Instrumental methods of analysis part1
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Transcript of Instrumental methods of analysis part1
INSMETHLecture 1: IntroductionLecture 1: Introduction
Ma’am Glenn Medina
De La Salle University
1
Areas of Analytical Chemistry
• QUALITATIVE - identification of substances
present in a sample. This area includes
structural elucidation.
• QUANTITATIVE - determination of the relative
concentration or amount of a particular
substance or chemical species often referred to
as the chemical constituent or analyte.
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What is Analytical Chemistry?
• A measurement science consisting of aset of powerful methods appliedthroughout industry, medicine and otheraspects of science.aspects of science.
• It involves qualitative and quantitativeanalyses which reveal the identity andamount of each substance in a sample,respectively.
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Instrumental Methods of Analysis
• Pertain to the application ofinstrumental methods to chemicalanalysis including electrochemical,spectrophotometric andspectrophotometric andchromatographic analysis.
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Instrumental Methods of Analysis
• Techniques:
1. Method Development2. Sample Collection3. Sample preparation
Defining Replicate Samples, Dissolving theDefining Replicate Samples, Dissolving theSamples, Eliminating interferences
4. Optimization5. Analysis
Measuring the amount of analyte, Calculatingthe concentration, Reliability of the data
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The role of Analytical Chemists
• To ensure quality of a product/service through the aid of through the aid of chemical instruments/standard analysis protocols
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THE ANALYTICAL PROCESS
• An analytical process does not only
involve the actual performance of
the experiment but actually starts the experiment but actually starts
with the planning and ends with the
reporting of the result.
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Quantitative Analytical Methods
1. Gravimetric
2. Volumetric
3. Electroanalytical3. Electroanalytical
4. Spectroscopic
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Quantitative Chemical Analysis
Chemical Sample
Analytical
Additional
Data
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Analytical
TechniqueClassical or Instrumental
Measurement
Data
Analyte Concentration
Steps in Quantitative Analysis
1. Formulating the Question
2. Method selection
3. Sample Collection
4. Sample Processing
5. Eliminating interferences5. Eliminating interferences
6. Calibration, Measurement
7. Calculations
8. Evaluation of Results
9. Conclusions
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1. Formulating the question
• The analytical process depends on the set of
problems or things that the analyst wants to
know and on the type of sample that will be
subjected to the analysis.subjected to the analysis.
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2. METHOD SELECTION
� The nature of the analyte and the extent of
analysis are determined.
3. SAMPLING (SAMPLE COLLECTION)
• The process by which arepresentative fraction of the sampleis acquired
• The most difficult step in the entire• The most difficult step in the entireanalytical process.
• The step that limits the accuracy ofthe procedure (eg sampling oflakewater; soil or animal tissue)
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4. SAMPLE PROCESSING (PREPARATION)
• Water is a common component present in samples.
Thus, analysis can be conducted on
• Dry basis. Moisture in the sample is removed • Dry basis. Moisture in the sample is removed before weighing.
• The sample can be dried at ambient temperature (air drying) or by heating to a temperature > 105°C.
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4. SAMPLE PROCESSING (PREPARATION)
• On an “as received” or wet basis. The
moisture content of the sample is
determined upon the receipt of the sample.
Representative sample obtained; weight loss Representative sample obtained; weight loss
determined after drying.
The rest of the sample is dried and all analyses
are performed.
The corresponding correction is made due to
the moisture content.14
• The sample and the analyte must be
in solution.
• For insoluble samples, it is necessary
to use more drastic conditions to
4. SAMPLE PROCESSING (PREPARATION)
to use more drastic conditions to
decompose and/or dissolve them.
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Decomposition/Dissolution of Samples:
1. concentrated HCl
2. hot concentrated HNO
4. SAMPLE PROCESSING (PREPARATION)
2. hot concentrated HNO3
3. hot concentrated H2SO4
4. HClO4 (NOTE: EXPLOSIVE when hot/conc’d)
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Decomposition/Dissolution of Samples:
5. Aqua regia (1HNO3 : 3HCl)
6. HNO3-HClO4
7. HF
8. Fluxes - sample is mixed with an alkali metal salt
4. SAMPLE PROCESSING (PREPARATION)
8. Fluxes - sample is mixed with an alkali metal salt (flux) and fused to form a water-soluble product called a melt by heating to a high temperature (300-1000°C)
9. Ashing (Dry or Wet)
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Interference –the presence of a substance changes
the signal in the analysis of another substance
1. Adjustment of the conditions within the solution
5. ELIMINATING INTERFERENCES
1. Adjustment of the conditions within the solution
2. Usage of blank to compensate for their effect
3. Precipitating the interference due to differences
in solubility
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6. QUANTITATIVE MEASUREMENT
• Calibration is done to ensure
accuracy in the results.
