 ELECTROCHEMICAL CELLS—WHAT ELECTROANALYTICAL CHEMISTS USE, 12 3 NERNST EQUATION—EFFECTS OF CONCENTRATIONS ON POTENTIALS, 12 4 FORMAL POTENTIAL—USE IT FOR DE?NED NONSTANDARD SOLUTION CONDITIONS, 12 5 LIMITATIONS OF ELECTRODE POTENTIALS, POTENTIOMETRICELECTRODESANDPOTENTIOMETRY 13 1 METAL ELECTRODES FOR MEASURING THE METAL CATION, 13 2 METAL–METAL SALT ELECTRODES FOR MEASURING THE SALT ANION, 13 3 REDOX ELECTRODES—INERT METALS, 13 4 VOLTAIC CELLS WITHOUT LIQUID JUNCTION—FOR MAXIMUM ACCURACY, 13 5 VOLTAIC CELLS WITH LIQUID JUNCTION—THE PRACTICAL KIND, 13 6 REFERENCE ELECTRODES: THE SATURATED CALOMEL ELECTRODE, 13 7 MEASUREMENT OF POTENTIAL, 13 8 DETERMINATION OF CONCENTRATIONS FROM POTENTIAL MEASUREMENTS, 13 9 RESIDUAL LIQUID-JUNCTION POTENTIAL—IT SHOULD BE MINIMIZED, 13 10 ACCURACY OF DIRECT POTENTIOMETRIC MEASUREMENTS—VOLTAGE ERROR VERSUS ACTIVITY ERROR, 13 11 GLASS PH ELECTRODE—WORKHORSE OF CHEMISTS, 13 12 STANDARD BUFFERS—REFERENCE FOR PH MEASUREMENTS, 13 13 ACCURACY OF PH MEASUREMENTS, 13 14 USING THE PH METER—HOW DOES IT WORK?, 13 15 PH MEASUREMENT OF BLOOD—TEMPERATURE IS IMPORTANT, 13 16 PH MEASUREMENTS IN NONAQUEOUS SOLVENTS, 13 17 ION-SELECTIVE ELECTRODES, 13 18 CHEMICAL ANALYSIS ON MARS USING ION-SELECTIVE ELECTRODES, REDOXANDPOTENTIOMETRICTITRATIONS 14 1 FIRST: BALANCE THE REDUCTION–OXIDATION REACTION, 14 2 CALCULATION OF THE EQUILIBRIUM CONSTANT OF A REACTION—NEEDED TO CALCULATE EQUIVALENCE POINT POTENTIALS, 14 3 CALCULATING REDOX TITRATION CURVES, 14 4 VISUAL DETECTION OF THE END POINT, 14 5 TITRATIONS INVOLVING IODINE: IODIMETRY AND IODOMETRY, 14 6 TITRATIONS WITH OTHER OXIDIZING AGENTS, 14 7 TITRATIONS WITH OTHER REDUCING AGENTS, 14 8 PREPARING THE SOLUTION—GETTING THE ANALYTE IN THE RIGHT OXIDATION STATE BEFORE TITRATION, 14 9 POTENTIOMETRIC TITRATIONS (INDIRECT POTENTIOMETRY), VOLTAMMETRYANDELECTROCHEMICALSENSORS 15 1 VOLTAMMETRY, 15 2 AMPEROMETRIC ELECTRODES—MEASUREMENT OF OXYGEN, 15 3 ELECTROCHEMICAL SENSORS: CHEMICALLY MODI?ED ELECTRODES, 15 4 ULTRAMICROELECTRODES, 15 5 MICROFABRICATED ELECTROCHEMICAL SENSORS, 15 6 MICRO AND ULTRAMICROELECTRODE ARRAYS, CHAPTERONE ANALYTICALOBJECTIVES,OR:WHAT ANALYTICALCHEMISTSDO “UNLESS OUR KNOWLEDGE IS MEASURED AND EXPRESSED IN NUMBERS, IT DOES NOT AMOUNT TO MUCH ” LEARNINGOBJECTIVES