basic analytical chemistry.ppt

BASIC ANALYTICAL CHEMISTRY TRAINING

ANALYTICAL CHEMISTRY

• Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of one or more of these components. The separation of components is often performed prior to analysis.

• Analytical methods can be separated into classical and instrumental. Classical methods (also known as wet chemistry methods) use separations such as precipitation, extraction, and distillation and qualitative analysis by color, odor, or melting point. Quantitative analysis is achieved by measurement of weight or volume. Instrumental methods use an apparatus to measure physical quantities of the analyte such as light absorption, fluorescence, or conductivity.

• Identification of one or more constituents of a sample qualitative analysis.

• Examination to determine how much of a particular species is present quantitative analysis.

• Information concerning the spatial arrangement of atoms in a molecule or crystalline compound or confirmation of the presence or position of certain organic functional groups

• structural analysis.

ANALYTICAL CHEMISTRY (Continued)

• A general classification of important analytical techniques

SPECTROMETRIC

• Molecular Spectrometry

UV, UV-Visible spectrometry

Quantitative determination of elements and compounds, mainly as trace and minor constituents

Infra red (IR) spectrometry Infra red (IR) spectrometry

Identification and structural analysis of organic compounds

Nuclear Magnetic Resonance (NMR) spectrometry


Mass Spectrometry (MS) Mass Spectrometry (MS)


Identification and determinations of elements and isotopes at trace levels

Three techniques are important for analytical purposes :

1. Visible and ultraviolet spectrometry (electronic)

2. Infrared spectrometry (vibrational)

3. Nuclear magnetic resonance spectrometry (nuclear spin)

UV/VIS SPECTROMETRIC

• The full electromagnetic radiation spectrum is continuous and each region merges slowly into the next. For spectroscopy purposes, we choose to characterize light in the ultraviolet and visible regions in terms of wavelength expressed in nanometers.

UV/VIS SPECTROMETRY (Continued)

• Instrumentation• The purpose of a spectrophotometer is to provide a beam of monochromatic radiation to

illuminate a sample and so measure the ratio I/Io. Any spectrophotometer will consist of the component parts of :




identification and structural analysis of organic compounds




•Three techniques are important for analytical purposes :





• The Beer-Lambert Law states that the concentration of a substance in solution is directly proportional to the 'absorbance ', A, of the solution.

•Absorbance A = constant x concentration x cell length

• The law is only true for monochromatic light, that is light of a single wavelength or narrow band of wavelengths, and provided that the physical or chemical state of the substance does not change with concentration.

• When monochromatic radiation passes through a homogeneous solution in a cell, the intensity of the emitted radiation depends upon the thickness (l) and the concentration (C) of the solution.

• Io is the intensity of the incident radiation and I is the intensity of the transmitted radiation. The ratio I/Io is called transmittance. This is sometimes expressed as a percentage and referred to as %transmittance.

• Mathematically, absorbance is related to percentage transmittance T by the expression:

•A = log10(Io/I) = log10(100/T) = kcL

where L is the length of the radiation path through the sample, c is the concentration of absorbing molecules in that path, and k is the extinction coefficient - a constant dependent only on the nature of the molecule and the wavelength of the radiation.


• The most conveniently available source of visible radiation with which we are familiar is the tungsten lamp. For the UV region, the most common source is the deuterium lamp and a UV/Visible spectrometer will usually have both lamp types to cover the entire wavelength range.

• A molecule of any substance has an internal energy which can be considered as the sum of the energy of its electrons, In complex molecules the energy levels are more closely spaced and photons of near ultraviolet and visible light can effect the transition. These substances, therefore, will absorb light in some areas of the near ultraviolet and visible regions.


• In the expression A = kcl, c is expressed in molar-1 and l in m, then k is replaced by the symbol τ and is called the molar absorption coefficient. The units of τ are mol-1m2. τ was formerly called the molar extinction coefficient and concentrations were often expressed as mol l-1, mol dm-3 or M and the cell length in cm to give units mol-1lcm-1, mol-1dm3cm-1 and M-1cm-1 respectively.




identification and structural analysis of organic compounds




•Three techniques are important for analytical purposes :




CHROMATOGRAPHIC

• Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus changing the separation.

• Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for further use (and is thus a form of purification). Analytical chromatography is done normally with smaller amounts of material and is for measuring the relative proportions of analytes in a mixture.

