Chemistry 155 Introduction to Instrumental Analytical Chemistry

293 Pages·2009·9.02 MB·English

Chem 155 Unit 1 Page 1 of 316

Chemistry 155
Introduction to Instrumental
Analytical Chemistry

Unit 1

Spring 2009
San Jose State University

Roger Terrill
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1 Overview and Review ........................................................................................ 7
2 Propagation of Error ......................................................................................... 56
3 Introduction to Spectrometric Methods ............................................................ 65
4 Photometric Methods and Spectroscopic Instrumentation ............................... 86
5 Radiation Transducers (Light Detectors): ...................................................... 102
6 Monochromators for Atomic Spectroscopy: ................................................... 116
7 Photometric Issues in Atomic Spectroscopy .................................................. 137
8 Practical aspects of atomic spectroscopy: ..................................................... 151
9 Atomic Emission Spectroscopy ...................................................................... 162
10 Ultraviolet-Visible and Near Infrared Absorption .......................................... 177
11 UV-Visible Spectroscopy of Molecules ........................................................ 195
12 Intro to Fourier Transform Infrared Spectroscopy ........................................ 211
13 Infrared Spectrometry: ................................................................................. 234
14 Infrared Spectrometry - Applications ............................................................ 247
15 Raman Spectroscopy: .................................................................................. 259
16 Mass Spectrometry (MS) overview: ............................................................. 279
17 Chromatography .......................................................................................... 294
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1 Overview and Review ........................................................................................ 7 
1.1 Tools of Instrumental Analytical Chem. ................................................ 8 
1.2 Instrumental vs. Classical Methods. ................................................... 12 
1.3 Vocabulary: Basic Instrumental .......................................................... 13 
1.4 Vocabulary: Basic Statistics Review .................................................. 14 
1.5 Statistics Review ................................................................................ 15 
1.6 Calibration Curves and Sensitivity ...................................................... 23 
1.7 Vocabulary: Properties of Measurements .......................................... 24 
1.8 Detection Limit ................................................................................... 25 
1.9 Linear Regression .............................................................................. 31 
1.10 Experimental Design: ....................................................................... 35 
1.11 Validation – Assurance of Accuracy: ................................................ 43 
1.12 Spike Recovery Validates Sample Prep. .......................................... 45 
1.13 Reagent Blanks for High Accuracy: .................................................. 46 
1.14 Standard additions fix matrix effects:................................................ 47 
1.15 Internal Standards ............................................................................ 52 
2 Propagation of Error ......................................................................................... 56 
3 Introduction to Spectrometric Methods ............................................................ 65 
3.1 Electromagnetic Radiation: ................................................................ 66 
3.2 Energy Nomogram ............................................................................. 67 
3.3 Diffraction ........................................................................................... 68 
3.4 Properties of Electromagnetic Radiation: ........................................... 71 
4 Photometric Methods and Spectroscopic Instrumentation ............................... 86 
4.1 General Photometric Designs for the Quantitation of Chemical Species
................................................................................................................. 87 
4.2 Block Diagrams .................................................................................. 88 
4.3 Optical Materials ................................................................................ 89 
4.4 Optical Sources .................................................................................. 90 
4.5 Continuum Sources of Light: .............................................................. 91 
4.6 Line Sources of Light: ........................................................................ 92 
4.7 Laser Sources of Light: ...................................................................... 93 
5 Radiation Transducers (Light Detectors): ...................................................... 102 
5.1 Desired Properties of a Detector: ..................................................... 102 
5.2 Photoelectric effect photometers ...................................................... 103 
5.3 Limitations to photoelectric detectors: .............................................. 105 
5.4 Operation of the PMT detector: ........................................................ 106 
5.5 PMT Gain Equation: ......................................................................... 107 
5.6 Noise in PMT’s and Single Photon Counting: ................................... 109 
5.7 Semiconductor-Based Light Detectors: ............................................ 111 
5.8 Charge Coupled Device Array Detectors: ........................................ 114 
6 Monochromators for Atomic Spectroscopy: ................................................... 116 
6.1 Adjustable Wavelength Selectors ..................................................... 117 
6.2 Monochromator Designs: ................................................................. 118 
6.3 The Grating Equation: ...................................................................... 119 
6.4 Dispersion ........................................................................................ 122 
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6.5 Angular dispersion: .......................................................................... 123 
6.6 Effective bandwidth .......................................................................... 125 
6.7 Bandwith and Atomic Spectroscopy ................................................. 126 
6.8 Factors That Control Δλ ............................................................... 127 
EFF
6.9 Resolution Defined ........................................................................... 128 
6.10 Grating Resolution ......................................................................... 129 
6.11 Grating Resolution Exercise: .......................................................... 130 
6.12 High Resolution and Echelle Monochromators .............................. 132 
7 Photometric Issues in Atomic Spectroscopy .................................................. 137 
8 Practical aspects of atomic spectroscopy: ..................................................... 151 
8.1 Nebulization (sample introduction): .................................................. 152 
8.2 Atomization ...................................................................................... 156 
8.3 Flame Chemistry and Matrix Effects ................................................ 157 
8.4 Flame as ‘sample holder’: ................................................................ 158 
8.5 Optimal observation height: .............................................................. 159 
8.6 Flame Chemistry and Interferences: ................................................ 160 
8.7 Matrix adjustments in atomic spectroscopy: ..................................... 161 
9 Atomic Emission Spectroscopy ...................................................................... 162 
9.1 AAS / AES Review: .......................................................................... 163 
9.2 Types of AES: .................................................................................. 164 
9.3 Inert-Gas Plasma Properties (ICP,DCP) .......................................... 165 
9.4 Predominant Species are Ar, Ar+, and electrons .............................. 165 
9.5 Inductively Coupled Plasma AES:  ICP-AES .................................. 166 
