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Short introduction into

Analytical Chemistry

by Prof. Dr. Manfred Sietz and Dr. Andreas Sonnenberg (PowerPoint slides)

What is Analytical Chemistry?

• study of methods for determining the composition of substances - qualitative ("what?")- quantitative ("how much?") • see also: emistry, the free encyclopedia

Analytical Chemistry

Quality controle.g. analysis of vitamin

content in food samples

Forensic analytical chemistrye.g. comparison of DNA codesor trace analysis of clothings("guilty or not?")

Environmental analyticalchemistry e.g. heavy metalsin soil or water Clinical analytical chemistrye.g. analysis of blood or urine

Overview

10 steps of chemical analysis

1. Sampling (sampling errors!)2. Sample naming3. Sample preparation4. Analysis5. Signal recording6. Signal processing7. Evaluation of analysis results (correctness,

exactness, reproducibility)8. Plausibility check9. Certification10. Filing

Dr. S. M. Condren

Instruments for Analysis

Components of a typical instrument

Signal

generator Input transducer or detector

Analytical

signal

Signal

processor

Electrical

or mechanical input signal

12.301

Output

signalMeter or Scale

Recorder

Digital

unit

Evaluation of analysis results

The average value

x of all single results in a series of measurements is to be calculated by following formula: nx nxxxxx in 321
and n i1 ; n = number of single results.

The precision P of an analysis is determined

by the range of standard deviation S 2/1 2 )(11 xxnS i und xSP

Types of errors

type of errorcoincidental errorbiased error gross error XXXX XXX XX X X X XX

XXXXXXX

miss precision optimal bad good - correctness optimal good bad -

Extend of correctness and precision

020406080100120

6,5 6,6 6,7 6,8 6,9 7,0 7,1 7,2 7,3

number of measurements average value true value extend of precision extend of correctness

Concentration units

• A one molecular solution contains 1 mole of a material solved in one liter of solvent (e.g. water). The unit is mole per liter.• Example: A one molecular saline solution contains

58, common salt NaCl solved in one liter water.

NaCl solved in 1 liter water would correspond to

1000 ppm; 1 mg NaCl solved in 1 L would correspond

to 1 ppm.• One liter water with 25 degree Celsius weighs or 1.000.000 mg; 1 mg NaCl in 1.000.000 mg water means, that the water contains 1 ppm NaCl; 1ppm =

1 mg per litre

Detection limit

Minimum concentration or weight of analytethat can be detected at a known confidence level

Dr. S. M. Condren

Applicable Concentration Range

Fig. 1-7 pg. 14

Useful range

LOQLOL

Instrument response

ConcentrationLOQ => limit of quantitative

measurement

LOL => limit of linear

response

Limit of determination,

detection limit and blank value

S = standard deviation, b = blank value

0123456789

01234567

amount in µg

Absorption

S b A b A b + 3 S b A b + 6 S b detection limitlimit of determination

Typical methods for

quantitative analysis • of heavy metals in soil, water or waste water is ATOMIC SPECTROSCOPY• of solvents in soil, air, water or waste water is GAS CHROMATOGRAPHY

We start with

CHROMATOGRAPHY

THIN LAYER

CHROMATOGRAPHY,

A SEPARATION METHOD

Example: Qualitative analysis of green grassWe take some green grass, add a little amount of a solvent and press and stir the mixture until it gets a dark green color. We take a small portion of that green liquid by a capillary glass and put a liquid spot on a thin layer of white (Si-O-)

3

Si-OH ("stationary phase"). We let the

solvent dry.Then we put the plate into some different solvent ("mobile phase") and let the solvent ascend.

Mechanisms I

The component stays mainly

at the surface of the stationary phase (adsorption) resp. in the stationary liquid phase (distribution), while the component ostays mainly in the mobile phase.

Mechanisms II

As soon as new mobile phase flows, the

components staying in the mobile phase are being transported. They get in contact with unallocated solid or liquid stationary phase. The stationary phase mainly adsorbes or disssolves the component .

Adsorbed resp. in liquid stationary

phase dissolved molecules otrespass in the mobile phase and are being transported further more.

Mechanisms III

After multiple repitition of the above

mentioned processes, the two components are being seperated.

The moleculso mainly stay in the

mobile phase and obviously move faster than the moleculs .

In other words: the R

f -value of ist smaller than the value of o.

The Retentionfactor R

f

Definition: R

f = Distance start-substance / Distance start-mobile phase mobile phase substance start start substance standard

A: the R

f -value

B: the R

st -value R f = b/a = dist. substance/dist. mob. phase R st = b/a = dist. substance/dist. standard

Thin layer chromatography is a qualitative

separation technique.

The substances are separated by their solubility

in the mobile phase and their affinity towards the stationary phase.

The balanced distribution of a substance is

described by: c stationary phase / c mobile phase = K T c = concentration of a substance

K = constant (depending on temperature)

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