• The mobile phase is the phase which moves in a definite direction. It may be a liquid (LC), a gas (GC). The mobile phase consists of the sample being separated/analyzed and the solvent that moves the sample through the column. In the case of HPLC the mobile phase consists of a non-polar solvent(s) such as hexane in normal phase or polar solvents in reverse phase chromotagraphy and the sample being separated. The mobile phase moves through the chromatography column (the stationary phase) where the sample interacts with the stationary phase and is separated.

• The stationary phase is the substance which is fixed in place for the chromatography procedure. Examples include the silica layer in thin layer chromatography.

CHROMATOGRAPHIC (Continued)

• Some techniques of chromatographic are :

• Chromatographic bed Shape

Column Chromatography : The stationary bed is within a tube.

Planar Chromatography : The stationary phase is on a plane.

- Paper Chromatography : Involves placing a small dot or line of sample solution onto a strip of chromatography paper.

- Thin Layer Chromatography : Similar to paper chromatography, stationary phase of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat, inert substrate.

• Physical state of mobile phase

• Gas Chromatography : Mobile phase is a gas. It is always carried out in a column, which is typically "packed" or "capillary"

• Liquid Chromatography : Mobile phase is a liquid. Liquid chromatography can be carried out either in a column or a plane.

GAS CHROMATOGRAPHY

• Is used to separate volatile components of a mixture. A small amount of the sample to be analyzed is drawn up into a syringe. The syringe needle is placed into a hot injector port of the gas chromatograph, and the sample is injected. The injector is set to a temperature higher than the components’ boiling points. So, components of the mixture evaporate into the gas phase inside the injector. A carrier gas, such as helium, flows through the injector and pushes the gaseous components of the sample onto the GC column. It is within the column that separation of the components takes place. Molecules partition between the carrier gas (the mobile phase) and the high boiling liquid (the stationary phase) within the GC column.

GAS CHROMATOGRAPHY (Continued)

• Instrumentation

• Carrier and Detector Gases• The carrier gas must be chemically inert. Commonly used gases include nitrogen, helium,

argon, and carbon dioxide. The choice of carrier gas is often dependant upon the type of detector which is used. The carrier gas system also contains a molecular sieve to remove water and other impurities. Hydrogen and air is commonly used for detector gases.


Injection Port• For optimum column efficiency, the sample should not be too large. The most common

injection method is where a microsyringe is used to inject sample through a rubber septum into a flash vapouriser port at the head of the column.

• There are 2 type of inlet system :• - Packed column inlet : Packed Column Injector

• Septum Purged Injector

• - Split/splitless inlet : Split Injector• Splitless Injector• Cold on Column Injector


• Column• There are two general types of column :• Packed columns : contain a finely divided, inert, solid support material (commonly based

on diatomaceous earth) coated with liquid stationary phase. Most packed columns are 1.5 - 10m in length and have an internal diameter of 2 - 4mm.

• Capillary columns : have an internal diameter of a few tenths of a millimeter. They can be one of two types; wall-coated open tubular (WCOT) or support-coated open tubular (SCOT). Wall-coated columns consist of a capillary tube whose walls are coated with liquid stationary phase. In support-coated columns, the inner wall of the capillary is lined with a thin layer of support material such as diatomaceous earth, onto which the stationary phase has been adsorbed. SCOT columns are generally less efficient than WCOT columns.


Detector• There are many detectors which can be used in gas chromatography. Different detectors

will give different types of selectivity. A non-selective detector responds to all compounds except the carrier gas, a selective detector responds to a range of compounds with a common physical or chemical property and a specific detector responds to a single chemical compound.

• Detector Support gases Selectivity• Flame ionization (FID) Hydrogen and air Most organic cpds.• Thermal conductivity (TCD) Reference Universal• Electron capture (ECD) Make-up Halides, nitrates, nitriles, peroxides,

anhydrides, etc.• Nitrogen-phosphorus Hydrogen and air Nitrogen, phosphorus• Flame photometric (FPD) Hydrogen, air possibly oxygen Sulphur, phosphorus, tin, boron, arsenic, etc. • Photo-ionization (PID) Make-up Aliphatics, aromatics, ketones, esters,

aldehydes, • Hall electrolytic conductivity Hydrogen, oxygen Halide, nitrogen, nitrosamine, sulphur


Recorder• Two devices are used to record the GC traces/areas under peaks:

•Integrating recorders•computer program

• Each type of device records the messages sent to them by the detector as peaks, calculates the retention time, and calculates the area under each peak; all of this information is included in the printout.

