Lecture 1 & 2-Intro and Sampling

8/20/2019 Lecture 1 & 2-Intro and Sampling

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STKK1702

Basic Analytical Chemistry

Kimia

Analisis

Asas

1

NURFAIZAH ABU TAHRIM

[email protected]

SCHOOL OF CHEMICAL SCIENCES AND FOOD TECHNOLOGY

FACULTY OF SCIENCE AND TECHNOLOGY


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Course Content

•

Introduction

–

What is analytical chemistry

•

Sample, sampling and sample treatment.

•

Error and small data analysis.

• Acid-base concept and acid-base equilibrium.

Basic volumetric analytical methods such as

acid-base titration, precipitation,compelxometry (EDTA) and redox titration.

Gravimetric and gravimetry analysis.

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What is Analytical Chemistry?

It is the Science of Chemical Measurements, providing methods

and tools needed for gaining insight into our material world.

There are four basic questions about a material sample?

What? (What is the identity of the substance in the sample?)

Where? (Does the sample contain substance X?)

How much? (How much of substance X is in the sample?)

What arrangement, structure or form?

The Division of Analytical Chemistry of the American Chemical

Society (ACS) provides a comprehensive definition of analytical

chemistry, which may be found on their website.

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Discipline of analytical chemistry consists of qualitative analysis and

quantitative analysis.

Concern with the chemical characterization of matter and the

answer to two important questions:

1) What is it (qualitative)?

2) How much is it (quantitative)?

Deals with the identification of elements, ions, or compounds

present in a sample

Deals with the determination of how much of one or more

constituents is present.

Sample may be solid, liquid, gas or mixture.

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What is Analytical Chemistry?


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Why we need Analytical

C

hemistry?• Everything is made of chemicals.

• Analytical chemists determine what and how much!

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Why we need Analytical

C

hemistry?

Analytical Chemistry seeks ever improved means of

measuring the chemical composition of natural and

artificial materials.

The techniques of this science are used to identify the

substances which may present in a material and to

determine the exact amounts of the identified substance.

Provide proven methodologies to new kinds of materials

or to answer new questions about their composition and

their reactivity mechanisms.

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• Nitrogen content of a fertilizer determines its value.

• Food must be analyzed for contaminants (pesticide

residue) and for essential nutrients (vitamin content).• Blood glucose must be monitored in diabetics.

• The presence of trace elements from gun powder on

a murder defendant’s hand will prove a gun was

fired.

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Examples of Application Analytical

Chemistry


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Examples of Application of

Analytical Chemistry

• Industry: means of testing raw materials and for assuring the quality

of finished products whose chemical composition is critical.

Household products such as fuels, paints, pharmaceuticals etc are

analyzed by the procedures developed by analytical chemists beforebeing sold to the consumer.

• Environmental quality is often evaluated by testing for suspected

contaminants using the techniques of analytical chemistry.

• Nutritional value of food is determined by chemical analysis for

major components such as protein and carbohydrates and tracecomponents such as vitamins and minerals.

• Medicine: basis for clinical laboratory tests which help physicians

diagnose disease and chart progress in recovery.

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What Do Chemical Analysts Do?• Analyst: Applies known

measurement techniques to welldefined compositional orcharacterization questions.

• Analytical chemists work to improvethe reliability of existing techniquesto meet the demands for better

chemical measurements whicharise constantly in our society.

• Research Analytical Chemist

-Creates and /or investigates novel techniques or principles forchemical measurements.

-Conducts fundamental studies of chemical/physical phenomenaunderlying chemical measurements.

-Develops new measurement methods on existing principles tosolve new analysis problems.


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Example of analytical Chemist’s job


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Qualitative and Quantitative

AnalysisQualitative and Quantitative Analysis: What

does each tell us?

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Selectivity & Specificity

Terms selective and specific are used inanalytical chemistry, especially for qualitative

tests

A selective reaction or test is one that can occurwith other substances but exhibits a degree of

preference for the substance of interest.

A specific reaction or test is one that occurs only

with the substance of interest.Qualitative/quantitative tests can be performed

by selective/specific chemical reactions or with

the use of instrumentation.13


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Qualitative tests

Unfortunately few reactions are specific butmany exhibit selectivity.

Selectivity may be achieved by a number of

strategies:

Sample preparation (e.g extractions,

precipitation)

Instrumentation (selective detectors)

Target analyte derivatization

Chromatography, which provides powerful

separation

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Examples of Qualitative tests

Qualitative test very often based on observation

of colour change or spectra of the analyte

Analyte is the substance analyzed for. Itsconcentration is determined.

Chemical reactions produce colors to indicate

the presence of classes of organic compounds,for example ketones.

