Transcript Quantitative Chemical Analysis 7e

Daniel C. Harris
Quantitative Chemical
Analysis
Seventh Edition
Chapter 0
The Analytical Process
Copyright © 2007 by W. H. Freeman and Company
How to make a
biosensorB
1.
2.
3.
4.
Find a biological receptor for
your analyte.
Couple the binding of the
analyte to some chemical or
optical response.
Calibrate.
Validate…
Live,
genetically
engineered
bacteria on
on test strip:
Specimen
Sample
Analyte 1
Theobromine
Analyte 2
Caffeine
Sample Preparation 1:
Grinding
Sample Preparation 2:
Interferants
First Extraction
Analytes +
complex
matrix with
interferants
Analytes +
simpler
matrix
Sample Preparation 3:
Second Extraction
Separation and
Analysis by
Chromatography
1.
Small volume (20 L) of
prepared sample solution is
injected into chromatographic
column.
2.
Components are separated.
3.
Individual components are
detected at column outlet by
absorption of ultraviolet light.
Chromatography:
1.
Mixture of compounds in
sample solution enters top of
column.
2.
Different compounds are
attracted more or less strongly
to the particles in the column
(the stationary phase or
packing).
3.
Solvent flow causes different
compounds to travel through
column at different rates.
Detector output versus
time: chromatogram.
1.
As different compounds elute,
peaks in detector signal
appear. This plot is called a
chromatogram.
2.
Peak area is proportional to
concentration.
3.
Retention time is characteristic
of the compound.
Analyte peaks from
sample areas are
compared to analyte
peaks from calibration
standards.
1.
Standards have known
concentration of analyte.
2.
For example, the standard that
resulted in this chromatogram
may have contained 10 ppm
caffeine and 10 ppm
theobromine.
3.
The unit ‘ppm’ stands for ‘parts
per million’. So, 10 ppm
means that every million grams
of solution contains 10 grams
of solute.
Standard Calibration
Plot is Prepared:
1.
Analyte Standard Signals are
plotted versus their
concentrations.
2.
Linearity of these plots
validates the calibration
method.
3.
Sample Signals are intersected
with Standard Calibration Lines
to compute Sample
Concentrations.
4.
Amounts of Analyte in Sample
are determined by auditing
sample preparation process.
Results and Error Estimates in
Informative Units:
Information by Comparisons
to Related Samples
Sampling Strategies to
Accurately Represent Specimen
Sampling in Segregated Material
Steps in Analysis Process:
1. Formulate Question: Translate ‘is it safe’ into something
measurable.
2. Select Procedure: Usually Find Existing Standard Methods of
Analysis – Validated and Interferants Known
3. Sample Representatively
4. Prepare Sample: Dissolve, Digest, Extract, Filter
5. Analyze Sample: Standards and Samples, Replicates,
Independent Measurements, Methods, Speciments.
6. Report and Interpret
7. Draw Conclusions Possible/Appropriate