Principles of Instrumental Analysis Chapter 1. Introduction

2014/9/10
Principles of Instrumental
Analysis
Chapter 1. Introduction
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1A. Classification of Analytical Methods
Analytical Chemistry: Qualitative method versus quantitative
method
Qualitative method: yields information about the identity of atomic or
molecular species or the functional groups in the sample.
Quantitative method: provides numerical information as to the relative
amount of one or more of these components.
z
Classical methods:
Separating analytes (分析物) by precipitation, extraction, or distillation.
Instrumental methods:
1) Physical and chemical properties of analytes.
2) Separation: chromatographic and electrophoretic techniques.
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1B. Types of Instrumental Methods
TABLE 1-1 Chemical and Physical Properties Used in Instrumental Methods
require a source of energy to
stimulate a measureable
response from the analyte.
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1C. Instruments for Analysis
An instrument for chemical analysis converts information about
the physical or chemical characteristics of the analyte to
information that can be manipulated and interpreted by human.
FIGURE 1-1 Block diagram showing the overall process of an
instrumental measurement.
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TABLE 1-2 Some Examples of Instrument Components
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FIGURE 1-2 Data-domain map. The upper (shaded) half of the map consists of
nonelectrical domains. The bottom half is made up of electrical domains. Note
that the digital domain spans both electrical and nonelectrical domains.
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FIGURE 1-3 A block diagram of a fluorometer showing (a) a general diagram of the
instrument, (b) a diagrammatic representation of the flow of information through
various data domains in the instrument, and (c) the rules governing the datadomain transformations during the measurement process.
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Detectors(檢測器): a mechanical, electrical, or chemical device
that identifies, records, or indicates a change in one of the variables
in the environment, such as pressure, temperature, electrical charge,
electromagnetic radiation, nuclear radiation, particulates, or
molecules.

Transducers(變換器): devices that convert information in
nonelectrical domains to information in electrical domains and the
converse. (photodiodes, photomultipliers, …)

Sensors(傳感器): analytical devices that are capable of
monitoring specific chemical species continuously and reversibly.
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FIGURE 1-7 Chemical sensor. The sensor consists of a molecular recognition
element and a transducer. A wide variety of recognition elements are
possible. Shown here are some fairly selective recognition elements
particularly useful with biosensors. The recognition phase converts the
information of interest into a detectable characteristic, such as another
chemical, mass, light, or heat. The transducer converts the characteristic into
an electrical signal that can be measured.
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1D. Calibration of Instrumental Methods
Calibration (校正) determines the relationship between the
analytical response and the analyte concentration. Usually this is
determined by the use of chemical standards.
1) Comparison with Standards
2) External-Standard Calibration (Figure 1-8)
ideal blank: identical to the sample but without the analyte. (matrix effects)
3) Standard-Addition Methods (when matrix effects are substantial)
adding one or more increments of a standard solution to sample aliquots
containing identical volumes.
4) The Internal-Standard Method: an internal standard is a substance
that is added in a constant amount to all samples, blanks, and calibration
standards in an analysis.
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Appendix a1D Method of Least Squares
FIGURE 1-8 Calibration curve for the
determination of isooctane in a
hydrocarbon mixture. The residual is
the difference between an experimental
data point yi and that calculated from
the regression model, mxi + b, as shown
in the insert.
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cx = bcs/mVx
cx = -(Vs)0cs/Vx
FIGURE 1-10 Linear calibration plot for the method of standard additions. The
concentration of the unknown solution may be calculated from the slope m and
the intercept b, or it may be determined by extrapolation, as explained in the text.
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FIGURE 1-11 Spreadsheet for standard-addition Example 1-1.
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FIGURE 1-12 Spreadsheet to illustrate the internal-standard method for the flame
spectrometric determination of sodium.
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1E. Selecting An Analytical Method
1) Defining the Problem
2) Performance Characteristics of Instruments
* Precision: random error (appendix a1A) (Table 1-5)
* Bias: systematic error
Δ = μ − τ (μ: population mean, τ: true value)
* Sensitivity
calibration sensitivity (m): S = mc + Sbl
analytical sensitivity: γ = m/sS (sS: standard deviation)
* Detection limit: cm = (Sm - Sbl)/m
* Dynamic range: between limit of quantitation (LOQ)
and limit of linearity (LOL).
* Selectivity: S = mAcA + mBcB + mCcC + Sbl
selectivity coefficient: kB,A = mB/mA ; kC,A = mC/mA
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TABLE 1-5 Figures of Merit for Precision of Analytical Methods
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TABLE 1-3 Numerical Criteria for Selecting Analytical Methods
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Figure of Merit (品質因素):
A quantity used to characterize the performance of a device, system
or method, relative to its alternatives. In engineering, figures of merit
are often defined for particular materials or devices in order to
determine their relative utility for an application. In commerce, such
figures are often used as a marketing tool to convince consumers to
choose a particular brand.
Examples
• Calorie per serving
• Contrast ratio of an LCD
• Frequency response of a speaker
• Battery life of a notebook computer
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TABLE 1-4
Other Characteristics to Be Considered in Method Choice
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FIGURE 1-13 Useful range of an analytical method. LOQ = limit of
quantitative measurement; LOL=limit of linear response.
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