9.6 ICP Torches ..................................................................................... 167 
9.7 Atomization in Ar-ICP ....................................................................... 168 
9.8 Direct Current Plasma AES: DCP-AES ........................................... 169 
9.9 Advantages of Emission Methods .................................................... 170 
9.10 Accuracy and Precision in AES ...................................................... 172 
10 Ultraviolet-Visible and Near Infrared Absorption .......................................... 177 
10.1 Overview ........................................................................................ 177 
10.2 The Blank ....................................................................................... 178 
10.3 Theory of light absorbance ............................................................. 179 
10.4 Extinction Cross Section Exercise: ................................................. 180 
10.5 Limitations to Beer’s Law: .............................................................. 182 
10.6 Noise in Absorbance Calculations: ................................................. 185 
10.7 Deviations due to Shifting Equilibria: .............................................. 186 
10.8 Monochromator Slit Convolution in UV-Vis: ................................... 189 
10.9 UV-Vis Instrumentation: ................................................................. 191 
10.10 Single vs. double-beam instruments: ........................................... 192 
11 UV-Visible Spectroscopy of Molecules ........................................................ 195 
11.1 Spectral Assignments ..................................................................... 196 
11.2 Classification of Electronic Transitions ........................................... 197 
11.3 Spectral Peak Broadening .............................................................. 198 
11.4 Aromatic UV-Visible absorptions: ................................................... 201 
11.5 UV-Visible Bands of Aqeuous Transition Metal Ions ...................... 202 
11.6 Charge-Transfer Complexes .......................................................... 205 
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11.7 Lanthanide and Actinide Ions: ........................................................ 206 
11.8 Photometric Titration ...................................................................... 207 
11.9 Multi-component Analyses: ............................................................ 208 
12 Intro to Fourier Transform Infrared Spectroscopy ........................................ 211 
12.1 Overview: ....................................................................................... 212 
1 molecular vibrations ....................................................................................... 212 
12.2 IR Spectroscopy is Difficult! ............................................................ 215 
12.3 Monochromators Are Rarely Used in IR ......................................... 216 
12.4 Interferometers measure light field vs. time .................................... 217 
12.5 The Michelson interferometer: ........................................................ 218 
12.6 How is interferometry performed? .................................................. 219 
12.7 Signal Fluctuations for a Moving Mirror .......................................... 220 
12.8 Mono and polychromatic response ................................................ 222 
12.9 Interferograms are not informative: ................................................ 223 
12.10 Transforming time (cid:198) frequency domain signals: ......................... 224 
12.11 The Centerburst: .......................................................................... 225 
12.12 Time vs. frequency domain signals: ............................................. 226 
12.13 Advantages of Interferometry. ...................................................... 227 
12.14 Resolution in Interferometry ......................................................... 228 
12.15 Conclusions and Questions: ......................................................... 232 
12.16 Answers: ...................................................................................... 233 
13 Infrared Spectrometry: ................................................................................. 234 
13.1 Absorbance Bands Seen in the Infrared: ........................................ 235 
13.2 IR Selection Rules .......................................................................... 236 
13.3 Rotational Activity ........................................................................... 238 
13.4 Normal Modes of Vibration: ............................................................ 239 
13.5 Group frequencies: a pleasant fiction! ............................................ 242 
13.6 Summary: ....................................................................................... 246 
14 Infrared Spectrometry - Applications ............................................................ 247 
14.1 Strategies used to make IR spectrometry work - ............................ 248 
14.2 Solvents for IR spectroscopy: ......................................................... 249 
14.3 Handling of neat (pure – no solvent) liquids: .................................. 249 
14.4 Handling of solids: pelletizing: ........................................................ 250 
14.5 Handling of Solids: mulling: ............................................................ 250 
14.6 A general problem with pellets and mulls: ...................................... 251 
14.7 Group Frequencies Examples ........................................................ 252 
14.8 Fingerprint Examples ..................................................................... 253 
14.9 Diffuse Reflectance Methods: ........................................................ 254 
14.10 Quantitation of Diffuse Reflectance Spectra: ................................ 255 
14.11 Attenuated Total Reflection Spectra: ............................................ 256 
15 Raman Spectroscopy: .................................................................................. 259 
15.1 What a Raman Spectrum Looks Like ............................................. 261 
15.2 Quantum View of Raman Scattering. ............................................. 262 
15.3 Classical View of Raman Scattering .............................................. 263 
15.4 The classical model of Raman: ...................................................... 265 
15.5 The classical model: catastrophe! .................................................. 266 
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15.6 Raman Activity: .............................................................................. 267 
15.7 Some general points regarding Raman: ......................................... 269 
15.8 Resonance Raman ........................................................................ 271 
15.9 Raman Exercises ........................................................................... 272 
16 Mass Spectrometry (MS) overview: ............................................................. 279 
16.1 Example: of a GCMS instrument: ................................................... 279 
16.2 Block diagram of MS instrument. ................................................... 280 
16.3 Information from ion mass .............................................................. 281 
16.4 Ionization Sources .......................................................................... 282 
16.5 Mass Analyzers: ............................................................................. 287 
16.6 Mass Spec Questions: ................................................................... 292 
17 Chromatography .......................................................................................... 294 
17.1 General Elution Problem / Gradient Elution .................................... 307 
17.2 T-gradient example in GC of a complex mixture. ........................... 309 
17.3 High Performance Liquid Chromatography .................................... 310 
17.4 Types of Liquid Chromatography ................................................... 311 
17.5 Normal Phase: ............................................................................... 311 
17.6 HPLC System overview: ................................................................. 314 
17.7 Example of Reverse-phase HPLC stationary phase: ..................... 315 
17.8 Ideal qualities of HPLC stationary phase: ....................................... 316 
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Overview and Review
Skoog Ch 1A,B,C (Lightly) 1D, 1E Emphasized
Analytical Chemistry is Measurement Science.
Simplistically, the Analytical Chemist answers the
following questions:

