Chapter 1 introduction
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Chapter 1: Introduction. Analytical Chemistry Qualitative analysis Quantitative analysis Classification of Analytical Methods Classical methods (wet chemical methods) Instrumental methods. Comparisons of Wet Chemical and Instrumental Methods. Types of Instrumental Methods

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Chapter 1: Introduction

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Chapter 1 introduction

Chapter 1: Introduction

  • Analytical Chemistry

    • Qualitative analysis

    • Quantitative analysis

  • Classification of Analytical Methods

    • Classical methods (wet chemical methods)

    • Instrumental methods


Comparisons of wet chemical and instrumental methods

Comparisons of Wet Chemical and Instrumental Methods


Chapter 1 introduction

  • Types of Instrumental Methods

    • Separation techniques

      • Chromatographic

        • Gas

        • Liquid

        • …….

      • Electrophoresis

        • Many types

    • Detection techniques

      • Optical spectroscopy

        • Absorption

        • Emission

        • Fluorescence

      • Mass spectroscopy

        • Atomic

        • Molecular


Chapter 1 introduction

  • Instruments for Analysis

Signal

Generator

Sample

Analytical

Signal

Input

Transducer

(Detector)

Signal

Processor

Output

Transducer

(Readout)


Chapter 1 introduction

  • Instruments for Analysis


Chapter 1 introduction

  • Selection of An Instrumental Method

    • Defining the problem

    • Performance characteristics

      Figure of Merits: Quantitative performance criteria of instruments that are expressed in numerical terms


Chapter 1 introduction

  • Precision

    A measure of the random or indeterminate error

Relative Standard Deviation


Chapter 1 introduction

  • Bias

    A measure of the systematic or determinate error

    Bias = µ - Xt

    µ - the population mean for the concentration of an analyte

    Xt – true concentration

    Standard reference materials (SRM)


Chapter 1 introduction

Signal

Signal

x

x

x

x

x

x

x

x

Sbl

Sbl

Concentration

  • Sensitivity

    A measure of the ability of an analytical method to discriminate between small differences in analyte concentration

    • Calibration sensitivity (S = mc + Sbl)

Concentration


Chapter 1 introduction

Signal

Concentration

  • Sensitivity

    • Analytical sensitivity ( = m/sS)

      m – slope; sS – standard deviation of the measurement

      Relative insensitive to amplification factors

Increase the gain of the instrument by a

Factor of two


Chapter 1 introduction

Sm = Sbl + ksbl

Standard deviation of

the Blank signal

Analytical Signal

Blank signal

  • Detection limit (Limit of detection, LOD)

    The analyte concentration giving a signal equal the blank signal, Sbl, plus three time standards deviation of the blank, sbl

Convert signal response, Sm, to analyte concentration


Chapter 1 introduction

Sm = Sbl + ksbl

Standard deviation of

the Blank signal

Analytical Signal

Blank signal

  • Dynamic Range

    Lowest concentration (LOQ) to the concentration where the calibration curve departure from linearity (limit of linearity, LOL)

Convert signal response, Sm, to analyte concentration


Chapter 1 introduction

  • Dynamic Range


Chapter 1 introduction

  • Guideline for Reporting Data (Recommended by ACS Committee of Environmental Improvement)

    Analyte

    ConcentrationRegion of reliability

    < 3σRegion of Questionable detection

    (unacceptable)

    3σDetection limit

    3σ-10σRegion of less certain quantitation

    10σLimit of quantitation

    > 10σRegion of quantitation


Chapter 1 introduction

99.7%

Question: When the value of 10 sbl (standard deviation of the blank) is used as LOQ, what is the relative standard deviation of the measurement at this point at the 99.7% confidential level, and why?


Chapter 1 introduction

  • Selectivity

    The degree to which the method is free from interference by other species contained in the sample matrix

    S = mAcA + mBcB + mCcC + Sbl

    The selectivitycoefficient for B with respect to A

    kB,A = mB/mA

    ……………………………………

    Note: this is the selectivity of an analytical detection technique


Chapter 1 introduction

  • Calibration Methods

    Analytical response

    • Comparison with Standard

      • Direct comparison

        • Colorimetric

      • Titration

Analyte Concentration


Chapter 1 introduction

Signal

Concentration

  • Calibration Methods

    • External Calibration Curve

Normally use the method of least squares

X

X

X

X


Chapter 1 introduction

  • Calibration Methods

    • External Calibration Curve

      Two Assumptions:

      1. Linear relationship

      2. deviation of the individual point from the straight line arises from the error in the measurement


Chapter 1 introduction

Signal

Without sample matrix effect

With sample matrix effect (signal suppressed)

Concentration

  • Calibration Methods

    • Standard Addition


Chapter 1 introduction

C1, C2, and C3 are the concentrations of analyte after spiked with stnard, with counting the amount of analyte in the original sample solution.

C0 is the concentrations of analyte in sample without spiking

  • Standard Addition

C0

C1

C2

C3

Signal

x

S = mC + Sbl

Sample signal

Sbl

x

x

C0 =Sbl/m

x

Conc. of analyte C0

Concentration


Chapter 1 introduction

  • Internal Standard

    Add a substance in a constant amount to all samples and, blanks, and calibration standard in an analysis

Sanalyte/Sinternal

Concentration


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