INSMETHLecture 1: IntroductionLecture 1: Introduction

Ma’am Glenn Medina

De La Salle University

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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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