Infrared spectra will give ‘fingerprints’ of organic

compounds of their functional groups.15


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Quantitative analysis

A history of the sample composition will often be known.

Example it is known that blood contains glucose or else

the analyst will have performed a qualitative test prior to

performing the more difficult quantitative analysis.

Modern chemical measurement systems often exhibit

sufficient selectivity that a quantitative measurement can

also serve as a qualitative measurement.

However simple qualitative tests are usually more rapid

than quantitative procedures.

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Quantitative analysis – Calibration CurveFor the purpose of

determine an unknown

analyte quantitatively

Standard solutions with

known concentrations of

analyte are used toconstruct the calibration

curve, i.e. Response vs

concentration.

Linear response is desirablefor a calibration curve

The response of an

unknown analyte is

obtained from the

calibration curve


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Quantitative Analysis –Standard Solution

When performing an analysis a chemist oftenuses a standard solution.

A standard solution:

A solution that has a concentration of achemical that is known to a high degree ofcertainty.Prepared from a chemical that has beendesignated as a primary standard.Complies with standards established by theEnvironmental Protection Agency, USA.

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An analysis involves several steps and

operations which depend on:

• the particular problem

• your expertise

• the apparatus or equipment available.

• The analyst should be involved in every step.

Analytical process


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Analytical process

Define the problem

Select a method

Obtain a representative

sample

Prepare the sample for

analysis

Perform any necessary

chemical separations

Perform the measurement

Calculate the results and report

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Define the problemWhat do we really need to know (not necessarily

everything)?Information: by whom?

For what purpose?

What type of sample?

The analyst must have good communication with theclient.

Eg. of clients may be the Environmental Protection

Agency (EPA), an industrial client, an engineer etc.

Each will have different criteria or needs and differentunderstanding of what a chemical analysis involves or

means.

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Define the problem

The concept of ‘safe’ or ‘zero/nothing’ is one that is hard to define or

understand by many people.

Telling someone their water is safe is not for the analyst to say.

All you can do is present the analytical data. The client must decide

whether it is safe to drink, perhaps relying on other experts.

Also never report an answer ‘zero’ but as less than the detection

limit which is based on the measurement device/instrument (ppm,ppb, ppt).

We are limited by our methodology and equipment and that is all

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Define the problem

A law may be passed that there should be zero

concentration of chemical effluent in water.

In practice, the acceptable level is defined by how low a

concentration can be detected; and the very low

detectability may be far below the natural occurrence of

the chemical or below the levels to which it can be

reasonably reduced.

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Define the problem

• Once the problem is defined:- how much is needed?

- how sensitive the method must be?

- how accurate and precise?

- what separations may be required to eliminate

interferences?

The analytical method to be used will depend on factors such as:

1) analyst’s skills and training in different techniques and

instruments

2) facilities, equipments and instruments available3) sensitivity and precision required

4) cost and budget available

5) time for analysis and how soon results are needed.

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Calculating the results and

reporting dataOnce the concentration of analyte in the prepared

sample solution has been determined, the results are

used to calculate the amount of analyte in the original

sample.

Either an absolute or a relative amount may be reported.

Replicate analyses can be performed (three or more)

and a precision of the analysis may be reported,

standard deviation.

Acknowledge of the precision is important – gives

degree of uncertainty in the result.

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The laboratory notebook

Notebook – Your critical record

All data should be recorded permanently in ink when they are

collected.

When you go into the analytical laboratory, you will find that this

orderliness is to your advantage:

FIRST: Saving of time in not having to reorganize and rewrite the

data. Chances for a mistake are reduced.SECOND: if you make an immediate record, you will be able to

detect possible errors in measurements or calculations.

Data will not be lost or transferred incorrectly if they are recorded

directly in a notebook instead of collected on scraps of paper.


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For practicing analytical chemists and on-the-job

applications, it is important to use the lab

notebooks for entering observations and

measurements directly.Complete documentation is essential for forensic

or industrial laboratories for legal and patent

considerations.

In industrial research labs, the notebook must

generally be signed (witnessed) and dated by

another person familiar with the work to assure

legal patent priority if applicable.


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Rules of laboratory notebook

Use a hardcover notebook (no loose leafs)

Label with number on pages consecutively

Record only in ink

Never tear out pages. If not used, put a line through

a page.

Date each page, sign it and have it signed and dated

by someone else, stating ‘Read and Understood by’Record the name of the project, why it is being done,

and any literature references.

Record all data on the day you obtain it.


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Sampling (Obtaining sample) for analysis

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Drainage water samplingCollecting water samples

Blood sample Forensic samples


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Sampling (Obtaining sample) for analysis

Sample can be solid, liquid or gas.This process can be the most critical aspect of

an analysis.

The significance and accuracy of measurements

can be limited by the sampling process.

