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Topic 1 - Nature of analytical chemistry

Nature of Analytical
BAC1044 - Forensic Analytical Chemistry 1
The analytical Perspective
Computational Chemistry
General terms used in Analytical Chemistry
Selecting an Analytical Method/Approach
Developing an Analytical Procedure
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What is Analytical
Analytical chemistry is the science of obtaining,
processing, and communicating information
about the composition and structure of matter.
In other words, it is the art and science of
determining what matter is (qualitative) and how
much of it exists (quantitative).
The craft of analytical chemistry is not in performing a
routine analysis on a routine sample (which is more
appropriately called chemical analysis), but in
improving established methods, extending existing
methods to new types of samples, and developing
new methods for measuring chemical phenomena.
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The analytical perspective
Identify and define the problem
Design the experimental procedure
Conduct an experiment and data acquisition
Analyze the experimental data
Propose a solution to the problem
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Identify and define the problem
Identify the scope/problem/research questions
Determine the required information
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Design the experimental procedure
Establish design criteria
Identify possible interferents
Method development and optimization
Establish validation strategy
Standardize sampling practices
Designing an experimental procedure involves selecting an appropriate method of
analysis based on established criteria, such as accuracy, precision, sensitivity, and
detection limit; the urgency with which results are needed; the cost of a single analysis;
the number of samples to be analyzed; and the amount of sample available for analysis.
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Data Acquisition
Instrument and equipment calibration
Standardize reagents (chemical standards)
Experimental activities
Data collection
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Data analysis & interpretation
Data transformation and translation (pre-processing)
Statistical analysis
Validation and verification
Results interpretation
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Key Questions to address
What is the analytical problem?
What type of information is needed to solve the problem?
How will the solution to this problem be used?
What criteria were considered in designing the experimental procedure?
Were there any potential interferences that had to be eliminated? If so, how
were they treated?
Is there a plan for validating the experimental method?
How were the samples collected?
Is there evidence that steps 2, 3, and 4 of the analytical approach are
repeated more than once?
Was there a successful conclusion to the problem?
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Case study
Wastewater from industry is causing
water and soil pollution. As an
investigator how would you collect
and analyze this sample?
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Qualitative vs. Quantitative
What is present?
How much is it?
Identification/Detection of chemical
constituents in a sample
Quantification/Determination of the
level of chemical constituents in a
Target & Untargeted analysis
Untargeted analysis
e.g. Detection of drug in urine sample
e.g. Glucose level in blood
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Advanced Analytical Chemistry
Characterization Analysis
An analysis in which we evaluate a sample’s
chemical or physical properties.
E.g. Chemical profiling; Mass spectrometry
imaging (MSI)
Fundamental Analysis
An analysis to improve an analytical
method’s capabilities.
Extending and improving the theory on
which a method is based, studying a
method’s limitations, and designing new
and modifying old methods are examples
of fundamental studies in analytical
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Let’s evaluate
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For each of the following problems indicate whether its solution
requires a qualitative, quantitative, characterization, or fundamental
study. More than one type of analysis may be appropriate for some
A hazardous-waste disposal site is believed to be leaking
contaminants into the local groundwater.
An art museum is concerned that a recent acquisition is a
A more reliable method is needed by airport security for
detecting the presence of explosive materials in luggage.
The structure of a newly discovered virus needs to be
A new visual indicator is needed for an acid–base
A new law requires a method for evaluating whether
automobiles are emitting too much carbon monoxide
Computational Chemistry
Branch of chemistry that uses computer simulation to assist in
solving chemical problems.
Examples:Using simulations to identify sites on protein molecules that are most
likely to bind a new drug molecule
Creating models of synthesis reactions to demonstrate the effects of
kinetics and thermodynamics.
Exploring the basic physical processes underlying phenomena such as
superconductivity, energy storage, corrosion, or phase changes.
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BAC1044 - Forensic Analytical Chemistry 1
An analyte is simply the
chemical species whose
properties we are trying to
measure in an analytical
chemistry experiment.
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All other constituents in a sample
except for the analytes.
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Sample universe
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Analysis vs. Determination
vs. Measurement
An analysis provides chemical or
physical information about a sample.
In an analysis we determine the
identity, concentration, or properties
of the analytes.
To make this determination we
measure one or more of the analyte’s
chemical or physical properties.
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In 1974, the federal government enacted the Safe Drinking Water Act to
ensure the safety of public drinking water supplies. To comply with this act
municipalities regularly monitor their drinking water supply for potentially
harmful substances. One such substance is coliform bacteria. Municipal
water department collect and analyze samples from their water supply.
