LECTURE 9: SEPARATION MATHODS // CHAPTER 9

Question 1

Three major techniques used in forensic science labs

Answer 1

1) liquid phase extraction
2) solid phase extraction
3) chromatography

Question 2

1) Liquid phase extraction

Answer 2

• Involves separation of two or more substances (analytes) in which two solvents that do not dissolve in each other compete for the analyte
• The distribution between the two solvents is called partitioning

Question 3

Partitioning occurs according to chemical properties, mainly

Answer 3

polarity and ph

Question 4

Polarity:

Answer 4

 Tendency of a compound to behave like a magnet
 Results from polarity of bonds and asymmetry of a compound
 Excess of electron density on the side of a compound
 Organic compounds tend to be non-polar
 ‘like-dissolves-like’; non-polar/ polar dissolves more readily and to a greater extend in non-polar/polar solvent
 Mixture of polar and non-polar analytes can. Be separates using a polar (e.g. Water) and non-polar solvent (e.g. Methylene chloride)

Question 5

pH

Answer 5

 Measure of acidity or alkalinity of a fluid relative to water
 pH = -log10 H+ concentration in mol/L
 Negative logarithm of hydrogen ion concentration
 Acidic = ph between 1&7  releases h+ or h3o+ into water upon dissolution
 Neutral = ph 7
 Alkaline = ph between 7&14  takes up h+, producing oh- upon dissolution

Question 6

2) solid phase extraction

Answer 6

relies on adsorption

Question 7

Adsorption

Answer 7

substance adheres to surface of solid phase

Question 8

Absorption

Answer 8

substance drawn into solid phase

Question 9

chromatography techniques

Answer 9

• Thin layer chromatography (TLC)
• Gas chromatography (GC)
• High performance liquid chromatography (HPLC)

Question 10

All chromatograph systems consist of

Answer 10

1. A stationary phase
2. A mobile phase
3. A way of getting the mixture into the system
4. A away of telling if the compound in a mixture are coming out of the system (detector)

Question 11

Analyte:

Answer 11

substance(s) being seprated

Question 12

Solvent:

Answer 12

liquid solution used to dissolve all or part of an analyte

Question 13

Solute:

Answer 13

describes substance dissolved in solvent, synonymous with analyte

Question 14

Polarity (define)

Answer 14

• Tendency of a compound to behave like a immature magnet, with positive side and a negative side

Question 15

organic

Answer 15

tend to be nonpolar or slightly polar

Question 16

inorganic

Answer 16

range from nonpolar to very polar

Question 17

symmetric compounds

Answer 17

tend to be nonpol;ar

Question 18

polarity is caused by

Answer 18

an excess of electron density on one side of a molecule and therefore a deficiency on the other side

• Side with the excess electron density has a negative charge
• Side deficient in electrons has a net positive charge

Question 19

like dissolves like

Answer 19

this means that polar compounds have a greater affinity for other polar compounds and in this case of solubility it means that polar solutes will dissolve more readily and to a greater degree in polar solvents

Question 20

Acidic substance

Answer 20

one that releases hydrogen ions (they become hydrated in presence of water so they are in form of H2O H or H3O+ called hydronium ions) when does solved in water

Question 21

Acids

Answer 21

have a ph value between 0-7

Question 22

Alkaline or basic substances

Answer 22

one that releases hydroxide ions when dissolved in water and it’s ph is 7 to 14

Question 23

Neutral substance

Answer 23

one that releases neither H3O+ no hydroxide ions (OH-) when dissolved

Question 24

The word chromatography literally means

Answer 24

‘to write with colour’

Question 25

Stationary phase

Answer 25

is a finely divided solid material or viscous liquid that is contained within a long column

Question 26

Mobile phase

Answer 26

is a liquid or gas under pressure it moves through the stationary phase carrying the analyte mixture with it and depending on their affinity of the stationary phase components analyte move slowly or quickly through the column separating from other components along the way