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1、Chapter overview IBO Assessment statements A.1.1 to A.10.2 This chapter covers the IB Chemistry syllabus Option A: Modern Analytical Chemistry. By the end of this chapter, you should be able to: describe the equipment and procedures used for the analysis of substances using atomic absorption (AA) sp
2、ectrometry, infrared (IR) spectroscopy, mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy describe how the structure of compounds may be deduced using information obtained from various spectroscopic techniques analyse IR, mass and NMR spectra in order to gain information about mole
3、cular structure understand that all chromatographic techniques require a stationary phase and a mobile phase describe how chromatography is used to identify and quantify the components of a mixture use a calibration curve in quantitative chromatographic and spectroscopic analysis calculate Rf values
4、 and describe the significance of Rf and Rt values in chromatography describe the equipment and procedures used for the analysis of substances by paper, thin-layer and column chromatography recognize that chromatographic techniques can be used to separate components of a mixture prior to analysis by
5、 other techniques such as mass spectrometry and IR spectroscopy describe the equipment and procedures used for the analysis of substances using gas and high performance liquid chromatography describe the equipment and procedures used for the analysis of substances using UVvisible spectrometry analys
6、e UVvisible spectra in order to gain information about molecular structure interpret splitting patterns and chemical shifts in NMR spectra to gain information about molecular structure. HL MODERN ANALYTICAL CHEMISTRY 1 2 N ews reports may tell us that a driver has been arrested for driving with a bl
7、ood alcohol content of 0.17%, an athlete has been tested for drugs and found to have consumed amphetamines, traces of water vapour have been found in the atmosphere of a new planet and that low fat foods have a high sugar content. How do scientists determine such information? It certainly is not jus
8、t with the laboratory equipment that we have access to daily. Modern methods of chemical analysis involve the use of instruments that routinely analyse samples rapidly and to high levels of accuracy. Although the instruments may be sophisticated and complex, they all use the basic principles of spec
9、troscopy and chromatography. Modern analytical chemistry offers a wide range of problem-solving techniques. Chemists use analytical techniques to identify and confi rm the structure of a substance, to analyse its composition and to determine its purity. The quantity and nature of substances present
10、in a mixture may be determined or the progress of a reaction may be followed by analysis. Instrumental analytical techniques are often more accurate and quicker than techniques involving experimental techniques such as those used in acidbase titrations in volumetric analysis or the precipitation of
11、a solid for gravimetric analysis. Quality control of consumer products requires that the composition of foodstuffs, building materials and even the materials from which our clothes are made be known accurately. Such knowledge can be life saving, or just a guide for people wanting to know the fat con
12、tent of the food they eat. In the design and manufacture of drugs, chemical analysis is of the utmost importance. The structure of a newly synthesized compound can be confi rmed by spectroscopic methods and its purity measured by chromatographic methods. Although there may be many analytical instrum
13、ents with varied components, they are essentially of only three types: those based on the interaction of electromagnetic radiation with the sample (spectroscopic techniques), those based on the interaction of magnetic and/or electric fi elds with the sample (mass spectroscopy and nuclear magnetic re
14、sonance) and those involving chromatography. Instrumental methods have several advantages over the more traditional laboratory methods (volumetric and gravimetric). They are faster, more sensitive, more accurate and less prone to human error. Their main disadvantage is cost! In an attempt to prevent
15、 cheating in sport, the urine of competitors is regularly tested for the presence of performance-enhancing drugs. In many schools, students suspected of illicit drug use may also fi nd themselves requested to undergo such tests. Chromatography is the basis of the Figure 1.0.1 A roadside breath test
16、determines whether the blood alcohol content of a driver is over the legal limit. 1.1 INTRODUCTION TO ANALYTICAL CHEMISTRY A.1.1 State the reasons for using analytical techniques. IBO 2007 Figure 1.1.1 An instrumental analytical technique known as high performance liquid chromatography (HPLC) is use
17、d to test the purity of an experimental AIDS vaccine. Analytical techniques CHEMISTRY: FOR USE WITH THE IB DIPLOMA PROGRAMME OPTIONS CHAPTER 1 MODERN ANALYTICAL CHEMISTRY 3 drug-testing cards that are used in these situations. In such dipstick tests, a simple colour change in the chemically treated
18、panel of the card indicates the presence of the drug for which the urine is being analysed. Chemical analysis is widely used in medicine for the detection of unwanted substances in the blood or urine. For example, the initial test for diabetes involves measuring the amount of glucose in the blood an
19、d ketones in the urine. Home pregnancy kits are another example of a urine dipstick test. These kits contain a treated panel that will change colour in the presence of a hormone called human chorionic gonadotrophin (hCG). Although chemical dipsticks are used for identifi cation of a substance in the
20、 urine or blood, the exact amount is often determined by instrumental methods. The concentration and identity of a compound in blood or urine can be determined using chromatography (in particular gasliquid chromatography) and spectroscopy. Modern chemical analysis can detect the presence of tiny, ye
21、t toxic, quantities of elements in our water supply and in our air. The technique of atomic absorption spectroscopy can detect up to 70 different metal elements in concentrations as low as parts per billion (ppb = g per kg) of sample. Environmental protection authorities can use this method to analy
22、se samples of water or air for pollution. Forensic science makes extensive use of modern chemical analytical methods. The presence of toxic chemicals in tissue samples or hair can be determined using high performance liquid chromatography. This may well reveal the cause of death of a murder victim.