To determine the concentration of coliform bacteria, a portion of water is
passed through a membrane filter. The filter is placed in a dish containing
a nutrient broth and incubated. At the end of the incubation period the
number of coliform bacterial colonies in the dish is measured by counting
(Figure 3.1). Thus, municipal water departments analyze samples of water
to determine the concentration of coliform bacteria by measuring the
number of bacterial colonies that form during a specified period of
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Techniques, Methods, Procedures, and
A technique is any chemical or
physical principle that can be
used to study an analyte.
A method is the application of a
technique for the determination
of a specific analyte in a specific
A procedure is a set of written
directions detailing how to apply
a method to a particular sample,
including information on proper
sampling, handling of
interferents, and validating
A protocol is a set of stringent
written guidelines detailing the
procedure that must be followed
if the agency specifying the
protocol is to accept the results
of the analysis.
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Ideally, a protocol uses a previously
validated procedure. Before
developing and validating a
procedure, a method of analysis
must be selected. This requires, in
turn, an initial screening of available
techniques to determine those that
have the potential for monitoring
the analyte.
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Types of Quantification
Analyzing a sample generates a chemical or physical signal whose
magnitude is proportional to the amount of analyte in the sample. The
signal may be anything we can measure; common examples are mass,
volume, and absorbance.
Absolute quantification
Measures the actual amount of analyte
Direct measurement - (gravimetry, titrimetry and coulometry)
Chemical reaction - precipitation, acid–base, complexation, or redox chemistry
Spectroscopy, potentiometry, voltammetry
Relative quantification
Compare the signal against a known concentration
Spectroscopy, potentiometry, voltammetry
Indirect quantification
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Selecting an analytical method
A method is the application of a technique to a specific analyte in a specific matrix.
The requirements of the analysis determine the best method. In choosing a method,
consideration is given to some or all the following design criteria: accuracy, precision,
sensitivity, selectivity, robustness, ruggedness, scale of operation, analysis time,
availability of equipment, and cost.
Methods for determining the concentration of lead in drinking water can be developed
using any of the techniques mentioned in the previous section. Insoluble lead salts such
as PbSO4 and PbCrO4 can form the basis for a gravimetric method. Lead forms several
soluble complexes that can be used in a complexation titrimetric method or, if the
complexes are highly absorbing, in a spectrophotometric method. Lead in the gaseous
free-atom state can be measured by an atomic absorption spectroscopic method. Finally,
the availability of multiple oxidation states (Pb, Pb2+, Pb4+) makes coulometric,
potentiometric, and voltametric methods feasible.
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• Accuracy is a measure of how closely
the result of an experiment agrees with
the expected result.
• % 𝑒𝑟𝑟𝑜𝑟 =
𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑟𝑒𝑠𝑢𝑙𝑡 −𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑟𝑒𝑠𝑢𝑙𝑡𝑠
𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑟𝑒𝑠𝑢𝑙𝑡𝑠
• <1% high accuracy
• 1% to 5% moderate accuracy
• >5% low accuracy
• When a sample is analyzed several
times, the individual results are rarely
the same.
• Instead, the results are randomly
scattered. Precision is a measure of
this variability.
• The closer the agreement between
individual analyses, the more precise
the results.
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• The ability to detect very low
concentrations of a given substance in
a matrix.
• Analytical sensitivity is often referred
to as the limit of detection (LoD). Often
confused with limit of quantification
• LoD is the actual concentration of an
analyte in a specimen that can be
consistently detected ≥ 95% of the time
• Typical acceptable signal-to-noise ratio
(SNR) is 3:1 for LoD
• ability to analyze the targeted analytes
without interference from other
• Selectivity in analysis can be improved
via sample processing steps, include
extraction and chromatographic
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Robustness and ruggedness
Scale of operations
• For a method to be useful it must provide reliable
results. Unfortunately, methods are subject to a
variety of chemical and physical interferences
that contribute uncertainty to the analysis. When
a method is relatively free from chemical
interferences, it can be applied to the
determination of analytes in a wide variety of
sample matrices. Such methods are considered
• Random variations in experimental conditions
also introduce uncertainty. If a method’s
sensitivity is highly dependent on experimental
conditions, such as temperature, acidity, or
reaction time, then slight changes in those
conditions may lead to significantly different
results. A rugged method is relatively insensitive
to changes in experimental conditions.
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Equipment & Instrument
Time and Monetary Cost
• Methods relying on instrumentation
are equipment-intensive and may
require significant expertise.
• The availability and applicability of the
equipment and instruments.