WHAT ARE SOME OF THE KEY THINGS WE WILL LEARN FROM THIS CHAPTER? ?ANALYTICAL SCIENCE DEALS WITH THE CHEMICAL CHARACTERIZATION OF MATTER—WHAT, HOW MUCH?, P ?THE ANALYST MUST KNOW WHAT INFORMATION IS REALLY NEEDED, AND OBTAIN A REPRESENTATIVE SAMPLE, PP 6, ?FEW MEASUREMENTS ARE SPECI?C, SO OPERATIONS ARE PERFORMED TO ACHIEVE HIGH SELECTIVITY, P ?YOU MUST SELECT THE APPROPRIATE METHOD FOR MEASUREMENT, P ?VALIDATION IS IMPORTANT, P ?THERE ARE MANY USEFUL WEBSITES DEALING WITH ANALYTICAL CHEM- ISTRY, P LORD KELVIN (WILLIAM THOMSON, 1824–1907) ANALYTICAL CHEMISTRY IS CONCERNED WITH THE CHEMICAL CHARACTERIZATION OF MATTER AND THE ANSWER TO TWO IMPORTANT QUESTIONS: WHAT IS IT (QUALITATIVE ANALYSIS) AND HOW MUCH IS IT (QUANTITATIVE ANALYSIS) CHEMICALS MAKE UP EVERYTHING WE USE OR CONSUME, AND KNOWLEDGE OF THE CHEMICAL COMPOSITION OF MANY SUBSTANCES IS IMPORTANT IN OUR DAILY LIVES ANALYTICAL CHEMISTRY PLAYS AN IMPORTANT ROLE IN NEARLY ALL ASPECTS OF CHEMISTRY, FOR EXAMPLE, AGRICULTURAL, CLINICAL, ENVIRONMENTAL, FORENSIC, MANUFACTURING, METALLURGICAL, AND PHARMACEUTICAL CHEMISTRY THE NITROGEN CONTENT OF A FERTILIZER DETERMINES ITS VALUE FOODS MUST BE ANALYZED FOR CONTAMINANTS (E G , PESTICIDE RESIDUES) AND FOR ESSENTIAL EVERYTHING IS MADE OF CHEMICALS ANALYTICAL CHEMISTS DETERMINE WHAT AND HOW MUCH NUTRIENTS (E G , VITAMIN CONTENT) THE AIR WE BREATHE MUST BE ANALYZED FOR TOXIC GASES (E G , CARBON MONOXIDE) BLOOD GLUCOSE MUST BE MONITORED IN DIABETICS (AND, IN FACT, MOST DISEASES ARE DIAGNOSED BY CHEMICAL ANALYSIS) THE PRESENCE OF TRACE ELEMENTS FROM GUN POWDER ON A PERPETRATOR’S HAND WILL PROVE A GUN WAS ?RED BY THAT HAND THE QUALITY OF MANUFACTURED PRODUCTS OFTEN DEPENDS ON PROPER CHEMICAL PROPORTIONS, AND MEASUREMENT OF THE CONSTITUENTS IS A NECESSARY PART OF QUALITY ASSURANCE THE CARBON CONTENT OF STEEL WILL IN?UENCE ITS QUALITY THE PURITY OF DRUGS WILL IN?UENCE THEIR EF?CACY IN THIS TEXT, WE WILL DESCRIBE THE TOOLS AND TECHNIQUES FOR PERFORMING THESE DIFFERENT TYPES OF ANALYSES THERE IS MUCH USEFUL SUPPLEMENTAL MATERIAL ON THE TEXT WEBSITE, INCLUDING EXCEL PROGRAMS THAT YOU CAN USE, AND VIDEOS TO ILLUSTRATE THEIR USE YOU SHOULD ?RST READ THE PREFACE TO LEARN WHAT IS AVAILABLE TO YOU, AND THEN TAKE ADVANTAGE OF SOME OF THE TOOLS