Many professional societies have specified

definite instructions for sampling given materials.

[American Society for Testing and Materials(ASTM), American Public Health Association

(APHA)].

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Sampling processes

The problem involves obtaining a sample that is

representative of the whole. This sample is called gross

sample.

Once a representative gross sample is obtained, it may

have to be reduced to a sufficiently small size to be

handled. This is called sample.

Once the sample is obtained, an aliquot or portion of it

will be analyzed. This aliquot is called the analysis

sample. Several replicate analyses on the same sample

may be performed by taking separate aliquots.32


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Steps in obtaining a laboratory sample

Reduce the gross sample to a laboratory sample

Collect a gross sample

Identify the population


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Obtaining a representative sample

Homogeneous gaseous or liquid sample No problem – any sample representative.

Solid sample - no gross heterogeneity

Take a number of small samples at random from throughout the bulk - this will give a

suitable representative sample.

Solid sample - obvious heterogeneityTake small samples from each homogeneous region and mix these in the same

proportions as between each region and the whole.

If it is suspected, but not certain, that a bulk material is heterogeneous, then it is

necessary to grind the sample to a fine powder, and mix this very thoroughly before

taking random samples from the bulk.

For a very large sample - a train-load of metal ore, or soil in a field - it is always

necessary to take a large number of random samples from throughout the whole.


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Sampling: Procuring a representative

sampleHomogeneous: same throughoutHeterogeneous: differs from region to region

In a random heterogeneous material,

differences in composition occur

randomly and on a fine scale.

For a segregated heterogeneous

material (in which large regions have

obviously different compositions), a

representative composite sample

must be constructed.


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Sampling processes

In the case of clinical analysis, e.g. collection of

biological fluids, the conditions under which the sample

is collected can be important, for example whether a

patient has just eaten.

Composition of blood varies considerably before and

after meals, for many analyses a sample is collected

after the patient has fasted for a number of hours.

certain precautions should be taken in handling and

storing samples to prevent or minimize contamination,

loss, decomposition or matrix change.36


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Example of Water Sampling technique (video link)

https://www.youtube.com/watch?v=BlePFFPt4HE&list=PLMSa5d-iIl6PjYhV9cc4S_-mNEteXts58&index=8


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How to measure the caffeine content

of a chocolate bar?


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1. Weighing

2. Removing fat with organic solvent

Step 1: Sample Preparation

--transforming a sample into a state that is suitable for analysis


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3. Extracting caffeine and theobromine (analytes) with water


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Step 2: Performing

analysis with liquid

chromatography


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Principles of liquid

chromatography


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Step 3: Preparing

calibration curves

A graph of detector response as a

function of analyte concentration iscalled a calibration curve or a

standard curve.

Standard solution: containing known

concentrations of analytes.


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Step 4: Analyzing theresults


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Why Precautions?

In general – must prevent contamination or alteration of the sample by:

1) container

2) atmosphere

3) light

The sample may have to be protected from atmosphere

or from light.

Alkaline substance for example, will react with CO2 in theair.

Blood samples to be analyzed for CO2 should be

protected from the atmosphere.

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What Precautions?

The stability of the samples must be considered. Examples:

Glucose is unstable and a preservative such as sodium

flouride is added to blood samples.

The preservation must not interfere in the analysis.

Proteins and enzymes tend to denature on standing and

should be analyzed without delay.

Urine samples are unstable and calcium phosphate

precipitates out, entrapping metal ions or other

substances of interest.

Precipitation can be prevented by keeping urine acidic

(pH 4.5) usually by adding 1 or 2 ml glacial acetic acid

per 100-ml sample. Store under refrigeration.48


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Performing necessary chemical separations

One or more separation steps are required during

chemical analysis because:

To eliminate interferences,

To provide suitable selectivity in themeasurement or

To preconcentrate the analyte for more sensitive

or accurate measurement

It is preferable to separate the analyte away

from the sample matrix, in order to minimize

losses of the analyte.

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Methods for Separation Chemical Analysis

Examples of separation steps:

Precipitation

Extraction into an immiscible solvent

Chromatography

Dialysis

DistillationElectrophoresis

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Why sample Preparation and Extraction?

May be many analytes present May be small amounts of analyte(s) in bulk

material.

Need to concentrate these before analysis. e.g.

heavy metals in animal tissue, additives in polymers, herbicide residues in flour etc. etc

May be helpful to concentrate complex mixtures

selectively.

Most general type of pre-treatment:

EXTRACTION

E.g. Soxhlet extraction, solid phase extraction


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Measurement Techniques in Analytical Chemistry


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As analyst, it is important to have goodcommunication and interaction with

the ‘customer’ about what the

analysis represents.

Documents

Lecture 1 & 2-Intro and Sampling