• High sensitivity vs. high resolution
• Sample preparation time and required
• Number of samples and replicates
needed. Analysis time per
• The cost of an analysis is determined
by many factors, including sampling,
equipment rental, chemical reagents,
human resources, required
maintenance, etc.
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Developing an analytical procedure
After selecting a method, it is necessary to develop a procedure that will
accomplish the goals of the analysis. In developing the procedure, attention
is given to compensating for interferences, selecting and calibrating
equipment, standardizing the method, acquiring a representative sample,
and validating the method.
Compensating for interference
The accuracy of a method depends on its selectivity for the analyte. Even the best
methods, however, may not be free from interferents that contribute to the
measured signal. Potential interferents may be present in the sample itself or the
reagents used during the analysis.
Inclusion of solvent blank, matrix blank, or negative control.
Use chemical standard (spiking)
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Calibrations and standardizations
Calibration ensures that the equipment or instrument used to measure the signal
is operating correctly by using a standard known to produce an exact signal.
Standardization is the process of experimentally determining the relationship
between the signal and the amount of analyte – calibration curves
A proper sampling strategy ensures that samples are representative of the
material from which they are taken.
Biased or nonrepresentative sampling and contamination of samples during or
after their collection are two sources of sampling error that can lead to significant
It is important to realize that sampling errors are completely independent of
analysis errors. As a result, sampling errors cannot be corrected by evaluating a
reagent blank.
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Validation is an evaluation of whether the precision and accuracy obtained by
following the procedure are appropriate for the problem
The process of verifying that a procedure yields acceptable results.
Besides all the considerations taken into account when designing the
procedure, a protocol also contains very explicit instructions regarding internal
and external quality assurance and quality control (QA/QC) procedures
Jabatan Kimia Malaysia follows laboratory quality assurance activities under
ISO/IEC 17025 standard and quality management system under ISO 9001
within the Department.
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EPA Contract Laboratory Program (CLP)
E.g. Analysis of trace metals in aqueous samples by graphite-AAS
Daily standardization with a reagent blank and three standards, one of which is at the
laboratory’s contract required detection limit.
The resulting calibration curve is then verified by analyzing initial calibration verification (ICV)
and initial calibration blank (ICB) samples.
The reported concentration of the ICV sample must fall within ±10% of the expected
concentration. If the concentration falls outside this limit, analysis problem shall be identified
and corrected before continuing.
After a successful analysis of the ICV and ICB samples, standardization is reverified by analyzing
a continuing calibration verification (CCV) sample and a continuing calibration blank (CCB).
Results for the CCV also must be within ±10% of the expected concentration.
The CCV and the CCB are analyzed before the first and after the last sample, and after every set
of ten samples. Whenever the CCV or the CCB is unacceptable, the results for the most recent
set of ten samples are discarded, the system is standardized, and the samples are reanalyzed.
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Initial Calibration Verification (ICV)
A solution of targeted method analytes of known concentration that is obtained from a
source external to the laboratory and different from the source of calibration standards.
Also known as Certified Reference Materials.
To evaluate the instrument health status.
Continuing calibration verification (CCV)
A type of quality control sample that is a mid- range calibration standard which checks the
continued validity of the initial calibration of the instrument.
Can be prepared internally from chemical standards.
To evaluate the consistency of the instrument and method.
Initial calibration blank (ICB) and continuing calibration blank (CCB)
Solvent blank that is used to prepare the samples and chemical standards.
The solvent purity grade must be specified and follows the recommendation (spectroscopy
grade, LC-grade, GC-grade, MS-grade, etc)
ICB: To ensure the instrument is clear from contaminants
CCB: To evaluate the carry over effects of the analysis.
BAC1044 - Forensic Analytical Chemistry 1
BAC1044 - Forensic Analytical Chemistry 1
The Duties and Responsibilities of
Forensic analytical scientist
Rigorously applying analytical techniques to evidence and
meticulously documenting each step.
They must also be able to clearly and concisely respond to
challenges to their findings, even in a court of law.
Excellent experimental technique; strong background in
instrumentation and quantitative/qualitative analysis
Sensitive to detail, critical thinking and problem solving
Excellent oral communication skills, even under duress (e.g., giving
expert testimony)
Written communication skills to prepare reports that will stand up
to intense scrutiny
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Sample details
source, sample state, quantity, date,…
Sample pre-processing & treatment, instrumentation, calibration, data
acquisition, data processing
Data interpretation
Statistical analysis
Chemists will customarily report their data graphically and display
accompanying error bars, employing both the mean and standard
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Thank you
BAC1044 - Forensic Analytical Chemistry 1