• All measurements depend on the • All measurements depend on the
relationship between concentration
of the analyte and a physical or
chemical property of the analyte.
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6. QUANTITATIVE MEASUREMENT
The choice of the analytical method to
adopt for an analysis may depend on
the
• Absolute Methods • Absolute Methods
• Relative Methods
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6. QUANTITATIVE MEASUREMENT
• Absolute Methods
–rely upon accurately known
fundamental constants (e.g. Molar
Mass) for calculating the amount of
fundamental constants (e.g. Molar
Mass) for calculating the amount of
analyte
Example: Gravimetric Method
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6. QUANTITATIVE MEASUREMENT
• Relative Methods
–require comparison against some
solution of known concentration
Examples: Titrimetric Method, Examples: Titrimetric Method,
Electrochemical Method, Instrumental
Method
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7. CALCULATIONS/INTERPRETATION OF DATA
8. EVALUATION OF RESULTS
• All analyses conducted in replicates.
• Statistical treatment of the results necessary.
• Uncertainties in measurements cause the
replicate values to differ with one another and
these cause the values to scatter. these cause the values to scatter.
• The experimental error is classified as either
(a) systematic error or determinate error and
(b) random error or indeterminate error.
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Classical vs Instrumental Techniques
• Classical analysis
– signal depends on the chemical properties
of the sample
– a reagent reacts completely with the– a reagent reacts completely with the
analyte
– the relationship between the measured
signal and the analyte concentration is
determined by chemical stoichiometry
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Classical vs Instrumental Techniques
• Instrumental analysis
– physical property is measured by theinstrument, such as the electrical potentialor the ability of the sample to absorb lightor the ability of the sample to absorb light
– capable of detecting individual atoms ormolecules in a sample
– analysis at the ppm (μg/mL) and even ppb(ng/mL) level
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Advantages of instrumental methods
• Trace analysis
• Large numbers of samples analyzed
quicklyquickly
• Automation
• Less skill and training required
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Classification of Instrumental analysis
1. Electrochemical methods of analysis- analyte participates in a redox reaction or other
process
– potentiometric analysis– potentiometric analysis• analyte is part of a galvanic cell, which generates a
voltage; magnitude of the voltage depends on theconcentration of analyte
– voltammetric analysis• analyte is part of an electrolytic cell; magnitude of the
current is directly proportional to the concentration ofanalyte
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Classification of Instrumental analysis
2. Spectrochemical methods of analysis
– analyte interacts with electromagnetic radiation
– absorption-based techniques• based on the measurement of the amount of light
absorbed by a sample• based on the measurement of the amount of light
absorbed by a sample– atomic absorption
– molecular absorption
– NMR
– emission-based techniques• generally based on the measurement of light emitted or
scattered by a sample– atomic emission
– molecular fluorescence
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Classification of Instrumental analysis
3. Mass spectroscopy
– analyte is ionized and subsequentlydetected
– most important use of mass spectrometersin quantitative analysis is as a gas or liquidin quantitative analysis is as a gas or liquidchromatographic detector.
– A more recent innovation is the use of aninductively coupled plasma (ICP) as an ionsource for a mass spectrometer; thiscombination (ICP-MS) is a powerful tool forelemental analysis.
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Classification of Instrumental analysis
• Chromatography and
Electrophoresis
–separate a chemical sample into its–separate a chemical sample into its
individual components, which are
then typically detected by one of
the methods listed above.
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Classification of Instrumental analysis(based on stoichiometry)
• Electrogravimetry, and potentiostatic
and amperostatic coulometry
–relatively sophisticated classical–relatively sophisticated classical
methods that have a significant
instrumental component
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CALIBRATION
• Involves the use of a set of standard solutions
which enables the determination of the
analyte concentration
• BLANK SAMPLE – a solution whose matrix is
the same as the standard solutions in the
absence of the analyte
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DETECTION LIMIT
• The smallest quantity of analyte that is
‘significantly different’ from a blank
• Also known as Limit of Detection or LOD
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Statistical Treatment of Analytical Data
• Mean/Average = Σx / n
• Median – middle result when replicate data are arranged according to increasing or decreasing value
• Mode – the value that occurs most frequently
• Absolute Error: E = Xi - Xt• Absolute Error: E = Xi - Xt
• Relative Error: Er = (Xi - Xt / Xt) x 100%
• Deviation: d = IXi - meanI
• Relative deviation: dr = (d / mean) x100
• Standard deviation:
• Relative Standard Deviation: RSD = s/mean
• Coefficient of Variation: CV = RSDx100
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