What chemicals are present in a sample?

QUALITATIVE ANALYSIS

At what concentrations are they present?

QUANTITATIVE ANALYSIS

Additionally, Analytical Chemists are asked:
• Where are the chemicals in the sample?
• liver, kidney, brain
• surface, bulk

• What chemical forms are present?
• Are metals complexed?
• Are acids protonated?
• Are polymers randomly coiled or crystalline?
• Are aggregates present or are molecules in
solution dissociate?
• At what temperature does this chemical
decompose?
• Myriad questions about chemical states…

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Tools of Instrumental Analytical Chem.
1.1.1 Spectroscopy w/ Electromagnetic (EM)
Radiation

Name of EM Wavelength Predominant Name of
regime: Excitation Spectroscopy
Gamma ray ≤ 0.1 nm Nuclear Mossbauer
X-Ray 0.1 to 10 nm Core x-ray absorption,
electron fluorescence, xps
Vacuum 10 - 180 nm Valence Vuv
Ultraviolet electron
Ultraviolet 180 - 400 Valence Uv or uv-vis
electron
Visible 400-800 Valence Vis or uv-vis
electron
Near Infrared 800-2,500 Vibration Near IR or NIR
(overtones)
Infrared 2.5-40 μm Vibration IR or FTIR
Microwave 40 μm – 1 rotations Rotational or
mm microwave
Microwave ≈30 mm Electron spin ESR or EPR
in mag field
Radiowave ≈1 m Nuclear spin NMR
in mag field
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1.1.2 Chromatography – Chemical Separations

Different chemicals flow through separation
medium (column or capillary) at different speeds
‘plug’ of mixture goes in (cid:198) chemicals come out of
column one-by-one (ideally)

Gas Chromatography ‘GC’
Powerful but Suitable for Volatile chemicals only

Liquid Chromatography High Performance
(pressure), ‘HPLC’ in it’s many forms –

Electrophoresis -Liquids, pump with electric
current, capillary, gel, etc.

Chromatogram
e
c
n
a
b
r
o
s
b
a
time / s
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1.1.3 Mass Spectrometry

Detection method where sample is:
volatilized,
injected into vacuum chamber,
ionized,
usually fragmented,
accelerated,
ions are ‘weighed’ as M/z – mass charge.
Often coupled to:
chromatograph
laser ablation
atmospheric “sniffer”.

Very sensitive (pg) quantitation
Powerful identification tool

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