23、Spectroscopy and chromatography both provide the opportunity for samples to be analysed qualitatively and quantitatively. In qualitative analysis, the identity of a sample, or its components is determined, whereas quantitative analysis is used to determine the amount of the sample or its components.
24、 The outputs from spectroscopic and chromatographic instruments have several common features. Spectra and chromatograms both show a series of peaks that can be used both qualitatively and quantitatively. The position of a peak on the horizontal axis provides information that identifi es the substanc
25、e causing the peak, while the peak area provides information that can be used to determine the amount of that substance. Faced with this array of instrumental techniques, how does a chemist choose the most appropriate technique for analysing a particular sample? Such decisions will depend on a numbe
26、r of factors: Is qualitative or quantitative information required? How much material is available for analysis? How low is the concentration of the component being analysed likely to be? What is the chemical nature of the sample? What is the level of expertise of the chemist? What accuracy is requir
27、ed? and, of course, the ever practical question: How much money is available for the analysis? Figure 1.1.2 (a) A drug test card is a simple way to test for the presence of drugs in urine. (b) A pregnancy can be confirmed by a simple urine test for the presence of a particular hormone (hCG). ab Figu
28、re 1.1.3 Spectra and chromatograms have several features in common. The position of peaks gives qualitative information. The area under the peaks gives quantitative information. 4 oxygenremaining oxygen weighed sample of CxHyOz CaCl2(s)NaOH(aq) HEAT Figure 1.1.4 Determining the empirical formula of
29、an unknown compound. Consider, for example, the analysis of an unknown organic compound to determine its molecular and structural formula. Classically, a sample of the compound would be burnt in air to produce water, carbon dioxide and any other products. From measurements of the masses of the compo
30、und and the products, an empirical formula could be determined. Molar mass, and hence molecular formula, could be determined using measurements of gaseous samples. Finally, chemical tests for functional groups would be conducted. Much of this classic chemistry has been replaced by modern instrumenta
31、l methods. When such chemical methods are used in conjunction with instrumental methods, chemists can quickly and accurately determine the structural formula of a compound. A mixture of hydrocarbons may fi rst be separated into its components by high performance liquid chromatography. Then each comp
32、onent can be passed through a mass spectrometer to fi nd its molecular mass and to determine its likely structure. This information may be supported by infrared spectroscopy, which is used to determine the nature of any functional groups. Information from only one technique is usually insuffi cient
33、to determine or confi rm a structure; the results from many different instrumental techniques are used in combination. One major advantage of using instrumental techniques is that great detail can be obtained from a very small amount of substance. The basis of spectroscopic analysis is the effect of
34、 electromagnetic radiation on matter. The sample for analysis is exposed to electromagnetic radiation and the effects of the interaction monitored. The study of the radiation absorbed or emitted by matter is called spectroscopy. The measurement of the amounts of light absorbed or emitted is called s
35、pectrometry. Instruments used for viewing the results of interactions between the sample and the radiation are called spectrometers. More elaborate instruments that measure amounts of radiation are called spectrophotometers. A wide variety of spectroscopic instruments are used in industry. Such inst
36、ruments include atomic absorption and UVvisible spectrophotometers, and infrared spectrometers. To understand spectroscopy, we need to review our basic understanding of the electromagnetic spectrum. Light consists of electromagnetic waves. The wavelength (distance between successive crests) of visib