CONCENTRATION

• In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent.

• To concentrate a solution, one must add more solute (e.g. alcohol), or reduce the amount of solvent (e.g. water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute.

• For scientific or technical applications, a qualitative account of concentration is almost never sufficient; therefore quantitative measures are needed to describe concentration.

• There are a number of different ways to quantitatively express concentration. They are based on mass, volume, or both. Depending on what they are based on it is not always trivial to convert one measure to the other, because knowledge of the density might be needed to do so. At times this information may not be available, particularly if the temperature varies.

• The most common used for unit of concentration are : Percentage, Molarity, Normality, Molality, Part per million, Part per billion, etc.

CONCENTRATION (Continued)

• Percentage (%)

• There are a number of different ways to quantitatively express percentage concentration. They are based on mass, volume, or both.

• Mass Percentage• The mass of a substance in a mixture as a percentage of the mass of the entire mixture.

(Mass fraction Xm can be used instead of mass percentage by dividing mass percentage to 100.) Commercial concentrated aqueous reagents such as acids and bases are often labeled in concentrations of weight percentage with the specific gravity also listed. In older texts and references this is sometimes referred to as weight-weight percentage (abbreviated as w/w% or wt%).

• Mass Percentage (wt %) = Weight of substance x 100 Weight of

mixture

• Example :• If a bottle contains 40 grams of ethanol and 60 grams of water, then it contains 40%

ethanol by mass or 0.4 mass fraction ethanol. • Note that the total weight of the solution will be 100 grams, but the total volume of the

solution will be more than 100 milliliters because ethanol is less dense than water.


• Mass - Volume Percentage• Mass-volume percentage, (sometimes referred to as weight-volume percentage or percent

weight per volume and often abbreviated as % m/v or % w/v) describes the mass of the solute in g per 100 mL of the resulting solution. Mass-volume percentage is often used for solutions made from a solid solute dissolved in a liquid. For example, a 40% w/v sugar solution contains 40 g of sugar per 100 mL of resulting solution.

• Mass – volume Percentage (% w/v) = Weight of substance x 100

Volume of mixture

• Example :

A 40% w/v sugar solution contains 40 g of sugar per 100 mL of resulting solution.

• Volume - Volume PercentageVolume-volume percentage (sometimes referred to as percent volume per volume and abbreviated as % v/v) describes the volume of the solute in mL per 100 mL of the resulting solution. This is most useful when a liquid - liquid solution is being prepared.

• Volume Percentage (% v/v) = Volume of substance x 100

Volume of mixture

• Example :• For example, a 40% v/v ethanol solution contains 40 mL ethanol per 100 mL total volume.


• Molarity (M)• Molarity (in units of mol/L, molar, or M) or molar concentration denotes the number of

moles of a given substance per liter of solution. A capital letter M is used to abbreviate units of mol/L.

• Example :

• Normality (N)• The normality of a solution is the number of gram equivalent weight of a solute per liter of

its solution.The definition of normality depends on the exact reaction intended.

• Example :• For example, hydrochloric acid (HCl) is a monoprotic acid and thus has 1 mol = 1 gram

equivalent. One liter of 1 M aqueous solution of HCl acid contains 36.5 grams HCl. It is called 1 N (one normal) solution of HCl.


• Molality (m)• The number of moles of solute per kilogram of solvent (not solution).

• Example :• Adding 1.0 mole of solute to 2.0 kilograms of solvent constitutes a solution with a molality

of 0.50 mol/kg. Such a solution may be described as "0.50 molal". The term molal solution is used as a shorthand for a "one molal solution", i.e. a solution which contains one mole of the solute per 1000 grams of the solvent.

• Equivalents (Eq)• Expression of concentration in equivalents per liter (or more commonly, milliequivalents

per liter) is based on the same principle as normality. A normal solution is one equivalent per liter of solution (Eq/L).

• Part per Million (ppm)• The amount of a given substance in a total amount of 1,000,000 regardless of the units of

measure used as long as they are the same. e.g. 1 milligram per kilogram. 1 part in 106.

• Part per Billion (ppb)• The amount of a given substance in a total amount of 1,000,000,000 regardless of the

units of measure as long as they are the same. e.g. 1 milligram per tonne. 1 part in 109.

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