37、le light ranges from about 8 107 metres for red light to about 4 107 metres for violet light. The frequency (the number of waves passing a given point each second) of light ranges from about 4 1014 for red light to about 7 1014 for violet light. CHEM COMPLEMENT Chemical analysisthe natural way While
38、 many analytical instruments are able to accurately detect and measure minute quantities of substances, few come close to the sensitivity shown by natural systems. Organisms have built-in detection devices that form part of the complex control systems used to regulate the levels of critical chemical
39、s such as hormones and neurotransmitters. Chemists are now making use of these supersensitive biodetectors. For example, hairs from Hawaiian red swimmer crabs can be attached to electrical analysis equipment to detect hormones at concentrations as low as 1012 mol dm3! A.1.2 State that the structure
40、of a compound can be determined by using information from a variety of analytical techniques singularly or in combination. IBO 2007 Principles of spectroscopy A.2.1 Describe the electromagnetic spectrum IBO 2007 CHEMISTRY: FOR USE WITH THE IB DIPLOMA PROGRAMME OPTIONS CHAPTER 1 MODERN ANALYTICAL CHE
41、MISTRY 5 The wavelength and energy of light are related by the equation: E = h = hc where is the frequency E is the energy is the wavelength c is the speed of light (3 108 m s1) h is a constant (Plancks constant = 6.63 1034 J s) The energy of light increases as the wavelength decreases, showing an i
42、nverse relationship. Of all the colours of visible light, violet light has the highest energy (and shortest wavelength) while red light has the lowest energy (and longest wavelength). Light is part of the broader electromagnetic spectrum, which also includes gamma rays, X-rays, ultraviolet (UV) rays
43、, infrared (IR) waves, microwaves and radio waves. Wavenumber is another wave property, and is equal to the inverse of wavelength ( 1 ). Wavenumber corresponds to the number of cycles the wave produces in a centimetre and has the units cm1. The wavenumber has traditionally been the most common metho
44、d of specifying IR absorption (see section 1.2). gamma raysX- raysultraviolet raysvisible lightinfrared raysradio wavesmicrowaves 1020101910181017101610151014101310121011 101210111010109108107106105104103102101100101102103 1010109108107106105 short- wave radio long- wave radio frequency in hertz (Hz
45、) 1 gigahertz (GHz) 1 megahertz (MHz) AM radio FM radio wavelength in metres (m) spectroscopic techniqueinfrared (I R)nuclear magnetic resonance (NMR) visible and ultraviolet (UVvis) 1 pico- metre (pm) 1 nano- metre (nm) 1 milli- metre (mm) 1 metre (m) 1 kilometre (km) 1 micro- metre (?m) spectrosco
46、pic techniqueinfrared (I R)nuclear magnetic resonance (NMR) visible and ultraviolet (UVvis) Increasing energy Increasing wavelength Figure 1.1.6 The electromagnetic spectrum. Different spectroscopic techniques use radiation from different parts of the spectrum. When sunlight (which contains all wave
47、lengths of visible light) passes through a prism, the different wavelengths are bent (or refracted) through different angles so that the light is broken into its components, producing a continuous spectrum of colours. ? wavelength distance travelled during one cycle Figure 1.1.5 The wavelength of an
48、 electromagnetic wave is the distance travelled by the wave during one cycle. Its frequency is the number of waves that pass a particular point every second. Electromagnetic spectrum 6 Figure 1.1.7 White light produces a continuous spectrum (ROYGBIV) when passed through a prism. white light slit scr
49、een Red Orange Yellow Green Blue Indigo Violet prism In chapter 4 of Chemistry: For use with the IB Diploma Programme Standard Level, we discussed atomic emission spectra (line spectra). These occur when energy is given to an atom, in the form of heat, electricity or light. An electron can move between energy levels within the atom if it absorbs energy that corresponds to the difference between two energy levels. When an electron moves to a higher energy level, the atom is said to be in an excited state. Electrons in higher than usual e